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Reference Transmittance Spectrophotometer (RTS)


The Reference Transmittance Spectrophotometer (RTS) is the national reference instrument for regular spectral transmittance measurements of non-fluorescent samples at room temperature.

The illuminator has two sources, a deuterium (D2) arc lamp and a quartz-tungsten-halogen (QTH) incandescent lamp, a spherical mirror, a chopper, a prism-grating monochromator, a parabolic mirror, a polarizer, and an iris. A sample carriage moves the sample in and out of the influx beam. The receiver has a block for the efflux beam, a spherical mirror, and integrating sphere, and a detector, either a photomultiplier tube (PMT) or a silicon (Si) or extended indium-gallium-arsenic (InGaAs) photodiode.

Specifications / Capabilities:

Conditions for transmittance measurements using RTS.


Illumination Angle

Viewing Angle

Sampling Aperture 4 mm to 20 mm


Wavelength 250 nm to 2500 nm

Bandwidth 1.5 nm or 3 nm

Polarization 0° to 90°

Sample Size 10 mm to 50 mm


Quantity Transmittance T

Technique Absolute

Range 0.001 to 1

Uncertainty (k=2) 0.1% to 0.5%

Reference transmittance spectrophotometer

Name: Catherine Cooksey
Phone: 301-975-6208
Email: ccooksey@nist.gov
100 Bureau Drive, M/S 8442
Gaithersburg, MD 20899-8442