Probably the best glued unit among the four.
Attachment #1: Mounting Block SN001
Attachment #2: PZT-Mounting Block bonding looks completely wet. Excellent.
Attachment #3: The other side of the PZT-Mounting Block bonding. Also looks excellent.
Attachment #4: Overall look.
Attachment #5: The mirror-PZT bonding also look excellent. The mounting block surface has many EP30-2 residue. But they were shaved off later. The center area of the aperture is clear.
Attachment #6: A small fracture of the mirror barrel is visible (at 7 o'clock).
Attachment #1: Mounting Block SN007
Attachment #2: Overall look.
Attachment #3: Some fracture on the barrel visible.
Attachment #4: It is visible that a part of the PZT removed. Otherwise, PZT-Mounting Block bonding looks pretty good.
Attachment #5: The other side of the PZT bonding. Looks fine.
Attachment #6: Fractured PZT visible on the fixture parts.
Attachment #7: Fractured glass parts also visible on the fixture parts.
Attachment #8: MIrror bonding looks fine except for the glass chip.
The most fractured unit among four.
Attachment #1: Mounting Block SN017
Attachment #2: Two large removals well visbile. The bottom right corener was chipped.
Attachment #3: Another view of the chipping.
Attachment #4: PZT-mounting block bonding look very good.
Attachment #5: Another view of the PZT-mounting block bonding. Looks very good too.
Attachment #6: Fractures bonded on the fixture.
Attachment #7: Front view. The mirror-PZT bonding look just fine.
Attachment #1: Mounting Block SN021
Attachment #2: PZT-Mounting Block bonding looks just excellent.
Attachment #3: The other side of the PZT-Mounting Block bonding is also excellent.
Attachment #4: The mirror-PZT bonding also look excellent. Some barrel fracture is visible at the lower left of the mirror.
Attachment 1: Shadow sensor setup for the PZT displacement test
Attachment 2: PZT endurance test. 4 PZTs were shaken at once.
Attachment 3~5: Function generator setup 100Hz, 3.5Vpp 1.75Voffset (meant be displayed for 50Ohm load)
Attachment 6: The above setting yields 7Vpp unipolar signal @Hi-Z load
Attachment 7: The output was monitored with a 1/10 probe with the PZTs connected. This shows 10Vmax 0Vin -> Good. This photo was taken at 17:35.
Attachment 8: The test is going well @9:15 next day. (t=15.7hours = 5.6Mcycles)
Attachment 9: The test went well. The modulation was stopped @15:35. (t=21hours = 7.6Mcycles)
D1200105 SN006 was selected as the breadboard for OMC(004).
The reason is the best parallelism among the unused ones.
The attached is the excerpt from T1500060 with the #006 highlighted.
We are going to use A5 and A14 for FM1 and FM2. (The role of these two can be swapped)
The reason for the selection is the better perpendicularity among the available prisms.
A11 has the best perpendicularity among them. However, the T didn't match with the others. The pair of A5 and A14 has a good matching with small compromise of the perpend.
The attachment is the excerpt from T1500060.
We are going to use B6 for the DCPD BS (BS2), and B1 for the QPD BS (BS3). Their role can not be swapped.
B6 has the best loss among the available ones, while the perpendicularity is not so critical due to the short arm.
B1 has the OK perpendicularity, while the loss is also moderately good.
The attachment is the excerpt from T1500060 with some highlighting.
We are going to use E6, E9, E11, and E14 for BS1, SM1, SM2, and SM3. They (and E18) are all very similar.
The attachment is the excerpt from T1500060 with some highlighting
After having dug into the past email, it turned out that these wires were the ones already replaced from the original teflonwires. The length of them were confirmed to be ~19" (480mm).
All four PZTs seem to be connected to Teflon coated wires. It needs to be checked if these
fulfill the vacuum compatibility requirements.
Apr 16, 2019
Borrowed two laser goggles from the 40m. (Returned Apr 29, 2019)
Borrowed small isopropanol glass bottole from CTN.
Apr 19, 2019
Borrowed from the 40m:
- Universal camera mount
- 50mm CCD lens
- zoom CCD lens (Returned Apr 29, 2019)
- Olympus SP-570UZ (Returned Apr 29, 2019)
- Special Olympus USB Cable (Returned Apr 29, 2019)
The spot on CM1 was found displaced by 3.4mm (horiz.) and 3.0mm (vert.) in the upper right direction looking from the face side.
