Koji asked me to take a profile of the output of the 1W NPRO that will be used for green locking. I used the razor-scan method, plotting the voltage output of a PD vs the position of the razor across the beam, both vertically and horizontally. This was done at 6 points along the beam path out of the laser box.
I determined the beam spot size at each point by doing a least-squares fit on the plots above in Matlab (using w as one of the fitting parameters) to the cumulative distribution functions (error functions) they should approximate.
I then did another least-squares fit, fitting the above "measured" beam profiles to the gaussian form for w vs z. Below is a summary.
It seems reasonable, though I know that M2 < 1 is fishy, as it implies less divergence than ideal for that waist size. Also, like Koji feared, the waist is inside the box and thus the scan is almost entirely in the linear regime.
There is a clearly a difference in the divergence angle of the x and y beams - maybe 10-20%. Since the measurements are outside the Rayleigh range and approximately in the linear regime, the slope of the divergence in this plot should be inversely proportional to the waists - meaning the x- and y- waist sizes should differ by about 10-20%. You should check your fitting program for the waist.
EDIT: I used an IFIT (inverse fast idiot transform) to change the x-axis of the plot from Hz to m. I think xlabel('Frequency [Hz]') is in my muscle memory now..
I have redone the beam fit, this time omitting the M2, which I believe was superfluous. I have made the requested changes to the plot, save for the error analysis, which I am still trying to work out (the function I used for the least squares fit does not work out standard error in fit parameters). I will figure out a way to do this and amend the plot to have error bars.
Are you sure about your x-axis label?
The laser is back. Test report is in the 40m wiki as New Pump Diode Mephisto 1000
It will go on the PSL table.
After adjusting the alignment of the two beams onto the PD, I managed to recover a stronger beatnote of ~ -10dBm. I managed to take some measurements with the PLL locked, and will put up a more detailed post later in the evening. I turned the IMC autolocker off, turned the 11MHz Marconi output off, and closed the PSL shutter for the duration of my work, but have reverted these to their nominal state now. The are a few extra cables running from the PSL table to the area near the IOO rack where I was doing the measurements from, I've left these as is for now in case I need to take some more data later in the evening...I
Innolight 1W 1064nm, sn 1634 was purchased in 9-18-2006 at CIT. It came to the 40m around 2010
It's diodes should be replaced, based on it's age and performance.
RIN and noise eater bad. I will get a quote on this job.
The Innolight Manual frequency noise plot is the same as Lightwave' elog 11956
Diagnoses from Glasglow:
“So far we have analyzed the laser. The pump diode is degraded. Next we would replace it with a new diode. We would realign the diode output beam into the laser crystal. We check all the relevant laser parameters over the whole tuning range. Parameters include single direction operation of the ring resonator, single frequency operation, beam profile and others. If one of them is out of spec, then we would take actions accordingly. We would also monitor the output power stability over one night. Then we repackage and ship the laser.”
I'm cleaning out to make room for our new optical cabinet. Are we keeping these? There are ~20 pieces of 10" od 1" wide tapes and large number of cassettes.
AJW, Zucker, Stuart A and Koji were notified in this matter.
Alan suggested to save data of Bruce Allen paper of observation of binary neutron stars in the 40m on 1994 November 14-20 and save back up tapes of his period in the 40m.
Mike: reels are not readable any more, it is time to let go
- High priority units: 2x 18AI / 1x 16AI / 3x 16AA
All six are reworked and on the electronics workbench. The rest should be ready by the end of the week.
To test the effect on EPICS latency, I've restarted daqd with modified ini files which disable all frame writing of 16Hz channels.
This happened at GPS:1131835955 aka Nov 17 2015 22:52:18 UTC
Last night, I started running a script written by Dave Barker that monitors a specified EPICS channel (in this case C1:IOO-MC_TRANS_SUM), to look for seconds in which it does not update the expected number of times. This is still running, so I will be able to compare the rate of EPICS slowdowns before and after this change.
I will revert back to the nominal state of things in a few hours, or until someone asks me to.
