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  402   Sat Nov 21 13:58:30 2020 KojiElectronicsCharacterizationDark Current Measurement for InGaAs QPDs

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.

Attachment 1: Q3000_dark_current.pdf
  403   Sun Nov 22 13:49:12 2020 KojiElectronicsCharacterizationImpedance Measurement for InGaAs QPDs

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.

Measurement setup:
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)

Attachment 1: impedance_measurement.pdf
Attachment 2: P_20201121_183830.jpg
Attachment 3: impedance_test.pdf
Attachment 4: Q3000_impedance_test.pdf
  404   Mon Nov 23 23:17:19 2020 KojiElectronicsCharacterizationThe dark noise of the Q3000 QPDs

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.

Attachment 1: Q3000_dark_noise_81.pdf
Attachment 2: Q3000_dark_noise_82.pdf
Attachment 3: Q3000_dark_noise_83.pdf
Attachment 4: Q3000_dark_noise_84.pdf
  405   Tue Nov 24 10:45:07 2020 gautamElectronicsCharacterizationThe dark noise of the Q3000 QPDs

I see that these measurements are done out to 100 kHz - I guess there is no reason to suspect anything at 55 MHz which is where this QPD will be reading out photocurrent given the low frequency behavior looks fine? The broad feature at ~80 kHz is the usual SR785 feature I guess, IIRC it's got to do with the display scanning rate.


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).

  406   Tue Nov 24 12:27:18 2020 KojiElectronicsCharacterizationThe dark noise of the Q3000 QPDs

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.

  407   Fri Feb 5 07:40:37 2021 StephenSupplyGeneralOMC Unit 4 Build Machined Parts

OMC Unit 4 Build Machined Parts are currently located in Stephen's office. See image of large blue box from office, below.

Loaned item D1100855-V1-00-OMC08Q004 to Don Griffith for work in semi-clean HDS assy.

This includes mass mounting brackets, cable brackets, balance masses, etc. For full inventory, refer to ICS load Bake-9527 (mixed polymers) and Bake-9495 (mixed metals).

Inventory includes all items except cables. Plasma sprayed components with slight chipping were deemed acceptable for Unit 4 use. Cable components (including flex circuit) are ready to advance to fabrication, with a bit more planning and ID of appropriate wiring.

Attachment 1: IMG_8117.JPG
  408   Thu May 20 17:03:50 2021 KojiGeneralGeneralSRS LCR meter SRS720 borrowed from Downs

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: P_20210520_154841.jpg
  409   Sun May 30 15:17:16 2021 KojiGeneralGeneralDCPD AF capacitance measirement

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

Attachment 1: PD_cap_meas.pdf
Attachment 2: 20210529013015_IMG_0577.jpeg
Attachment 3: 20210529013114_IMG_0580_2.jpeg
Attachment 4: 20210529013200_IMG_0584.jpeg
Attachment 5: 20210529013229_IMG_0586.jpeg
  410   Sun May 30 15:32:56 2021 KojiGeneralGeneralDCPD AF capacitance measirement

Measurement result:

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.

Attachment 1: highQEPD_capacitance.pdf
Attachment 2: C30665_capacitance.pdf
  411   Wed Jul 7 14:21:50 2021 StephenSupplyGeneralOMC Unit 4 Build Machined Parts

More explicit insights into the inventory for the Unit 4 build. Image of inventory included below.

Machined Parts:

Cable Components:

  • Hughes Circuits made us Kapton flex circuits. These have not been processed in any way.
  • Rich had supplied a spool of Gore 4-conductor in-vacuum wire (see below image). I returned the sppol for Rich but it is living in Downs and available for use.
  • PEEK cable ties were damaged during bake, and will be replaced by SYS inventory.

Retrofit/Repair Capabilities:

  • Aluminum reinforcement brackets D1600316
  • Glass reinforcement brackets (Edmund Optics 45-072 and 45-071)

ref: E1900034 and other associated documents.

Attachment 1: IMG_9238.JPG
Attachment 2: IMG_9236.JPG
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