The spot on CM2 was found displaced by 1.2mm (horiz.) and 1.8mm (vert.) in the upper left direction looking from the face side.
The drawing on the left side of the attachment shows the estimated misalignment when we think they all come from the curved mirrors.
As for the yaw misalignment, CM1 and CM2 were 3.9mrad and 5.6mrad rotated (misaligned) in CW, respectively.
As for the pitch misalignment, CM1 and CM2 has 1.7mrad (narrowing) and 3.5mrad (widening), respectively. We have no adjustment for this.
Let's say if this comes from the dusts on the bottom of the prisms, CM1 has ~17um one, and CM2 has ~35um one beneath them. The question is if we can believe this or not? This should be checked with the Newton fringes we can see at the bottom of the prisms.
Similarly to OMC ELOG 349 the spot positions after the replacement of CM2 were measured (Attachment 1)
Also, the spot positions after the realignment were measured. (Attachment 2)
Tried a few things.
1. Replaced CM1 (PZT ASSY #10=M21+PZT#22+C12) with PZT ASSY #7 (=M1+PZT#13+C13)
We tried PZT ASSY #7 at the beginning and had the spots at almost at the top edge of the curved mirrors. As we found a particle on the bottom of the M1 prism (and removed it), I gave it a try again. Resulting spots are again very high. This results in rejecting PZT ASSY #7 and we set the combination of the PZT ASSYs as #8 (M7+P11+C11) and #10 (M21+P22+C12). This combination nominally gives the spot ~1mm above the center of the curved mirrors.
2. Swapped FM1 and FM2. Now FM1=A5 and FM2=A14.
No significant change of the scattering features on the FMs. The transmitted power was 14.85mW (Ref PD Vin = 3.42V), Reflection PD Vrefl,lock = 54.3mV and Vrefl,unlock = 2.89V (Vin=3.45V), Vrefl,offset = -6.39mV. The incident power was 17.43mW (Vin 3.69V).
==> Coupling 0.979 , OMC transmission 0.939 (This includes 0.6% loss to the QPD path) ...Not so great number
3. Built better camera setups to check the spot position and the scattering from the cavity mirrors.
Now the spot heights are fixed and safe to move the camera up for inches to obtain better views of the mirror faces. The camera was set 15" away from the mirrors with 1.5" height from the beam elevation. This is 0.1rad (~ 5 deg) and Cos(0.1)~0.995 so the distortion (compression) of the view is negligible. (Attachment) The spot photo were taken with the fixed CCD gain, the focus on the glass, and lens aperture F=8.0. Later the focus and aperture were adjusted to have clear view of the scattring points.
The intensity of each scattering was constant at different views. I suppose this is because the scattering is coming from a spot smaller than the wavelength. The bright spots does not show any visible feature on the mirror surfaces when they were inspected with a green flash light.
CM2 has the excellent darkness and we want to keep this spot position. FM1, FM2, and CM1 showed bright scattering.
The spot at CM1 is not well centered on the mirror. And this is the way to avoid this scattering point. So let's think about to move the spot on CM1 by 1.3mm towards the center while the spot on the CM2 is fixed. Note that this is going to be done by the micrometers for CM1 and CM2.
By turning right micrometer of CM1 forward (50um = 5div = 1/10 turn) and the left micrometer of CM2 backward (60um = 6div) moves the spots on FM1, FM2, CM1, and CM2 by (0.43, 0.87, 1.3, 0)mm. This basically moves the spots toward the center of each mirror. Let's give it a try.
Experiment on 5/1
- CM1 right knob was moved 1div (10um) backward such that the spots were better centered on the mirrors
FM1 (A5): h=-0.2mm -> 0.4mm made the spot much darker but still it has a few scattering spots.
FM2 (A14): h=-0.8mm -> 0.2mm reduced the number of spots from 2 to 1. And it is darker. The remaining spot at the center.
CM1 (C11): h=-1.3mm -> +1.0mm made the spot much darker.
CM2 (C12): h=-0.7mm -> +0.2mm remains dark.
Note: CM1 h=1mm and CM2 h~0mm are good locations. h+ is the good direction to move. Avoid h-.
FM1 and FM2 has the scat spots at the center. Want to go h+ more.
Uniformly go h+ is the good move. => This can be done by rotate CM1 positive => CM1 right knob CCW.
