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We report precision measurements by Fourier transform spectroscopy of the vacuum wavenumber, line width, and relative signal strength of 928 lines in the Ar I spectrum. Wavelength in air and classification of the transition are supplied for each line. A comparison of our results with other precision measurements illustrates the sensitivity of Ar I wavelengths to conditions in the light source.

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The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. The name indicates that the process of stimulated emission makes a laser work. Stimulated emission is studied in detail in this book. The name does not describe the special characteristics of laser light that makes lasers so useful. Compared to conventional sources of light such as an incandescent light, the light from a laser may be quite intense, very monochromatic, and may be emitted in a beam with an angular divergence limited by diffraction. The monochromaticity and high degree of collimation of a laser beam are manifestations of the coherence of the laser beam. If one repeatedly samples the electromagnetic field in a light beam at different points in space either longitudinally along the beam axis or transversely across the beam axis and finds that definite phase differences are maintained, then the light is said to be coherent. These properties imply that laser light is nearly a perfect classical sinusoidal electromagnetic wave.Lasers have many applications in scientific or engineering research, in telecommunications, in industry, and in medicine. For example in scientific or engineering research variable wavelength lasers are used for spectroscopy experiments, for the ultra-sensitive detection of atoms or molecules, for atom trapping experiments, for laser isotope separation experiments, for measurements of the time dependence of physical or chemical reactions, for studies of laser induced chemical reactions, and for many other research projects. In commercial or industrial applications lasers are used for the transmission of communication signals, for reading bar codes, for cutting of precise patterns in metal tooling, and for many other operations. In medicine lasers are used for the treatment of detached retinas, for sculpting corneas, for the treatment of ulcers, for use as a precision scalpel, and

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