With high power lasers any part of the beam that is absorbed by an optic will cause that element to heat up. No mirror is 100% Reflective, and no lens is 100% Transmissive. The power not transmitted or reflected is absorbed. (Scattering is neglible at infra red wavelengths)

Metal mirrors are particularly rugged, 1% absorption (ie 99% reflective) is perfectly acceptable even with 25KW lasers. Zinc Selenide components such as lenses and output windows are much more sensitive, 0.2% (just 2 parts per thousand) absorption can cause optical distortion or catastrophic failure.

This critical specification of a laser optic is not easy to measure, requiring a “calorimeter”.

The optic under test, which could be a mirror, lens, output couple or beam splitter is exposed to a stablised and accurately known laser power. The test optics rate of heating is measured continuosly for a minute or two. The test optics rate of cooling is also measured to allow for correction of the heating rate. Then by simply knowing the mass and heat capacity of the test optic the amount of power absorbed can be calculated.

LBP’s calorimeter uses a 150Watt CO2 laser, and a 20 bit A/D PC controlled data logger. This automates the measurement process, and produces a hard copy of the absorption measurement.

To see a schematic of the calorimeter click here

To see a picture of a typical result click here mrw to do a scan

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Laser Beam Products offer Laser Mirrors & Optics ZnSe laser lenses, ZnSe laser optics, CO2 laser mirrors, Infra Red optics, Copper mirrors, Aluminium mirrors, silicon mirrors, Molybdenum mirrors, beam expanders, phase retarding mirrors, Potassium Chloride (KCl) windows, gold coated mirrors, beam delivery optics, gold coated copper mirrors, reflectors for industrial cutting and welding.