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2036   Fri Feb 26 23:13:02 2016 KojiNMiscPD QEBRDF measurement around the peak

The BRDF of the PD (C30665GH) for 15 deg incident angle was measured arond the peak with the same was as elog2035 and elog2034 but with the additaional Iris as shown in Fig. 1.

For calculating the BRDF. the fomular in elog2034 is used.

(Please note that r_l becoms the radius of the Iris in front of the PDA100A and d becomes the distance between PD (C30665GH) and the Iris)

The Iris diameter is 3.5 mm.

There is no difference for polarization as the wider scan.

The result for p-pol is shown in Fig. 2 with the wider scan (the relsult of the elog 2034). This result was wrong.

There is a asymmetry around the -30 deg and the data around -35 deg are not consistent to the previous data.

We think these are come from the slight tilt of the Iris.

We will confirn that after tomorrow.

Attachment 1: BRDF_log.pdf
Attachment 2: BRDF_setup_fine.pdf
2037   Sun Feb 28 15:47:06 2016 KojiNMiscPD QEBRDF measurement around the peak

The result shown in the elog2036 looks not to consistent to the previous result.

Thus we checked the alignment of the Iris.

First, the effect of the tilt of the Iris was checked and it was found that the tilt effect is very small.

Second, we found that the center of the Iris was off from the center of the lens.

This off effect is dominant in the BRDF measurement.

The off was about 1 mm. However, the diameter of the Iris was 3.5 mm and 1 mm is about 30% and large to 3.5 mm.

Thus we re-align the Iris and measure the BRDF of the PD (C30665GH) at the 15 deg incident angle again as shown in Fig. 1.

Figure 1 shows that the new result is consistent to the previous wide range measurement in the error.

The reason why the error at -29 deg and -31 deg is very large is the effect of the main reflected beam.

The result that the new data arond peak and the previous wide range data are combined for p-pol and s-pol is also attached.

Note that the incident beam is at 0 deg and the angle is that we must take care in terms of the back scattering.

Attachment 1: BRDF_log_compare.pdf
Attachment 2: BRDF_log_all_wide.pdf
Attachment 3: BRDF_log_all_narrow.pdf
Attachment 4: BRDFat30deg.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm)
-70 5.43 0.029 280.8 280.2 276.2 23
-60 5.44 0.030 280.3 282.1 271.8 23
-50 5.44 0.030 283.0 284.2 266.7 23
-45 5.45 0.029 311.5 317.2 267.2 23
-40 5.43 0.029 348.1 350.1 267.1 23
-35 5.44 0.029 468.6 470.1 263.9 23
-25 5.43 0.027 440.3 439.7 270.6 23
-20 5.43 0.028 349.5 349.1 278.6 23
-15 5.45 0.029 329.5 324.3 278.5 23

... 3 more lines ...
Attachment 5: BRDFat30deg_again.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm) d(cm)
-35 5.44 0.029 276.5 276.5 261.4 23 0.35
-36 5.44 0.027 288.2 289.1 276.4 23 0.35
-37 5.43 0.028 293.6 291.3 280.5 23 0.35
-23 5.43 0.027 295.2 295.1 277.6 23 0.7
-25 5.43 0.030 290.2 287.2 283.2 23 0.35
2038   Mon Feb 29 08:19:53 2016 KojiNMiscPD QEMeasurement of the reflectivity, EQE, and IQE of the PD without glass window

The reflectivity of the PD (C30665GH) at 15 deg incident angle was measured precisely with PDA100A as shown in Fig. 1.

Ref_wow_again.txt

Attachment 1: Reflectivity.pdf
Attachment 2: Ref_wow_again.txt
angle inc(V) zero ref(V,P) ref(V,S) zero
-80 5.40 0.030 2.33 2.89 0.030
-70 5.42 0.030 0.919 1.205 0.029
-60 5.41 0.030 0.335 0.498 0.027
-50 5.42 0.030 0.141 0.262 0.027
-40 5.43 0.028 0.107 0.215 0.024
-30 5.42 0.029 0.153 0.241 0.021
-20 5.42 0.030 0.234 0.282 0.022
-15 5.43 0.030 0.271 0.301 0.023
-10 5.43 0.027 0.302 0.317 0.024

... 9 more lines ...
2039   Tue Mar 1 09:12:51 2016 KojiNMiscPD QEMeasurement of the BRDF with the Iris in the incident path

The BRDF at 15 deg incident angle with the Iris in the incident path was measured for p-pol with the same way as elog2034.

(Please note that, in this measurement, d is the distance between the PD (C30665GH) and the Iris in fron of the PDA100A.)

The setup is shown in Fig. 1.

The result is shown in Fig. 2.

Figure 2 indicates that the Iris reduced the BRDF by about 10 times.

Attachment 1: BRDF_setup.pdf
Attachment 2: BRDF_withIris.pdf
2040   Tue Mar 1 09:55:28 2016 KojiNMiscPD QEEstimation of the back scattering

In terms of the BRDF, the mount of the back scattering of our technique can be estimated using the result of elog2038 and elog2039.

In our new technique, there are two effect of the back scattering:

1. the first incident light effect,

2. the second reflection light effect.

If the reflector is placed on the 5 cm far from the PD, the two effect is estimated as follows.

The BRDF of the first effect is roughly estimated as 5*10^(-5) [1/st] form the result around 0deg of elog2039.

The BRDF of the second effect is roughly estimated as 1.5*10^(-4) (= 3*10^(-3) * 0.05) [1/st] from the result at 31 deg of elog2039 (2*10^(-3) [1/st]) and the reflectivity at 15 deg of elog2038 (0.05).

The Iris 1 diameter was 1.4 mm.

For confirming this estimation is reasonable, the back scattering effect was measured with the setup as shown in Fig. 1.

In this setup, the PBS and the QWP are used as a isolator.

The Iris 1 is place on the beam waist.

We measured with/without Iris 1 and with/without the reflector, i.e. in four pattern.

For calculating the BRDF, the formula in elog2034 is used.

For r_l, the Iris radius in front of the PDA100A (5.83 mm) is used and, for d, the distance between the PD (C30665GH) and the Iris in front of the PDA100A (35.56 cm) is used.

The result is shown in Fig. 2.

Taking the difference of the result between w/ Iris, w/o reflector and w/ Iris, w/ reflector, we can obtain the effect of the reflector, i.e. the second effect.

The difference is (1.0 +/- 0.8)*10^(-4) [1/st].

This is comparable of the upper estimation.

From these estimations, the second effect is larger by a factor of two or three.

However, considering the BRDF result arond the peak of elog 2039, we can reduce the second effect easily and dramatically by the reflector placed closer to the PD (e.g. 2.5 cm).

We will check this with more precise measurement.

Attachment 1: BackSca_setup.pdf
Attachment 2: BRDF_enh.pdf
Attachment 3: BRDF_enh2.txt
cond sca(mV) error zero(mV) dist(cm) d(cm)
incident power was 5.44 V (PDA100A gain 0 dB)
1 337.0 0.4 284.1 35.56 1.166
2 324.0 0.2 246.0 35.56 1.166
3 327.6 0.2 251.2 35.56 1.166
4 329.4 0.2 250.8 35.56 1.166

2041   Wed Mar 2 10:17:56 2016 KojiNMiscPD QEMeasurement of the BRDF with the Iris in the incident path

With the chopper, the BRDF at 15 deg incident angle with the Iris on the laser path was measured again.

This is because the BRDF with the Iris on the laser path was limited by the sensitivity even at the scattering angle very close to the peak (e.g. 35 deg).

The setup up is shown in Fig. 1.

The diameter of the Iris2 was 7 mm at -25, -27, and -33 deg, and was 3.5 mm at -29 and -31 deg.

In angles wider than -35 deg, the Irs 2 wad removed for obtaining larger light and the lens diameter is 1.905 cm.

We determined the choppwer frequency as 253 Hz, considering the PD dark noise.

The PD dark noise at 253 Hz is about 100 uV as shown in Fig. 2.

The peak value at 253 Hz is read and the value is calbrated to the voltage of the PD.

The calibration constant is determined cahnging the laser power and measureing the DC value of the PD (without chopper) and the peak value of the FFT analyzer and the constant is determined as 0.80 +/- 0.01. (from FFT to PD)

The result of the BRDF is shown in Fig. 3.

Attachment 1: BRDF_chopper_setup.pdf
Attachment 2: BRDF_with_chopper.pdf
Attachment 3: PD_darknoise.pdf
2042   Wed Mar 2 13:07:36 2016 KojiNMiscPD QEDistance between the 1st incident beam and the 2nd reflected beam

Using the setup for the measurement of the back scattering (in elog2040), the relative distance between the 1st incident beam and the 2nd reflected beam was measured.

