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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.


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%


Created October 21, 2009, Updated November 15, 2019