Feedthrough channel (as seen from the connector outside of the chamber)
1-6: heater on cavity#98 : 85.4 Ohm
3-7: Temp sensor on cavity #98
4-8: heater on cavity#99: 156 Ohtm
5-9: Temp sensor on cavity#99
So I put together a little test circuit to test out a NPN BJT buffer circuit with a TIP122 transistor and an OP27 op amp. Power voltages are ~ +-14V, just used the positive rail as V+ for the transistor.
(diagram from https://www.allaboutcircuits.com/technical-articles/how-to-buffer-an-op-amp-output-for-higher-current-part-1/)
I verified that the op amp functioned alone in a buffer configuration.
Putting the BJT in the loop added a (negative) offset, though:
WIth a 51ohm load, inputs of 1.5Vpp and 2Vpp respectively:
WIth a 910 ohm load, with inputs of 1.5Vpp and 2Vpp respectively:
I realized afterwards that this circuit theoretically shouldn't be able to go below ground. I'm surprised that the output is basically offset so that the entire output signal is below ground. I guess I will test it again with the input signal being entirely positive, but I'm not sure if this is even related.
Side note: also made measurements of the metal slab (including the tape that is currently around it) to do some calculations later:
34.5mm by 61.5mm (basically flat in the third dimension, plus it's crinkly from tape so hard to measure consistently)
What exactly is the offset? Is there some threshold voltage the BJT requires before it starts conducting, maybe one should expect a ~0.7 V difference between the op-amp output and the load voltage? There should be some opamp configuration where can you can bias the feed back to the -ve pin of the op-amp: this is commonly done for op amps running with single sided supply.
Is it possible to make use fo the full +/- 15 V range?
Also, want to use a FET on the output BJT, it has lower noise and better thermal stability.
The RefCav pole is 37 kHz, not 37 MHz.
To minimize the RFAM, you just look at the PMC REFL PD with the PMC unlocked and adjust the waveplate to minimize the peak. Before doing this, make sure that there is no signal on the PD with the light blocked.
Ah right, that's embarassing. I'll try that.
does anyone know the typical operating current for the 100mW lightwave laser model ? (M126N-1064-100) It's typically ~1.1A for the 200mW model. I've set up everything and it starts to lase around 0.44A, so at least its not dead but i don't know how high up i can go. My guess is that it is something around 0.8A but i have no datasheet which tells me...
found four old Minco heaters (model HR5494-106) (from 1995) . This type with 106 Ohms is not in their system anymore.
But corresponding to their data the maximum current for this type of heater is about 7.5A. So driving this heater with 24V would give us 5.4W of heating power beeing well below the limit. Using the standard power supply for heating refcavs we can get even more power. Due to the age (14years!) the adhesive back is not sticky anymore so i will use aluminum tape for first tests.
- personal notes -
current cross-connect connections
1 - LO
2 - HI
connected to ?
1 - LO
2 - HI
connected to J2-3113A 43/44 (CH21)
5 - LO
6 - HI
connected to J2-3113A 53/54 (CH26)
3 - LO
4 - HI
connected to J3-3113A (CH34) (?)
12/25 : FSS_RMTEMP
6/19 : FSS_MINCOMEAS
2/14 : FSS_RCTEMP
over the weekend we baked the two AR-coated windows for the new chamber. Bob doesn't need the oven the next couple of days so i restarted the baking again and will continue to bake the remaining parts the next couple of days. We also set up peters old vacuum pump. We got lots of stuff from 40m and cleaned all parts today. The pump is now running and pumping the whole system including the hose to the chamber. We also wrapped some heaters around the parts and started heating the stuff to make it a bit cleaner as no one knows for what the parts have been used before. They all looked pretty clean and wiping everything didn't show any obvious contamination. We can't bake it to high as some parts are viton sealed.
