MC1 and MC3 seem to have kept themselves together, but all the other optics' watchdogs tripped.
Some of the suspensions got watchdog tripped -> enabled -> damped.
The MC mirrors got slightly misaligned.
The oplev plots clearly show the alignment effect of this eq.
Someone adjusted the Guralp2 mass position last night??
Last night (Mar 17) I checked the PLL setup as Mott have had some difficulty to get a clean lock of the PLL setting.
Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...
Last night (Mar 17) I checked the PLL setup as Mott had some difficulty to get a clean lock of the PLL setting.
I also had noticed the progressive change of the aux NPRO alignment to the Farady.
I strongly agree about the need of a good and robust PLL.
By modifying the old PDH box (version 2008) eventually I was able to get a PLL robust enough for my purposes. At some point that wasn't good enough for me either.
I then decided to redisign it from scratch. I'm going to work on it. Also because of my other commitments, I'd need a few days/1 week for that. But I'd still like to take care of it. Is it more urgent than that?
We use the current PLL just now, but the renewal of the components are not immediate as it will take some time. Even so we need steady steps towards the better PLL. I appreciate your taking care of it.
In this LVC meeting I discussed about triple resonant EOMs with Volker who was a main person of development of triple resonant EOMs at University of Florida.
Actually his EOM had been already installed at the sites. But the technique to make a triple resonance is different from ours.
They applied three electrodes onto a crystal instead of one as our EOM, and put three different frequencies on each electrode.
For our EOM, we put three frequencies on one electrode. You can see the difference in the attached figure. The left figure represents our EOM and the right is Volker's.
Then the question is; which can achieve better modulation efficiency ?
Volker and I talked about it and maybe found an answer,
We believe our EOM can be potentially better because we use full length of the EO crystal.
This is based on the fact that the modulation depth is proportional to the length where a voltage is applied onto.
The people in University of Florida just used one of three separated parts of the crystal for each frequency.
Did you find what is the merit of their impedance matching technique?
I checked the setup further more.
Now I have significant fraction of beating (30%) and have huge amplitude (~9dBm).
The PLL can be much more stable now.
It looks like Steve used a GND-12V supply to power the Guralp through the little breakout box (the box is for checking the centering of the mass). This is BAD. The Guralps want +/- 12V.
We centered all of the channels on Gur2, and checked the channels on Gur1, so we'll see how they're feeling after a while.
This trend of the last 200 days shows that GUR2 has been bad forever...until now anyways.
I went and double-checked and aligned the styrofoam cooler at ~5:00 UTC. It was fine, but we really need a better huddling box. Where's that granite anyway?
Here's the new Huddle Test output. This time I show the X-axis since there's some coherence now below 0.1 Hz.
You'll also notice that the Wiener filter is now beating the FD subtraction. This happened when I increased the # of taps to 8000. Looks like the noise keeps getting lower as I increase the number of taps, but this is really a kind of cheat if you think about it carefully.
Yes, I found it.
Their advantage is that their circuit is isolated at DC because of the input capacitor.
And it is interesting that the performance of the circuit in terms of gain is supposed to be roughly the same as our transformer configuration.
From this morning, now in calibrated units, and with the Güralp self noise spec from the Güralp manual.
We are going to set the waist size to 0.1 mm for the beam going through the triple resonant EOM on a new PSL setup.
When we were drawing a new PSL diagram, we just needed to know the waist size at the EOM in order to think about mode matching.
This figure shows the relation between the waist size and the spot size at the aperture of the EOM.
The x-axis is the waist size, the y-axis is the spot size. It is clear that there is a big clearance at 0.1 mm waist size. This is good.
Also it is good because the waist size is much above the damage threshold of the EO crystal (assuming 1W input).
The attached file is the python code for making this plot.
You don't need a lengthy code for this. It is obvious that the spot size at the distance L is minimum when L =
zR, where zR is the Rayleigh range. That's all.
Then compare the spot size and the aperture size whether it is enough or not.
It is not your case, but if the damage is the matter, just escape to the large zR side. If that is not possible
because of the aperture size, your EOM is not adequate for your purpose.
It took too long to get this box ready for action. I implemented all of the changes that I made on the previous one (#1437). In addition, since this one is to be used for phase locking, I also made it have a ~flat transfer function. With the Boost ON, the TF magnitude will go up like 1/f below ~1 kHz.
