I am trying to track down possible errors in our measurements. 

So as a first step I am recomputing the IPPOS waist location with respect to the MC waist, using the same optical layout diagram as the one used by Jenne in her calculations.  Pic of Jenne's lab notebook showing location of optics is attached.  

 Let us compare it with the old measurement of the IPPOS beam from June/18/2010.

Note that there is a discrepancy of about 3.2 m in the waist location for the vertical profile and about 3.5 m for the horizontal profile between these two measurements. 

Let us compare these measurements with what is expected from calculations.  Jenne uses the known parameters of MC waist and the locations of the MMT optics to compute the parameters for the IPPOS beam:

 As the 2010 measurements are reported wrt to MMT2 and calculations are wrt MCwaist, I have used the distance between the MCwaist to MMT2 = 3.910 m to shift the reference from MMT2 to MC waist. Refer to the attached diagram from Jenne's notes for this MMT2 <--> MC waist distance.

There is a discrepancy of 1.5 meters between the calculations and recently measured waist location.  The discrepancy with the 18Jun2010 measurement is much larger, about 3 meters in both v and h.

Are such variations to be expected between two successive measurements?  I looked at another case where we have two measurements of a beam to see what to expect.

I looked at the REFL (Reflection from PRM) case, where we repeated a measurement, to see how much variation could happen in w0 and zr, between repeated measurements. This was a particularly bad case as our first attempt had problems due to OL servo loop oscillations in the PRM suspension damping.  We fixed that later and measurement 2 has smaller residuals. And I think we are doing okay in IPPOS case as seen by the reduced scatter of the residuals.

 These are the fits from the REFL beam measurement 1

 I have also recomputed the fits to the data from REFL beam measurement 2.  They match the earlier fits reported by kiwamu in his elog 6446

Note that between these two measurements the beam waist location has shifted by 0.5 m for the vertical and about 1.3 m for the horizontal cases.  So variations of 1.5 m in the waist locations are possible if we are not careful.  But this is a particularly extreme example, I think we are doing better now and the measurement is unlikely to change significantly if we repeat it.

Some notes:

Fits for IPPOS and both REFL measurements 1 and 2 are attached. 

The zero reference for the z axis of the IPPOS beam plot is at a distance of 6.719 m from MC waist for a beam propagating towards the IPPOS QPD.

The zero reference for the z axis of the REFL beam plots is at a distance of 5.741 m from the MMT2 in the direction of a beam reflected by PRM and propagating towards the REFL port.

[Suresh, Jenne]

  The input beam is most probably being clipped at the Faraday Isolator.  

Evidence: 

a)  The beam scan of the IPPOS beam showed a nongaussian beam in the horizontal direction.  This was visible in the beam scan since it overlays a gaussian-fit over the data.

b)  I was able to remove this departure from gaussian profile by introducing an offset of 5 into the C1:IOO-WFS2_YAW_OFFSET.  

c)   We made a few measurements of the beam diameter as a function of distance at an offset of 7.  At a distance of beyond 3 m the deviation from gaussian profile was once again apparent. 

d)  We increased the offset to 14 to remove this deviation. 

e)  When we measured the beam diameter again with this new offset the horizontal diameter and vertical diameters dropped by 2.sigma.  Indicating there the beam was clipped till then.

f)   We increased the offset to 16 and the beam diameter did not change further (within 1.sigma). Implying no more clipping, hopefully. 

And then the earthquake stopped us from proceeding further. 

We plan to investigate this further to be sure..  Data attached.

Subsidiary effects to keep track of:

1) Introducing an offset into the WFS loops decreases the coupling from PSL into MC. 

2) If the beam is being clipped at the Faraday Isolator then the REFL beam would also show lesser clipping with WFS offsets.

I tried to determine an optimal WFS2YAW offset to be used so that we may avoid clipping.

Initially, I just measured the beam diameter as a function of offset.  If the beam diameter would become independent of offset if it is not clipped.  However a systematic effect became apparent when I shifted the beam on the detector to a slightly different location.  So I repeated the measurements while recentering the beam to the same location everytime  (centered at -1650+/- 50 for both H and V directions).

I have attached plots of the scans for both cases, with recentering and without.    I have not been able to figure out what is going on since the beam diameter does not become independent of the offset.  While the beam profile becomes more gaussian beyond offsets of about 7 or so, the beam diameter does not seem to follow a clear pattern.  The measurements are repeatable (within one sigma) so the experimental errors are smaller than 1 sigma.

The photographs below show the improvement of Horizontal beam profile with WFS2Yaw offset.  These seem to indicate a good gaussian beam for offsets beyond 7 or so.  At offsets more than 12 the MC unlocks.

Offset = -2	Offset = 0	Offset = 2	Offset = 8

This seems to indicate that the beam diameter does not vary for WFS2Yaw offset > 8	But if we recenter the beam for each measurement this effect seems to vanish

 Will continue tomorrow.   Jenne wants to do some IFO locking now.

 From the mode measurement I and Suresh have done yesterday, I calculated what beam size we expect at ETM ((1) upper Fig.1)  and at ETM after one bounce ((2) lower Fig.1).

Fig.1 (Yarm)

In case of (1), we expect approximately w=6300 um (radius), and w=4800 um for one-bounce spot (2) from the measured mode, see Fig.2.

Fig.2

This roughly agree with what we observed on CCD camera. See, pic1 for (1) and pic2 for (2). The spot at the ETMY (1) is larger than the one-bounced spot (2). From the monitor it is difficult to assume the radius ratio. The observed spot of (2) is a bit smaller than the prediction. It could happnen when (A) the ETMY (as a lens) is slightly back of the ideal position (= the distance between the ITM and ETM is longer than 40m) (B) the real waist is farer than ITM position toward MC (I assumed roughly 5 m from Jenne's plot, but could be longer than that).

pic1 (left): beam spot hitting on the suspension frame. pic 2 (right): the one-bounced beam spot hitting on the suspension frame.

[Kiwamu, Suresh]

   Today we attempted to measure the beam profile of the REFL beam under two conditions:

              (a) with PRM aligned and ITMs misaligned 

              (b) with PRM misaligned and ITMs aligned

The raw data is shown below.  In each of the above conditions we measured in both the vertical (v) and horizontal (h) directions.   The measurements in the vertical direction were better than the ones in the horizontal direction because the optics had a horizontal oscillation which gave larger errors in measurement.