First, the 1st incident beam position was detemined by aligning the reflector and overlapping the 2nd reflected beam on the 1st incidnet beam with the monitor of the value of the multimeter ("worst angle").

After that, the reflector was aligned onto the point that the back scattering is smallest and the relative angle of the knob of the reflector mount was noted ("best angle").

Using the value of the relative angle and some geometrical features of the mount, the relative reflector angle between "worst angle" and "best angle" was determined 0.4 degree, i.e. the incident angle to the reflector was 0.4 deg.

From this value, relative distance between the 1st incident beam and the 2nd reflected beam on the PD was determined 0.8 mm as shown in Fig. 1.

And the 1st incident beam and the 2nd reflected beam on the Iris was determined as 1.6 mm.

This means the main reflected beam was dumped by the Iris. (The Iris apature radius is 0.65 mm.)

The distance on the PD is designed as 1 mm.

The design value and the measured value is consistent.

For obtainning the design value, the 1st incident beam should be miscentered a bit more.

Attachment 1: Beam_Position.pdf
2043   Wed Mar 2 14:38:31 2016 KojiNMiscPD QEMeasurement of the reflectivity, EQE, and IQE of the PD without glass window

Using the improved reflectivity measurement, the IQE is calculated again (see also elog2031).

The QEs are calcurated with the same way as elog2020 and elog2022 and the results are shown in Figs. 1 and 2.

Figure 1 shows that, for p-pol, the not-enhanced EQE and the IQE are 0.90 +/- 0.03 and 0.94 +/- 0.04 at 15 deg, respectively.

Figure 2 shows that, for p-pol, the EQE is enhanced 4.0 +/- 0.4% and, between 30 deg and 50 deg, the EQE is enhanced almost up to the IQE.

Attachment 1: QE3.pdf
Attachment 2: QE_ratio2.pdf
2045   Sat Mar 5 01:42:02 2016 KojiNMiscPD QEMeasurement of the BRDF with the Iris in the incident path

The BRDF with Iris was measured with the chopper and FFT analyzer again because in the previous measuremt it is suspected that there may be a beam clip.

This time, the BRDF was measured after is is confirmed that the are no clipping using a IR view.

The result is shown in Fig. 1.

The error estimation has not yet be done.

The two data shown in Fig. 1 are consistent in the skirt ares by are not consistent arond the peak.

Thus, we checked the clipping effect by making a clip intentionally and measuring the BRDF at several point.

When there is a clip, the previous BRDF is reproduced.

There, we conclude that there was a clip in the previous measurement.

Attachment 1: BRDF_with_chopper.pdf
2047   Sun Mar 6 10:19:14 2016 KojiNMiscPD QEEstimation of the back scattering

(This is the work on Thursday.)

Background:

We observed large discrepancy of the back reflection between the values measured with a BS and estimated from the BRDF. The back-scattering from the PD (C30665GH) without the reflector measured in elog2040 (2*10^(-3) [1/sr]) was about 40 times larger than the value expected from the BRDF measurement (elog20455*10^(-5) [1/sr]). We thought this came from the ampbient light, scattering from other optics (e.g. PBS), and scattering from the chopper. We tried to measure the back reflection again with a refined setup.

What we did:

As the first attempt, for dumping the scattering light from the chopper, a "wall" to dump the light with the aluminum foil was mede and was placed between the lens and PBS as shown in Fig. 1. Before the wall was placed, the back reflection was about 162.6 mVrms (PDA100A gain 70dB). After the wall was placed, the back reflection was improved to about 82.5 mVrms (PDA100A gain 70dB).

Secondly, the chopper was tilted to reduce the direct reflection. Then the back reflection was reduced to about 3.48 mVrms (PDA100A gain 70dB).

Thirdly, we found that the incident beam was clipped at the incident Iris and the level was 0.4% in terms of the transmitted light power. (The Iris had been opened 1.2 mm in diameter.) The clip was small but could not be negligible. Thus we opened the Iris to 1.8 mm in diameter and the clip level was less than 0.1%, which is the detection limit of the degital multimater used to measure the output signal of the PD (C30665GH).

In order to obtain a reference calibration, we placed an HR mirror right before the target PD and measured the reflected power on the measurement PD (PDA100A).

All the numbers were measured with an FFT analyzer to read the peak value at the chopping frequency.

After that, we measured the back reflection with the same way as elog2040.

Measurement:

We measured the back scattering in following conditions:

1. d_ref = 5 cm, theta_ref = 0.8 deg, without the reflector,

2. d_ref = 5 cm, theta_ref = 0.8 deg, with the reflector,

3. d_ref = 5 cm, theta_ref = 1.7 deg, without the reflector,

4. d_ref = 5 cm, theta_ref = 1.7 deg, with the reflector,

5. d_ref = 2 cm, theta_ref = 4.3 deg, without the reflector,

6. d_ref = 2 cm, theta_ref = 4.3 deg, with the reflector,

where the paremeters are explanes in Fig. 2. In conditions 3--6, using the CCD camera, the primary incident beam on the PD aligned was  on 1 mm far from the boundary of the PD, i.e. the beam was aligned at 0.5 mm off from the center of the PD as shown in Fig. 2. (I'm sorry but in the condition 1 and 2 the beam position was unknown.) The theta_ref is determined as widely as we can keeping the output signal of the PD (C30665GH) maximum.

For calculating the BRDF. the fomular in elog2034 is used.

(Please note that r_l becoms the radius of the Iris in front of the PDA100A and d becomes the distance between PD (C30665GH) and the Iris)

The Iris diameter was 1.143 cm, the distance between PD (C30665GH) and the Iris, d, was 43.1 cm.

Result:

The measured value with HR mirror in front of the PD (C30665GH) was 2.400 Vrms (PDA100A gain was 0 dB.)

The voltages measured in the conditions were as follows (PDA100A gain was 70 dB).

1: 3.192 +/- 0.007mVrms

2: 27.3 +/- 0.01 mVrms

3: 3.347 +/- 0.004 mVrms

4: 3.786 +/- 0.008 mVrms

5: 3.881 +/- 0.009 mVrms

6: 3.846 +/- 0.007 mVrms.

The BRDF results are shown in Figs. 3 and 4.

The error estimation was not yet be done.

Discussion:

* Primary incident beam effect

When we see the values measured in the condtions 1, 3, and 5, the primary incident beam effect is about 8*10^(-4) [1/sr] which is still larger about 10 times larger than the expected value from the  BRDF measurement, 5*10^(-5) [1/sr].

This means that, for observing the back reflection of the primary incident beam, we must reduce the noise, i.e. the scattering which does not come from the PD.

* Secondary reflected beam effect

When we see the the gaps of the value between condition 1 and 2, between 3 and 4, and between 5 and 6, when theta_ref is made larger, the secondary reflection beam effect was reduced.

The difference between condition 3 and 4 is 1.1*10^(-4) [1/sr] and the expected secondary reflection light effect from the BRDF measurement was 0.8*10^(-4)  [1/sr].

They look consistent.

The difference between condition 5 and 6 can not be seen in current sensitivity and the expected secondary reflection light effect from the BRDF measurement was 1*10^(-5) [1/sr]

Thus it is reasonable that there is no difference between 5 and 6.

The difference between 3 and 5 is considered to come from the laser power drift.

Therefore, the secondary reflected beam effecte can be explained with the BRDF measurement.

Attachment 1: setup.pdf
Attachment 2: ref_ps.pdf
Attachment 3: Backscat.pdf
Attachment 4: BackScat2.pdf
2048   Mon Mar 7 15:34:46 2016 KojiNMiscPD QEBack reflection measurement with the chopper

Background:

We are still suffering from excess amount of back reflection compared with the predicted number from the BRDF measurement. Assuming this light is not coming from the target PD, we want to reduce the scattering from other optics. As an attempt, we decided to use a BS instead of the combination of a cube PBS and a QWP. This way we can reduce the number of the optics involved, particularly the PBS which may cause more scattering than others.

What we did:

The PBS and the QWP were removed, and then a 50:50 BS was inserted as shown in Fig. 1.

The distance between the target PD and Iris2 was measured to be 38.1 cm. The diameter of Iris2 was set to be 7 mm.

As a part of the calibration, the incident power on the target PD was measured using PDA100A (Gain 0dB). The measured value was 3.973 V with no chopper blocking the beam.