The main trouble that I had was with the -12V regulator. The output noise level was ~500 nV/rHz, but there was a large oscillation at its output at ~65 kHz. This was showing up in the output noise spectrum of U1 (the first op-amp after the mixer). Since the PSRR of the OP27 is only ~40 dB at such a high frequency, it is not strange to see the power supply noise showing up (the input referred noise of the OP27 is 3.5 nV/rHz, so any PS noise above ~350 nV/rHz becomes relavent).
I was able to tame this by putting a 10 uF tantalum cap on the output of the regulator. However, when I replaced the regulator with a LM7912 from the blue box, it showed an output noise that went up like 1/f below 50 kHz !! I replaced it a couple more times with no benefit. It seems that something on the board must now be damaged. I checked another of the UPDH boxes, and it has the same high frequency oscillation but not so much excess voltage noise. I found that removing the protection diode on the output of the regulator decreased the noise by a factor of ~2. I also tried replacing all of the 1 uF caps that are around the regulator. No luck.
Both of the +12 V regulators seem fine: normal noise levels of ~200 nV/rHz and no oscillations.
Its clear that the regulator is not functioning well and my only guess is that its a layout issue on the board or else there's a busted component somewhere that I can't find. In any case, it seems to be functioning now and can be used for the phase locking and PZT response measurements.
For your reference: Voltage noise of LM7815/LM7915 (with no load)
There was more jackhammering this morning just about 20 ft north-west of the beamsplitter chamber, outside.
We changed the pointer on /cvs/cds/caltech/target/gds/bin/awgtpman from
Then killed the megatron framebuilder and testpoint manager (daqd, awgtpman), restarted, hit the daq reload button from the GDS_TP screen.
This did not fix everything. However, it did seem to fix the problem where it needed a rtl_epics under the root directory which did not exist. Alex continued to poke around. When next he spoke, he claimed to have found a problem in the daqdrc file. Specifically, the cvs/cds/caltech/target/fb/ daqdrc file.
set gds_server = "megatron" "megatron" 10 "megatron" 11;
He said this need to be:
set gds_server = "megatron" "megatron" 11 "megatron" 12;
However, during this, I had looked file, and found dataviewer working, while still with the 10 and 11. Doing a diff on a backup of daqdrc, shows that Alex also changed
set controller_dcu=10 to set controller_dcu=12, and commented the previous line.
He also changed set debug=2 to set debug=0.
In a quick test, we changed the 11 and 12 back to 10 and 11, and everything seemed to work fine. So I'm not sure what that line actually does. However, the set controller_dcu line seems to be important, and probably needs to be set to the dcu id of an actually running module (it probably doesn't matter which one, but at least one that is up). Anyways, I set the gds_server line back to 11 and 12, just in case there's numerology going on.
I'll add this information to the wiki.
It looks like the PLL drifted alot over the weekend, and we couldn't get it back to 9 dBm. We switched back to the new focus wideband PD to make it easier to find the beat signal. I replaced all the electronics with the newly fixed UPDH box (#17) and we aligned it to the biggest beat frequency we could get, which ended up being -27 dBm with a -6.3V DC signal from the PD.
Locking was still elusive, so we calculated the loop gain and found the UGF is about 45 kHz, which is too high. We added a 20 dB attenuator to the RF input to suppress the gain and we think we may have locked at 0 gain. I am going to add another attenuator (~6 dB) so that we can tune the gain using the gain knob on the UPDH box.
Finally, attached is a picture of the cable that served as the smb - BNC adaptor for the DC output of the PD. The signal was dependent on the angle of the cable into the scope or multimeter. It has been destroyed so that it can never harm another innocent experiment again!
We have managed to lock the PLL to reasonable stability. The RF input is attenuated by 26 dBm and the beat signal locks very close to the carrier of the marconi (the steps on the markers of the spectrum analyzer are coarse). We can use the marconi and the local boost of the pdh box to catch the lock at 0 gain. Once the lock is on, the gain can be increased to stabilize the lock. The locked signals are shown in the first photo (the yellow is the output of the mixer and the blue is the output to the fast input of the laser. If the gain is increased too high, the error signal enters an oscillatory regime, which probably indicates we are overloading the piezo. This is shown in the second photo, the gain is being increased in time and we enter the non-constant regime around mid-way through.