Looking at the general trend of these lines it is clear that modes are not matched since the beam reflected by the PRM has a different divergence than that reflected from ITMs.  The beam is also astigmatic as the vertical and horizontal directions have different divergences.

I could find beam parameters only for the Blue line above (Profile in the vertical direction while PRM was aligned).   The fit is quite sensitive to the data points close to the waist, so we need to make better (lower St.Dev.) measurements near the AP table closer to the beam waist.  The intensity with only one ITM aligned is too low and also contributes to the errors.   The beam size is close to 6mm in the horizontal direction, this coupled with yaw oscillations give large errors in this measurement.

Here is the only reliable fit that could be obtained, which is for the prompt reflection from the PRM in the vertical direction

The fit function I used is  Beam Dia = Waist { Sqrt [ 1+  ((z + z0)/zr)^2). The fit parameters we get for this data are

z0 = 7.7 m 

Waist = 2.4 mm

zr = 6.9 m

Will make another attempt later today...

Gabriele left the DataRay beam profiler + peripherals (see Attachment #1) in his office. I picked them up just now and brought them over to the 40m.

I had measured the y-profile of the beam of Friday at 5 axial locations and fit them to an erfc function using the lsqcurvefit function of MATLAB. 

The results were as follows - 

z(cm)    w (in)

4          0.0131

10        0.0132

15        0.0137

20       0.0139

25        0.0147

I left w in inches in the intensity plots as MATLAB gave more accurate fits for those values.

I converted these to S.I while making the spot-size vs z plot and the corresponding values in microns were 

332.74, 335.28, 347.98, 353.06, 373.38.

On fitting these values to the formula for the spot size of a Gaussian beam, the beam waist came out to be 330.54 microns and the location of the beam waist was at z=-2cm, where z=0 marks the head of the laser. 

TO-DO : Measure the spot size of the beam at more axial points to obtain a better fit. 

              Measure the x-profile of the beam. 

              Analyse the error in the spot sizes and corresponding error in the beam waist. 

I have attempted to calculate the instrument error (micrometer least count) using the values of the spot size obtained by the least squares fitting method. This error is large towards the centre of the beam as the power varies significantly between adjecent markings of the micrometer. Using the new values of error obtained, I used the chi-square fitting minimisation method to further optimise the waist size. 

The modified values are - 

z(cm)    w (in)

4         0.0134

10        0.0135

15        0.0140

20        0.0142

25        0.0150

And the revised values for the beam waist and location are 338.63 microns and -2.65 cm respectively. 

I will now try to use the chi-square stastitic to estimate the error in spot size. 

1. Include several sources of error. Micrometer error is one, but you should be able to think of at least 3 more.
2. There should be an error bar for the x and y axis.
3. Also, use pdftk to put the PDFs all into a single file. Remove so much whitespace.
4. Google 'beautiful plots python' and try to make your plots for the elog be more like publication quality for PRL or Nature.

You may compare your results with this.

RXA: please no, that's not the right way

​Updates in the He-Ne beam profiling experiment. 

1. I've made intensity profile plots at two more points on the z-axis. The additition of this plots hasn't affected the earlier obtained beam waist significantly. 
2. I have added other sources of error, such as the statisitical fluctuations on the oscilloscope(which is small compared to the least count error of the micrometer) and the least count of the z-axis scale.
3. I have also calculated the error in the parameters obtained by fiiting by calculating the covariance matrix using the jacobian returned by the lsqcurvefit function in MATLAB. 
4. I have also added horizontal error bars to all plots. 
5. All plots are now in S.I. units 

New and improved plots for the He-Ne profiling experiment 

Font size has been increased to 30. 

The plots are maximum size (Following Rana's advice, I saved the plots as eps files(maximized) and converted them to pdf later).

There is a shaded region around the trendline that represents the parameter error. 

Function that I fit my data to (should have mentioned this in my earlier elog entries) 

Description of my error analysis -

1. I have assumed a 20% deviation from markings in the micrometer error. 

2. Using the error in the micrometer, I have calculated the propogated error in the beam power :

I added this error to the stastistical error due to the fluctuation of the oscilloscope reading to obtain the total error in power. 

3. I found the Fisher Matrix by numerically differentiating the function at different data points  with respect to the parameters    and .

I then found the covariance matrix by inverting the Fisher Matrix and found the error in spot size estimation. 

EDIT : Residuals added to plots and all axes made equal 

Andrew and I set up the razor blade beam profiling experiment for He-Ne lasers on the "SP" table.  Once I receive the laser safety training, I will make power measurements and fit it to an erfc curve from which I will calculate the gaussian profile of the beam. I'm attaching some pictures of the setup. 

Least count of the micrometer - 2 microns 

Laser  : Lumentum 22037130:1103P

Photodetector : Thor Labs PDA100A

The beam scan (which has been living in the bridge subbasement for a bit now) is in a state of imperfection.

I noticed that:

• The waist reading seems to change by not insignificant amounts as you move the spot across the head, even for just small perturbations about the center.
• None of the features which require two slits seem to be working (unsure if this is software or hardware related)

I took some pictures to try and illuminate the situation - The inverted images are included to make it easier to see the flecks (?) in the slits

I am not sure how to figure out if any bit of the scan is/has been fried.

Pending further investigation, enjoy large error bars in your scan measurements!

PICTURES OF BOTH SLITS ON THE BEAMSCAN HEAD:

There was something wrong with the Beam Scan PC.  The  mouse and screen were not responding and the PC was asking for drivers for any new hardware that we plugged in.  We called in the services of Junaid and co. since we do not have a Win98 Second Edition installation disk in the lab.   Junaid came with the disk, we changed the screen and the mouse and installed everything. 

We tried to get the network going on the PC so that we could update stuff easily over the net.  This didnt succeed. For now, we still have to depend on a Win98se CD to get drivers if any new hardware is connected to this machine. 

For future reference, some notes:

1)  We will get a copy of Win98SE for the lab from Junaid

2) We have to use a USB mouse from Dell. We have several spares of this. The drivers for these are present in the machine. 