An HR mirror was then placed before the target PD to measure the reflected light power with the chopper still halted and the iris 1 is oped using PDA100A (Gain 0dB) which is placed at the position as shown in Fig. 1. It was measured to be 1.253 V. This means that the reflectivity of the BS is about 0.315. This reduction is considered to be the clipping at Iris1 as the returning beam has the bigger beam size (i.e. the iris worked as a sort of mode cleaner).

(==> There might be a misunderstanding because of my not clear explanation. So, I edited this paragraph again. KN)

Then, the chopper was started at 253 Hz. The reflected light from the HR mirror was measured using a FFT analyzer to be 642 mVrms (PDA100A gain 0 dB).
(==> mVrms? KA ==> mVrms. I fixed. KN)

Throughout the measurement, the opening of Iris1 was adjusted such that the clip level was less than 0.1% of the incident power (see also elog2047).This yielded the Iris1 diameter of 1.8 mm.

Finally, the back reflection was measured in the same way as elog 2040 , and also with Iris1 opend as much as possible.

Result:

The measured voltage with Iris1 with the diameter of 1.8 mm: 720 uVrms (PDA100A gain 70 dB)
==> This corresponds to the BRDF of 1.4 x 10-3 [1/sr].

The measured voltage with Iris1 completely open: 640 uVrms (PDA100A gain 70 dB)
==> This corresponds to the BRDF of 1.2 x 10-3 [1/sr].

These values are much (x40) larger than the BRDF value expected from the BRDF measurement (5x10-5 [1/sr], see also elog2045).
In fact, these are much (x2) larger than the ones with the PBS & the QWP (8x10-4 [1/sr], see also elog 2047).

(It is not so clear how these numbers were calculated. How these calibrations were used? How did you incorporate the BS transmissivity and reflectivity??? KA)

==> For calculating the BRDF, the fomular as shown elog2034 is used. Seeing the fomular, we need the ratio of the incident light power and the scattered (reflected, in this measurement) light power, the incident angle, and the solid angle. The ratio of the incident light power and the scattered light power can be obtained by taking the ratio of the measured voltage with the chopper as a part of the calibration, Vin (642 mVrms), and the measured voltage with Iris1 with the diameter of 1.8 mm (720 uVrms) or with Iris1 completely open (640 uVrms), Vsca, considering the difference of the PDA100A gain. In this calculation the BS reflectivity and transmissivity do not appear, see also Fig. 2. In addition, using the incident angle, 15 deg, and the solid angle from the PD(C30665GH) to the Iris2, 2.6x10-4 sr, the BRDF can be calculated.

And when the Iris was closed, the value was larger. This means that the Iris may make a scattering.
(==> This didn't make sense compared with the numbers above. KA ==> The numbers were written conversely. I fixed. KN)

[Ed.: KA]

Attachment 1: setup.pdf
Attachment 2: BRDF_cal.pdf
2049   Mon Mar 7 15:47:03 2016 KojiNMiscPD QEBack reflection measurement with the chopper

To reduce the scattering, we did some try and error.

The setup was same as the elog2048.

First, to reduce the scattering from the Iris 1, in front of the Iris 1 the aluminum foil which has the hole for the laser was placed.

We made several foils, different hole sizes and different shapes.

We cannot found the reasonable tendency, but with the best foil the measured scatterd value became 350 uVrms (BRDF = 7.1 * 10^(-4) [1/sr]).

This is the comparable value to the BRDF measured with PBS and QWP (elog2047).

After that, we changed the steering mirror #2 from Newfocus 5104 to Newport 10Q20HE.1.

Then, without aluminum foil, i.e. in completely same setup as elog2048, the measured scatterd value became 11 mVrms.

And we tried to place the best aluminum foil and the measured valued as reduced to 820 uVrms.

147   Wed Jul 1 17:06:30 2009 MStephensMiscGeneralNew Gyro Design and Week 2 Summary

I've done a few things this week. Connor and I characterized his laser's beam divergence, the results of which can be found on a previous entry. I'll do the same measurement for my laser once we're allowed to turn it on. The table now has a mock-up of the Fabry-Perot cavity locking scheme, it's still missing a few mirrors but the gist of it is there. I also changed the setup for our actual gyro design. In order to increase the finesse of the cavity, we got rid of one of the partially transmitting mirrors in the triangular cavity. So there is now a setup with two highly reflective mirrors and one partially transmitting, and both the clockwise and the counterclockwise beams will be injected into that one. We're also going to set it up so the clockwise mode goes through the AOM twice in order to double the effect. My first progress report is attached to my 40m wiki page. (Sorry, no LaTeX yet, will figure that out).

Attached here is the new diagram for the gyro setup.

Attachment 1: NewerGyroDesign.PNG
71   Tue Jul 29 00:47:37 2008 MashaLaserFibermach zehnder setup
As per dmass's prodding, I am putting up some pictures of what I'm doing.

Currently there is a working Mach Zehnder, but it needs to be improved.
Right now the fluctuations due to phase are about 15% of the total DC voltage,
where they were over 50% back at the 40m.On the list are more stable mounts
and better mode matching for fiber input and output with the laser. Also, we
will be putting in an AOM in the fiber arm.
Attachment 1: setup1.JPG
Attachment 2: setup3.JPG
Attachment 3: setup4.JPG
72   Tue Jul 29 00:58:36 2008 MashaLaserFiberfirst fiber noise measurement
I'm attaching the fiber noise measurement from one mach zehnder channel
along with some noise sources. The total rms phase noise comes out to about
0.075 radians, which translates to a frequency noise of 20Hz rms.

I will take spectra at lower frequencies once the DAQ is back up so I don't
have to wait an hour for the spectrum analyzer.
Attachment 1: MZnoise_sources0727.png
1940   Fri Jun 19 18:29:31 2015 MeganMiscSeismometerBuilding the seismometer frame

I started building the frame for the seismometer out of the McMaster-Carr aluminum rods. It is the same size as the previous seismometer, but with the flat plate corner joints replaced with 6" diagonal struts in the corners. There were only 8 of these new corner joints, so they are placed in the four corners of the vertical faces on opposing sides of the frame. All remaining joints use the smaller corner joints that sit flush with the edges of the beams.

In the interest of keeping all the joints as uniform as possible, the same amount of torque was used to tighten each nut. Via the product data page (http://www.mcmaster.com/#5537t271/=xp5c7n) and a chart of fastener torques (http://imperialsupplies.com/pdf/A_FastenerTorqueCharts.pdf), it was determined that each should be tightened to 25 Nm. The closest the torque wrench could come to 25 Nm was 25.02 Nm (still pretty good).

The two different corner joints have the same screw size, but each has a flat collar at the base of the nut that differs in size: the nuts for the small joints have a narrow collar, and the nuts for the struts have a very wide collar. Kate believes that this difference won't have much effect on the rigidity of the frame at the end, so all nuts were tightened in the same manner.

As of Friday late afternoon, the bottom of the frame and the four vertical bars have been put together, and next week I will finish building the rest of the frame. I will add photos to this log soon!

1944   Wed Jun 24 17:02:03 2015 MeganMiscSeismometerFurther details on seismometer design

Here is a summary of what Rana, Kate, Steve and I have come up with today about the design of the seismometer:

Kate and I decided that the aluminum sheets will be attached to the frame via 1/4 20 McMaster Carr double-spring tab fasteners that will not slide to the bottom of the frame when the screws are taken out. These will be spaced equally about the perimeter of each face of the frame. Each screw will go through a thin outer layer of aluminum sheeting, the insulating foam (whether one or two layers of foam is yet to be determined), and the inner layer of aluminum sheeting. Steve suggested the outer layer of aluminum in order to keep the foam more evenly pressed against the heaters and the inner layer of aluminum. There will be small holes cut in the aluminum and the layer(s) of foam so that the heater wires (and any other wires) are accessible.

The heaters will be attached to the inner layer of aluminum, and the foam will be placed on top of them. Rana has ordered six heaters, so we could potentially put one heater per face of the frame. So many may not be needed; once I calculate the fow of heat through the foam we can decide the most useful number of heaters. Several temperature sensors will also measure the temperature at various points on the frame. Only one of the sensors will be used in the feedback loop.

1948   Fri Jun 26 11:19:24 2015 MeganMiscSeismometerThermal Calculations for Seismometer Housing

Below are calculations to determine the power needed to heat the seismometer, then to keep it at a steady-state temperature.

