it might be the low input impedance of the board which the coil driver cannot drive..
I suggest you use probes to see where in the noisemon circuit the distortion is starting
Trying to figure out the nature of the distortion found in noisemon (1843), I made a piece of DSUB9 breakout like attachment 1. I just used two wires and two clippers wires to break the DSUB connector into something I can clip into the board.
I sent a 10Hz drive to the coil driver and measured the spectrum at all the test points (including one pair on the coil driver board).
First, I compared the distortion situation at the input and output of noisemon (attachment 2). I measured the spectrum at TP10 and TP12 of coil driver (this is where noisemon picks up the differential input, reference DCC: D070483), and subtracted them quadratically, which gives us the input signal of noisemon. Then I measured the spectrum at the output of noisemon. Looking at attachment 2, it seems the coil driver does not contribute to the distortion.
Then I used the probe and measured all the test points individually. Attachment 3 also shows TP10 and TP12 but instead of measuring them individually and subtracting them, I just put one probe on TP10 and another on TP12. It looks like the coil driver does have a little distortion, contrast to the conclusion above.
Attachment 4 shows the spectrum at the noisemon input. There is a buffer between TP10/TP12 on coil driver and the input of noisemon (reference D070483). It looks like the distortion is less, somehow.
Attachment 5 is the spectrum after the passive filters, between TP3 and TP4. It seems the distortion comes back a little under 60Hz.
Attachment 6 shows the spectrum after the instrument amplifier.
Attachment 7 and 8 shows the output of two stages of high pass filters. The distortions gets much worse after two HP filters.
Attachment 9 shows the output of the low pass filter. We can see the high frequency harmonics are gone.
Attachment 10 is very confusing. Between TP8 and TP9 is just a buffer (LT1128 buffer unfortunately) - why does it give so many lines even without any drive? I tried to see them in the oscilloscope but there wasn't anything significant. Maybe it was the clippers/wires making the noise? I did check the signal at the conjunction point between the clipper and the wire using oscilloscope (attachment 11) - it is indeed bad (attachment 12) - but why these lines only show up in TP9?
I am very confused and need to think about what is going on now. I think a couple immediate questions are:
1. Why do I see so many lines at the output of noisemon even when there is no input? I should only see noisemon noise when there is no drive, but I did not short the inputs like when I measure the noise. I did shorted the inputs and checked the noise after the measurement - it is normal. Thus, the lines could be caused by not shorting the inputs of the coil driver, but I did not short the inputs in other measurements either - I just unchecked the excitation on diaggui.
2. Besides the TP9 confusion, we still see a lot of harmonics in uppersteam testpoints. Considering the TP9 situation, I think we should first ask - are they real? Then, if they are real, how bad are they? Considerations could include the functionality of noisemon board at the sites? This potentially include risk of saturation, increase of the noisemon noise and errors in measuring the DAC noise.
I measured the spectrum with the digital system at all test points on noisemon with 10Hz sine drive (1845), but I saw a lot of distortion harmonics and other confusing stuff. At the end, I realized it could be caused by the clipper wire I used to breakout the DSUB9 connector. After talking to Chris today, I also realized that the low input impedance of the digital system could be invasive to the circuit. Considering these potential issues, I repeated yesterday's measurements with SR785 (attachment 3). There is not much difference - instead of using the digital system to send the drive and do the measurements, I used SR785 to drive and measure. SR785 has 1MOhm of input impedance while the ADC has only 10-20kOhm, according to Chris, so it could resolve the input impedance issue. Also, there is no DSUB connectors used; it also let me get rid of the clipper wires.
I sent a 10Hz, 10mV p-p sine signal to the coil driver and measured all the test points from the output of the coil driver to the output of the noisemon. The results are in attachment 2, plotted in attachment 1. The test points can be referenced in the schematics in attachment 4. The plots with two numbers after 'TP' means the measurement is between the two test points - with postive clipper on one, negative on the other. Others are between the test point and ground.
We can see there is a little bit distortion lines in the spectrum under 100Hz, but they are very small compared to the response to the drive. I think maybe they could explain the low frequency bump logged in 1843. However, it seems unlikely that they will be a serious issues in the passband, but still needs a little more rigorous justification.