The Beam Scan is working okay now.  We will proceed with the beam profile measurements.  

Purpose

To use a razorblade to measure beam waist at four points along the optical axis, so as to later extrapolate the waist. This information will then be used to effectively couple AUX laser light to fibers for use in the frequency offset locking apparatus.

Data Acquisition

1) Step the micrometer-controlled razorblade across the beam at a given value of Z, along optical axis, in the plane orthogonal to it (arbitrarily called X).

2) At each value of X, record the corresponding output of a photodiode, (Thorlabs PD A55) here given in mV.

3) Repeat in Y plane at the same value of Z

4) Repeat process at multiple points along Z

Analysis

Data from each iteration were fitted to the error function shown below.

y(x) = (.5*P)*(1-erf((sqrt(2)*(x-x0))/wz))

'P' corresponds to peak power, 'x0' to the corresponding value of x (or y, as the case may be), and 'wz' to the spot size at the Z value in question.

The spot sizes from the four Z values were then fit to:

y(x) = w0*sqrt(1+((x*x)/(zr*zr)))

Where 'w0' corresponds to beam waist, and 'zr' to Rayleigh Range.

Conclusion

This yielded a Y-Waist of 783.5 um, and an X-Waist of 915.2 um.

The respective Rayleigh ranges were 2.965e+05 um (Y) and 3.145e+05  um (X).

Next

I will do the same analysis with light from the optical cables, which information I will then use to design a telescope to effectively couple the beams.

 Goal

To design an optical setup (telescope / lens) to couple 1064nm NPRO light into PANDA PM980 fibers in order to characterize the fibers for further use in the frequency offset locking setup.

Design

Calculations

 The beam waist of the NPRO was determined as 233um 6cm in front of the NPRO. This was used as the seed waist in ALM.

The numerical aperture of the fiber was given as 0.12, which allowed me to calculate the maximum angle of light it would accept, with respect to the optical axis, as NA = sin(theta) where theta is that angle.

Given that the coupler has a focal length of 2mm, I used the formula r = f * tan(theta), to yield a "target waist" for efficient coupling into the fiber. This ended up being 241.7um.

Since there was not a huge difference between the natural beam width of the NPRO and our target waist, I had no need for multiple lenses.

I used 230um as a target waist for a la mode, to leave myself some room for error while coupling. This process gave me a beam profile with a lens (f=0.25m), and a target waist of 231um, located 38.60cm from the coupling lens

I have attached ALM code, as well as the beam profile image. Note that the profile takes zero to be the location of the NPRO waist.

Next Steps

After this setup is assembled, and light is coupled into the fibers, we will use it to run various tests to the fiber, for further use in FOL. First of all, we wish to measure the coupling efficiency, which is the purpose of the powermeter in the above schematic. We will measure optical power before and after the fibers, hoping for at least ~%60 coupling. Next is the polarization extinction ratio measurement, for which we will control the input polarization to the fibers, and then measure what proportion of that polarization remains at the output of the fiber. 

I was finally able to get a reasonable measurement for the beam waist(s) of the spare NPRO.

Methods

I used a razorblade setup, pictured below, to characterize the beam waist of the spare 1064nm NPRO after a lens (PLCX-25.4-38.6-UV-1064) in order to subsequently calculate the overall waist of the beam. The setup is pictured below:

After many failed attempts, this was the apparatus we (Manasa, Eric Q, Koji, and I) arrived with. The first lens after the laser was installed to focus the laser, because it's true waist was at an inaccessible location. Using the lens as the origin for the Z axis, I was able to determine the waist of the beam after the lens, and then calculate the beam waist of the laser itself using the equation wf = (lambda*f)/(pi*wo) where wf is the waist after the lens, lambda the wavelength of the laser, f the focal legth of the lens (75.0 mm in this case) and wo the waist before the lens.

We put the razorblade, second lens (to focus the beam onto the photodiode (Thorlabs PDA255)), and the PD with two attenuating filters with optical density of 1.0 and 3.0, all on a stage, so that they could be moved as a unit, in order to avoid errors caused by fringing effects caused by the razorblade.

I took measurements at six different locations along the optical axis, in orthogonal cross sections (referred to as X and Y) in case the beam turned to be elliptical, instead of perfectly circular in cross section. These measurements were carried out in 1" increments, starting at 2" from the lens, as measured by the holes in the optical table.

Analysis

Once I had the data, each cross section was fit to V(x) = (.5*Vmax)*(1-erf((sqrt(2)*(x-x0))/wz))+c, which corresponds to the voltage supplied to the PD at a particular location in x (or y, as the case may be). Vmax is the maximum voltage supplied, x0 is an offset in x from zero, wz is the spot size at that location in z, and c is a DC offset (ie the voltage on the PD when the laser is fully eclipsed.) These fits may all be viewed in the attached .zip file.

The spot sizes, extracted as parameters of the previous fits, were then fit to the equation which describes the propagation of the spot radius, w(z) = wo*sqrt(1+((z-b)/zr)^2)+c, w(z) = w0*sqrt(1+((((z-b)*.000001064)^2)/((pi*w0^2)^2))) where wo corresponds to beam waist, b is an offset in the z. Examples of these fits can be viewed in the attached .zip file.

Finally, since the waists given by the fits were the waists after a lens, I used the equation wf = (lambda*f)/(pi*wo), described above, to determine the waist of the beam before the lens.

Plots

note: I was not able to open the first measurement in the X plane (Z = 2in). The rest of the plots have been included in the body of the elog, as per Manasa's request.

Conclusion

The X Waist after the lens (originally yielded from fit parameters) was 90.8 27.99 ± .14 um. The corresponding Y Waist was 106.2 30.22 ± .11 um.

After adjustment for the lens, the X Waist was 279.7 907.5 ± 4.5 um and the Y Waist was 239.2 840.5 ± 3.0 um.

edit: After making changes suggested by koji, these were the new results of the fits.

Attachments

Attached you should be able to find the razor blade schematic, all of the fits, along with code used to generate them, plus the matlab workspace containing all the necessary variables.

NOTE: Rana brought to my attention that my error bars need to be adjusted, which I will do as soon as possible.

