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Spectrometer benchmark

A set of tests were performed in order to understand the repetitivity, reproducibility, and the effects of some components of the spectrometer in the transmittance measurements of PWO crystals with the Lambda 750 UV/VIS/NIR spectrometer at CUA.

Two types of measurements are planned to be taken with this spectrometer to quantify the crystals transmittance: longitudinal measurement and transverse scan along crystal length. For each of these, a set of benchmark tests were done as described in the following subsections.

Longitudinal Transmittance

→ Reproducibility

This first test allowed us to check for reproducibility of the measurements in the spectrometer. This was done by placing a crystal at the center of the spectrometer twice, trying to reproduce the same conditions and seeing how the positioning of the crystal in the spectrometer affects our measurements.

Measurements/tests:

• 1 - Measure transmittance with the PbF2 cube at the center of the compartment.

Pictures:

Perkin Elmer spectrometer Lambda 750 UV/VIS/NIR used for all the measurements.

PbF2 crystal at center of the spectrometer sample compartment.

Results:

Graph showing two measurements of Transmittance (%) vs. Wavelength (nm) of PbF2 crystal cube at different times to check for reproducibility of measurements.

Graph showing the difference between the two measurements of the PbF2 crystal cube.

→ Position dependence along the compartment

We measured the difference relative to the sample compartment, and along the beam for the PbF2 crystal cube. This test was done to demonstrate

Measurements/tests:

• 2 - Measure transmittance with PbF2 cube at 4 additional points along the beam. Compare results to those of the previous point.

Pictures:

PbF2 cube closer to lamp port at the spectrometer sample compartment.

PbF2 cube shifted from center at the spectrometer sample compartment.

Results:

Graph showing measurements of Transmittance (%) vs. Wavelength (nm) of PbF2 crystal cube oriented at the center of the compartment and beam or 10 cm away from the lamp window (red), 1 cm away from the window oriented along the beam (green), 5 cm away from the window oriented along the beam (dark blue), 15 cm away from the window oriented along the beam (teal/light blue), and 19 cm away from the window oriented along the beam (magenta).

Graph showing measurements of Transmittance (%) vs. Wavelength (nm) of PbF2 crystal cube oriented at the center of the compartment (red) and the the crystal shifted at the center of the compartment (green) in order to demonstrate the uniformity of the cube relative to the beam.

Graph showing difference of Transmittance (%) vs. Wavelength (nm) measurements of PbF2 cube centered at the compartment and shifted at the center of the compartment.

→ Interlaboratorial comparison

Comparing transmittance results with Giessen Univ and others.

Measurements/tests:

• 3 - Measure transmittance of 10-cm CRYTUR crystal installed at the center of the compartment. Compare the result to those from Giessen Univ. and earlier results from summer 2015.

Pictures:

Crytur crystal at spectrometer for longitudinal transmittance measurement.

Results:

File:Benchm longitudinal plot crytur CUA Giessen.jpg ...

File:Benchm longitudinal plot crytur Diff CUA Giessen.jpg ...

→ Slit width effects

We tested varying slit width effects on transmittance measurements. This was configured via UV WinLab software.

Measurements/tests:

• 4 - Measure transmittance of 10-cm CRYTUR crystal installed at the center of the compartment with different slit widths (different beam sizes at the center). Compare results to those from previous point.

Pictures:

A screen shot of the configuration panel for changing the spectrometer slit width in front of the PMT. The nominal slit width is 2.00 nm, as shown on the configuration panel.

Results:

Graph showing Transmittance (%) vs. Wavelength (nm) of CRYTUR 10-cm Crystal at 2.00 nm slit width (red) and at 4.00 nm slit width (green).

Graph showing difference of results of CRYTUR 10-cm Crystal at 2.00 nm and 4.00 nm.

→ Compartment windows effects

We test the effects of changing the compartment windows in the spectrophotometer on our transmittance measurements.

Measurements/tests:

• 5 - Measure transmittance of the PbF2 cube and the 10-cm CRYTUR crystal installed at the center of the compartment without the windows. Compare results to those of point 1 and 3.

Pictures:

Sample compartment windows (need to remove them for the measurement of longitudinal transmittance of 20-cm crystals).

