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Thickness Measurement Technology

How It Works

Utilizing the unique properties of light, the Optical Thickness Gauge (OTG) accurately measures the thickness of transparent and semi-transparent materials. To make a measurement, light is transmitted into the material resulting in reflections at each surface and layer interface which is then collected and analyzed by optical interferometry. Bristol’s proprietary interferometer design includes an “optical ruler” that very precisely measures the difference in length traveled by each reflection to determine the thickness of each layer and total thickness.

Because this optical technique is so effective, the Optical Thickness Gauge can collect and analyze the reflections from a sample as thin as 12 μm to as thick as 80 mm and simultaneously measure as many as 31 layers.

The Measurement Process



(1) The Optical Thickness Gauge System includes a super-luminescent LED (SLED), interferometer assembly, and a digital signal processor (DSP) housed within a rugged, rack-mountable chassis.

(2) Light from the SLED is sent to the material under test through an optical probe that is connected to the OTG system by a flexible fiber-optic patch cord.

(3) Reflections from the material under test are collected by the optical probe and returned to the OTG system's interferometer for analysis.

(4) Thickness data is calculated using the onboard processor and then transferred via USB or Ethernet to connected PC. The Windows-based Opti-Cal™ software is used to control measurement parameters and report thickness data in a variety of formats.

Measurement Accuracy Guaranteed

All of our Thickness Gauges include a built-in HeNe laser that provides a continuous light source for calibration as an invariant standard of length. Every measurement is compared to this high quality calibration standard, guaranteeing the accuracy of your results.

Ready to see this technology at work?

Send us your part in advance and we'll provide a free demonstration of our measurement capabilities. Contact us today to discuss your application.