Tomorrow I will use this locked system to measure the PZT response (finally!).
This is the first touch to the MC mirrors after the earthquake on 16th.
So far, I have aligned in Yaw such that the yaw peak is minimized.
This seal is good for daily use- operation only. The IFO has to be sealed with light metal doors every night so ants and other bugs can not find their way in.
Our janitor Kevin is mopping the hole IFO room floor area with 5% ant killing solution in water in order to discourage bugs getting close to our openings of the vented chamber.
You may be sensitive to this chemical too. Do not open chamber till after lunch.
Old control room air condition failed yesterday around noon. It was blowing 80-85F hot air for about 2-3 hours at racks 1Y4-7 and the entry room 103
I found the elog down and I restarted it.
Then, after few seconds it was down again. Maybe someone else was messing with it. I restarted an other 5 times and eventually it came back up.
After realigning and getting the lock today, I tried to add in the SR785 to measure the transfer function. As soon as I turn on the piezo input on the PDH box, however, the lock breaks and I cannot reacquire it. We are using an SR650 to add in the signal from the network analyzer and that has worked. We also swapped the 20 dB attenuator for a box which mimics the boost functionality (-20 dB above 100 Hz, 0 dB below 6Hz). I took some spectra with the SR750, and will get some more with the network analyzer once Alberto has finished with it.
The SR750 spectra is posted below. The SR750 only goes up to 100 kHz, so I will have to use the network analyzer to get the full range.
I spent some time trying to understand how touching the metal cage inside or bending the PCB board affected the photodiode response. It turned out that there was some weak soldering of one of the inductors.
Matt and Koji:
We closed the light doors of the chambers.
We are leaving the PLL as it is locked in order to see the long term stability. And we will check the results in early morning of tomorrow.
DO NOT disturb our PLL !!
(what we did)
After Mott left, Matt and I started to put feedback signals to the temperature control of NPRO.
During doing some trials Matt found that NPRO temperature control input has an input resistance of 10kOhm.
Then we put a flat filter ( just a voltage divider made by a resistor of ~300kOhm and the input impedance ) with a gain of 0.03 for the temperature control to inject a relatively small signal, and we could get the lock with the pzt feedback and it.
In addition, to obtain more stable lock we then also tried to put an integration filter which can have more gain below 0.5Hz.
After some iterations we finally made a right filter which is shown in the attached picture and succeeded in obtaining stable lock.
Now some pedestals, mirrors and lenses are left on the PSL table, since we are on the middle way to construct a PLL setup which employs two NPROs instead of use of PSL laser.
So Please Don't steal any of them.
Modified one of the PD assemblies carrying a large SI-Diode (~10mm diameter).
Removed elements used for resonant operation and changed PD readout to transimpedance
configuration. The opamp is a CLC409 with 240 Ohm feedback (i.e. transimpedance) resistor.
To prevent noise peaking at very high frequencies and get some decoupling of the PD,
I added a small series resistor in line with the PD and the inverting opamp input.
It was chosen as 13 Ohm, and still allows for operation up to ~100MHz.
Perhaps it could be smaller, but much more bandwith seems not possible with this opamp anyway.
Changes are marked in the schematic, and I list affected components here.
(Numbers refer to version 'PD327.SCH' from 30-April-1997):
-connected L3 (now open pad) via 100 Ohm to RF opamp output. This restores the DC sognal output.
-connected pin 3 of opamp via 25 Ohm to GND
-connected kathode of PD via 13 Ohm to pin 2 of opamp
-removed L6, C26, L5, C18, and C27
-shorted C27 pad to get signal to the RF output
Measured the optical TF with the test laser setup.
(Note that this is at 1064nm, although the PD is meant to work with green light at 532nm!)
Essentially it looks usable out to 100MHz, where the gain dropped only by about
6dB compared to 10MHz.
Beyond 100MHz the TF falls pretty steeply then, probably dominated by the opamp.
The maximal bias used is -150V.
If the bias is 'reduced' from -150V to -50V, the response goes down by 4dB at 10MHz and
by 9dB at 100MHz.
The average output was 30mV at the RF output, corresponding to 60mV at the opamp output (50Ohm divider chain).
With 240 Ohm transimpedance this yields 250µA photo-current used for these transfer functions.
