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Encyclopedia of Laser Physics and Technology

Powermeters

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Definition: devices for optical power measurements, based on heating of an absorber structure

thermal powermeter

Figure 1: Head of a typical thermal powermeter. The photograph was kindly provided by Ophir-Spiricon Inc.

An optical powermeter (or laser power meter) is a device for the measurement of the power in a laser beam. Most powermeters are based on the principle that the optical power is converted to heating power in some absorber structure, and the resulting temperature rise (or some temperature difference) is measured, e.g. with a thermopile. Such thermal powermeters (see Figure 1) are useful for average powers between ∼ 0.01 W and several kilowatts; typically, some water cooling is required for powers above roughly 10 W. They are fairly robust (although too tight focusing onto the absorber should be avoided), moderately precise, usable in a wide wavelength range (with fairly wavelength-independent sensitivity), and relatively slow.

Faster and more sensitive powermeters can be made with photodiodes. These can also be used for measurement of high powers when a suitable attenuator is used. They are, however, less robust than thermal powermeters. Also, their sensitivity is rather wavelength-dependent, so that a photodiode-based powermeter usually requires the user to make a setting for the wavelength. The device then uses an internal calibration table to compensate for the wavelength-dependent responsivity. Obviously, this method does not work for beams with a very broadband or variable optical spectrum, whereas it may be perfectly convenient in situations where the laser wavelength is rarely changed.

A possible problem with all kinds of optical powermeters is the uniformity of response. For thermal powermeters, a lack of uniformity can result from a dependence of the resulting absorbance or temperature distribution for different beam positions. For photodiodes, a nonuniform response can easily result from damage with too high optical intensities.

Hints for Selecting a Device

For finding the most appropriate type and model of optical powermeter, a significant number of aspects needs to be considered. The most basic aspects are:

Some additional aspects of possible practical relevance are:

See also: photodetectors, photodiodes

Category: photonic devices


cover of print encyclopedia

Since October 2008, the Encyclopedia of Laser Physics and Technology is also available in the form of a two-volume book. Maybe you would enjoy reading it also in that form! The print version has a carefully designed layout and can be considered a must-have for any institute library, laser research group, or laser company.

You may order the print version via Wiley-VCH.

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