Heating the Frame and Siding

To bring the frame and the aluminum sides of the seismometer from the assumed room temperature (25oC) up to operating temperature (35oC), the heaters must supply the amount of energy that it takes to bring that mass of aluminum up by 10oC. This amount of energy can be calculated quite simply with the equation:

$Q_{total}=\big(m_{frame}c_{frame}+m_{siding}c_{siding}\big)\Delta T$

where $m$ is the mass of each of the separate components, and $c$ is the specific heat of each of the aluminum alloys used. Assuming that the 10oC temperature difference is what we'll always use for this frame, the value $Q_{total}$ is a constant. Once I measure the mass of the frame and the siding and find the specific heat values for the alloys, it can be calculated. When the interior components of the seismometer are added, their mass and materials must be included in this calculation as well.

How quickly this amount of energy can be delivered into the system is controlled by the heaters. Once the specific energy value is known and a desired heating-up time is decided on, it is a simple calculation to determine how much power the heaters need to supply:

$P_{heaters}=\frac{Q_{total}}{t_{warm-up}}$

My to-do now: measure the mass of the aluminum sheets and frame (or calculate it via given densities/volumes), and calculate the needed energy. Also, a warming time needs to be decided on.

Steady State Heating

Once the frame and aluminum panels have been brought up to temperature, a certain amount of heating is needed to maintain the 10oC temperature gradient across the foam insulation. McMaster Carr gives the K-factor (thermal conductivity) of the foam as 0.26, no units provided. Because McMaster Carr uses mostly imperial units, and the units of the K-factor are typically imperial, I assumed units of BTU/ft2/oF/hr/in, or energy transferred per sqaure foot, per unit degree difference between the two sides, per hour, per inch thinckness. The area of each foam panel, the temperature difference in oF, and the thickness of the foam are all known, so for the given K-factor a specific energy transfer rate can be calculated:

$0.26\frac{BTU}{ft^2\cdot F^{\circ}\cdot hr\cdot in}(1 in)(18^{\circ}F)(6.875ft^2)=32.175\frac{BTU}{hr}=9.429W$

$0.26\frac{BTU}{ft^2\cdot F^{\circ}\cdot hr\cdot in}(1 in)(18^{\circ}F)(5.252ft^2)=32.175\frac{BTU}{hr}=7.203W$

where the top line is for the vertical sides of the frame, and the bottom line is for the top and bottom faces of the frame. After the heaters (assuming one per face of the frame) have brought the seismometer up to temperature, they must supply at least these amounts of power to keep the temperature gradient in place. This amount is well within the 200W limit of the heaters being used.

1949   Fri Jun 26 13:41:28 2015 MeganMiscSeismometerMore on the seismometer frame

Yesterday afternoon I finished building the seismometer frame by adding the cross bar across the top face. Picture below is the frame as of yesterday afternoon (25 June):

This morning Ignacio and I went with Steve to the machine shop and cut the aluminum siding panels to the correct size. Sheets were cut for the top and bottom faces as well; the sheet for the top will be modified to fit around the cross bar. Picture below is one of the aluminum sheets next to the frame:

The next steps will be measuring where thru holes can be drilled for the M8 attachment screws, and testing the die cuts (to punch holes for electronics wires) on scrap aluminum.

1952   Mon Jun 29 11:13:21 2015 MeganMiscSeismometerTime constant for heating the seismometer frame

To determine the time constant of the system, a model of the heat flows through the system was made, starting with the basic ΔQ=mcΔT.

$dQ = mc\cdot dT$

$\frac{dQ}{dt}=P=mc\frac{dT}{dt}$

$T(t)=\frac{1}{mc}\int P dt$

Where the value $P$ is the net power flowing through the system, or Pin-Pout. Pin is the power supplied by the heaters, and Pout is the power lost radiatively through the insulation. Pin is a known value, while Pout can be calculated via the K-factor, the thickness of the insulation, the area of a side, and the temperature difference between the two sides. Taking all this into account, the differential equation becomes:

$T_{Al}(t)=\frac{1}{mc}\Big[P_{in}t-\int_{0}^{t}P_{out}dt\Big]$

$T_{Al}(t)=\frac{1}{mc}\Big[P_{in}t-\int_{0}^{t}KA_{side}d_{insul}(T_{Al}(t)-T_{lab})dt\Big]$

This is just a differential equation where the temperatue of the frame (Tal(t)) is related to the integral of itself. The equation can be rearranged such that the temperature is related to the derivative of the temperature (as differential equations typically are).

$T'_{Al}(t)=A-BT_{Al}(t)$

where A and B are defined as follows: A=(1/mc)(Pin-KAsidedinsulTlab), and B=(KAsidedinsul)/(mc). Solving the differential equation via Mathematica yields:

$T_{Al}(t)=\frac{A}{B}+C_1e^{-Bt}$

Therefore the time constant tau is just the reciprocal of B:

$\tau = \frac{1}{B}=\frac{mc}{KA_{side}d_{insul}}$

The units of tau do work out to be time, given that the units of K are taken to be [E]/[A]/[T]/[t]/[d]. Plugging in numbers to get an estimation of the order of magnitude gives:

$\tau=\frac{(10kg)(0.9\frac{J}{g\cdot K})(1000\frac{g}{kg})}{(58.121\frac{J}{K\cdot s\cdot m^2\cdot m})(0.75m^2)(0.0254m)}\approx\boxed{2.25\text{ hours}}$

This value is an estimation so far; within the next couple days I will go measure the frame and get more accurate values. I will also recheck the calculation, because I think that the time constant should have some dependence on the power input to the system.

1960   Mon Jul 6 17:10:54 2015 MeganMiscSeismometerHoles drilled in aluminum sheeting

Today Ignacio and I drilled the holes in the aluminum side sheeting for the seismometer housing. A 3/8 drill bit (0.375" dia.) was used for the M8 screws (0.31" dia.) in order to leave some room for error.

Attachment 1: One of the side panels held against the frame.

Attachment 2: One of the smaller side panels to be used in the lid part of the housing. These will be attached to the top panel of the housing via hinges, so they did not require any holes along the top or bottom edges.

Attachment 1: IMG_5102.JPG
Attachment 2: IMG_5103.JPG
1966   Thu Jul 9 10:29:49 2015 MeganMiscSeismometerHeater test, more panel work

Yesterday I tested one of the heaters that will be used to warm the seismometer housing. I soldered wires onto the heater leads, finished with shrink tubing, and then hooked them up to a power supply. The power supply was set to the max power output that our new temperature controller can provide, which is 18W = (750 mA)(24 V). After the system equilibrated, the small frame piece we were using for the test was at 37oC. This power output was no trouble for heater, other than its adhesive paper backing starting to cook (this backing will be gone once the housing is assembled).

Clarification: the heaters are going to go inside on the aluminum sheets, not between the aluminum and the insulation on the outside. When they're on the inside, we don't have to worry about the heaters burning or melting the foam, and routing the heater wires through the side of the box becomes easier. Thanks to Rana for clearing this up for me.

Lastly, yesterday I drilled the last holes in the aluminum sheeting. These will allow hignes to connect the sides of the lid to the top face of the housing.

Attachment 1: The setup used to test the heater. The heater is the small orange strip laying on the yellow kevlar band, and the silver box on top of the heater is a small piece of the supports that make up the frame. The power supply is on the left, and the thermocouple used to check the framing's temperature is on the right. The power supply reads 25.1V and 0.81 A, and the thermocouple reads 37.1oC.

Attachment 2: Koji and I were wondering where the heater's bad smell was coming from... the paper protecting the heater's adhesive started to burn.

Attachment 3: The new holes that I drilled in the aluminum sheeting yesterday are the smaller ones in the center, that come in sets of two.

Attachment 1: IMG_5113.JPG
Attachment 2: IMG_5114.JPG
Attachment 3: IMG_5112.JPG
1971   Tue Jul 14 13:49:56 2015 MeganMiscSeismometerSeismometer thermal housing taking shape

Yesterday I began to contruct the thermal housing for the seismometer. I cut foam panels for the four sides of the frame, the four sides of the lid, and the top of the lid. I then assembled the aluminum sheets making up the lid via hinges. I dropped the spring-loaded nuts into the McMaster-Carr posts, and began to fasten the sides of the lid, foam included, to the posts. I discovered that even though the nuts are spring-loaded, they still have a tendency to move quite a lot when you are trying to get the bolt to find them in the track. And once one pair is fastened, it closes off the whole line such that you can't see if you're putting the bolt in the right place to meet the nut. It was also more difficult than expected to have the nut pass through the foam as well as the aluminum sheeting. Nonetheless, I assembled the whole lid save the foam panel on the top face. See photos below:

Attachment 1:The top face of the lid and its four side panels, connected by hinges.

Attachment 2: Two of the sides connected to the corner posts; six bolts per face.

Attachment 3: All four of the sides secured up.

Attachment 4: The day's final product, right side up, with the corners sealed up with aluminum tape.