The new, insulated feet should be finished by wed or so. Tomorrow we start cutting the remaining foam to size and glue the parts together. I ordered the remaining heaters, one is already attached to the chamber and it fits good except that the sticky back is not sticky enough to hold it in place. The bending force is too high, so i added some aluminum tape which holds it in place now (the corners didn't want to stick). We have plenty of space for temp sensors and we will add several AD590 and a couple of platinum sensors. If we find out that the AD590 is not good enough we can easily switch to the other sensors. We should discuss how many we want and especially where. My guess is that we should add some more on this first prototype to get a feeling for the gradients or so. We can then reduce the amount on the second chamber if we want. The platinum sensors are cheap. Typically one is about $8-10 each, but I bought a pack of 100 directly from the manufacturer and so its about $1 each only.
We opened the vacuum chamber and brought the stack with the 8" cavities out to the clean bench. New 1.45" cavities are under preparation to go in the chamber.
The 8" cavities and the double seismic isolation stack were removed from the chamber. The connector had to be removed from the inside of the mini flange for the feedthrough [add pic]. We replaced the top seismic stack along with 8" cavities and their mounts, with the new stack/new mount for the shorter cavities. We reuse the bottom stack.
Next is to modify the wiring for heaters and temp sensors. Currently, the connector is wired for 3 sensors and 1 heaters (for 9-pin connector). Soldering at the 9-pin connector seems to be a tough job. Koji suggested that I remove one of the temp sensor at its legs, not at the connector end. Then connect the unoccupied cables to the heating wire.
I found all necessary parts for the heater (crimp connectors, heating wire). I'll bake all parts once all the wiring is ready
fig1: left Dsub connector for the cable, Right, heater(yellowish wire around the tube) is connected to wiring cable with crimp connectors.
fig2: crimp connector( vacuum compatible material). I need to borrow the suitable crimp tool from Down, see PSL:775
fig3: above, previous wiring (one heater,3 sensors), below current wiring (two heaters, two sensors)
I planned the layout for new fss setup.
The new setup has 1) both cavities placed in the same vacuum chamber, 2) two AOMs used in both RCAV and ACAV paths, 3) more compact beat path.
In the layout, I assumed that
This is just a plan, no mode matching has been calculated yet.
I am concerned that the mode matching lens might block the beam in ACAV path where the incoming beam and reflected beam cross, but this can be adjust later.
The outer foam box will be smaller, but it should have enough space to keep some electronics inside like we have now.
I should find two similar sets of beam splitters/ mirrors for beams in the beat path behind the cavity. So the pick up beams from two cavities can have same power.
Right now the power going into two PDs for RCTRANSPD are not the same because the splitter are not the similar.
Note that we might install a platform behind the cavities so that we don't need the periscopes to lower the beam, and get rid of their associated mechanical peaks.
I added more details on the layout, and necessary half wave plates in the beam path.
The mode matching for new FSS is calculated. The plan is shown below.
Note for the setup:
1) the spotsize in the AOM is 200um, the specsheet says 550 um (I might have to correct this).
2) Two AOMs are of the same model.
3) For mode matching to the AOM in acav path, I used only a single lens.
4) focal lengths of the lenses are in mm, We have to order the one with * (f = 57.4 mm)
5) Both cavities are 1" apart (3" from center to center)
6) Mistake in the drawing: the x2 QWPs just before the beams enter the vacuum chamber should be placed before the periscopes, not after.
The new mode matching for optics in front of the cavities is done. The rest (for beat measurement) will be finished soon.
A few changes in this layout are:
1) spotsize for AOM is 500 um, as specified by the datasheet.
2) Mirrors behind the AOMs will be changed to R= 2.0 m instead of 0.3 m.
3) Spot size in the 35.5 MHz EOM is ~300um which is good for the model.
4) More mirrors (for steering the beam) for the AOMs are added.
I'm a bit worried about using f=57.4mm lenses because they are quite sensitive when we have to move the lenses around, but the space is very limited this time.
I'll let Raphael double check my calculation so he can learn how to do mode matching.
There's no need to use such a large spot size on either the AOM or the EOM.
When using high power this could be an issue, but you can use a beam radius of more like 100-200 microns for the AOM to get fast response time.
I edited the layout so that the spots in both AOMs are 200 um. I'll list what optics we might have to buy.
Most of the optics are already used on the table. I need to find:
The optics on ACAV path have been removed, I left the optics on RCAV path for now because Raphael might want to remeasure EOM TF.