Improvement of the transmission from 93.9%->95.3%
- Further moved CM1 right knob 0.5div (0.5um) backward such that the spots were moved to h+ directions.
FM1 (A5): h=0.4mm -> 1.1mm (there is only one spot rather than multiple spots)
FM2 (A14): h=0.2mm -> 1.1mm (darker but multiple spots)
CM1 (C11): h=1.0mm -> 1.8mm (brighter but single spot)
CM2 (C12): h=0.2mm -> 1.5mm (dark multiple spots)
Not much improvement of the transmission but kept 95% level.
- Replaced FM1 (A5) with A1 mirror (No photo)
Good news: This did not change the cavity alignment at all.
- Tweaked the CM1 angle
=> A1 mirror does not improve the transmission much.
Next Plan: Use A5 (or something else) as FM2 and see if A14 caused the dominant loss.
Notes on the OMC cavity alignment strategy
- x3=1.17 γ + 1.40 δ, x4=1.40 γ + 1.17 δ
- This means that the effect of the two curved mirrors (i.e. gouy phases) are very similar. To move x3 and x4 in common is easy, but to do differentially is not simple.
- 1div of a micrometer is 10um. This corresponds to the angular motion of 0.5mrad (10e-6/20e-3 = 5e-4). ~0.5mm spot motion.
- ~10um displacement of the mirror longitudinal position has infinitesimal effect on the FSR. Just use either micrometer (-x side).
- 1div of micrometer motion is just barely small enough to keep the cavity flashing. => Easier alignment recovery. Larger step causes longer time for the alignment recovery due to the loss of the flashes.
- After micrometer action, the first move should be done by the bottom mirror of the periscope. And this is the correct direction for beam walking.
- If x3 should be moved more than x4, use CM2, and vise versa.
- If you want to move x3 to +x and keep x4 at a certain place, 1) Move CM2 in (+). This moves x3 and x4 but x3>x4. 2) Compensate x4 by turning CM1 in (-). This returnes x4 to the original position (approximately), but leave x3 still moved. Remember the increment is <1div of a micrometer and everytime the cavity alignment is lost, recover it before loosing the flashes.
(Now the CCD image is captured as a movie and the screen capture is easier!)
Various spot positions on CM1 and CM2 were tried to test how the transmission is dependent on the spot positions. CM1 has a few bright spots while CM2 shows very dark scattering most of the case. Attachment 1 is the example images of one of the best alignment that realized the transmission of ~96%. FM1 and FM2 also showed bright spots. The replacement of the FM mirrors does not improve nor degrade the transmission significantly. The transmission is still sensitive to the spot positions on the alignment. This indicates that the loss is likely to be limited by CM1.
Attachment 2 shows the distribution of the (known) scattering spots on CM1. The bright spots are distributed every ~1mm on the spot height and the beam (with beam radius of .5mmm) can't find a place where there is no prominent spots.
We will be able to examine if the transmission can be improved or not by replacing this CM1 mirror.
Suddenly something dirty emerged in the lab. What is this? It looks like an insulation foam or similar, but is quite degraded and emits a lot of particulates.
This does not belong to the lab. I don't see piping above this area which shows broken insulation or anything. All the pipes in the room are painted white.
The only possibility is that it comes from the hole between the next lab (CRIME Lab). I found that the A.C. today is much stronger and colder than last week. And there is a positive pressure from CRIME Lab. Maybe the foam was pushed out from the hole due to the differential pressure (or any RF cable action).
We want to perform a damage test of OMC DCPDs with high power beam. The OMC DCPD is the 3mm InGaAs photodiodes with high quantum efficiency, delivered by Laser Components.
The sites want to know the allowed input power during the OMC scan for beam mode analysis. The nominal bias voltage of the PDs is +12V. Therefore, 30mA of photocurrent with the transimpedance of 400 Ohm is already enough to saturate the circuit. This means that the test is intended to check the damage of the photodiode mainly by the optical power.
The test procedure is as follows:
1. Illuminate the diode with certain optical power.
2. Measure the dark current and dark noise of the PD with no light on it.
3. Check the condition of the PD surface with a digital camera.
4. Repeat 1~3 with larger optical power.
The beam from an NPRO laser is delivered to the photodiode. The maximum power available is 300~400mW. The beam shape was regulated to have the beam radius of ~500um.
- When the PD is exposed to the high power beam, the circuit setup A) is used. This setup is intended to mimic the bias and transimpedance configuration used in the DCPD amp at the site.