Back to nominal FB configuration at 1131857782, aka Nov 18 2015 04:56:05 UTC.
Weirdly, during this time, the script watching MC_TRANS_SUM from pianosa saw tons of freezes, but another instance watching LSC-TRY_OUT16 on optimus saw no freezes.
I temporarily turned off the 166 modulation.
I turned off the modulation at 166MHZ becasue I don't need it if I'm only locking the PRC.
It was introducing extra amplitude modulations of the beam which interfered with the AbsL's PLL photodiode.
I'm going to turn it back on later on.
I turned back on the 166MHz modulation just a bit. I set the slider at 4.156.
When it was totally off the MZ seemd quite unhappy.
You can turn the 166 off if you want. MZ is unhappy after its turned off, but that's just the thermal transient from removing the RF heat. After a several minutes, the heat goes away and the MZ can be relocked.
One of these days we should evaluate the beam distortion we get in EOMs because of the RF heat induced dn/dT. Beam steering, beam size, etc.
I replaced the SMA end connector for the 166 MHZ Local Oscillator signal that goes to the back of the flange in the 1Y2 rack. The connector had got damaged after it twisted when I was tigheting the N connector of the Heliax cable on the front panel.
I temporarily disconnected the Heliax cable that brings the 166MHz LO to the LSC rack.
I'm doing a couple of measurement and I'll put it back in as soon as I'm done.
These are the losses I measured on a RG-174 cable for the two frequencies that we're planning to use in the Upgrade:
(The cable was 2.07m long. The input signal was +10dBm and the output voltages at the oscilloscope where: Vpk-pk(11MHz)=1.90V, Vpk-pk(11MHz)=1.82V )
I apologize for the lack of correctness on the units in yesterday's elog entry, but I wasn't very sharp last night.
I repeated the measurement today, this time also making sure that I had a 50ohm input impedance set in the scope. These the results for the losses.
I also measured the losses in the Heliax cable going from the 166 MHz LO to the LSC rack:
Seems like very strange cable loss numbers. The Heliax is lossier than the RG-174? I wonder how these compare with the specs in the cable catalog?
I did the measurement on a 4.33 meter long cable with SMA connectors at the ends.
I looked through the lab area to do a fast photodiode inventory check, as we may need to buy some for the higher order mode spectroscopy SURF project. I looked on the following optical tables: ETMY, ITMY, BS, AS, PSL, SP, ITMX, Jenne laser table, and ETMX, as well as the photodiode cabinet, and could only find two 1611s. Here is a summary of the inventory:
I have not yet checked if these photodiodes are in working order.
I did a quick calculation to determine the amount of sideband transmission through the FP cavity.
The modulation frequency of the end PDH is 216kHz. The FSR of the cavity is about 3.9MHz. So the sidebands pick up about 0.17 radians extra phase on one round trip in the cavity compared to the carrier.
The ITM reflectance is r_ITM^2 = 98.5% of power, the ETM reflection is r_ETM^2 = 95%.
So the percentage of sideband power reflected from the cavity is R_SB = r_ITM*r_ETM*(exp(i*0.17) - 1)^2 / (1 - r_ETM*r_ITM exp(i*0.17) )^2 = 0.85 = 85%
So about 15% of the sideband power is transmitted through the cavity. The ratio of the sideband and carrier amplitudes at the ETM is 0.05
So, on the vertex PD, the power of the 80MHz +/-200kHz sidebands should be around sqrt(0.15)*0.05 = 0.02 = 2% of the 80MHz beatnote.
Once we get the green and IR locked to the arm again, we're going to look for the sidebands around the beatnote.
I have configured one of the spare Supermicro X8DTU-F chassis as a dual-CPU, 12-core CDS front end machine. This is meant to be a replacement for c1sus. The extra cores are so we can split up c1rfm and reduce the over-cycle problems we've been seeing related to RFM IPC delays.
I pulled the machine fresh out of the box, and installed the second CPU and additional memory that Steve purchased. The machine seems to be working fine. After assigning it a temporary IP address, I can boot it from the front-end boot server on the martian network. It comes up cleanly with both CPUs recognized, and /proc/cpustat showing all 12 cores, and free showing 12 GB memory.
