Laser Testing Procedure

Written from NTS notes NTS, 9/15/2015

Note: Must have a laser sample processed and ready to test.

Prep

1. Setup detector

   1. Fill dewar with LN2 (from loading dock)

   2. Put InSb detector on spectrometer, be careful with it

   3. Fill detector red reservoir with LN2, in portions

      1. Pour til LN2 spouts out (this is cooling the reservoir), pause

      2. We know it’s cold when the fog is tiny.

   4. Pour LN2 in to fill reservoir

      1. Don’t pour too fast

      2. Watch for detector overflow and stop pouring

   5. Remove funnel and wait for LN2 geyser to stop; fog will now just escape from hole. Top off.

      1. We know it’s full when overflowing after a top off or two.

   6. Do not turn on detector til it’s at 77K

2. Do first! InSb detector needs LN2 cooling. Do not turn on detector without LN2. Always turn detector off.

3. Mount sample with screw-bolts

   1. Setup Laser Test jig

   2. Slide jig into place (almost)

4. Extend PL setup rails

5. Put on lense, slide jig into place.

6. Turn on green laser (slowly) and align jig. Only need 0.9-1.3 amps.

7. Shutter laser with iris when done (for now)

8. Setup vacuum for probes

   1. Connect red tubes on probes to vacuum line (clear green)

   2. Seal connection with kapton tape

   3. Turn on vacuum

9. Make System Connections

   1. Probe cable to T junction on vector board

   2. Back of TE cooler to other BNC

   3. The vector board connects to a PCB resistor tuning network

   4. Connect PCB current output to Oscope

   5. Cap other BNC on PCB with 50 Ohm cap

   6. Change lock-in ref-in cable to back of pulsed current source (trigger out T)

   7. Connect chuck BNC cables

      1. Connect chiller hoses

      2. Connect TE cooler cable to stage

10. Turn on most electronics

    1. Turn on Oscope

    2. Turn on alignment laser driver (align laser sample soon)

    3. Turn on chiller (box under table)

       1. Flip both switches on chiller box

       2. Check for leaks where hose meets chuck

    4. Turn on TEC control/laser driver

    5. Set TEC temp and turn on output

    6. Can switch from TEC to current with knobs

11. Position system components

    1. Align system, lens in front of sample

    2. Position microscope

    3. Get probes in place, do not land!

    4. Do not land probes til current supply is on

    5. Put laser mount on chuck and screw in to front screwset (by chuck edge)

12. 7a. Turn on lock-in amp

    1. Turn on the current supply (output should be and stays off)

    2. Supply output will be off

13. Land probes carefully

    1. Unshutter green laser to perform alignment

    2. Want laser as dim as possible while still visible to align

    3. Do coarse alignment (no microscope) first by adjusting lense (on rails)

       1. Want to get as small and bright a spot as possible, with smaller and a little dimmer better; we’re going for ballpark here.

    4. Now use microscope and do fine alignment with micrometers.

       1. Get green hazy spot at right level and XY alignment to be in line with laser bar.

14. Turn on spectrometer

    1. Setup spectrometer software (was with old labview software)

    2. Setup your grating and filter wheel

    3. Filter wheel is needed to choose lambda range (and avoid signal from substrate PL)

15. Turn on current output

    1. Set pulse width to 0.2 us and rep rate to 100 us (10 kHz)

    2. Turn up current (~50-100 mA/s) [seems fast]

16. Wait for lock-in amp to show signal

    1. Typically channel 1 will go from bouncy # to large # ( >8 uV) suddenly, e.g. after one amp input

Test

1. Setup and run spectrometer scan

2. Setup PL software [for old labview]

3. Choose filter (150 4) and slits

4. Set start position and hit Go To to setup spectrometer

5. Look at the center of this spectrum

6. On current box press display to toggle between current and pulse width

   1. Change lock-in to positive edge triggered if needed

   2. Set PL software endpoint and step, and check start position (press Go To just to be sure)

   3. Setup filepath, sample ID, notes, etc.

7. When you increase current, you’ll get electroluminescence

   1. Start Scan

   2. E.g. Today we’re starting at 1500 mA and increasing by 200 mA each run

   3. We’re starting each line at 3200-3700 nm and then focusing in as needed

   4. Turn current output down and off (and back on) as needed

8. Look at the center of this spectrum

9. To finish:

   1. Take current down and turn off output

   2. Lift up probe

   3. Move microscope out of way and turn off

   4. Turn off chiller and TE cooler

   5. Turn off detector and remove sample

   6. Turn off green laser