The periscope design for beam elevation of the green beams is posted. The design for the 90 deg steering version is also coming.
(2010-03-29: update drawings by daisuke)
90deg version: http://nodus.ligo.caltech.edu:8080/40m/2725
Can I please get the network analyzer back?
Hartmut suggested a possible explanation for the way the electronics transfer function starts picking up at ~50MHz. He said that the 10KOhm resistance in series with the Test Input connector of the box might have some parasitic capacitance that at high frequency lowers the input impedance.
Although Hartmut also admitted that considering the high frequency at which the effect is observed, anything can be happening with the electronics inside of the box.
Matt checked it in this morning and he found it's been locked during the night.
The same thing happening again. The intermittent offset upstream of the seismometer that never got fixed.
The granite plate and ball bearings are in. I will place seismometers on it.
In this afternoon, Mott and I tried to find a beat note between two NPROs which are going to be set onto each end table for green locking.
At first time we could not find any beats. However Koji found that the current of innolight NPRO was set to half of the nominal.
Then we increased the current to the nominal of 2A, finally we succeeded in finding a beat note.
Now we are trying to lock the PLL.
P.S. we also succeeded in acquiring the lock
I upgraded the old REFL199 to the new REFL55.
To do that I had to replace the old photodiode inside, switching to a 2mm one.
Electronics and optical transfer functions, non normalized are shown in the attached plot.
The details about the modifications are contained in this dedicated wiki page (Upgrade_09 / RF System / Upgraded RF Photodiodes)
Safety glasses 1064 nm transmission measured at ~200 mW level. They are all good.
Kiwamu and Koji
Last night we have released PRM from the gluing fixture. All of the six magnets are successfully released from the fixture.
We put SRM on the fixuture and glued a side magnet which we had failed at the last gluing.
We let it cure in the Al house. This should be the last magnet gluing until ETMs are delivered.
ITMX (ITMU03): all of magnets/guiderod/standoffs glued, mirror baked; balance to be confirmed
ITMY (ITMU04): all of magnets/guiderod/standoffs glued, balance confirmed, mirror baked
SRM (SRMU03): magnets/guiderod/standoff glued; a side magnet gluing in process, balance to be confirmed, last stand off to be glued, mirror to be baked
PRM (SRMU04): magnets/guiderod/standoff glued; balance to be confirmed, last stand off to be glued, mirror to be baked
TT: magnets/guiderod/standoff glued; balance to be confirmed, last stand off to be glued, mirror to be baked
Last Friday, Matt made a frequency discriminator circuit on a bread board in order to test the idea and study the noise level. I think it will work for phase lock acquisition of Green locking.
As a result a response of 100kHz/V and a noise level of 2uV/rtHz @ 10Hz are yielded. This corresponds to 0.2Hz/rtHz @ 10Hz.
The motivation of using frequency discriminators is that it makes a frequency range wider and easier for lock acquisition of PLLs in green locking experiment.
For the other possibility to help phase lock acquisition, Rana suggested to use a commercial discriminator from Miteq.
The diagram below shows a schematic of the circuit which Matt has built.
Basically an input signal is split into two signals right after the input, then one signal goes through directly to a NAND comparator.
On the other hand another split signal goes through a delay line which composed by some RC filters, then arrive at the NAND comparator with a certain amount of delay.
After going through the NAND comparator, the signal looks like a periodic pulses (see below).
If we put a signal of higher frequency we get more number of pulses after passing through the NAND.
Finally the pulse-signal will be integrated at the low pass filter and converted to a DC signal.
Thus the amplitude of DC signal depends on the number of the pulses per unit time, so that the output DC signal is proportional to the frequency of an input signal.
By putting a TTL high-low signal, an output of the circuit shows 100kHz/V linear response.
It means we can get DC voltage of 1 V if a signal of 100kHz is injected into the input.
And the noise measurement has been done while injecting a input signal. The noise level of 0.2Hz/rtHz @ 10 Hz was yielded.
Therefore we can lock the green PLL by using an ordinary VCO loop after we roughly guide a beat note by using this kind of discriminator.
Not that this is an urgent concern, just a data point which shows that it doesn't just not work at the sites.
Just before working on the FSS today, I noticed that the VCO RF output level was set incorrectly.