The plan is:
Obviously the when of all this needs to be done when it won't interfere with locking work. fwiw, I am around tomorrow (Tuesday, 2/11), but will likely be leaving for LHO on Wednesday.
Riju hasn't been in the lab in a long time to do any measurements, so I put the signals back to how they should be.
I turned off / confirmed off the things which were sending signal to the EOM: the network analyzer, the RF generator box, and the Marconi which supplies the 11MHz.
I removed the cavity scanning cable, and terminated it, and put the regular 11MHz cable back on the splitter.
I then turned on the RF gen box and the Marconi. The Marconi had been off, so we were not getting any 11MHz or 55MHz out of the RF gen. box. This is why I couldn't lock any cavities last night (duh).
On to locking!
----------------- In other news,
While swapping out the EOM cable, I noticed that the DC power supply sitting under the POX table was supplying a weird value, 17 point something volts. I checked on the table to remind myself why that power supply is there...it's powering an RF amplifier right after the commercial PD that is acting as POP22. The amplifier wants +15 and GND, so I reset the power supply to 15V. We should add this to the list of things to fix, because it's dumb. Either we need to put in the real POP22 (long term goal), or we need to get this guy some rack power, and do the same for any amplifiers for the Beat setup. It's a little hoakey to have power supplies littering the lab.
During checking the 11MHz demod boards I found that the I-Q relative phase showed funny LO power dependence.
It is now under investigation.
In the plot above the green curve represents the I-Q phase of a 11MHz demod board (see here).
It showed a strong dependence on the LO power and it changes from -60 deg to -130 deg as the LO power changes.
This is not a good situation because any power modulation on the LO will cause a phase jitter.
For a comparison I also took I-Q relative phase of a 33MHz demod board, which hasn't been modified recently.
It shows a nice flat curve up to 5 dBm although it looks like my rough measurement adds a systematic error of about -5 deg.
- to do -
* check RF power in every point of LO path on the circuit
* check if there is saturation by looking at wave forms.
[Rana, Koji, Kiwamu]
Moreover the amplitude of the I and Q signals are highly unbalanced, depending on the LO power again.
This implies the coil for a 90 degree splitting won't work at 11 MHz since the coil is home made and used to be designed for a specific frequency (i.g. 24.5 MHz).
We decided to use a Mini circuit 90 deg splitter instead. Steve will order few of them soon and we will test it out.
One way to avoid some of the bad stuff in there is to take the 1 dBm input and amplify it to ~21 dBm before splitting and sending in to the Level 17 mixers.
One way to do this is by using the A3CP6025 from Teledyne-Cougar. Its an SMA connectorized amp which can put out 25 dBm and has a gain of 24 dB. We can just glue it onto the demod boards. Then we can remove the ERA-5 amplifiers and just use the broadband splitter as Kiwamu mentioned.
Use 10 Ohms for the resistance - I have never seen a diode with 25 Ohms.
p.s. PDFs can be joined together using the joinPDF command or a few command line options of 'gs'.
I read a few datasheets of the C30642GH photodiode that we're going to use for the 11 and 55 MHz. Considering the values listed for the resistance and the capacitance in what they define "typical conditions" (that is, specific values of bias voltage and DC photocurrent) I fixed Rd=25Ohms and Cd=175pF.
Then I picked the tunable components in the circuit so that we could adjust for the variability of those parameters.
Finally with LISO I simulated transfer functions and noise curves for both the 11 and the 55MHz photodiodes.
I'm attaching the results and the LISO source files.
After a power outage, a Marconi comes back to it's defaults. It needed to be reset to the values in elog 5530. I'm putting a label on the Marconi so we don't have to look it up next time.
Before fixing the Marconi, POY11, AS11 and AS55 all looked like noise, no real signals, even though the arm is flashing. Now they all look PDH-y, so things are better.
Manasa and Steve,
Is this what you want? Dashed lines are dark.
BS and PRM oplevs are blocked for this measurement. I will restore to normal operation at 4pm today.