- Plots should be directly attached on the elog. (Attaching codes in a zip is OK.)

- Plot legends should not touch or hide any data points.

- Don't exclude data points.

- The model for the beam profile fitting is incorrect: zr and w0 are dependent

- The code needs to be reviewed by someone for refinement.
  (EricQ, or possibly Jamie, Jenne while he is absent).

 Today, I borrowed the beam profiler from Brian (another SURF) in order to double check my razor blade measurement figures, using the below setup:

Measurements are included in the a la mode code that is attached entitled beamfit.m. The beam fitting application yielded me waists (after the lens) of 35.44 um in the x plane, and 33.26 um in the y plane. These are both within 3 um of the measurements I found using the razor blade method. (I moved and resized the labels for the waists in the figure below for readability purposes.)

I then plugged these waists back into ALM, in addition to the lens specifications, to determine waist size and location of the NPRO, which turned out to be 543 um in the x located at Z = 1.160m, and 536 um in the y, located at 1.268m. These measurements are based upon zero at the waist after the lens, and the positive direction being back toward the NPRO.

The only systemic difference between these measurement and my original razor blade measurements was that I had taken the focal length of the lens as 75mm, which is advertised on the manufacturer's site. However, the more detailed specs revealed that the focal length was 85.8mm at 1064nm, which made a difference of about 400 um for the final waist determination.

After yesterday's changes in the MC cavity state today it was necessary to optimize the alignment to the Faraday.

The way I did it was by tuning the PSL periscope in pitch and yaw trying to maximize TRX with the arm locked. After a small change in either one of the two directions I first maximized the MC transmitted power and then I ran the alignment script for the X arm.

I explored the space for both pitch and yaw and the max that I could get from TRX was 0.91. I'm not sure whether the increase in TRX is entirely due to a better alignment to the Farady rather than to a higher MC transmitted power.

Also I'm not sure I'm well interpreting the image from the camera pointing at the Farady. I guess I need someone more familiar with it to tell me if it shows any sign of clipping.

Anyway, last week, even before the MC got misaligned, TRX didn't go above 0.90. So now I wonder whether it's the MC's fault or something else's if we have that value..

[Jenne, Raji (before dinner)]

We put the beam attenuation optics in place.  Before putting any optics down, I centered the IOO QPDs, then adjusted the HWPs and PBS such that we remained centered on those QPDs.

Now, I'm about to unblock the beam and let ~100mW into the vacuum so I can lock the MC.  Steve and Manasa were putting on the light access connector when I left earlier, so I'm excited to use it!

1. With TRX and TRY maximized using ASS, I centered the Oplev spots on the respective QPDs for the four test masses and the BS. I also centered the spot onto the IPPOS QPD by moving the available steering mirror.
2. At EX, I tweaked the input pointing of the green beam into the arm by manually twiddling with the PZT mirrors. I was able to get GTRX~0.4.
3. On the AS table - Koji and I found that there was a steering mirror placed in the AS beam path such that there was no light reaching the AS110 or AS55 PDs. Please - when you are done with your measurement, return the optical configuration to the state it was in before so that the usual locking activity isn't disturbed by a needless few hours troubleshooting electronics.

Once Koji is done with his checkout of the whitening electronics, I will try and lock the PRMI.

[yutaro, ericq]

We made the beam spot on QPD for the oplev of ETMY centered by changing the orientation of the mirror just before the QPD.

Before doing this, we ran dithering for Y arm and froze the output of ASS for Y arm.
 

[yutaro, Koji]

We made the beam spot on QPD for the oplev of ITMY centered by changing the orientation of the mirror just before the QPD.

Before doing this, we ran dithering for Y arm and froze the output of ASS for Y arm.

I made the beam spot on QPD for the oplev of ITMY centered by changing the orientation of the mirror just before the QPD.

Before doing this, I ran dithering for Y arm and froze the output of ASS for Y arm.

Here are some beam centering strategies...

Beam height around PRC:
 - From our in-vac inspection today, we noticed that the beam is high on TT2 and PRM, and was slightly clipped (or maybe not) by the earthquake stop of TT2.
 - According to the beam spot position measurements (Attachment #1; includes measurements taken today), beam spot on PRM and PR2 are vertically mis-centered by +1 cm, but vertically pretty centered on PR3, BS and ITMs.
 - These imply we need to play with TT1 and PR2 to level the beam inside the PRC.
 - This is consistent with the height issue we found during the last vent on POP_SM4 (1 inch mirror in front of LO1). We had to place a spacer to make POP_SM4 high to extract the POP beam coming from PR3 to PR2 (40m/16832). So we should be able to remove the spacer after the fix.
 - This fix should be done iteratively without losing flashing in the arms, sacrificing BHD alignment.

Horizontal beam mis-centring on PR3:
 - According to the beam spot position measurements, beam is vertically centered, but horizontally mis-centered by ~1.5 cm at PR3.
 - This is consistent with beam clipping we have in Y green transmission in YAW (Y green is clipped in YAW at PR3).
 - Since the beam is horizontally centered on PRM and PR2, we probably need to physically move PR3 to center the beam and to un-clip Y green transmission.

Beam mis-centering around LO and AS:
 - After these fixes, we probably need to re-align AS path and LO path, as the beams are not centered on LO1, LO2, AS1, AS4.
 - Hopefully these will improve LO-AS mode matching...
 - These probably will not require physical moving of the suspensions.
 - AS RF path after AS2 (90:10 splitter) is also clipped in YAW. This issue also needs to be addressed when re-aligning AS beam.
 - It is probably better to install BHD platform first, before doing LO and AS beam alignment, as BHD platform changes the balancing of ITMY stack, which has AS1 and AS4 suspensions.

[Murtaza, Tomo, Radhika]

In preparation for alignment of vertex optics, went through the exercise of acquiring low-power IR lock of the arm cavities. Arm transmission ndscope in Attachment 1 (max transmission 0.1).

LSC settings and oplev positions in Attachment 2.

Tomorrow morning we plan to complete the alignment work.

