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Chapter 2:
What Your Beam Analyzer Manual Didn't Tell You: How to Build Your Own M2 Device (or Understand Theirs)
In 1998, the author was assigned to measure the beam quality of an optical parametric oscillator using a commercial beam analyzer. After aligning the analyzer according to the manufacturer's instructions, it would display an M2 of either 1.4 or 7, sometimes randomly fluctuating between the two with no apparent change in the system. Consulting the users' manual was frustrating; the answer to every truly important question was hidden behind the word proprietary. The beam analyzer was placed back on the shelf. Armed with a video acquisition card, motion control stage, digital camera, and control software, the author built his own laser beam analyzer, which automatically measured M2 both with a camera and with a knife edge in front of a large-area pyroelectric. In the process, he made nearly every mistake possible and learned how to take poor M2 measurements in many ways before learning to make good, reproducible, and traceable ones. This chapter is a product of that experience. The beam analyzer was built in accordance with the international standard for M2, the ISO 11146:1999. As of 2005, this standard was superseded by three different standards: ISO 11146-1:2005; ISO 11146-2:2005, and ISO 11146-3:2004. The purpose of this chapter is to inform the potential purchaser of commercial beam analyzers of some of the issues with automated M2 measurement equipment and to pass on some "tricks of the trade" to anyone wishing to build their own laser beam analyzer.
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