On Monday, tested a 1998 (Rev. 0) RFPD originally found in Crackle (serial #010). Looks like it was first resonant at 24.493 MHz, but was later tuned for 14.75 MHz. I used the AG4395A network analyzer in CTN following the procedure in the previous ELOG post, splitting R output into the test input of the RFPD. Driving at up to -10dBm, couldn't see any resonant feature in the TF below 150 MHz. Tuning the inductor L1 made no difference. The regulator (U3 and U4 near bottom right in picture below) outputs were nominal.
I borrowed a flat response (DC to 125 MHz) PD from CTN lab (New Focus 1811) along with its power supply for short term use.
Below are some photos of the aformentioned RFPD. I added some kapton to keep dust off the PD.
Today, after struggling to find a 4-pin circular power supply cable for the UPDH box (still interested btw) punched a hole for connec power connector in the back panel and found an appropriate cable. See attached photo. Intended for +- 15 VDC.
Record TF for RFPD SN09, resonant at 36 MHz, using the exact procedure as with EOM Resonant Driver.
UPDHv3 box (serial 17142) is bogus. While retrieving values of some of the components to plug into working zero model, saw the VGA stage is bypassed by a previously unnoticed hack. Verified this by taking TF and not seeing any changes with respect to the gain knob (shown below are zero's model TFs suggesting a tunable UGF from ~ 10 Hz to 1 kHz), so this box is not good for a standalone servo.
As suggested a few meetings ago, made a quick and dirty lock using a single SR560 and took measurement of something* CLTF (SR560 gain = 10) below. New goal is to find a decent replacement, for which decided to use RedPitaya's python API "pyRPL". Just using the GUI out of the box can also lock the cavity relatively quickly but neither method results in longer than 1 minute lock... so took one step back to polish the pdh error signal.
* Something = Use SR785 TF measurement with source on Ch1, and to B input in SR560. The SR560 in (A-B) mode, and demodulated signal connected to A. The loop was closed with the SR560 output driving the PZT, and Ch2 of SR785. Wouldn't call this CLTF...
Upon closer inspection the error signal seems to vary quite significantly on the scope (scanning @ 2 Hz), sometimes completely flipping its sign even though it always triggers on the same side of the ramp (see attachment for video, along with some neck excersise).
This might be the same behaviour from before, whereby the demodulated signal might still be "riding" a low-freq componen which can't be compensated with the LO (Marconi's carrier resolution = 1 Hz). Using the 10 MHz external Rb reference doesn't change anything. It seems that even with the coupler, reflections may be entering the mixer...
Adding a LP filter (BLP-1.9+) right at the mixer output solves this for good. Even using 36 MHz LO vs anything else doesn't make a difference so this explains the previous issue. Moving back to lock using stable err signal.
For reference, the LO carrier is set to 36.000 MHz, +7 dBm (so the EOM is driven with an estimated +30 dBm well below the saturation or damage threshold +40 dBm).
Achieved a good lock for pretty much all of the afternoon today. The laser ran at 937 mA current, the optimal gain on SR560 was found to be 50, with a LP cutoff at 300 Hz (12 dB/oct rolldown). The 300 Hz cutoff supresses most of the nasty 8 kHz noise (and harmonics) which I can hear with enough gain. Source still to be determined.
Johannes and I have taken the following equipment from the crackle lab to the 40m between Friday, June 1, and Sunday, June 3 2018.
Apart from the NPRO which was taken from the optical bench, everything else was taken from the storage cabinet by the lab entrance.
I placed the two beam profilers with the two laptops and chargers right inside the Crackle lab, as requested by Paco.
Note: Please don't try to connect these old Windows to the network. We just extract the data via USB etc, and that's all the connection we allow.
Shruti took back the beam profilers today AM to Cryo.
Shruti: returned to Gabriele's office
Borrowed 1 (new focus) broadband EOM from CTN for temporary use in Crackle (2 um OPO exp)
Received one Marconi 2023A (#539) from CTN and an SRS FS725 Rb clock. (See CTN/2605)
QIL elog entry: QIL/2524
Photos, please, because we don't allow a free-rolling cylinder in a lab.
Borrow both beam profilers and laptops from WB 264A.
See equipment borrowing note here.
