This page summarizes the equipment, procedures, and software used to collect and analyze Transmission and Reflection (T&R) data.

Last updated: 8/30/2014 - Stephen

Reading References

• http://eceweb1.rutgers.edu/~orfanidi/ewa/

  • chp 5 - EM intro for T&R at simple boundaries

  • chp 6 - T&R for multi-layered structures

Data Sheets

• Filter Wheels

  • Thorlabs filter wheels stepper motor driven

• Detectors

• Illumination Sources

  • Newport Model #6363 - IR Emitter, 140 W Element

Safety

• Wear long pants and close-toed shoes when handling liquid nitrogen (LN2)

• Wear gloves to avoid contaminating samples

Experimental Set-up

This section describes the equipment needed and its operation to collect T&R data. The following presentation is an example of the optical table set-up and the basic components required for data collection.

Illumination Source

• Pick one of two different sources by toggling the switch on the source housing box

  Open

  

  Illumination source power supply

  • Quartz Tungsten Halogen - operation from 0.8 - 1.6 um, max. power 100 W

  • IR Emitter - operation 1.5+ um, max. power 140 W

• Turn on source using the illumination Power Controller (68938 Power Supply)

  • Slowly increase power at a rate of 0.5 A/min

  • Use the "Meter Function" button to toggle between voltage and current

  • Do not exceed the maximum power for the sources!

• If changing between sources

  • Slowly ramp down power supply at 0.5 A/min

  • Toggle between source options on the source housing box

  • Slowly ramp up new source at 0.5 A/min

Detector

• InGaAs

  • Operation 0.8 - 1.7 um

  • Electrically cooled using temperature controller (ILK Lightwave LDT-5412 temperature controller). Keep at -20 deg C. Temperature controller should be pre-programmed to correct temperature, just turn it on.

  • Power supply required

  • No pre-amplifier needed -- output from detector feeds directly into lock-in amplifier

• InSb

  • Operation 0.8 - 1.7 um

  • Cooled with LN2. Use funnel to fill with LN2 before using. Let sit for 10-20 minutes to cool to the proper levels.

  • No power supply required

  • Pre-amplifier needed -- output from detector becomes input to pre-amplifier. AC coupled output of pre-amplifier feeds into input of lock-in amplifier (Stanford Research Systems, Model SR830 DSP LIA)

  • When finished using for measurements

    • Unscrew and detach detector

    • Quickly cover spectrometer-facing side (use metal plate from where detectors are stored when not in use). The InSb is sensitive to high energy light (UV) and can become damaged if exposed while cool.

    • Pour out LN2

    • Set detector + cover in detector storage bin

Carefully handle detector when switch from one to the other. Gently pull from spectrometer port. Sometimes it is good to use some leverage if it is stuck (e.g. flathead screwdriver).
Set detector slit to 2.5 mm

Open InGaAs detector with proper connections	Open InGaAs detector temperature controller
Open InSb detector properly connected and attached to spectrometer	Open Filling InSb detector with LN2 and funnel
Open Pre-amplifier with input from a detector and output	Open Lock-in amplifier

Filter Wheel

If not already in place, position the filter wheel immediately in front of the input port of the spectrometer.
If the filter wheel is missing, check the PL set-up, because it is shared between both T&R and PL measurement stations.
Turn on and check the power/USB connectors on the filter wheel.
Change to one of three different filters using the selector switch. Filters should be used for:

• Filter 1: 0.8 - 1.5 um

• Filter 2: 1.5 - 3.0 um

• Filter 3: 2.5 - 7.0 um

Chopper Wheel

Open

Chopper wheel control box

Position the chopper wheel immediately in front of the illumination source.
Turn on and connect filter wheel to chopper wheel control box (Stanford Research Systems, ModelSR540 Chopper Control) via telephone-looking cord. Set speed as 4 kHz.

Labview

Open LabView software module on PL lab computer
Copy of LabView software from July 7 2014

• starting position = where to start taking measurements

• end position = where to stop taking measurements

• set-up

  • Pick a grating (more details below)

  • Select entrance mirror. Since the PL and T&R share the same spectrometer, they use different entrance mirrors -- might need to be switched if PL was last experiment using spectrometer

  • Time constant. 300 works well

  • Set slit entrance/exit to 2.5 mm

Grating

Pick the best spectrometer grating for the experiment. There are three reflective gratings housed in the spectrometer.

• 300 g/mm, 1.2 um blaze: 0.8 - 1.6 um

• 300 g/mm, 2.0 um blaze: 1.4 - 2.6 um

• 150 g/mm, 4.0 um blaze: 2.4 - 5.0 um

Attaching Sample

• Turn on sample vacuum chuck holder

• Place sample on vacuum chuck while chuck face is pointed up

• Once firmly attached, slide sample chuck onto the chuck holding bars on the rest of the optical set-up

Collecting Data

For each measurement session, collect spectra for:

• Background

• Grown sample

• Substrate (not required, but strongly recommended to see effects of grown structures)

Background references are needed to normalize all measurements (i.e. determine what fraction of 100% is T or R)
Transmission:

• Background: uncovered sample chuck hole

Reflection:

• Background: gold mirror

Clean Up

• Remove sample

• Turn off sample chuck vacuum

• Slowly ramp down illumination source power at 0.5 A/min and turn off power supply once at 0.0 A

• Turn off filter wheel

• If using InGaAs detector, turn off temperature controller

• Throw away gloves and wash hands

Full Spectrum Measurement

A full spectrum from 0.8 - 5.0 um can be measured with the correct combination of detectors, illumination sources, filter wheels, and gratings. Below is the recommended recipe of combinations for 3 different ranges of measurements. The data from these three can be spliced together using a MABLAB script.
NOTE: there is a 0.2 um overlap for each of the ranges. This is used to better connect the two regions since the data is spurious at the edge of the recommended ranges.

Wavelength ranges and equipment

Open

Suggested ranges for equipment usage to perform complete spectrum data collection

• 0.8 - 1.6 um

  • InGaAs detector

  • Quartz Tungsten source

  • Filter wheel 1

  • 1.2 um 300g/mm grating

• 1.4 - 2.6 um

  • InSb detector

  • IR Emitter

  • Filter wheel 2

  • 1.2 um 300g/mm grating

• 2.4 - 5.0 um

  • InSb detector

  • IR Emitter

  • Filter wheel 3

  • 4.0 um 300g/mm grating

MATLAB

Full spectrum analysis requires splicing the three collected data curves into a single curve. The data from the three curves (collected with Labview) are spliced together using MATLAB. The following MATLAB scripts are used for data parsing and splicing. All the files listed are needed to processes the T or R data. These files are designed to handle a sample data set for E130302. The data required to successfully run these scripts, for demonstration purposes, is . Modify the code with your input file names and the sample names on the output graphs generated.

The following presentation is a summary of the effect of the curve splicing software