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Chapter 4:
Specifications, Measurements, and International Standards
There are numerous occasions where component suppliers and their customers disagree about the quality of the components supplied. This is usually because the specification is flawed and/or incorrect for the application. Most specifications are written in terms of parameters that can be measured. However, this does not mean that all of the parameters are necessary or that all of the necessary parameters are specified. Many laser applications depend on a high degree of definition of the laser parameters, and as the subject matures the precise parameters of importance are gradually being recognized. In the 1970s, when data on the laser-induced damage thresholds of optical materials were being published for the first time, the range of values measured for even high-quality materials varied markedly. A collation of the LIDTs of high-quality fused silica showed that there was a published variation of about 103. These values were investigated and the conclusion was reached that although all of the values were genuine, the workers had not given enough data on the parameters used to allow a meaningful comparison to take place. The measurement and reporting of three areas of parameters were concluded to be suspect. The first was the measurement of the pulse energy delivered to the sample under investigation. At that time there was a severe difference between calibration of energy measurement devices across the world. The second area was in the measurement - and particularly the reporting - of the focused beam spatial and temporal beam profiles. The third area was in the measurement and reporting of the component characteristics. Even cross-laboratory comparisons, with two or more laboratories making measurements on the same samples, have yielded differences outside the expected error limits. When these differences have been investigated it has usually been found that some difference in the measurement procedure has proved critically important.
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