Attachment 5: The lid upside down, so you can see the foam sealing around the corners.

Problems & Potential Solutions

The first two sides that I brought up to the posts went fairly easily. However, I was only able to secure 8 of the planned 12 nut/bolt connections on the remaining two sides (the 8 corners of the two faces).

For assembling the rest of the housing (the non-lid part), I want to try and find a way to more securely keep the spring-loaded nuts in place. Assembly would be much easier if the nuts were more stable in the tracks. Also, I will find some washers to put between the bolts and the foam. I tested this on one connection, and it helps the bolt from breaking through the foam after many fasten/unfasten attempts. Lastly, I want to perhaps adhere the foam to the centers of the aluminum panels as well. This would serve the dual purpose of keeping the foam from bowing out from the aluminum, and keeping the holes in the foam aligned with the holes in the aluminum if (when) the side is removed from the rest of the frame.

Attachment 1: IMG_5149.JPG
Attachment 2: IMG_5151.JPG
Attachment 3: IMG_5152.JPG
Attachment 4: IMG_5153.JPG
Attachment 5: IMG_5155.JPG
1973   Wed Jul 15 11:29:11 2015 MeganMiscSeismometerThermal housing walls progress

This morning I put one of the walls of the thermal enclosure onto the frame. Pictures below:

Attachment 1: The side of the thermal enclosure attached to the frame. The second bolt down on the left side wasn't connected because the nut's spring lost its grip and slid down the track (after the bolts on either side had been tightened). I added washers to three of the four corners to relieve some stress on the foam, and will find more of that size washer so that all the connections can have one.

Attachment 2: The view down the top of one of the beams. When the bolt is tightented, the nut's springs aren't enough to hold it in place and it rotates slightly. This means that if the bolt is removed, the nut is likely to slide down the track. The connection is good, but this means that the removability of the side panels is more difficult than anticipated.

Attachment 3: The tape on the corners of the lid is coming undone! It doesn't stick well to the foam's paper backing; I will either glue this tape down or find some other tape that adheres better.

I will put two more sides of the enclosure on like this one, and leave the last one off until I am able to use the punches to make holes in the aluminum sheeting for the electronics wires to go through.

Attachment 1: IMG_5180.JPG
Attachment 2: IMG_5181.JPG
Attachment 3: IMG_5182.JPG
1976   Wed Jul 15 16:32:50 2015 MeganMiscSeismometerMore enclosure sides done

This afternoon I finished putting together three of the four sides of the thermal enclosure. I will leave the fourth side off until I use the die cut to make a hole for the 15- or 25-pin connector for all the electronics inside the enclosure. I also won't tape the corners of the base until I know that they will be staying on the frame for an extended period.

On each of the three sides, I was able to make 12 of the 14 connections. I used washers as needed; if the bolt held fine, I skipped a washer, and if the bolt started to snap the threads in the foam's paper backing, I put a washer in. There are washers on approimately half of the connections. By the last side I put on, I had made a process for getting the connections made, so it became not quite so time-consuming as when I started.

Attachment 1: The inside of the enclosure with three of the four sides attached.

Attachment 2: The enclosure with the lid on top. The lid fits very well; eventually when we attach it while the interferometer is running we can tape the seam between the lid and the rest of the enclosure.

Attachment 1: IMG_5184.JPG
Attachment 2: IMG_5183.JPG
1987   Fri Jul 24 15:55:05 2015 MeganMiscSeismometerMini thermal enclosure test

Today I built a miniature thermal enclosure in order to test the temperature controller box. I found a small aluminum box and surrounded it with scrap pieces of foam.

I soldered extension wires to the leads of the thermistor and the heater, and to these extension wires I soldered small pieces of resistor wire that fit into the main output connection on the back of the controller. The heater was then adhered to the inside of the aluminum box (via its own sticker-back), and the thermistor was attached near the heater via masking tape.

I set the target temperaure to 35oC, and adjusted all the necessary parameters on the controller. The initial test was the heater inside the box, with foam only beneath the bottom of the box. In this setup, it took about about 25 minutes to equilibrate. The next test was with the box completely enclosed with foam, and held up from the desk by a glass dish. This equilibrated more quickly, reaching the specified temperature after about 15 minutes.

After the warm-up time, the temperature of the box tends to overshoots the set 35oC target, before settling down to the target temperature. I'm working on using the USB interface of the controller so that I'll be able to have plots of the temperature of the enclosure as a function of time.

Attachment 1: The cable I made, with the connections to the controller at one end, and the heater and thermistor at the other end.

Attachment 2: The first test of the control system.

Attachment 3: How the heater and the thermistor are fastened to the inside of the box.

Attachment 4: The second, more quickly equilibrating test where the aluminum box is surrounded by foam.

Attachment 1: IMG_5371.JPG
Attachment 2: FullSizeRender.jpg
Attachment 3: IMG_5374.JPG
Attachment 4: IMG_5373.JPG
1989   Mon Jul 27 16:15:24 2015 MeganMiscSeismometerDB 25 Punches

Today I added the two DB 25 punches into the last side panel of the seismometer enclosure. These will be used to get the electronics wires from inside the enclosure to outside.

Attachment 1: IMG_5402.JPG
1991   Thu Jul 30 16:35:00 2015 MeganMiscSeismometerInitial test of new heaters

Today I did the first test of the new 6" x 24" heaters from McMaster-Carr. I wired them in series, and connected the two leads directly into the TC200 temperature controller. The setup for testing them was a stack of foam, a sheet of aluminum siding, the heater, and then another piece of foam. Since there is currently no way to get temperature data directly from the TC200 controller yet, for this initial test I just took a temperature reading every 30 seconds as the setup was warming up to the set temperature.

Starting from 23.7oC, the setup took 83.5 minutes to first make it to 35oC. The time constant is the time that it takes for a system to reach 1-(1/e) (about 63.2%) of its final asymptotic value, so the time constant of this data, assuming an ideal (1 - e^(-t)) curve, was calcuated to be 25 minutes. The attached plot shows the raw data, and overplotted is an exponential temperature curve with a time constant of 25 minutes (a relatively good fit for values in the center of the range).

The section of aluminum siding used in this test is much smaller than the whole enclosure, so if this controller were used to drive these heaters on the sull-size enclosure, the time constant would be very, very long. So for bringing the whole enclosure up to temperature, a bigger power source will be needed.

Attachment 1: The setup for the heaters. My laptop + a textbook were used to weigh the foam down.

Attachment 2: The plot described above.

Attachment 1: IMG_5407.jpg
Attachment 2: temp_data_theory.jpg
1995   Tue Aug 4 17:22:40 2015 MeganMiscSeismometerThermal enclosure progress

Progress today on the seismometer's thermal enclosure:

1. I found better aluminum tape to seal all the corners of the enclosure, and taped up all the edges that are currently put together.
2. I made a plan to attach the bottom face of the enclosure to the frame, complete with feet to take the weight of the enclosure. Aluminum corner braces will press the aluminum sheeting to the frame, and the typical bolt/drop-in nut will be used to fasten them. In the middle of the corner brace, the threaded part of a foot will pass through and be fastened on the inside with a locking nut. The foot will pass through the foam that covers the aluminum, and keep the foam from touching the ground.
3. I started to implement the plan for the bottom of the enclosure: I retrieved the corner braces from West Bridge, found suitable feet for the enclosure, drilled pilot holes in the corner braces, and tapped the holes so the foot can screw in.

Attachment 1: The enclosure with newly-taped corners. If there were slight gaps between sheets of foam, I stuffed them with smaller pieces of foam before taping over them.

Attachment 2: The aluminum corner brace, with the foot through its hole.

Attachment 3: Side view of the brace and foot. In the actual setup the locking nut will be above the brace, allowing for the height of each foot to be individually adjusted.

Attachment 1: IMG_5428.jpg
Attachment 2: IMG_5432.jpg
Attachment 3: IMG_5431.jpg
1996   Wed Aug 5 15:20:44 2015 MeganMiscSeismometerEnclosure has feet!

Today I finished attaching the bottom of the thermal enclosure. See images:

Attachment 1: The bottom of the enclosure before the foam and feet are put on (the enclosure is sitting on its head in this photo). There are two holes per corner brace that fasten the brace and the aluminum to the frame, and one hole drilled and tapped for the feet to go through.

Attachment 2: The feet and the foam attached to the bottom of the frame.

Attachment 3: The feet screwed in to a proper height, secured with lock nuts on the other side of the aluminum, and the edges of the foam sealed up.

Attachment 4: The enclosure sitting on its feet!

