> Coherent does have an extensive line of sturdier and more expensive > power meters. So do several other manufacturers, so one can shop around. One factor in the cost is the accuracy, you can get a cheap power meter accurate only to about 10% (LaserCheck is specified for 5% accuracy) but you have to pay nearly $2000 for one that is accurate to about 1%. And you really have to take good care of them if you want to retain that accuracy! There a two common types of power meters: Those that use a photodiode to read the signal, and those to use the heating of a black target surface to determine power. Photodiode power meters react faster and more easily read low powers, but they are strongly wavelength-dependent, so you have to dial in the wavelength or use a calibration chart, and they have a more limited spectral range. Thermal power meters have to be adjusted for the environmental temperature if you want to read off low powers (they will react to the temperature of your hand) but they have a flat efficiency curve over a much wider range (say 250nm to 11000nm). Emmanuel Gustin
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