Results:

Graph of PbF2 Cube showing Transmittance (%) vs. Wavelength (nm) with windows (green) and without windows (red).	Graph showing difference of Transmittance (%) vs. Wavelength (nm) measurements of PbF2 Cube with and without magnetic windows.
Graph of 10-cm CRYTUR crystal showing Transmittance(%) vs. Wavelength(nm) with the magnetic windows (red) and without windows (green) inside the spectrometer.	Graph showing difference of 10-cm CRYTUR crystal Transmission (%) vs. Wavelength (nm) measurements with and without windows.

→ Final test - interlaboratorial crosscheck

We compare our transmittance results to other universities/labs' measurement of transmittance on the same crystals.

Measurements/tests:

• 6 - Measure transmittance of 20-cm BTCP crystal (windows removed) and compare results with those from Giessen Univ.

Pictures:

File:Benchm longitudinal BTCP.jpg BTCP crystal at spectrometer sample compartment for longitudinal transmittance measurement.

Results:

File:Benchm longitudinal plot BTCP CUA Giessen.jpg ...

File:Benchm longitudinal plot BTCP Diff CUA Giessen.jpg ...

Transverse Transmittance

Testing the effects of using a black tarp instead of lid to cover compartment to prevent possibilities of escaped light during transverse transmittance measurements

→ Cloth to cover the spectrometer This test allowed us to make sure there is no effect on the transmittance measurements when working with a cloth covering the sample compartment instead the spectrometer's lid. Using the cloth will be necessary since the 20 cm crystals can only be fully scanned in the spectrometer if the lid is removed, since the sample compartment is not big enough.

Measurements/tests:

• 1 - Measure transmittance of a 20-cm BTCP crystal installed at the center of the compartment with the compartment cover installed and closed.
• 2 - Measure transmittance of 20-cm BTCP crystal installed at the center of the compartment without the compartment cover and a black cloth covering the setup. Do not move the crystal between point (1) and this measurement. This test is done without the diagonal slider. Compare the result with that of the previous point. If there is significant noise in the data, check the positioning of the black cloth.

Pictures:

BTCP crystal positioned at the center of spectrometer.

Spectrometer with sample compartment cover.

Spectrometer with cloth covering sample compartment (in place of cover).

Results:

Graph showing the transverse transmittance (%T vs. nm) of BTCP 20-cm crystal with the sample compartment cover (red) and with the dark cloth in place of the cover (green).

Graph of BTCP 20-cm crystal showing difference between the two measurements.

→ Slider installation

A slider powered by a stepper motor was configured to position the crystal in the spectrometer compartment for the measurement of transverse transmittance along the crystal. This test allowed us to check for alignment of the crystal to the light beam and for the reproductibility of the measurement using the slider.

Measurements/tests:

• 3 - Install and test the diagonal slider stepper motor with the crystal installed, but no actual transmittance measurement.
• 4 - Measure transmittance of a 20-cm BTCP crystal without the compartment cover, with the black cloth, and with the diagonal slider installed (single crystal position only). If there is significant noise in the data compared to the previous two points, stop to evaluate before proceeding. Check alignment of the crystal to the beam. Check for temporary black cover or paint for the base and any other reflecting surface on the sliding device.

Pictures:

File:Benchm transverse slider1.jpg Slider installed at the spectrometer for transmittance scan along the crystal.

File:Benchm transverse slider2.jpg Tests of reproductibility with slider in place.

Results:

File:Benchm transverse plot slider noslider.jpg Measurements of transverse transmittance of BTCP crystal with and without slider in place.

File:Benchm transverse diff slider noslider.jpg Difference between these two measurements.

→ Actual transverse transmittance measurement

This test allowed us to evaluate, for the first time, the full setup for transverse transmittance scan at a BTCP crystal.

Measurements:

• 5 - Measure transmittance of a 20-cm BTCP crystal at 5-6 points along the crystal with the diagonal slider (compartment cover off, black cloth installed). Determine the variation of the mean at 50% transmittance.

Pictures:

File:Benchm transverse severalPts1.jpg Slider positioning crystal at edge 1.

File:Benchm transverse severalPts2.jpg Slider positioning crystal at edge 2.

Results:

File:Benchm transverse plot severalPts.jpg Transmittance of BTCP crystal at several points along its length, positioned with the slider.

File:Benchm transverse plot variation.jpg Variation of transmittance...