It doesn't work with the lens in there, but it seems pretty close. Please leave it as is and I'll play with it after 5 today.
To test what the inherent angular noise of the HeNe 1103P laser is, we're testing it on a table pointing into the BS OL QPD with only a few steering mirrors.
From the setup that I found today, I've removed the lens nearest to the laser (which was used for the BS and PRM) as well as the ND filter (what was this for?) and the lens placed just before the BS QPD.
With the ND filter removed, the quadrant signals are now ~15000 if we misalign it and ~9000 each with the beam centered.
In order to calibrate the OLPIT_IN1 and OLYAW_IN1 signals into mm of beam motion, I misaligned the mirror just before the QPD. The knobs on there actuate the 100 TPI screws and the knurling on the knob itself has 10 ridges, so that's 36 deg per bump.
PIT cal ~ 1.55 (knob deg / count) -->> 10 microns / count --->>> 10 urad / count
YAW cal ~ 1 (knob deg / count) -->> 6.5 microns / count --->>> 6.5 urad / count
Distance from the 45 deg turning mirror to the QPD silicon surface is 23 cm. Distance between knob tip and fixed pivot point is ~4 cm. 1 knob turn = 0.01" = 0.254 mm = 0.254/40 radians of mirror angle.
So 360 deg of knob gives 2*0.254/40 = 0.012 radians of beam angle = 0.012 * 230 mm ~2.3 mm of beam spot motion. Or 6.4 microns of translation / deg of knob.
The distance from the face of the laser to the QPD is 96 cm.
The punchline is that the laser shows a level of noise which has a similar shape to what's seen at LLO, but 10x lower.
The noise at 0.05 - 0.2 Hz is ~2-3x worse than the PR3 at LLO. Not sure if this is inherent to the HeNe or the wind in our setup.
As I see it, we have a few options for getting the 110 MHz LO to both the POP110 and AS110 demod boards.
The current situation is described by Kiwamu in elog 5746. The 55 MHz signal comes into the box, and is split 4 ways, with each path having 19.7 dBm. One of these 4 is for 110. It has a 2dB attenuator (giving us ~17.7 dBm), and then it goes to an MK-2 frequency multiplier. I'm a little lost on why we're giving the MK-2 17 dBm, since it says that it can handle an input power between 1 - 15 dBm. It has ~16 dB conversion loss, so the 110 output of the distribution board has (according to the drawing) 1.9 dBm. The demod boards have a 10 dB attenuator as the first element on the LO path, so we're giving the ERA-5 -8 dBm.
We can either amplify the 110 leaving the distribution box, split it, and then attenuate it to the appropriate level for the demod boards, or we can change the attenuators on the POP110 and AS110 demod boards.
Since we seem to be over driving the 2x frequency multiplier, I think I should change the 2dB attenuator to a 5dB attenuator, so we're giving the 2x multiplier ~15 dBm. The conversion loss of ~16 dB means we'll have -1 dBm of 110 MHz. I want to amplify that by ~10 dB, to give 9 dBm. Attenuate by 5 dB to get to 4 dBm, then split into 2, giving me 2 110 MHz spigots, each of ~1 dBm. Since the demod boards expect between 0-2 dBm for the LO's, this should be just fine.
Thoughts, before I start scrounging parts, and pulling the RF distribution box?
- Do we have an appropriate amplifier?
- True challenge could be to find a feedthrough for the new port. (or to find a space for the amplifier in the box)
- PDXXX channels is on the DC whitening filter module. There could be some modification on this module (like diabling the whitening gain selector).
- We don't have AS11 and AS165, and so far it is unlikely to use AS11. i.e. The feedthrough, the slot on the crate, the whitening, and the channels can be trasnsition from 11 to 110.
I want to amplify that by ~10 dB, to give 9 dBm. Attenuate by 5 dB to get to 4 dBm, then split into 2, giving me 2 110 MHz spigots, each of ~1 dBm.
11MHz modulation source was turned off (disabled) at Marconi at 12:00.