Steve just told those of us in the control room that the custodian who goes into the IFO room regularly steps on the blue support beams to reach the top of the chambers to clean them.  Since we have seen in the past that stepping on the blue tubes can give the tables a bit of a kick, this could help explain some of the drift, particularly if it was mostly coming from TT2.  The custodian has promised Steve that he won't step on the blue beams anymore.

This doesn't explain any of the ~1 hour timescale drift that we see in the afternoons/evenings, so that's still mysterious.

I'm not sure when this was done, but there were beam dumps in front of the lasers for BS/PRM oplevs as well as ITMY/SRM oplevs.  MICH wasn't holding lock very nicely, so I poked around, and the Sum values for all of these optics' oplevs seemed too low, so I went to look, and found dumps.  I have removed these, and now BS and ITMY oplevs are back to normal.  (PRM and SRM are still misaligned right now, so I'll check those later, but they should be fine).

BS's oplev has been enabled while non-existant, at least for the whole weekend, since I found it enabled.  ITMY I found misaligned, so it's oplev servos were off.

In other news, we should get back in the habit of restoring all optics before we leave for the night / whenever locking activities are finished. 

Steve has finished installing the enclosure on the new endtable. So Eric and I decided to try and lock the X arm and measure the beam height of the transmitted IR beam relative to the endtable. We initially thought of using POX DC as a the LSC trigger but this did not work as there was no significant change in it when the arm was flashing. Eric then tried misaligning the ITM and using AS110 as a trigger - this worked. We then recompiled the ASS model to take AS110 as an input, and ran the dither alignment. After doing so, I measured the beam height at two points on the new endtable.

Bottom line:

• The beam is roughly level across the table (along the North-South direction, within the precision to which I could place the irides and measure the height). The table has also been levelled pretty well...
• The beam height is ~4.7" across the endtable

So the beam is about 0.7" higher relative to the endtable than we'd like it to be. What do we do about this?

• Is it even possible to raise the table by 0.7" so we can have a level beam everywhere? Are there some constraints related to how the enclosure is attached to the window?
• Are we okay with tolerating a solution where we keep the beam level at 4", and use Y10 and Y11 (see layout in elog 12060) to raise the beam by 0.7", and then have slightly higher posts for the optics downstream of this point?

I've also placed two irides extending the cavity axis on the endtable. These should be helpful in aligning the green to the arm eventually.

The MC WFS have had beam dumps in front of them for the past ~2 weeks, until I could find the appropriate optic to put in the WFS path, to avoid melting the WFS' electronics. 

Koji noted that Steve had a W2-45S in a secret stash near his desk (which Steve later had put into the regular optics storage shelves down the Yarm), so I used that in front of the black hole beam dump on the AS table.  Now the beam is ~1W reflected from the unlocked mode cleaner, and ~100mW goes to the MC REFL PD.  The other 900mW now goes to this W2, and only ~5mW is reflected toward the MC WFS.  Most of the 900mW is transmitted through the window and dumped in the black hole.  There is a ghost beam which is reflected off the back surface of the wedged window, and I have blocked this beam using a black anodized aluminum dump.  I will likely change this to a razor dump if space on the table allows.  I have aligned the beam onto WFS1 and WFS2, although I did not re-align the mode cleaner first, so this alignment of the WFS will likely need to be redone. 

WFS1 has about 2mW incident, and WFS2 has about 3mW incident, when the mode cleaner is unlocked.  I have not yet measured the power incident when the MC is locked, although obviously it will be much smaller.

Except that I might temporarily remove one of the WFS for more quantum efficiency measurements later today, the WFS should be ready to turn back on for alignment stabilization of the mode cleaner. 

I was investigating several issues on the IFO. As many of you noticed and not elogged, ITMX had frequent kicking without its oplev servo.
Also I had C1:LSC-TRY_OUT flatted out to zero even though I could see some fringes C1:SUS-ETMY_TRY_OUT.

Restarted all of the realtime models (no machine reboot).

Now I don't find any beam on REFL/AS/POP cameras.

If I look at BS-PRM camera, I can see big scattering, the beam is in the BS chamber.
I jiggled TT1 but cannot find neither a Michelson fringe nor POP beam.

So far I can't figure out what has happened but I'm leaving the lab now.

IMC is locked fine.
I can see some higher order mode of the Yarm green, so the Y arm alignment is no so far from the correct one.

I have organized the resulting data from running dither lines on MC1,2,3. The data has been collected from diaggui as shown in attachment 1.

Mirror		Avg Re (+/- 1000)	Avg Im (+/- 1000)	Peak Power ()	Cts/urad
MC1	21.12	7000	4000	8062	12.66
MC2	25.52	13000	10000	16401	6.83
MC3	27.27	4000	-600	4044	11.03

Next using the following equations we can find :

Where is the change in length in result of the dithering and is the overall change in beam spot position

Delta L can be calculated by:

where is the peak power of the line frequency and is found by taking the square root of the magnitude of the Real and imaginary terms, is frequency the laser light is traveling at (281 THz) and is the lenght of the IMC (13.5 meters).

can then be calculated by:

where  is the angle at which the mirror was shaken at a given frequency. We can find  by converting the amplitude of the frequency that the mirror was shaken at and converting it into radians using the conversion constants found here: 17481.

is then shown to be found by this angle diveded by the line frequency.

The final values are calculated and displayed bellow:

Mirror
MC1	157.9 urad	0.35 urad	0.38 nm	1.08 mm
MC2	146.4 urad	0.23 urad	0.78 nm	3.39 mm
MC3	226.7 urad	0.31 urad	0.19 nm	0.61 mm

I have changed the MC SUS output matrices by a few % for some A2L decoupling - if it causes trouble, please feel free to revert.

Anchal came to me and said, "I think those beam offsets are a bunch of stinkin malarkey!", so I decided to investigate.

Instead of Alex's "method" of trusting the actuator calibration, I resolved to have less systematics by adjusting the SUS output matrices ot minimize the A2L and then see what's what vis a vis geometry.

The attached screenshot shows you the measurement setup:

1. copy the DoF vector from DoF column into the LOCKIN1 column.
2. Turn on the OSC/LOCKIN for the optics / DoF in question (in this example its MC2 PITCH)
3. Monitor the peak in the MC_F spectrum
4. Also monitor the mag and phase of the TF of MC_F/LOCKIN_LO
5. use the script stepOutMat.py to step the matrix

Next I'm going to modify the script so that it can handle input arguments for optic/ DOF, etc.