Attachment 5: The threaded part of the foot on the inside of the enclosure. If this ends up getting in the way of any seismometer components, it can be cut down later.

Attachment 6: One of the feet on the floor. I adjusted the height such that the base of the foot is flush with the foam, but if other heights are needed all of the feet are adjustable.

Attachment 1: IMG_5434.jpg
Attachment 2: IMG_5435.jpg
Attachment 3: IMG_5436.jpg
Attachment 4: IMG_5437.jpg
Attachment 5: IMG_5439.jpg
Attachment 6: IMG_5440.jpg
1997   Fri Aug 7 10:39:44 2015 MeganMiscSeismometerMichelson layout diagram

Since Kate had the breadboard for the top of the seismometer's rhomboid machined, I was able to make a diagram of the layout for the Michelson (see attached image).

Pros:

• There is plenty of room between the fiber coupler and the beamsplitter, in case extra lenses need to be added to the path to collimate the beam, or a Faraday isolator to protect the laser.
• All components are on the rhomboid (with the exception of one of the end mirrors). This way, there is no difficulty in keeping everything aligned if(when) the rhomboid moves.

Cons:

• The beam splitter and the photodiode are on the small one-by-three hole bases, while all the other optics are on full size three-by-three hole bases. I'm not sure if some bases hold optics better than others, so this may not be an issue. But if it is, then it's also possible to change all the full-size bases in the diagram to the smaller ones so everything matches.
• This setup isn't balanced, which will cause the rhomboid to hang off-balance. Also, this setup will cause the center of mass of the rhomboid to rise above the rhomboid's suspension point. Counterweights can be added to fix this, it's just a question of where and how heavy.

All of these components are in the lab now, so I can start making this layout right away. Let me know if anyone has suggestions, changes that need to be made, etc.

Attachment 1: michelson_layout_diagram.jpg
1999   Mon Aug 10 11:15:28 2015 MeganMiscSeismometerSecond Michelson layout diagram

Koji gave me some suggestions and changes to my first Michelson layout diagram, so in this second one I have implemented them:

1. I rotated the whole setup by 90o. I had been unclear on the orientation of the two suspension wires with respect to the rhomboid, but after checking the setup I've changed the layout so that the Michelson will actually measure the correct dimension of motion.
2. I added the cut-outs to the inverted pendulum. These are in place to allow the wires through without them rubbing against anything. I kept a 1" gap between the two slots, but the height of the slots is arbitrary (at least in my drawing). Before machining, this dimension can be decided based on the rhomboid's range of swing motion.
3. There is still enough room between the fiber coupler and the beamsplitter for lenses that might be needed.
4. I added base part numbers to give a more concrete idea of how the setup will fit together. Besides the one for the fiber coupler, all bases are only one hole wide by two or three deep. These were chosen based on the constraints of end mirror 1 being in the center of the short face of the inverted pendulum, and the arms of the Michelson being of equal length. All the bases are from Thorlabs:
5. There is still enough room on the other side of the inverted pendulum and rhomboid to add weights to counteract all the optics on the top side.

Edit to the image: The base of the photodetector should be either a BA1S or a BA1V.

Attachment 1: michelson_layout_diagram_2.jpg
2001   Wed Aug 12 16:04:22 2015 MeganMiscSeismometerLight through fiber + beam scans

Yesterday (08/11/15) Koji helped me get some light through the fiber that will eventually bring light to the seismometer's Michelson. A fiber illuminator was attached on the output end of the fiber, and this produced a beam bright enough to see on the input end of the fiber. This beam was aligned on all of the optics between the fiber and the premode cleaner. The laser was then turned on, and the IR beam was then aligned from the PMC to the fiber. Both beams could be seen on the detector cards, so we were able to co-align the two beams through many small adjustments. Once the beams were co-aligned, the illuminator was taken off of the output end of the fiber, and the fiber was replaced into its mount. Then, using a power meter, we were able to take readings on either end of the fiber to see how much of the light was actually making it through the fiber. Before the fiber, the beam was at ~64mW, and after the fiber, the beam was at ~18mW, which is about 28% throughput.

After getting some light through the fiber, we set up the beam scan CCD in front of the output end of the fiber. A long rail was fastened to the table parallel to the beam, so that the CCD could slide in a straight path down the table (see Attachment 1).

After making sure the beam spot remained on the CDD's face over the whole length of the rail, the width of the beam was recorded at every inch interval down the length of the rail. Measuring the distance from the fiber in inches was convenient, because the holes in the table are placed at one-inch intervals. The value shown by the beam scan software is the Gaussian diameter of the beam (the point at which the beam intensity is ~13.5% of its peak value), so when plotting the data the recorded value was divided by 2 to give the Gaussian radius. Attachment 2 is the plot of the beam profile, beam radius as a function of distance from the fiber's collimating lens. The plot shows the clear dispersion of the beam as it gets further away from the beam.

The next beam scan that was done was after a lens that is upstream from the input of the fiber. The setup to do this scan was similar, but I used a ruler rather than the larger rail used in the previous scan (see Attachment 3).

Attachment 4 shows this beam's profile.

This part of the beam may need to be scanned further out than just 12", and that can be done next. Another task is to measure the Y values of the beam as well. The next step for the exisitng data is to fit a Gaussian to them, which will give the size of the waist and the position of the waist. These values can then be used in a la mode to find the optimal lens placement to maximize the amount of light that makes it through the fiber.

Attachment 1: IMG_5463.jpg
Attachment 2: beam_scan_1.pdf
Attachment 3: IMG_5464.jpg
Attachment 4: beam_scan_2.pdf
2002   Wed Aug 12 16:28:20 2015 MeganMiscSeismometerMichelson layout diagram - Final (?) version

Attached is my final (?) version of the layout for the seismometer's Michelson.

Features:

• All of the bases are Newport bases from Koji's most recent order: two 9914 bases, and five 9912 bases (three of which are machined).
• The machining of three of the 9912 bases is cutting off 1.25" of the length, and milling the slot in closer towards the mounting hole. Cutting off some of the length allows elements to be placed closer together, and milling the slot further inwards allows for two connection points to the rhomboid.
• The two bases on to the inverted pendulum (one is to hold an end mirror, and the other is a couterweight) can each be attached with 1/4-20's in four places.
• The rest of the bases (all on the rhomboid) can be attached with 1/4-20's in two places. Two connection points ensures that the optics can't rotate/cause noise. The exception is the base for the photodiode; it is fastened in just one place because it is in the breadboard's corner. I'm not sure if just one connection for the photodiode will be an issue; I will check with Koji how important it is to have more than one connection point.
• All of the mounts leave some room in the slots for movement of the optics. The beamsplitter's base and end mirror 2's base have just 1/8" leeway when moving away from each other; they are in close proximity so this limits their range of motion.
• The whole lower half of the rhomboid breadboard is empty, so there is plenty of room for any counterweights that may be needed.
• There is ~2" of space after the fiber coupler for a lens (if needed).
Attachment 1: michelson_layout_diagram_3.pdf
1956   Tue Jun 30 16:24:06 2015 Megan, KateMiscSeismometerRhomboid is suspended

Today Kate and I suspended the rhomboid and made bumpers for it using some McMaster-Carr frame pieces-

Kate's finger points to the upper pin vise that had not yet been tightened, while the rhomboid's full weight is on the wires.

This is frame after the addition of bumpers. Rubber sheeting was placed along the Al beams, and corners were placed on the beams to protect the other two sides of the rhomboid.

This is the clamp setup above the two upper pin vises. The wires go between the flate plates, which are adjustable. This is where the lengths of the wires can be adjusted (carefully) so the rhomboid hangs straight.

The period of the rhomboid's oscillations was just over 23 seconds, which is about as slow as it should be. The rhomboid did not hang perfectly straight; possible factors are a weight imbalance or an unevenness of the wires due to different pin vise heights. When the left upper pin vise was tightened, the rhomboid did hang closer to straight, suggesting that the height of the pin vises does affect the balance of the rhomboid.

The rhomboid was left suspended when we left this afternoon, to see if the wires and pin vises can hold its weight for a long period of time.

142   Thu Jun 25 10:44:46 2009 MichelleMiscGeneralWeekly Summary 1

Over the course of the first week here I've done several things. The first thing we're going to try to do in the lab (once we have all our parts in) is lock a simple cavity using Pound-Drever-Hall. I've been reading some of the literature on that and familiarized myself with that technique. Through these readings, I've come across various terms and equipment used in optical setups that I was unfamiliar with, so I've become acquainted with those. I attended the laser safety training meeting and have started to find my way around the lab. Connor and I also began characterization of the Nd-YAG laser. While I will not be working with that one, I will have to do the same thing for the one I will be working with. We first made some measurements of its output power versus the drive current, and results from that can be found in an entry to the eLog on 6-23-09. Today we are going to use the BeamScan to figure out the divergence of the laser.