Absolutely hokey. What are our requirements for this RFPD? What are the power levels and SNR that we want (I seem to remember that its for 22 as well as 110 MHz)? Perhaps we can test an aLIGO one if Rich has one sitting around, or if the aLIGO idea is to use a broadband PD I guess we can just keep using what we have.
This is a simple representation of the schematic:
gnd# |# Cw2# |# n23# |# Lw2# |# n22# |# Rw2 # | |\ # n2- - - C2 - n3 - - - - | \ # | | | | |4106>-- n5 - Rs -- no# iinput Rd L1 L2 R24 n6- | / | |# nin - | | | | | |/ | Rload # Cd n7 R22 gnd | | | # | | | | - - - R8 - - gnd # gnd R1 gnd R7 # | |# gnd gnd# ##
I chose the values of the components in a realistic way, that is using part available from Coilcraft or Digikey.
Using LISO I simulated the Tranfer Function and the noise of the circuit.
I'm attaching the results.
I'll post the 55MHz rfpd later.
oops, forgotten the third attachment...
here it is
1064 nm Semiconductor Laser Fiber Distribution System and Mirror Tomography
Below threshold these Semiconductor Fabry-Perot lasers have an axial mode structure with a spacing of about a THz. As you turn up the current to above threshold the first mode to oscillate saturates the gain down on all the modes and only it oscillates. The laser I have here in my office (a backup for the one you have at the 40 meter) has a wavelength of 1064.9 nm at 70 Degrees C. We should be able to temperature tune it down to 1064.3 nm although this could be a bit tedious the first time we do it. The specifications claim a "spectrum width" of 1.097 nm which I believe is the temperature tuning range. I don’t know what the line width is but it will be single frequency and we shouldn’t have mode hoping problems. So we should be able to use it in the “Mirror Tomography” experiment. You might want to use some sort of polarization diversity to avoid the problems of fiber polarization drift.
There have been 2 student projects on using the fiber distributed PD frequency response at1064 nm laser.
“Automated Photodiode Frequency Response Measurement System,” Alexander Cole - T1300618
“Final Report: Automated Photodiode Frequency Response Measurement System for Caltech 40m lab,” Nichin Sreekantaswamy - P140021
I’ll look up a few more references and add include them in the next elog.
I noticed that we have not been saving the 1/sqrt(TRX) and 1/sqrt(TRY) data, so I modified the c1lsc model and added them to the DAQ channels block. I restarted the c1lsc model, and the _DQ channels are now archived.
[Jenne, Kyung Ha]
We made some good progress on suspending the Tip Tilt ECDs today. We finished one whole set, plus another half. The half is because one of the screw holes on the lower right ECD somehow got cross threaded. The ECD and screws in question were separately wrapped in foil to mark them as iffy. We'll redo that second half tomorrow. This makes a total of 2.5 (including yesterday's work) ECD backplanes suspended. The only thing left for these ones is to trim up the excess wire.
We also (with Koji) took a look at the jig used for suspending the mirror holder. It looks like it was designed for so many Tip Tilt generations ago as to be basically useless for the 40m TTs. The only really useful thing we'll get out of it is the distance between the suspension block and the mirror holder clamps. Other than that we'll have to make do by holding the mirror and block at the correct distance apart, utilizing a ruler, calipers, or similar. Rana pointed out that we should slightly bend the blade springs up a bit, so that when they are holding the load of the mirror holder, they sit flat.
Attached below are 2 different pictures of one of the ECD backplane sets that has been suspended. One with black background to illustrate the general structure, and one with foil background to emphasize the wires.
Currently, DC power for amplifiers ZHL-1000LN+ is supplied by Aligent E3620A.
I tried to use power supply from the side of 1X1 rack, but fuse plug(Phoenix Contact ST-SI-UK-4) showed red LED, so I couldn't use it.
We fixed things so that we are now using regular fused rack power for these amplifiers. The fuse no longer had a red LED, but it measured open when we checked the resistance. Although, somehow (magic?) 13.73V were getting to the other side of the fuse.
Anyhow, replacing the fuse with a new one fixed the problem right up.