FYI, the LOCKIN screens do have a TRAMP field, but its not on the screens for some reason . Also the screens don't have the optic name on them. :

SUS>caput C1:SUS-MC2_LOCKIN1_OSC_TRAMP 3
Old : C1:SUS-MC2_LOCKIN1_OSC_TRAMP   0
New : C1:SUS-MC2_LOCKIN1_OSC_TRAMP   3

After finishing the tuning of all 3 IMC optics, I have discovered that 27.5 Hz is a bad frequency to tune at: the Mc1/MC3 dewhtiening filters have a 28 Hz cutoff, so they all have slightly different phase shifts at 27-28 Hz due to the different poles due to tolerances in the capacitors (probably).

*Also, I am not able to get a real zero coupling through this method. There always is an orthogonal phase component that can't be cancelled by adjusting gains. On MC3, this is really bad and I don't know why.
 

Today, we ran dither lines on the MC1,2,3 mirrors in YAW from 136598007 to 1365981967 and similarly on PIT from 1365982917 to 1365984618.

The following frequencies and amplitudes were recorded for each dither line:

The urad conversions used to calculate theta DC and AC can be found at 17481

The dither lines were then demodulated in python and the steps shown in 17516 were followed to calculate the beam offset that each dither line represented in pitch and yaw. 

The following results were found:

Attatched bellow is the power spectrums for both yaw and pitch.

Mayank and I worked on finalizing the plots for the beam offset from the dithering test done in 17552. Plotted in attachment 1 are the beamspot demodulated signals from MC_F_DQ which are averaged over 1 second each (blue) for YAW and PIT in MC1,2,3. The yellow line over each plot shows the 3 Hz lowpassed signal of the beamspot movement.

Additionally, we have seen no direct correlation to the WFS1 or 2 sensors due to the MC movements. This may be because the WFS display a complete signal that includes all changes in the cavity length due to the shaking of the mirrors. Thus, the signal (shown in red) of the WFS sensors will show a combined average of movement from all 3 dither lines.

I checked how POXDC level changes when the angle of ITMX is varied. ETMX was misaligned.

Then I found that in YAW direction the POXDC level is maximized but it doesnt have plateau, and in PIT direction it is not maximized so that it is at the slope and it doesnt have plateau, as shown in attached figures. These results indicate that the beam size on POX11 is not small enough compared to the size of the diode and it is not centered well.

To focus POX beam on POX11 PD, I added an iris and a lens before POX11 PD as you can see in Attachment 1.

It seemed that the beam is well focused, but the behavior of POXDC has not changed, as shown in Attachments 2 & 3.    

[yutaro, Koji]

Now, the beam on POX11 PD is well centered and well focused.

We found out why POXDC had behaved as reported in elog 11839. There were a few reasons: the beam was not focused enough, hight of a mirror was not matched to the beam well, path of the light reflected by misaligned SRM was occasionally close to the path of POX beam.

Then, What we did is following:

- changed orientation of SRM slightly

- changed the hight of the mirror whose hight had not matched well, by changing the pedestal (hight of which mirror was changed is shown in Attachment 1.)

- put a lens with f=250 mm (where the lens is located is shown in Attachment 1.)

- refined alignment for the POX beam to hit on the center of POX11 PD.  

As a result, POX DC level behaved as shown in Attachment 2&3 when the orientation of ITMX was varied (Attachment 2: POX DC vs ITMX PIT, Attachment 3: POX DC vs ITMX YAW). 

You can see broad plateau when varied in both PIT and YAW directions, and the beam is at the center of the plateau if ITMX is aligned ideally.

The NPRO from ATF has been installed on the POY table.

I have been making measurements to characterize the beam profile of this laser. I am using an AR coated laser window as a beam sampler at 45deg and the razor blade technique to measure the beam size along z. Details of the procedure along with analysis and results from this will follow.

Summary

I've finished up the remaining characterization of the repaired 1W Innolight NPRO - the beamscan yielded results that are consistent with an earlier beam-profiling and also the numbers in the datasheet. The output power vs diode current plot is mainly for diagnostic purposes in the future - so the plot itself doesn't signify anything, but I'm uploading the data here for future reference. The methodology and analysis framework for the beamscan is the same as was used here.

Attachment #1 - Beam-scan results for X-direction

Attachment #2 - Beam-scan results for Y-direction

Attachment #3 - Beam profile using fitted beam radii

Attachment #4 - Beam-scan data

Attachment #5 - Output power vs Injection current plot

Even though I remember operating at a diode current of 2.1A at some point in the past, while doing this scan, attempting to increase the current above 2.07A resulted in the "Clamp" LED on the front turning on. According to the manual, this means that the internal current limiting circuitry has kicked in. But I don't think this is a problem as we don't really even need 1W of output power. This is probably an indicator of the health of the diode as well?

Attachment #6 - Output power vs Injection current data

It remains to redo the mode-matching into the doubling oven and make slight modifications to the layout to accommodate the new laser + beam profile. 

I plan to do these in the morning tomorrow, and unless there are any objections, I will begin installing the repaired 1W Innolight Mephisto on the X endtable tomorrow (18 April 2016) afternoon. 

[MikeJ, Jenne]

We have a plan for how we're going to measure the beam after PR3.  Mike is going to write up a nifty program that will spit out the waist of the beam if you give it a bunch of razor blade measurement data.

Since the beam bounced off of the pitched ITMX is coming out of the chamber so high, it's kind of a pain to setup optics to steer the beam down the walkway next to the Yarm.  So, I have a new vision.

I think that we can get the beam right after PR3 onto the PRM/BS oplev table using 3 clean mirrors (of which we have many spares, already clean).  Once on the oplev table, we can put a 2" Y1 mirror to steer the beam down the walkway, after taking off the short east side of the table.  Then we can use the little breadboard on the mobile blue pedestal for the razor blade / power meter setup.