Attempting TF measurement for resonant EOM driver, but not having luck reproducing the measurements done recently (Dec-03), so I started debugging the circuit. Both power supply connections (+- 18 VDC) seem nominal. The MAX2470 buffer regulated input is nominal at 5VDC. Looking at MMBT5551 HF transistor, base-emitter voltage is -0.60 VDC (nominal wrt -0.66 V). Using a scope, I feed a single tone (36 MHz, 190 mVpp) and look at the RFmon output and it looks ok (gain ~ 1). I changed the RFmon SMA cable and that seemed to do the trick... Bad cable (now in trash) stole my morning.
Tune EOM driver resonance to 35.993 MHz (shown below for reference).
With Aidan's assistance, I borrowed
for ~ 2 um imaging in the Crackle lab.
- First test to grab frames was done in my personal Win10 machine, with no success. Either I was unable to configure the server correctly, or the software "ArraySoft" is not supported in Win10. Upon contacting Heimann, I received instructions to update to a newer version but was warned that it's just a new GUI, nothing really changed from v1 --> v2. So didn't even bother.
- Instead, wrote a simple python-socket UDP server to catch the video stream. Most trouble happened when using temperature mode (command "K"). The client streams a bunch of zeros... My guess is that this unit does not have an internal temperature calibration, and one could in principle be uploaded but we probably don't care. Streaming in raw voltage mode (command "t") works well, as shown by the sample frame shown in Attachment 1.
- After recovering the CTN Win7 laptop from Radhika, I gave "ArraySoft" another change just to know the frames I was getting in python were not bogus. For this I pointed a 532 nm laser pointer straight to the sensor and got an image shown in Attachment 2. The key difference is the processing of the video stream. Attachment 1 is a single frame, while Attachment 2 is the average of 30 frames with no offsets present.
- Another issue present during this task was a faulty USB connection. Sometimes moving the sensor around would interrupt the stream (power lost). I carefully removed the case and exposed the TO-39 package and surrounding electronics to inspect and search possible failures but after seeing none, I swaped the USB power cable with my portable battery charger and had a more robust operation... So I dumped the old USB cable, and will get a new one.
- Since this one was borrowed from TCS lab, I placed an order for another one which will be set up permanently in the lab. Hopefully this will be enough for the OSA.
The SR785 I am using for the AOSEM noise measurements (the one that was in the TCS lab) doesn't seem to want to boot up all the way. After sitting at the "Backup OK" screen for ~30 secs, a dialog box pops up reading "WaitDone Error", after which the machine reboots. This continues forever.
I remember this having happened when I first liberated it from the TCS lab a few weeks ago. I turned the thing off for a while and it eventually worked just fine. I tried the same thing now and it didn't work. I am going to give it another go in the morning.
Has anyone experienced this error before?
Same thing happened when I went in this morning. I left it for a while (on this time) and it seems to be working. We might want to have this machine looked at.
I've turned the main turbo back on and aligned the readout now. The vacuum is already down to 1e-6torr. It seems that the the offset pin on the bottom of the mass is causing the fiber to move a lot as the isolation mass rotates. The movement does not appear much to the eye, but is taking up most of our readout range at the moment.
We can wait to see if this motion dies down. If not we may be forced to replace this intermediate mass with one where the pin is in the center.
I took the liberty of tidying up the Crackling table a bit.
The Cryo people left us a friendly reminder to "get our own shit": they had found many parts from their own experiment being used or lying around on our Crackling table. Parts belonging to the Cryo experiment are labeled with a dot of gold nail polish. I'm fairly sure I found, switched out and put away all these gold-dotted parts that were lying around on our Crackling table as I was cleaning up.
The lab floor is being mopped tomorrow. Perhaps this would be a good time to clean/put stuff away? (I did start on this a little last week, but much can still be done)
We built a Low Noise Preamplifier (D060205), and added voltage regulators for external power supply, so one can switch between battery and external supply. Some may know this one as the Ray Rai box (which it is once you put it inside a box...). The heart of the 100x amplifier is a high-gain, low-noise FET amplifier from InterFET (IF3602) that can have voltage noise as low as 0.3nV/rtHz. First a picture of the amplifier:
Terminating the preamp input with 50 Ohm, and using another 100x amplification from an SR560 (in battery mode) and AC-Coupling, we measured the following spectral noise density recorded with one of the DAQ systems that was designed by Vladimir:
As one can see, the (single-sided) noise spectrum is below 2 nV/sqrt(Hz), and there is almost no difference between the two cases in which the preamp has external and battery supply. The 60Hz lines are unusually strong. We already saw spectra that only had one weak 120Hz line. So our guess is that this is picked up by the cables that we rearranged recently. Anyway, it is good news that no significant noise seems to couple in from the external power supply to the preamp output.