Once the measurement is done, all optics will be removed. We will clean the table, clean the optics before put them back on the table.
the lens and mirror are in the ATF, a second VCO is in the left cabinet.
I got the mirror blanks for optical contact practicing. I tried to contact them together, but I have not succeeded yet.
The mirrors are not transparent on the back, but we can still see the fringe due to the gap between the two surfaces clearly with just room light, see the picture below. I might not clean it well enough. I'll try to do it again later.
I checked that the optical gain in PMC loop increases as the power in the sideband increases. The result is 10.7 dB/V.
This measurement is for checking how much gain (in optical path) will we get from changing power in the side bands.
The excitation is sent to EXT DC channel on PMC. Reference signal is at HV mon, response is picked up at Mix mon.
This TF includes PZT and OPT paths, PZT TF should remain the same independent from the side band power.
I vary the RF voltage, and adjust the gain slider for maximum stability. The gain setup should not matter
in the TF part we are measuring as long as the loop is stable.
I measured the gain at 3 different frequencies, 290.8 Hz, 1.035 kHz, 5.09 kHz where the TF look reasonable and smooth.
(The loop UGF is ~ 500-900 Hz, Thus the data at 1k and 5 kHz are nicer than that of 290 Hz)
the slopes from each fit are
The results are fairly linear in our region (RF between 4.8 to 5.9 V). The gain slider for this voltage range is between 13 - 20 dB.
At higher RF voltage, PMC_RCTRANSPD starts to drop significantly.
At lower RF voltage, the gain is too low.
This means we can increase the gain in OPT TF up to 10 dB by adjusting RF voltage (increase side band power)
I added mirrors to pick up stray beams just before the cavities. These beams will be used for monitoring RFAM.
I arranged the optics so that stray beams at the beam splitters (just in front of the cavities) could be used. The power of the beam is ~ 9 uW, but it can be increased by changing the polarization of the input beam later.
Two photodiodes are needed, I haven't checked yet if I still have some spare PDs left.
Then the signal from PD will be demodulated with 35.5 MHz signal (modulation frequency). The cable length + PD position will be adjusted so that the phase is the same as the PDH signal.
I made some minor adjustment to the optics layout so that the reflected beam at the PBS before the cavity can be used to measure RFAM. Now RCAV's beam can be picked up for RFAM measurement.
The PBS just before RCAV was moved Eastward a bit so that the reflected beams from both PBSs are not blocked. I removed mirrors with soft mounts and use only rigid 1" posts only.
I used a spare 35.5MHz RFPD for the pickup beam from RCAV path (in red). The power cable for RFPD was made and checked. It works properly. There is a spare new focus 1811 RFPD, but the connector is broken, the pins are bent. I'll try to fix this and use it for ACAV's RFAM pickup.
The AC signal from RFPD will be demodulated with 35.5 MHz signal which is split from the LO signal for ACAV PDH's lock. I have not adjusted the phase by trying different cable lengths yet. This will be done later.
There is one thing I'm a bit concerned with. The RF signal from the RFPD has DC level ~ 120 mV, I'm not sure if it's unusual or not. I'll check with another RFPD.
I used optimization codes for ETM. The optimization reduce the PSD of Brownian noise by ~ 3/4 (in units of [m^2/Hz]) from QWL structure.
Since we have not had all the material parameters for aSi:H at 120K with 1550nm, the optimization here is for room temperature with 1550 nm (for Brownian noise only).
fig1: optical thickness for ETM with minimized BR noise. The transmission is 5.4 ppm and the reflected phase is ~ 179 degree.
Parameters/configuration used in the optimization:
It is remarkable that 5ppm transmission can be achieved with just 17 layers of coatings due to the largely different values between nL and nH. This makes the total thickness down to ~ 3 um.
BR noise from the optimized coating is 3.3x 10^-42 [m^2/Hz] at 100 Hz. This is converted to the strain of ~ 5x10^-25 [1/sqrt Hz] for 4 km interferometer.
Note: for QWL structure, with 14 layers + half wave cap of SiO2 (total of 15 layers), the transmission is ~5.2 ppm and the coating Brownian noise is 4.2x10^-42 [m^2 /Hz]. So the optimization reduced the PSD of BR noise by ~ 25%.