The razor blade on a micrometer translation stage will be the first thing on that table that the beam sees. Then, a 2" lens to get the beam small enough to fit on the power meter.  Then, obviously, the power meter.  We can measure the distance between the oplev table and the razor blade using the laser range finder, which has pretty good accuracy (it's sub-centimeter, but I don't remember the exact number for the precision).

A lens is not okay if we're trying to get the beam directly onto the beam scanner, since it will distort the beam.  However, as long as the razor blade is before the lens, and we're just using the lens to get the full intensity of the non-obscured part of the beam onto the power meter, I think using a lens should be fine.  If we don't / can't use a lens, we're going to run into the same problem we have with the beam scanner, since the power meters all have a fairly small aperture.  Even the big 30W power meter's aperture will be on the order of the size of the beam, so we won't be able to guarantee non-clippage.

The main problem I see with the technique as I have described it, is that the beam is going to hit 4 mirrors (3 in-vac, one outside) before going to the razor/lens/power meter.  We have to make sure that we're not clipping on any of those mirrors.  Also, this measurement version takes the beam after PRM, PR2 and PR3, but not after the BS and ITM.  I don't think we're concerned with either of those 2 optics, (especially since this is refl off the front of the BS, so won't see any potential clipping on the BS cage), but just in case we are, this measurement isn't so useful, and we'd have to come up with a different way of placing the mirrors on the in-vac tables to get a beam bounced off  of  a yaw-ed ITMX. 

Perhaps it would be easier to just go with the pitched ITMX version of the measurement, but I could use some ideas / advice on how to mount mirrors and lenses ~4 feet off the ground outside of the chambers, and not have them waving around on skinny sticks.

EDIT: Another idea is to instead use the beam transmitted through the BS, put a single clean steering mirror in the ITMY chamber, and get the beam out of the ITMY door.  This could either be the beam before the ITM, or we could yaw the ITM a little and take the reflected beam.

 I misaligned ITMX pitch on Friday and brought out the beam at 44" height. The beam was bouncing to much. I only realized it this morning why. The OSEM voltages are 1.8, 1.7, 0.2 and 0.9V  Even with a stable 8-9 mm diameter beam you would be clipping

on the beam scanner 9 mm aperture. You can bring out the beam with one mirror right after  PR3, just remove  PRMOP2

[Begüm, Paco, Yuta]

Beamspot position measurements were done using A2L, assuming all the coils are balanced.
Beam centering on PR3, LO2, AS1, AS4 are off by more than 1 cm.
ITMX centering (which we ignore in XARM ASS) is pretty good.

Results:

# Optic LSCDoF  freq(Hz)   amplitude   gpstime v (mm)   h (mm)
ETMY    YARM    211.11    100.0    1382413915    0.20    -0.20
ITMY    YARM    211.11    100.0    1382413976    -0.01    0.07
ETMX    XARM    211.11    100.0    1382414046    0.08    -0.17
ITMX    XARM    211.11    100.0    1382414280    0.43    0.42
BS      MICH    211.11    1000.0    1382414504    2.00    -2.30
PRM     PRY     309.21    300.0    1382415273    -7.70    -1.85
PR2     PRY     309.21    300.0    1382415349    5.37    0.25
PR3     PRY     309.21    300.0    1382415473    0.85    13.59
ITMY    PRY     309.21    300.0    1382415569    -0.25    0.15
LO1     HPC     113.13    1000.0    1382416132    -5.78    -4.43
LO2     HPC     113.13    1000.0    1382416189    -13.79    18.33
AS1     HPC     113.13    1000.0    1382416253    0.85    12.61
AS4     HPC     113.13    1000.0    1382416315    -4.21    10.65
SR2     HPC     113.13    1000.0    1382416389    -0.38    5.45

Method:
 - Lock some interferometer configuration which involves the optic you want to measure (e.g. PRY for PRM).
 - Put a notch filter at the frequency you want to dither in the LSC loop.
 - Dither C1:SUS-(optic)_LSC_EXC and demodulate the error signal to get the optical gain of the error signal.
 - Dither C1:SUS-(optic)_ASC(PIT|YAW)_EXC and demodulate the error signal. Calibrate the demodulated error signal into meters using the optical gain derived above. Calibrate the optic motion using angular actuation efficiency estimated using the method described below. By dividing the length change by angular motion, you get the mis-centering.
 - This method asumes that there is no clipping, all the coils are balanced, POS/PIT/YAW are purely actuated, and optic center is the same as actuation node.
 - For measuring the beam spot positions on ETMs and ITMs, signle arm locking configurations were used.
 - For measuring the beam spot position on BS, MICH configuration was used.
 - For measuring the beam spot position on PRM, PR2 and PR3, PRY configuration was used.
 - For measuring the beam spot position on LO1, LO2, SR2, AS1, and AS4, ITMY single bounce vs LO configuration was used.
 - Attachment #1 shows the spectra of error signals during dither, showing SNR is pretty good.

/opt/rtcds/caltech/c1/Git/40m/scripts/ASC/measureBeamSpotPosition.py

Estimating angular actuation efficiency:
 - Angular actuation efficiencies were estimated using the following

A_ang = A_lsc * dd * mass / (2*I)

where A_lsc is the length actuator efficiency measured in 40m/17886 and 40m/17918, and

rr = 3*inch/2    # radius of the optic
tt = 1*inch  # thickness (ASSUMPTION!!!; they are random for BHD optics (;x;) (╯°□°)╯︵ ┻━┻)
dd = 1.945*inch # distance between magnets https://dcc.ligo.org/LIGO-D960002
rho = 2.201*g/(cm**3) # density of fused silica (note that BHD optics have 2inch -> 3inch sleeve made of aluminum)
mass = pi*rr**2*tt*rho # mirror mass
I = mass*rr**2/4+mass*tt**2/12 # moment of inertia

 - In summary, they are the following. Note that A_ang is not the physical angle you move, but is what you see by LSC through A2L.