Various other things that I've done over the past week include learning how to work with Matlab and Linux (both of which I am relatively unfamiliar with), and attending talks about the LIGO project by Dr. Weinstein.

159   Wed Jul 8 10:36:44 2009 MichelleMisc Week 3 Update

We have mirrors! And clamps! And posts! In short, everything we need to actually put all the optics in their proper places. Thus, this week I have successfully placed the steering mirrors and the high reflectance mirrors into their mounts without touching/breaking any of them, and soon I'll be clamping them in their proper locations.

Connor and I  found out that Aidan's laser isn't behaving itself. The manufacturer specifies the waist as being in a different location than where we calculated it to be. We sent the beam through a half-wave plate and then a polarizing beam splitter and then measured the power along each axis, and the ratios are strange. We can't get the beam to be entirely transmitted along one axis by rotating the half-wave plate, like we should be able to if the beam is coming out linearly polarized. So the hypothesis is...it's not coming out linearly polarized. It may be elliptical. For the time being we're going to split the beam from the other NPRO and use it for both experiments, at least while the alignment is taking place. In the case of the gyro, we'll actually be feeding back to the laser and altering its frequency, so we'll definitely need separate lasers for each experiment at that time.

The 495 mW NPRO's SOP has finally been (mostly) approved and it first lased on Monday. This laser's power supply is a bit weird - the display for the power it thinks the laser is putting out doesn't match at all with what the powermeter actually says the laser is putting out. So we're not paying attention to the power display. The drive current goes up to 1.00 A, and at this maximum current, the laser is putting out ~150 mW. Apart from not being able to get a higher power than this, the laser is fairly well behaved - the power fluctuations as measured by the powermeter are small. The results of output power vs. drive currentmeasurements are on the eLog.

Connor and I also measured the electronics noise and intensity noise at various different powers, and then did a theoretical shot noise calculation for each of these. The setup and procedure are described in more detail in a recent eLog entry, which also includes graphs and the matlab code used to generate them.

Over the next week I'll be setting up the optics table for a simple PDH lock using a fabry-perot cavity, aligning the laser, and setting up the proper feedback using the DAQ. (Which I'll need to talk to Dmass about).

Oh, and we found out yesterday that Connor and I can't do any hazardous tasks in the lab without supervision, which includes aligning the lasers, even at low power. Aidan and Alastair will both be gone from tomorrow until next week Friday, so this poses a slight challenge. Hopefully Dmass will be around?

That's about it for now, I think.

169   Mon Jul 13 13:59:19 2009 MichelleLaserGeneralNPRO acting up

I'm having some issues with the 495 mW NPRO, or possibly with its power supply. I ran the laser for about 15 minutes at 2 mW while doing some aligning. I closed the shutter to move a mirror, and upon opening the shutter the laser was no longer lasing. The power supply read 0.0 A driving current. I closed the shutter again and checked all connections between the laser and the power supply. All in order. I opened the shutter and turned the dial a bit on the power supply, and lo and behold the current was back up to 0.46 A, the lasing threshold, but still no light coming out.

The drive current jumped around a lot, sometimes to 0.0 A, and even when I put it up to around 0.54 A, which the laser should definitely be lasing at, nothing came out the aperture. The internal laser temperature was normal and not fluctuating. The lab itself is pretty warm today, in the 70s. Unless someone changed the temperature, it felt like the heat was on. I don't think this would have any effect on the laser, but I'm not really sure.

So, I'm going to search for the manual online and see if anyone over at the 40m had problems with this power supply.

170   Mon Jul 13 21:39:11 2009 MichelleLaserGeneralNPRO acting up

 Quote: I'm having some issues with the 495 mW NPRO, or possibly with its power supply. I ran the laser for about 15 minutes at 2 mW while doing some aligning. I closed the shutter to move a mirror, and upon opening the shutter the laser was no longer lasing. The power supply read 0.0 A driving current. I closed the shutter again and checked all connections between the laser and the power supply. All in order. I opened the shutter and turned the dial a bit on the power supply, and lo and behold the current was back up to 0.46 A, the lasing threshold, but still no light coming out. The drive current jumped around a lot, sometimes to 0.0 A, and even when I put it up to around 0.54 A, which the laser should definitely be lasing at, nothing came out the aperture. The internal laser temperature was normal and not fluctuating. The lab itself is pretty warm today, in the 70s. Unless someone changed the temperature, it felt like the heat was on. I don't think this would have any effect on the laser, but I'm not really sure. So, I'm going to search for the manual online and see if anyone over at the 40m had problems with this power supply.

We should get back to trending the lab temperature. I think there are some long standing problems with the HVAC setup. It would help to quantify this.

172   Wed Jul 15 10:47:55 2009 MichelleLaserGeneralNPRO acting up

 Quote: I'm having some issues with the 495 mW NPRO, or possibly with its power supply. I ran the laser for about 15 minutes at 2 mW while doing some aligning. I closed the shutter to move a mirror, and upon opening the shutter the laser was no longer lasing. The power supply read 0.0 A driving current. I closed the shutter again and checked all connections between the laser and the power supply. All in order. I opened the shutter and turned the dial a bit on the power supply, and lo and behold the current was back up to 0.46 A, the lasing threshold, but still no light coming out. The drive current jumped around a lot, sometimes to 0.0 A, and even when I put it up to around 0.54 A, which the laser should definitely be lasing at, nothing came out the aperture. The internal laser temperature was normal and not fluctuating. The lab itself is pretty warm today, in the 70s. Unless someone changed the temperature, it felt like the heat was on. I don't think this would have any effect on the laser, but I'm not really sure. So, I'm going to search for the manual online and see if anyone over at the 40m had problems with this power supply.

I took the power supply over to the 40m to see if Alberto's laser would work when hooked up to it. It did, so I suspect that the problem lies with the laser rather than the power supply. Alberto was able to get double the drive current that we were getting, so that is also suspect. He said the "ADJ" readout (power adjustment) on the supply was usually set to zero, but when the "Pwr" readout (supposedly the power coming out of the laser) is changed, it changes the ADJ and drive current and anything else which would obviously be associated with power. I hooked up the power supply to my laser again and here's what I found:

-It lases for short periods of time, usually <5 mins, before it stops.

-It lases for longer periods of time at higher drive currents.

-I still can't get more than 1.02 A and less than 0.30 A out of the power supply.

-The "Pwr" display on the supply still doesn't correspond to the power as measured by the Ophir powermeter.

My next steps are to see if Alberto can come and take a look, in case I'm doing something on the operator side which is obviously wrong. I will also consult with Rana.

174   Wed Jul 15 14:40:44 2009 MichelleLaser NPRO ... fixed?

Alberto came over to have a look at the laser and discovered that the diode temperature was continuously increasing the longer the laser was kept on. The crystal temperature remained constant. He turned off the laser and shut the shutter, jiggled the cable connected to the laser a bit, and turned it back on. Lo! The temperature no longer increased...

So for the time being the laser seems to be fixed. If these problems start happening again, however, I may have to do some more rigorous troubleshooting/actually find out what's causing the problem.

190   Wed Jul 22 11:09:45 2009 MichelleMisc Weekly Update 5

Over the course of the past week I've done a few things. When I began alignment I discovered that our laser was periodically shutting itself down. This was a very perplexing problem for about 2 days before Alberto came in with the diagnosis: the diode was overheating. We'll be sending that in to get it fixed, and we'll also put a heat sink on its casing. Hopefully that will be up and running by the time we really need it.

Right now, Aidan's laser is set up with a 50/50 beamsplitter, and then a half wave plate at each output of that. That way we can run the laser at full power, and each of us can independently adjust the power going into our respective experiments. This is working well while we're aligning things, but it clearly won't work long-term - we need to act directly on the laser's frequency to lock it to a cavity. This may not fare so well for fiber noise suppression.

We have our setup mostly aligned. The beam is going through some steering mirrors, through a lens, into the Faraday Isolator, through another set of steering mirros and a lens, and into the EOM. There is very little loss inside the isolator (putting in ~35 mW and getting out 33-34 mW), however I have not been able to get the power at the output of the EOM higher than ~ 24 mW. I don't think this is normal, but I will check that with people who know better than I do. I think it is probably the fault of poor alignment - the aperture is ~ 2mm and it's about 2 cm from the lens in the middle of the table, so it's hard to reach it or even view it properly to see what needs tweaking.