- When the dark noise is measured, the circuit setup B) is used. This setup is low noise enough to measure the dark noise (and current) of the PD.
- The test procedure is going to be tested with an Excelitas 3mm InGaAs PD (C30665), and then tested with the high QE PD.
C30665 (3mm) camera test. The camera was Canon PowerShot G7X MkII. Exposure 1/15s, F 5.6, ISO 125, MF (~the closest), no zoom.
This image was taken before the beam illumination. Will tune the green lighting to have some gradient on the surface so that we can see any deformation of the surface.
An Excelitas C30665 PD with the cap removed (SN07 in Case H slot #2) was exposed to the beam with the optical power of 1.4mW to 334mW.
After each illumination, the dark current and the dark noise level were tested. Also the photo image of the PD surface was taken each time.
- No significant change of the dark current after each illumination.
- No significant change of the dark noise after each illumination.
- No visible change of the surface observed.
LaserComponents IGHQEX3000 (Cage B2: Serial# B1-23) was exposed to the beam with the optical power from 1.6mW to 332mW.
After each illumination, the dark current and the dark noise level were measured. Also the photo image of the PD surface was taken each time.
(During this dark noise measurement, the current amp gain was set to be 1e8 V/A, instead of 1e7 for the measurements yesterday.)
The perpendicularity of some of the A and M prisms were tested.
- The measurement results are listed as Attachment 1 and 2 together with the comparisons to the measurement in 2013 and the spec provided from the vendor.
- Here, the positive number means that the front side of the prism has larger angle than 90deg for the air side. (i.e. positive number = facing up)
- The RoC of the curved mirrors is 2.5m. Therefore, roughly speaking, 83arcsec corresponds to ~1mm beam spot shift. The requirement is 30 arcsec.
- The A prisms tend to have positive and small angle deviations while the M prisms to have negative and large (~50arcsec) angle deviations.
- The consistency: The measurements in 2013 and 2019 have some descrepancy but not too big. This variation tells us the reliability of the measurements, say +/-30arcsec.
- The photos of the setup is shown as Attachments 3/4/5. Basically this follows the procedure described in Sec 2.2.2 of T1500060.
- The autocollimator (AC) is held with the V holders + posts.
- The periscope post for the turning Al mirror was brought from Downs by Stephen.
- The turning mirror is a 2" Al mirror. The alignment of the turning mirror was initially aligned using the retroreflection to the AC. Then the pitching of the holder was rotated by 22.5deg so that the AC beam goes down to the prism.
- The prism is held on a Al mirror using the post taken from a prism mount.
- If the maximum illumination (8V) is used, the greenish light becomes visible and the alignment becomes easier.
- There are two reflections 1) The beam which hits the prism first, and then the bottom mirror second, 2) The beam which hits the bottom mirror first and then the prism second. Each beam gains 2 theta compared to the perfect retroreflection case. Therefore the two beams have 4 theta of their relative angle difference. The AC is calibrated to detect 2 theta and tells you theta (1div = 1 arcmin = 60 arcsec). So just read the angle defferencein the AC and divide the number by 2 (not 4).
Liyuan's scattering measurement for the A and C mirrors.
[Stephen, Shruti, Koji]
We worked on the gluing of the PZT sub-assy (#9 and #10) along with the designed arrangement by Shruti (OMC ELOG 374).
The detailed procedures are described in E1300201 Section 6.2 PZT subassembly and Section 7.3 EP30-2 gluing.
We found that the PZTs, which were debonded from the previous PZT sub assy with acetone, has some copper wires oxidized. However, we confirmed that this does not affect the conductivity of the wires, as expected.
The glue test piece cooked in the toaster oven showed excellent curing. GO SIGNAL
Stephen painted the PZT as shown in Attachment 1.
The fixtures were closed with the retaining plate and confirmed that the optics are not moving in the fixtures.
At this point, we checked the situation of the air-bake oven. And we realized that the oven controller was moved to another vacuum oven and in use with a different setting.
Stephen is going to retrieve the controller to the air bake oven and test the temp profile overnight. Once we confirm the setting is correct, the PZT sub assys will be heat cured in the oven. Hopefully, this will happen tomorrow. Until then, the sub-assys are resting on the south flow bench in the cleanroom.
Friday: [Stephen, Koji]
As the oven setting has qualified, we brought the PZT assys in the air bake oven.