Susp. | LSC meas. nm/count | Gain adj. | AoI deg | POS nm/count | ANG urad/count
BS   +69.54 +2.325 45 +21.15 +4.12
ITMX +14.73 +0.653  0 +22.55 +0.87
ITMY +14.50 +0.659  0 +21.99 +0.86
ETMX +12.20 +0.414  0 +29.47 +0.72
ETMY +10.66 +0.480  0 +22.21 +0.63
MC2  +2.27 +0.105  0 +21.62 +0.13
PRM  -19.00 +0.773  0 -24.58 -1.13
PR2  -36.19 +1.000  0 -18.09 -2.15
PR3  -29.57 +1.000 45 -20.91 -1.75
LO1  +28.25 +1.000  0 +28.25 +1.67
LO2  +11.19 +1.000 45 +15.83 +0.66
AS1  -25.92 +1.000  0 -25.92 -1.54
AS4  +25.82 +1.000  0 +25.82 +1.53
SR2  -16.63 +1.000 45 -23.52 -0.99

Next:
 - Check the sign of mis-centering. It is kind of random now.
 - Put uncertainty in these measurements.
 - Include HPC in the LSC screens

I looked at this code and it is a little untrustworthy. The demod is not being done correctly so there can easily be some aliasing going on.

in this lab we really, really should never use a moving average instead of low pass filtering.

And why import math instead of using numpy??

[Murtaza, Paco, Radhika]

After the input beam path alignment was complete (arm flashing recovered), we attempted to run Yuta's beam centering measurement script (scripts/ASC/measureALLBeamSpotPosition.py). I was able to align and lock the arms at low power following the procedure here. The resulting ITM/ETM beam mis-centering measurements can be seen below.

Next I struggled to lock MICH to measure mis-centering on the BS using Yuta's instructions. We noticed the AS beam was clipping horizontally. Paco and I aligned the AS beam using SR2/AS1 and the beam now appears unclipped. We found the demod angle that minimized AS55_I to be 86.56 deg, not far off from Yuta's value. We mananged to lock MICH with: 1. ASDC trigger matrix element: -30; trigger threshold lowered to -0.5 (enable). We then obtained the BS mis-centering measurement below. Note that the uncertainties here are on the order of the mis-centering value.

Attachments 1 and 2 compare the vertical and horizontal beam mis-centering values before and after the in-chamber alignment. In summary, beam spots on ETMs and ITMs have more or less converged towards center vertically (BS is the exception). However, the beam spots seem to have diverged horizontally from center. This means our pitch corrections were in the right direction, but we'll need to take measurements on PRM/PR2/PR3 to confirm this. It seems like trying to mitigate horizontal clipping at PR3 has propagated mis-centering downstream.

Measuring the beam spot on PRM/PR2/PR3 requires PRY locking, but it seems that little to no light is hitting REFLDC or any of the RF REFL PDs. This will be debugged next.

Beam spot position measurements were done for the first time in air pressure at low power.
Dither amplitudes were increased to overcome lower SNR, but still the uncertainties are large.

Results:

# Optic    LSCDoF     freq.(Hz)    ampl. (counts)    gpstime    Opt. gain (counts/nm)    Opt. gain_std    v (mm)    v_std    h (mm)    h_std
ETMY    YARM    211.11    1000    1383331863    64.55    3.78    -4.33    0.37    0.47    0.40
ITMY    YARM    211.11    1000    1383331936    65.15    2.67    -0.97    0.17    -0.20    0.11
ETMX    XARM    211.11    1000    1383331957    59.96    2.10    3.40    0.30    -1.33    0.18
ITMX    XARM    211.11    1000    1383332021    62.73    2.35    0.88    0.15    0.38    0.19
BS    MICH    211.11    3000    1383333747    0.02    0.00    3.21    3.90    -3.33    2.26
PRM    PRY    309.21    3000    1383335425    6.23    6.28    13.55    29.00    -2.05    2.82
PR2    PRY    309.21    3000    1383335499    7.57    4.51    7.70    7.09    3.67    12.17
PR3    PRY    309.21    3000    1383335562    5.88    1.17    3.60    10.33    -16.91    15.18
LO1    HPC    113.13    3000    1383336782    0.05    0.01    9.12    3.44    6.50    5.91
LO2    HPC    113.13    3000    1383336842    0.05    0.01    14.51    6.63    21.34    5.13
AS1    HPC    113.13    3000    1383336901    0.05    0.01    2.62    3.36    14.91    2.70
AS4    HPC    113.13    3000    1383336963    0.05    0.01    -5.84    3.28    14.56    3.47

Locking configurations:
 - YARM and XARM can be locked by increasing the trigger matrix C1:LSC-TRIG_MTRX elements by a factor of 10.
 - MICH can be locked by changing AS55 demodulation phase C1:LSC-AS55_PHASE_R from 2.1 deg to 92.1 deg (why?). Play with trigger matrix C1:LSC-TRIG_MTRX so that it does not trigger filters.
 - PRY can be locked by changing REFL55 demodulation phase C1:LSC-REFL55_PHASE_R from 76.02 deg to 166.02 deg (why?) and by increasing the PRCL gain by a factor of 10, C1:LSC-PRCL_GAIN from -0.04 to 0.4. REFL55 is glitchy and making the measurement uncertainties big. Play with trigger matrix C1:LSC-TRIG_MTRX so that it does not trigger filters.
 - ITMY single bounce-LO can be locked by increasing the gain by a factor of 10, C1:HPC-LO_PHASE_GAIN from 1.5 to 15.
 - These changes are summarized in the following script.

/opt/rtcds/caltech/c1/Git/40m/scripts/ASC/measureAllBeamSpotposition.py

Attachment #1 is the current PRFPMI BHD alignment, and Attachment #1 is the history of the measurements.

Beam spot position measurements were done, oplevs aligned.
Attachment #1 shows IFO alignment with PRFPMI BHD aligned.
Attachment #2 shows oplev values.
Attachment #3 shows the history of beam spot position measurements since Saturday.

Updates on beam spot position measurements:
 - PR2 mass and moment of inertia were updated using the numbers from Solidworks model (40m/17937).
 - Script to measure all of them were prepared. This script still requires human to check the alignment and locking status. /opt/rtcds/caltech/c1/Git/40m/scripts/ASC/measureAllBeamSpotposition.py
 - Script to plot the history: /opt/rtcds/caltech/c1/Git/40m/scripts/ASC/plotBeamSpotPositionMeasurements.py

FROM THE POINT OF VIEW OF IFO, WE ARE READY TO VENT