I filled in more values for a-Si at 120 K into the wiki that Matt Abernathy set up. Then I ran the optimization code for Brownian noise only:
The above plot shows the comparison between the optimized aLIGO coating (silica:tantala at 300K) v. the a-Si coating at 120 K.
Then, finally, I compared the TO and Brownian noise of the two designs using the plotTO120.m script:
The dashed curves are silica:tantala and the solid lines are a-Si:silica. The Brownian noise improvement is a factor of ~6. A factor of ~1.6 comes from the temperature and the remaining factor of ~3.9 comes from the low loss and the lower number of layers.
I think this is not yet the global optimum, but just what I got with a couple hours of fmincon. On the next iteration, we should make sure that we minimize the sensitvity to coating thickness variations. As it turns out, there was no need to do the thermo optic cancellation since the thermo-elastic is so low and the thermo-refractive is below the Brownian almost at all frequencies.
Started characterizing the cable-delay setup with the right length of cable (134ft of RG58 for 160MHZ). After checking the change in sensitivity with load impedance i've changed the load to 500 Ohms (instead of the usual 50 Ohms). I think an additional low-impedance path for the 2f has to be put in parallel later (to have proper 50Ohms @ 2f) to not get it reflected at the input of the low-pass filter back into the IF port of the mixer. (see first schematic).
However, the following simple setup has been used for the measurements:
I've measured the output signal vs different LO power levels while keeping the RF signal strength constant (8.29dBm) to find out the optimum signal strength in terms of size (not noise at this point!).
The following plots show the result:
now as we know that the optimum loss of the delay line is 8.68dB we can calculate the optimum cable length.
optimum length for 160MHz are:
cables which introduce more delay for the same amount (8.68dB) of loss are better.
Now, we compare the minicircuits low-pass filter SLP-200 (datasheet) with the cables.
so we could add 22 filters for an optimum total delay/loss ratio. Total group delay would be 132ns.
If we compare now with the delays we get from the cables we see that even the simple RG58 gives us 50% more delay for the same loss ( and the price for the cable is the same as a single filter).
Using RG142 instead we get almost a factor of 2 more sensitivity and even more using lower loss cables.
So i don't see an advantage using those LP filters instead of cables.
If you can't install python, you can run it all in the Sage Math Cloud for free.
Also, please post the final design for the heat shields which you've sent out for fab.
exchanged the old mirror (T330-HR, T331-AR) by a simple Y1-1025-45P to get more power.
measured laser power : 7.17W
downstream of the new output coupler : 134.6mW
added waveplates & pbs to make the power adjustable. current power through the EOM is 8mW which gives about 4.33V on the RF-PD (Thorlabs PDA10CS, 0dB-setting, 17MHz)
I"m packing the mirrors so that they are ready to be shipped to G. Cole. The mirrors are packed properly, see picasa.
I make a list of parameters found in literature. This will be used for estimate the coating Brownian noise level and its error.
* the values reported by Crooks etal in 2006, are supposed to be more accurate than the results in 2004, because of the better estimation of energy stored in the coatings and the corrected thermoelastic contribution. They mention that the Poisson's ratio has small effect on the level of the estimated thermal noise.
The numbers from Penn et al are extracted from the multilayer coating ringdown measurement. Since they measure the ring down of the coating which has both materials. The values depend on Young's moduli of the materials as well. They use Ysio2= 72 GPa/ YTa2O5 = 140GPa. Thermoelastic loss is not taken into account.
The values for Young moduli are usually measured directly with nanoindentation technique.
SiO2, Young modulus (Thin film)
Ta2O5, Young modulus (Thin film)
SiO2, Poisson's ratio:
Ta2O5, Poisson's ratio
The uncertainties in Poisson's ratios of the materials have small effect on the coating noise level. For examples, the 10% increase of SiO2's, and Ta2O5 Poisson's ratios, causes the thermal noise to increase by 0.09%, and 0.06%, respectively.
list of all materials' properties,here.
Coating Brownian noise with uncertainty (worst & best case scenarios)
I use the parameters found in the literature for coating Brownian noise calculation.