We were wondering a little about the high noise. The specs promise something that should be weaker by a factor 5 or so. In fact, measuring the preamp noise with the network analyzer, we got noise spectra that were weaker by more than a factor 2. It is quite tricky to pin this down to some specific problem. Calibration seems to be fine since signals from the frequency generator show up with the correct amplitude in the time series. One thing that we still need to look at is some C code used to read out data from the DAQ. Some simple data averaging happens there without anti-aliasing filter, and this could cause extra noise.
We should soon have new FETs to be able to make more preamps. Also, if someone wants to have this amplifier, you can get the parts from us. Only the FETs are missing and you could nicely ask Peter King to get a FET from him. We also have a complete digikey parts list for the preamp in case you prefer to buy parts yourself. Unfortunately, we don't have a suitable box yet for the amplifiers.
As mentioned in th epost from Aug 22nd, we biult a Low Noise Preamplifier (D060205). When we measured its noise level, we did not use any anti-aliasing filter and therefore the noise level of the amplifier laid above its specs.
For better measurents, we have now implemented this filter in the data acquisition process (written in C): We use an inverse chebyshev filter with variable order, attenuation and stopband frequency. For the following results, we used the filter with an order of 10 ( which for numerical reasons is the highest stable order we achieved), a stopband frequency of 2048 Hz and an attenuation of 80 dB, which leads to a 3 dB-cutoff frequency of 1340 Hz.
This new noise spectrum comes very close to the specification, as the noise level now is about or below 1 nV/rtHz. Unfortunatly, you can still see the 60 Hz lines and its harmonics.
see entry here
Given all the input parameters such as the geometry, material properties, and thermal source beam - it will loop through and calculate the eigenfrequencies for the heat fluctuation at all time.
Given all the input parameters such as the geometry, material properties, and thermal source beam - it will loop through and calculate the eigenfrequencies for the heat fluctuation at all time.
[Eric Q, Zach]
Per Rana's request, we ordered some parts for the C3 (Coating, Crackle, Cryo) lab last week. The parts will ship today. Here is the PO:
There were a couple of SR560 in the lab which I notice have been unplugged for months. Since this slowly degrades the batteries and causes us to spend money/time to replace them, I have moved these to the EE shop and put them on charge.
please plug these in whenever they are not in use
I brought in the instrument and components for 2um ECDL:
1. SAF Gain chip / SAF1900S / Qty2
2. Grating / GR25-0616 / Qty2
3. 3axis piezo mount / POLARIS-K1S3P / Qty2
4. Lens / 390093-D / Qty2
5/6 Thorlabs small components / F3ES20, F3ESN1P / Qty2 ea
8~13 Machines Metal Components / D1900435, D1900429, D1900433, D1900432, D1900430, D1900434 / Qty 2ea
14~17 McMaster Carr fastners / 92196a192, 92196a110, 92196a079, 92196a081 / Qty 100 ea
18 Temp Controller / TED200C / Qty 2 Note One unit temporary used by 2um PD test setup
19 Laser Current Driver / LDC220C / Qty 2
20 Piezo Driver MDT694B / Qty 2
I entered Crackle lab circa ~11:15. I started some basic lab inventory and started cleaning/organizing stuff. We will use the first optical table (as you enter the lab) because it's the easiest to clear (see below before and after clearing). Some of the cleared items on the table include:
- UHV foil (moved to top left cabinet above the work bench)
- OSEM components for Crackle (?) (moved to top left cabinet above the work bench)
- Various metallic parts/components (moved some in a plastic container to the second drawer from the bottom of the second red tool storage, and others to the second optical table)
- Various screw/screwdriver kits (moved some to work bench right by the electronic storage area and others to the second optical table)
- Power supply and laser diode driver (moved to control/acquisition rack)
I then moved the 1064nm pump Innolight Mephisto 800NE to the clear table, clamped it down, and cleaned/organized the lab a little, which involved:
- Shelve orphan/incomplete PCBs and electronic components from the work bench up to the cabinets.