Monday: [Stephen, Shruti, Koji]
We brought the PZT assys to the clean room. There was not bonding between the flexture and the PZT subassy (Good!). Also the bonding o at each side looks completely wetted and looks good. The package was brought to the OMC lab to be tested in the optical setup.
From Cryo Cav setup
Borrowed LB1005 Servo box -> OMC
20 glass beamdumps were bonded at the 40m cleanroom.
Attachment 1: We had 20 fused silica disks with a V-groove and 40 black glass pieces
Attachment 2: The black glass pieces had (usual) foggy features. It is well known to be very stubborn. We had to use IPA/acetone and wiping with pressure. Most of the feature was removed, but we could still see some. We decided to use the better side for the inner V surfaces.
Attachment 3: EP30-2 expiration date was 1/22/2020 👍. 7.66g of EP30-2 was poured and 0.38g of glass sphere was added. Total glue weight was 8.04g
Attachment 4: Glue test piece was baked at 200F in a toaster oven for ~12min. It had no stickiness. It was totally crisp. 👍👍👍
Attachment 5: Painted glue on the V-groove and put the glass pieces in. Then gave a dub of blue at the top and bottom of the V from the outside. In the end, we mostly had the glue went through the V part due to capillary action.
Attachment 6: The 20 BDs were stored in stainless vats. We looked at them for a while to confirm there is no drift and opening of the V part. Because the air bake oven was not available at the time, we decided to leave the assys there for the room temp curing, and then later bake them for the completion of the curing.
The beamdumps were taken out from the oven and packed in bags.
The bottom of the V are completely "wet" for 17 BDs among 20 (Attachment 1/2).
3 BDs showed insufficient glue or delamination although there is no sign of lack of rigidity. They were separated from the others in the pack.
Item lending as per Ian's request: Particle Counter from OMC Lab to QIL
The particle counter came back to the OMC lab on Aug 10, 2020
Black and Decker Glue Baking Oven came back to the OMC lab on Aug 10, 2020, Georgia had lent the unit for the SAMS assembly/testing.
Check-in to the OMC lab to see the status. Nothing seemed changed. No bug. The HEPA is running normal. The particle level was 0.
Went into the HEPA enclosure and put a cover on the OMC. Because of the gluing template, the lid could not be close completely (that's expected and fine).
The IPA vector cloth bag was not dry yet but seemed expired (some smell). There is no stock left -> 5 bags to be ordered.
According to the past backscatter test of the OMC (and the black glass beamdump: not V type but triangular type on a hexagonal-mount), the upper limit of the back reflection was 0.13ppm. https://nodus.ligo.caltech.edu:8081/OMC_Lab/209
I don't have a BRDF measurement. We can send a few black glass pieces to Josh.
The output of Mephisto 800NE (former TNI laser) was measured.
The output power was measured with Thorlabs sensors (S401C and S144C). The reference output record on the chassis says the output was 837mW at 2.1A injection.
They all showed some discrepancy. Thus we say that the max output of this laser is 1.03W at 2.1A injection based on the largest number I saw.
To spare some room on the optical table, I wanted to mount the two TFT monitor units on the HEPA enclosure frame.
I found some Bosch Rexroth parts (# 3842539840) in the lab, so the bracket was taken for the mount. This swivel head works very well. It's rigid and still the angle is adjustable.
BTW, this TFT display (Triplett HDCM2) is also very nice. It has HDMI/VGA/Video/BNC inputs (wow perfect) and the LCD is Full-HD LED TFT.
The only issue is that one unit (I have two) shows the image horizontally flipped. I believe that I used the unit with out this problem before, I'm asking the company how to fix this.
The image flipping of the display unit was fixed. The vendor told me how to fix it.
- Open the chassis by the four screws at the side.
- Look at the pass-through PCB board between the mother and display boards.
- Disconnect the flat flex cables from the pass-through PCB (both sides) and reconnect them (i.e. reseat the cables)
That's it and it actually fixed the image flipping issue.
See this entry: https://nodus.ligo.caltech.edu:8081/40m/15642
Thorlabs' powermeter controler + S401C head was lent from OMC Lab.
I helped to complete the 5th OMC Transport Fixture. It was built at the 40m clean room and brought to the OMC lab. The fixture hardware (~screws) were also brought there.
FEMTO DLPCA200 low noise preamp (brand new)
Keithley Source Meter 2450 (brand new) => Returned 11/23/2020
were brought to the OMC lab for temporary use.