The upper limit ( high noise level) has
The lower limit (low noise level) has
The rest of the parameters are their nominal values. The max/min values are ~ 18% from the average level. @ 100 Hz, the average noise level is 4.097 mHz/rtHz. The upper limit is 4.815mHz/rtHz, the lower limit is 3.324 mHz/rtHz.
I measured the optical transfer function with more points (again after the floppy didn't properly save the data from yesterday) and I made some shot noise measurements (after finding out that the shot noise measurements I made yesterday weren't as good as I thought they were). Matlab is acting stupid on me right now, so I will post the plots tomorrow.
Did a little bit of peak hunting to clear our frequency span of interest from those massive mechanical resonances we currently have. After replacing the combining beam splitter mount we got rid of the 1.4kHz peak already. Yesterday i've focused on the mounts within the beat setup, but not the periscope, as we already know that this is very unstable and we will take care of that soon. I didn't want to replace things, just know where which stuff comes from.
I've found (only) one mirror mount which is currently clearly visible in our noise spectrum . Tapping the other mounts or damping the front plate or springs does not change the spectrum (at least i don't see any changes). Tapping (even slightly) is very difficult anyway as you also excite all the mounts surrounding your DUT, especially the periscopes and your whole spectrum changes and it's hard to figure out which is your primary resonance you are looking for. So i prefer damping it with a large piece of rubber and than compare it with a spectrum taken before with a reasonable.amount of averages.
Anyway, i found only one mirror mount (out of six) which i could clearly identify in our current noise spectrum. It's one of the mirrors right in front of the combining beam splitter.
Below a comparison before and after damping the front plate of the mirror mount. Resonance frequency is 544Hz. I have to check but i think we can replace this one with a non-adjustable turning mirror.
We still don't know where the 1.1KHz stuff is coming from.
- incoming -
We did optimize the alignment, power levels etc and tweeked almost every knob of the system to get an idea where we have to look for the current limit in sensitivity. Didn't find anything dominant. A lot of already known things can limit if you intentionally make it worse / misalign things, but once optimized they are below the current measured noise performance. Detail later.
Tue Feb 28 21:28:53 2012
Beat measurement after optimization, floated table.
The beat noise is roughly a factor of 2 above the coating noise at 130 Hz. This gives us a good reason to change the springs for the seismic stack in order to get better sensitivity at lower frequency, as it is getting closer to the coating noise at lower frequency. At 2kHz and above, the noise spectrum's feature is similar to the noise budget, but with some offset. We might miss a few other flat noise sources( noise from RFPD, electronics) that we have to add into the noise budget. Most of the mechanical peaks around 100 - 1kHz are probably from the mirror mounts.
A perl script/ an medm screen are created for SLOWDC PID control. The gain is not optimized yet. Some debugging might be needed.
The script for SLOW_PID.pl is similar to rcav_PID_2011_01_25.pl. I just changed the channel names for SLOWDC.
The process is C3:PSL-FSS_FAST
The actuator is C3:PSL-FSS_SLOWDC
Setpoint is C3:PSL-FSS_SLOWPID_SETPOINT (set to 0)
and other parameters follow the form of C3:PSL-FSS_SLOWPID_...
The perl scripts can be executed on the sun machine, but the result is abnormal. I tried to adjust P gain,
but for either signs I chose for Kp, SLOWDC seems to rail, instead of being steady at a certain value.
I'll check this later, for now it's not very important, since another loop for SLOWDC is also working, and
we can lock the cavity for a long time without SLOWDC feedback.
note for thermal PID
P -0.9 -0.9
I -0.006 -0.0028
D 0 0
after rebooting both crates i found that the perl script parameters for both loops are inconsistent with what's documented in the elog here.
Tara, can you plz check what the right numbers are. The numbers in the startup script are totally different from the values you posted.
Yes, I changed the numbers to see the response and haven't logged
or changed the values in the start up file yet. Will do that.