- Organized some cables by the fume hood.
- Organized other random hardware on the work benches.
I found the Emergency STOP (OMRON STI #A22EM02B) button buried on the fume hood, so I gave it a quick test, and after confirming it worked I wired it to the interlock on the back of the laser controller. Then tested it along with the interlock and verified it's working, but I have yet to solder it nicely (I didn't commit to the wire lengths yet).
Left at ~ 14:45. Noted that we had more cockroaches in the floor at the beginning of the day than 2 um laser sources. Now we are tied.
Today; entered lab at ~09:08. I verified the orientations of the aspheric lenses and blaze gratings relative to the flextures, packaged and then dropped the parts for epoxying to Koji in 40m ~ 11:00. Spent some time between 12:00 and 12:45 finishing the ECDL connections. Everything looked good so I hooked it up to the TED200C controller. After a bit of research, I found out the Steinhart constants for the 10k thermistor;
Plugging these into the Steinhart equation give the actual temperatures from the Tact output on the TED200C (otherwise read as kOhm). According to the spec sheet, the TEC was tested at 250 mA (0.40 V), so not knowing a bunch more, set I_TEC on the TED200C to this limit and inspect the actual TEC current by scanning the Tset (setpoint) and recording the current in the ~ 15 - 25 deg C (attached plot, horizontal line marks room temperature). The diode current driver is hooked up, and everything is on the table as is. Left Crackle ~ 18:30.
Here is a summary for how to connect the SAF1900S gain chip to TED200C temperature controller and LDC220C diode current driver. The chip itself lacked substantial documentation, so this comes after requesting tech support from the manufacturer. The SAF1900S pinout is
1 - TEC+
6 - TEC-
2 - Thermistor
3 - Thremistor
4 - Anode
5 - Cathode
The TED200C has a DSub15 output, but the cable provides a DSUB9 adapter. Then, only the following pins are connected to the SAF1900S
The LDC220C has a DSUB9 output, and its bipolar nature allows it to drive either anode-grounded or cathode-grounded diodes, so the question was wether the SAF1900S is AG/CG? In a first attempt, I assumed the diode was meant to be driven with a floating source (and that the LDC220C could do that), but the driver remained in "LD OPEN" state. Then, I revised the documentation for TLK1900 (an old, discontinued laser kit using the same gain chips). There, the bottom line seemed to suggest CG, but to be sure I asked a technician in thorlabs. They say most of their 14 pin butterfly chips are AG, but the 6pin ones seem to be CG. Anyways, the relevant pins (for either connection) are:
3: Ground (for AG/CG)
7: LD Cathode (for floating / AG)
8: LD Anode (for floating / CG)
After some communication with ANU's Disha, I found the diode pins are floating from the case (personally confirmed this), and an additional connection between pins 1 and 5 of the LDC220C needs to be established to override the interlock. The suggested connections are three: shortcut, resistance < 430 Ohm, or LED || 1 kOhm resistor (to match the Laser ON status in the front panel). I opted for this last one, made the connections and was able to correctly feed the SAF gain chip.
The gratings and aspheric lenses glued on the mounts were delivered to the lab on Thu.
The powermeter controler + S401C head was lent from OMC Lab. Returned to OMC Jul 15, 2020 KA
Entered Crackle ~ 8:47 AM.
Briefly fixed the LDC220C connection to the SAF1900 as described previously, and then installed the aspheric flexture and shoulder to the assembly (pictures below). Then, I used the thermal power meter head borrowed from OMC to check for emission as a function of laser diode current at a fixed temperature of 25 C (to match testing conditions). The result is below, where I seem to be getting slightly better amplified spontaneous emission (ASE) power than the attached test sheet. It may as well be that I am not measuring the ASE power alone, but I cannot presently determine this.
I added the grating and moved the power meter to the correct output aperture, but failed to detect any power. This suggests a wrong grating orientation, although I will try to verify this more carefully.
Very exciting to see the gain chip curve!
Grating orientation: Whaaat... If you already have the 1um laser SOP approved, you can use that laser to check the grating orientation.