Dark current measurement for InGaAs QPDs (OSI FCI-InGaAs-Q3000) has been done using Keithley 2450 and Frank's diode test kit. Frank's setup uses various custom instruments which are no longer exist, therefore the kit was used only for switching between the segments.
The diodes were serialized as 81, 82, 83, 84, continuing the numbering for the OMC QPDs. The numbers are engraved at the side and the back of the diode cans.
Overall, the QPDs nominally indicated the usual dark current level of <10nA.
SEG1 of #82 showed a lower voltage of reverse breakdown but this is not a critical level.
#83 showed variations between the segments compared to the uniform characteristics of #81 and #84.
To know any anomaly to the junction capacitance of the QPD segments, the RF impedances were tested with a hand-made impedance measurement.
All segments look almost identical in terms of capacitance.
The impedance of a device can be measured, for example, from the complex reflection coefficient (S11). To measure the reflection, a bidirectional coupler was brought from the 40m. Attachments 1 and 2 shows the connection. The quantity A/R shows S11. The network analyzer can convert a raw transfer function to an impedance in Ohm.
Calibration and Measurement limit:
The network analyzer was calibrated with 1) a piece of wire to short the clips 2) 50ohm resistor 3) open clips. Then the setup was tested with these three conditions (again). Attachment 3 shows the result. Because of the impedance variation of the system (mainly from the Pomona clip, I guess), there looks the systematic measurement error of ~1pF or ~25nH. Above 100MHz, the effect of the stray impedance is large such that the measurement is not reliable.
The setup was tested with a 10pF ceramic capacitor and this indicated it is accurate at this level. The setup is sufficient for measuring the diode junction capacitance of 300~500pF.
Impedance of the QPD segments:
Then the impedances of the QPD segments were measured (Attachment 4). The segments showed the identical capacitance of 300~400pF level, except for the variation of the stray inductance at high freq, which we can ignore. Note that there is no bias voltage applied and the nominal capacitance in the datasheet is 225pF at 5V reverse bias. So I can conclude that the QPDs are quite nominal in terms of the junction capacitance.
(Ed: 11/23/2020 The RF components were returned to the 40m)
The dark noise levels of the four Q3000 QPDs were measured with FEMTO DLPCA200 low noise transimpedance amp.
The measurement has been done in the audio frequency band. The amp gain was 10^7 V/A. The reverse bias was set to be 5V and the DC output of the amplifier was ~40mV which corresponds to the dark current of 4nA. It is consistent with the dark current measurement.
The measured floor level of the dark current was below the shot noise level for the DC current of 0.1mA (i.e. 6pA/rtHz).
No anomalous behavior was found with the QPDs.
Note that there is a difference in the level of the power line noise between the QPDs. The large part of the line noises was due to the noise coupling from a soldering iron right next to the measurement setup, although the switch of the iron was off. I've noticed this noise during the measurement sets for QPD #83. Then the iron was disconnected from the AC tap.
The amplifier BW was 400kHz at the gain of 1e7 V/A. And the max BW is 500kHz even at a lower gain. I have to setup something special to see the RF band dark noise.
With this situation, I stated "the RF dark noise should be characterized by the actual WFS head circuit." in the 40m ELOG.
Item loan: SRS LCR meter SRS720 borrowed from Downs. The unit is at the 40m right now for testing with an excelitas PD. Once it is done, the setup will be moved to the OMC lab for testing the high QE PDs
Attachment 1: System diagram. The reverse bias voltage is controlled by DS335. This can produce a voltage offset up to 10V. A G=+2 opamp circuit was inserted so that a bias of up to +15V can be produced. The capacitances of the photodiodes were measured with SR720 LCR meter with a probe. DS335 and SR720 were controlled from PC/Mac via serial connections.
Attachment 2: Overview
Attachment 3: How was the probe attached to the photodiode under the test
Attachment 4: The bias circuitry and the power supply
Attachment 5: G=+2 amp
The capacitance at no bias was 460~500pF. This goes down to below 300pF at 1.0~1.5V reverse bias. At maximum +15V, the capacitance goes down to 200~220pF.
On this opportunity, the capacitances of a couple of Excelitas C30665 photodiodes were measured. In Attachment 2, the result was compared with one of the results from the high QE PDs. In general the capacitance of C30665 is lower than the one from the high QE PDs.