Measurements for ensuring the laser safety for the user are not often necessary, since the class of the laser is normally known and the ANSI Z136.1 document, The Safe Use of Lasers, has been designed to utilize this class system and thus minimize the need for measurements. However, for unusual circumstances such as when the class of the laser is not known, or for unusual conditions of use measurements may still be required by the user. Also for manufacturers who must determine the class of a laser or for scientists establishing safety thresholds, and other assorted reasons it is often necessary to determine the laser beam power, or pulse characteristics by actual measurement. In such cases it is important that the uncertainty of the measurements be accurately determined since incorrect measurements for safety purposes may be worse than no measurements. Fortunately today there are an assortment of good instruments available for most laser wavelengths and power or energy ranges and an availability of national measurement services which can ensure the traceability to national standards of laser power or energy if that is necessary or desired.
Unfortunately however accurate laser power or energy measurements are still sometimes subject to a host of errors unless one is familiar with the techniques needed for setting up these measurements. This paper will try to list many of the considerations and pitfalls associated with making these measurements.