Set grating in front of 1064 nm beam (current set to 1.058 A for a beam visible on the IR card). After testing both orientations, it becomes clear the grating is misoriented. The difference is very clear, there is only specular reflection in the current configuration, whereas the m=0, and +- 1 orders are visible in the 180 deg flipped configuration.
Attempted two methods to soften EP30-2, the results are summarized below.
(a) Heat -- Used the heat gun set to 200 F (~ 93 C) and held it near the back of the part so that the grating surface was never in direct exposure. The airflow was kept constant for a period of ~ 10 min, while I periodically checked to see if there were any signs of bond softening. After no signs of softening, I stopped and moved to method (b).
(b) Solvent -- After brief investigation and referring to T1400711, I got some acetone from CTN, and set up a ~ 50 ml bath. The part was not completely submerged and was arranged such that the grating face was always exposed to air, which I left for ~14 hours. The drawback of this method is that some of the acetone evaporated and at some point the EP30 bond stopped being in contact with the solvent. A picture for reference is attached, with the light blue line indicating the highest acetone level, and the red line indicating the EP30 bond level at the beginning of the bath.
Log of the output power vs current in the 1064 nm (Innolight) pump laser. The crystal temperature was set to 45.5 C, and the current limit is set to 2.1 A
> Temp Controller / TED200C / Qty 2 Note One unit temporary used by 2um PD test setup
I brought the brand new TED200C from QIL to Crackle (Permanent move).
The unit used for 2um PD test setup will stay in QIL (Permanent)
Today entered lab ~ 09:00. Over the weekend I coded a PySerial wrapper for the thorlabs MDT694B single channel piezo controller. I spent some time testing and debugging the code but it now works fine (tested on Linux, python=3.8.6 and PySerial=3.4-4). The wrapper refers to the manual available here. The code is available in the labutils repo
Wow! This is really cool! I didn't realize that this small box has such many remote capabilities.
We have this piezo controller everywhere in the labs and your code gives us a lot of opportunities to implement process automation.
In the process of adding a PC/controls, and other related instruments, reorganized items in the lab. Threw out some boxes and stored cabling and unused power dock. Moved the sticky mat and put out large trash bin. Organized electronics rack to which a Sorensen (DCS33-33) power supply was attached. For this, took a 14 AWG wire (should be fine up to 15 A at 115 VAC) and cut plug end. Then connect neutral and live as indicated by the rear of the panel and add chassis ground. Tested DC output voltage of 3 V and it works ok.
There are now two workstations in the lab attached to the same monitor (VGA and DVI ports), and it is ok to ssh from one to the other. They both now have fresh debian 10 installs.
After getting what looked like a decent cavity reflection signal, installed RFPD yesterday. For this, removed the lens that was right before the PD because the RFPD area is large enough, but keep ND filter in place. Powered with +- 18 VDC and monitor DC out on the scope, and RF out is sent to the IF of the mixer in the PDH box. For the LO, split the Marconi RF output and connected the demodulated signal into Ch2 of the scope in hopes that there was an error signal.
A hint of the error signal is present (blue trace below), although deeply buried in line noise (and harmonics up to ~180 Hz) so there really are two things to optimize now -->
Other things attempted so far -->
The plan during these past few days has been to have fast control loop of the cavity (locked to laser using PZT, which succeeded using SR560s), and slow control loop where the laser temp. actuator is fed back the integrated PZT input to follow the long term cavity drift. For that, have been messing around with the high-level (GUI) API of PyRPL, with basically no success. In fact currently the RedPitaya cannot even replace the SR560 fast controls, which probably has to do with the +- 1 Volt limits on the RP input/output.
Another issue is that any loop gain depends on the REFL power, which will be at some point slowly ramped up to cross the OPO operating threshold, and while there is a (PBS + HWP) knob on how much light is hitting the RFPD, the lock is not yet good enough to keep up with the slow human action.
WIth the cavity locked, and under ~ 220 mW of pump (right before the cavity, i.e. 1.3 Amps of current on the driver), noticed a tiny green dot coming from within the crystal oven. This is pretty great news in terms of phase matching, but not necessarily so in terms of the right parametric conversion process (understanding is that SHG is easier to attain even with single pass). See tiny green spot as caught using phone camera in the attachment.