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Spectrometer benchmark

A set of tests were performed in order to understand the repetitivity, reprodutibility, 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 performed with this spectrometers 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.

Transverse Transmittance

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:

BTCM crystal positioned at the center of spectrometer.

File:Benchm transverse lid.jpg Spectrometer with lid.

Spectrometer with cloth.

Results:

File:Benchm transverse plot lid cloth.jpg Measurements of transverse transmittance of BTCM crystal with lid and cloth covering the spectrometer's sample compartment.

File:Benchm transverse diff lid cloth.jpg Difference between these 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 BTCM crystal with and without slider in place.

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

Actual trasverse transmittance measurement

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