Over the next week I plan to finish the alignment and hopefully get a lock. I'll get a picture up once the rest of the setup is in place and aligned.

Oh, and I also helped clean the lab this week. It's pretty shiny, except for the heaps of garbage boxes now sitting in the hallway. We'll take care of that soon.

197   Thu Jul 23 16:31:28 2009 MichelleLaser I've done some things in lab.

Update:

Today I aligned the laser beam through the EOM with something resembling a normal shape at the output. This was tricky. The powermeter isn't giving me very reasonable readouts, the aperture on the EOM is impossible to see with the IR viewer, the EOM is in the middle of the table where I can't really reach it, and it's very close to a focusing lens. The point being that I may have to tweak it a bit, but I really don't want to have to redo the alignment of that particular optic. So no earthquakes for a while.

A note on the power meter: It's been registering anywhere between -6 mW and 11 mW with no beam on it at all. I've been zeroing it before putting it in the beam before each use, but I don't know how much I trust it.

The beam shape coming out of the EOM  is still a bit funny - with one bright beam, and then a very faint ring, so it looks like a ring you would wear on your finger with a diamond on top. I am attributing this to the fact that the beam is slightly larger than the EOM's aperture; I have set it up so the center of the EOM coincides with the beam's waist. I'm also (according to the power meter) getting a high attenuation inside the EOM, but whether this is correct or normal I haven't yet figured out.

We need another mount for a beam splitter, this will go at the input to the cavity. We are also still in need of a quarter waveplate, and Aidan says he has a spare that he won't need to use for a few weeks. Also, CVI doesn't specify the damage threshold for the cavity mirrors for cw lasers, only for pulsed sources. Alastair has sent them an email requesting this information, and once we know that we can send the beam into the cavity at appropriate power levels.

229   Wed Aug 5 10:10:11 2009 MichelleMiscGeneralWeekly Update (7?)

A number of things made the past week somewhat unproductive, until yesterday. I was at a conference Mon-Wed. last week and was sick that Friday. This Monday I finished my second progress report (now on the wiki).

Yesterday we made major progress in the setup and alignment of the cavity. It was really helpful to have optics people (Zach and Frank) down in the lab, I learned a lot about alignment. We replaced the two lenses we had initially (one before the FI and one before the EOM) with one slowly converging lens which would place the waist in the EOM. Frank also said there was no need to have two steering mirrors before different optics, since our laser height is fixed. We were initially going to use a curved mirror for the high reflectance mirror at one end of the cavity, but Rana suggested that we would get a lock faster if we just used two flat mirrors with a lens in between them (since the finessed of the cavity doesn't really matter right now). We're also not going to worry about mode-matching just yet.

The cavity is now roughly aligned. It will need some fine-tuning, but we should be able to start trying to lock today. We're going to start with an analog system to get a feel for the parameters and just to get some sort of error signal, and then later we'll switch everything over to the DAQ. That's about all for now.

236   Fri Aug 7 10:39:20 2009 MichelleLab Infrastructure Changing Lasers

We have to tweak the alignment of our PDH setup a bit, as well as change the cavity and profile the beam at different locations.

So we figure this is as good a time as any to stop using Aidan's laser and put in our one. We'll be working on that today, and we'll try to minimize the disruption this will cause to the fiber noise experiment.

241   Mon Aug 10 17:34:43 2009 MichelleLaserGeneralWorking Beam Profiler

We do, as of now, have one entirely working beam profiler. I believe we have borrowed it from Peter's lab.

Today we used it to profile the beam after realigning our setup (two or three times - so we actually have two or three profiles, but one of them is a razor blade measurement). We have much more bench space for the cavity now, and we can actually figure out what the beam is supposed to look like at different points, since we can get an accurate measurement of the waist size.

The beam is ~20% elliptical (estimate, we have yet to fit the data). It appears that the BeamScan software automatically compensates for ellipticity, so that on our readout we have one of the axes along the semimajor axis and the other along the semiminor axis. If we find out that we are wrong about this we will rotate the axes on the beam profiler head to get the correct orientation.

Pictures of new setup and beam profiles to follow - (tomorrow).

140   Tue Jun 23 19:16:53 2009 Michelle Stephens, Connor MooneyLaserFiberCalibration of FS NPRO output power vs drive current

We measured the output of the FS NPRO Laser at drive currents between 1 and 2.4 A, with 0.1A imcrements. The OPHIR powermeter was used with a 50W head, and was set to the 0.8W-6W range. The model is L50A-SH. We took two sets of measurements. For the first, the curve found was non-linear, starting off shallow, then becoming steeper, and finally levelling off. We weren't sure why the curve exhibited this behavior and we took a second set of measurements to verify our results. For the second set, we took the maximum and minimum values of the power fluctuations at each current. We found an average power from these values and generated error bars.

C = [1.002 1.101 1.201 1.301 1.400 1.501 1.600 1.701 1.801 1.901 2.00 2.100 2.200 2.301 2.384];
Pd = [6 46 94 154 225 301 398 501 625 759 870 978 1062 1131 1191];
Pu = [9 49 98 158 229 312 405 514 679 772 890 985 1068 1140 1198];

C is an array of the current values in Amperes.

Pd and Pu are the lower and upper bounds of power ouptut , in milliwatts, measured  at the power meter.

The directory in which the above data was analyzed is /users/cmooney/power2.m

Attachment 1: Power_output_for_Nd-YAG_Plot.pdf
143   Fri Jun 26 17:20:45 2009 Michelle Stephens, Connor MooneyLaserFiberNPRO beam width divergence measurements

We used the BeamScan to characterize the divergence of the NPRO laser as a function of distance. Measurements were taken at (1/e^2)*Imax. We then fit the data to the function characteristic of gaussian divergence to find the location and size of the waist. The results are shown graphically in the attached file. Extrapolating, we found that the waist is 21.5 cm behind the laser aperture, and the (virtual, assuming that the laser beam encounters a diverging lens before the aperture) waist size is 124 micrometers.

Here is our data:

The distances, measured in inches from the base of the laser, are

[0 0.5 1 3 5 7 9 11 13 15 17 19 21 23 25]. The distance from the aperture of the laser to the base is 0.75 inches.

The beam sizes, measured in micrometers along one axis, are

[1334 1399 1542 1655 1968 2234 2537 2785 3063 3359 3638 4001 4253 4561 4708]

The directories for each of the Matlab files used to generate a graph of the data and carry out a least-squares regression are

/users/cmooney/BeamScans.m

/users/cmooney/myfun.m

Attachment 1: NPRObeamdiv.pdf
154   Mon Jul 6 16:59:47 2009 Michelle Stephens, Connor MooneyLaser Power Output of 495 mW NPRO

We characterized the power output vs. drive current of the 495 mW NPRO laser for the gyro experiment. The current supply  goes up to 1.00 A. Here is our data:

C = [0.46 0.52 0.60 0.66 0.74 0.80 0.88 0.94 1.00];
Pd = [2 18 38 55 71 93 110 125 146];
Pu = [2 20 39 56 72 94 110 126 147];

C is drive current, Pd is lower limit on power output in mW, and Pu is upper limit.

We graphed the results and fit a line to it. The slope is 261.5 mW/A, and the intercept is -118.2 mW. The graph is attached.

directory is: \users\cmooney\Power495mW.m

Attachment 1: PowervCurrent495mW.pdf
158   Tue Jul 7 16:49:05 2009 Michelle Stephens, Connor MooneyLaserGeneralNoise Measurements

We used an SRS Spectrum Analyzer in parallel with an oscilloscope to measure various sources of noise in the 495 mW NPRO laser. We sent the beam into a PDA10CS photodetector and fed that signal to the spec analyzer and the scope. We measured the dark noise, and then the total noise at 2 mW, 4 mW, 7mW, and 9mW. We then did a theoretical calculation for the shot noise, as follows:

N = (Po*dt) / (h*f)

dN = sqrt(Po*dt / h*f)

dE = sqrt(h*f*Po*dt)

dI = dE*(Responsivity of PD)

dV = dI*(Gain of PD)

We plotted all three of these noise sources in matlab. The plot and the code are attached. The directories are:

/users/mstephens/NPRONoise.m

/users/mstephens/495mW_NPRO_Noise.pdf

Attachment 1: 495mW_NPRO_Noise.pdf
Attachment 2: NPRONoise.m
load -mat SRS003.MAT
load -mat SRS005.MAT
load -mat SRS006.MAT
load -mat SRS007.MAT
load -mat SRS008.MAT

h = 6.626E-34;
mu = 3E8/1.604E-6;
deltaT = 1.0;


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