This should ALWAYS be set so as to give the maximum power in the first order diffracted sideband. One should set this by maximizing the out of lock FSS RFPD DC level to max.
The value was at 2.8 on the VCOMODLEVEL slider. In the attached plot (taken with the FSS input disabled) you can see that this puts us in the regime where the output power to the FSS is first order sensitive to the amplitude noise on the electrical signal to the AOM. This is an untenable situation.
For adjusting the power level to the FSS, we must always use the lamba/2 plate between the AOM and the RC steering mirrors. This dumps power out to the side via a PBS just before the periscope.
What is the Transfer Function of the suspension of the reference cavity? What were the design requirements? What is the Q and how well does the eddy current damping work? What did Wolfowitz know about the WMD and when? Who cooked the RTV in there and why didn't we use Viton??
To get to the bottom of these questions, today I shook the cavity and measured the response. To read out the pitch and yaw modes separately, I aligned the input beam to be misaligned to the cavity. If the beam is mis-aligned in yaw, for example, the transmitted light power becomes first order sensitive to the yaw motion of the cavity.
In the attached image (10 minute second-trend), you can see the second trends for the transmitted and relfected power. The first ringdown comes from the pitch or vertical mode. The second (shorter) one comes from the yaw misalignment and the yaw shake.
To achieve the up/down shake, I leaned onto the table and pumped it at its eigenfrequency. For the yaw shake, I put two fingers on the RC can's sweater and pushed with several pounds of force at the yaw eigenfrequency (2.6 Hz). For the vertical, I jumped up and down at half the vertical eigenfrequency (4 Hz).
I also made sure that the .SCAN field on these EPICS records were set to 9 so that there is no serious effect from a beating between the eigenfrequency and the EPICS sample rate.
f_vert = 4 Hz
tau_vert = 90 seconds
Q_vert = 1000 (yes, that number over there has 3 zeros)
f_hor = 2.6 Hz
tau_hor = 30 seconds
Q_hor = 250
This is an absurd and probably makes us very sensitive to seismic noise - let's make sure to open up the can and put some real rubber in there to damp it. My guess is that these high Q modes
are just the modes of the last-stage steel spring / pendulum.
This is the error point spectrum - it is filled with huge multiples of ~75 kHz as Yoichi noticed a couple years ago.
I tried to use the netgpib.py package to read out the Agilent 4395, but the SVN had been corrupted by someone saving over the netgpib.py package. To get it to work on rosalba I reverted to the previous version, but whoever is busy hacking on netgpib.py needs to checkin the original package and work on some test code instead.
I also noticed that the default output format for the AG4395.py file is in units of Watts. This is kind of dumb - we need someone to develop this package a little as Yoichi did for the SRS785.
I measured the open loop gain of the FSS (as usual, I have multiplied the whole OLG by 10dB to account for the forward loop gain in the box). I used a source level of -20 dBm and made sure this was not saturating by changing the level.
Its clear that the BW is limited by the resonance at ~1.7 MHz. Does anyone know what that is?
I measured the RF spectrum coming out the FSS RFPD to look for saturations - its close to the hairy edge. This is with the 8x power increase from my AOM drive increase. I will increase the FSS's modulation frequency which will lower the Q and gain of the PD to compensate somewhat. The lower Q will also gain us phase margin in the FSS loooop.
I put in a bi-directional 20 dB coupler (its only rated down to 30 MHz, but its only off by ~0.3 dB at 21 MHz) between the RFPD and the FSS box. I looked at the time series on the 300 MHz scope and measured the power spectrum.
The peak signal on the scope was 40 mV; that translates to 400 mV at the RFPD output. Depending on whether the series resistor in the box is 20 or 50 Ohms, it means the MAX4107 is close to saturating.
As you can see from the spectrum, its mostly likely to hit its slew rate limit (500 V/us) first. Actually its not going to hit the limit: but even getting within a factor of 10 is bad news in terms of distortion.
Besides the multiples of the modulation frequency, you can see that most of the RMS comes from the strange large peaks at 137.9 and 181.1 MHz. Anyone know what these are from?
On the middle plot above, I have enabled the 20 MHz BW limit so you can see how much the amplitude goes down when only the 21.5 MHz SB is included. You can also see from the leftmost plot that once in awhile there is some 400mV/10ns slewing. Its within a factor of 10 of the slew rate limit.