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Student Worksheet

MCT photoconductor test-bench simulator — practical exercises. Open the simulator in another tab while you work.

MCT Photoconductor Webinar Worksheet · Student Copy

MCT Photoconductor Test & Measurement Worksheet

Practical webinar exercises using the toy test-bench simulator.

Name

Date

Instructions

Record values directly from the simulator during the presentation.
Show units clearly.
Use the worksheet to compare dark behavior, illuminated behavior, spectral features, and responsivity.
Unless stated otherwise, assume the simulator settings are held fixed except for the quantity being changed.

Open test-bench simulator (new tab)

1. Simulator Orientation

Goal: Identify what the simulator measures and what you can control.

Main controls observed:

Bias voltage
Temperature
BB cover open / closed
Chopper on / off
Chopper frequency
Grounded / ungrounded
Preamp on / off
Preamp gain

Your notes (optional)

Main instrument views:

Spectrum Analyzer
Oscilloscope
I–V Characteristics

Your notes (optional)

Question: In one sentence, what is the difference between this toy simulator and a full transport solver?

Your answer

2. Dark Resistance Extraction

R_dark = V / I

Exercise: With the detector covered, record dark current (mA) at three bias points and compute dark resistance.

Bias V	Dark Current (mA)	Calculation R = V / I	Dark Resistance (Ω)
0.5 V
1.0 V
1.5 V

Does the detector appear approximately ohmic over this bias range?

Yes No

Why?

Your answer

3. Temperature Dependence of Dark Behavior

Exercise: Compare dark resistance at room temperature and at 77 K.

Condition	Measured Resistance (Ω)	Notes
Room Temperature (~298 K)
77 K

Question: How does the dark resistance change with temperature in the simulator?

Your answer

4. Steady-State Photocurrent Extraction

Setup: Chopper off, grounded on, preamp off. Use current readout only.

Exercise: At each bias, record dark (BB closed), then photo and total current (BB open).

Bias	Dark Current (µA)	Photocurrent (µA)	Total Current (µA)
0.5 V
1.0 V
1.5 V

I_total = I_dark + I_photo

Question: Why is current readout the right tool here, not the oscilloscope?

Your answer

5. Normalized Response Versus Bias

Exercise: Use either photovoltage or photocurrent to compute a normalized response.

Units note: Keep one consistent unit set within each table (for example V or µV for photovoltage; mA or µA for photocurrent).

If photovoltage is used:
Norm. Response = V_ph(V) / V_ph(0.5 V)

If photocurrent is used:
Norm. Response = I_ph(V) / I_ph(0.5 V)

A. Using Photovoltage

Bias	Photovoltage (your chosen unit)	Normalized Response
0.5 V
1.0 V
1.5 V

B. Using Photocurrent

Bias	Photocurrent (your chosen unit)	Normalized Response
0.5 V
1.0 V
1.5 V

Question: What does the normalized response trend tell you about the effect of bias on detector output?

Your answer

6. Chopping and the Spectrum

Exercise: Turn the chopper on and observe the Spectrum Analyzer.

Record observations

Chopper frequency used (Hz)
Was a visible peak present at that frequency?
Yes No

Question: Why does chopping help isolate the optical signal?

Your answer

7. Grounding and Hum Contamination

Exercise: Compare grounded and ungrounded operation in the Spectrum Analyzer.

Feature	Grounded	Ungrounded
60 Hz peak visible?
120 Hz peak visible?
Chopper peak easier to interpret?

Question: Why is grounding part of measurement quality, not just a setup detail?

Your answer

8. Signal Quality Versus Bias

Exercise: For each bias point, compare the chopper peak with the nearby noise floor in the spectrum view.

Bias	Peak Height (nV/√Hz)	Nearby Floor (nV/√Hz)	Better / Worse / Same
0.5 V
1.0 V
1.5 V

Question: Does increasing bias improve measurement quality, or only signal amplitude?

Your answer

9. Preamp Interpretation

Exercise: Turn the preamp on and compare the signal and floor.

Idealized preamp model: V_out = G × V_in

Record observations

Signal peak change with gain
Noise floor change with gain

Question: In this toy model, what is the main role of the preamp? (Answer in one sentence)

Your answer

10. Oscilloscope View and RMS Voltage

Setup note: For this section, turn the chopper on and begin grounded.

Interpretation note: Use the oscilloscope to view time-varying AC behavior (modulation, hum contamination, and RMS), not steady DC illuminated offset.

Exercise: In Oscilloscope view, record RMS voltage at the conditions below (use the simulator's displayed RMS unit consistently).

Condition	V_rms (simulator displayed unit)
Grounded, chosen bias
Ungrounded, same bias
Higher bias, grounded
Preamp on, same bias

RMS formula:
V_rms = √[ (1/N) · Σ_i=1^N v_i² ]

Question: Why is RMS voltage useful, and why is it not automatically the same thing as pure optical signal?

Your answer

11. Absolute Voltage Responsivity

Reveal the hidden toy-model optical input: P_incident = 4.315 × 10⁻⁷ W

Voltage responsivity: R_v = V_ph / P_incident

Exercise: Use your measured photovoltages (in V) to compute absolute voltage responsivity.

Bias	Photovoltage (V)	Calculation	R_v (V/W)
0.5 V
1.0 V
1.5 V

Question: Why could you calculate normalized response earlier without optical input, but not absolute responsivity?

Your answer

12. Final Reflection

Write one or two sentences for each:

1. What was the most important thing you learned about interpreting detector measurements? 2. What was the most important difference between detector physics and bench/setup effects? 3. What would you check first if a spectral feature looked suspicious in a real measurement?