KP -0.7 -0.85
KI -0.007 -0.0035
set 35.03 37.1
VERY IMPORTANT ! (HAS TO BE MEASURED NEXT BEFORE ANYTHING ELSE):
seismic is not important at the moment as it will change end of the week anyway
see this entry
measured the delay for the old cable (RG58): dPhi=180deg, df=600KHz
1.67ns/ft (value from datasheet: 1.53ns/ft)
typical values for other cables using the following dielectric materials:
Dielectric Type Time Delay (ns/ft)
Solid Polyethylene (PE) 1.54
Foam Polyethylene (FE) 1.27
Foam Polystyrene (FS) 1.12
Air Space Polyethylene (ASP) 1.15-1.21
Solid Teflon (ST) 1.46
Air Space Teflon (AST) 1.13-1.20
Tara and I put another photodiode behind ACAV, so that now there are two photodiodes behind each cavity.This is necessary because one is needed for monitoring and another is needed as a detector for feedback. The following image shows the setup of the second pd behind ACAV, note that there are no beam steering mirrors for alignment:
Now we have to think of a sensible solution for wiring all of the cables (8 in total)
After installing the second pd behind ACVA, I tried to re-measure RIN behind ACAV and RCAV again. The measured RIN from ACAV and RCAV are about the same as we measured before.
I was having problem with the measured RIN after we installed the second PD for ACAV. It turned out that the beam was not dumped properly. The measurement was done after I realigned the beam to ACAV/RCAV and centered the beam on the PD. I'll use the coupling we measured in PSL:1008 to add the contribution from RIN in ACAV to beat noise (assuming no common mode rejection).
just for reference which part is/was where for later...
I add the photo thermal noise effect in the noise budget. With ISS, photothermal noise should be sufficiently small.
What I did
Comment about the beat
Note about RIN measurement
Note about loss angles: For SiO2 and Ta2O5 loss angles = 1e-4 and 7.5e-4 (a factor of 3 above the regular number), the noise budget matches the measurement well. I'll see if it is the same for the data from 8" cavities or not.
I compared our beat measurement with results from Numata2003 and TNI. They agree well. I'm quite certain that we reach Brownian thermal noise from coatings.
To make sure that what we measure is real Coating Brownian noise (It could be something else, i.e thermal noise in the support, spacer , or optical bond), we should compare our result to previous measurements to make sure that the numbers agree.
Numata etal and TNI reported coating thermal noise measurement from suspended cavities (no spacer). They adjusted loss in the coatings to fit the measurement. Phi coatings as reported in Numata is 4e-4 while TNI gives phi perp = phi_para = 2.7e-4. Both agree with our result, see the plot below. This means that our result is comparable with what they measured. It should be an evidence to support that we see real coating thermal noise, not contribution from something else (spacer, optical bond between the mirrors and the spacer).
Another evidence is from our previous measurement from 8" cavity.
So It is clear that our beat measurements from both 8" and 1.45" cavities are coating Brownian noise limited (around 50Hz-1kHz).
Koji and i updated the shaker today. We replaced the short multilayer piezoelectric actuator (10mm) by a longer one (20mm) from the NEC TOKIN’s we have. (datasheet)
The pzt is glued to a brass disk, about 2" diameter and clamped between the side of the table and the steel frame around it using a aluminum base on the other side. (will add photo later).
We use a modified PMC servo card as a HV piezo driver. The modified schematic can be found below.
We added a 1kOhm resistor in the output which forms a ~100Hz low-pass with the 1.5uF capacitance of the PZT.
We get a good SNR ratio for TF measurements even when using white noise as the source. doing some low-frequency TF measurement over night.
WiIl also try a swept-sine measurement if required, but takes too long at low frequencies.
We also tried to build a simple loop using two stanford preamps to suppress the horizontal seismic motion of the table but couldn't see any improvement. Will wait for the measured TF to design the right loop.
HV amplifier schematic (modified PMC servo):
The 1.45" cavities have arrived. So I think it is a good time I layout the plan for the next phase of the experiment:
fig2: proposed new setup with 2 laser sources
Since we want to upgrade the current setup to 2-laser setup, we need to find:
by tuning the servo Tara unlocked both cavities and they are out of range right now, so plz no more temp servo tuning until further notice
New Focus PD:
power from ACAV: 0.958mW
power from RCAV: 0.967mW
AC-OUT: 1.27Vpp @160MHz in 50R