Light amplification by stimulated emission of radiation, or the laser, dates to about 1957, emerging in theoretical papers by Townes and Schalow. The term laser was coined by Gould, who eventually received credit for this. The laser concept has three fundamental elements from a remote-sensing perspective. The light from a laser is monochromatic, meaning it has a single discrete wavelength. The spectral lines are typically quite narrow, i.e., a few angstroms wide. In general, the light is naturally linearly polarized. Lasers can be formed into continuous wave (CW) or pulsed systems. The ability to quickly switch a laser on-and-off is what makes it particularly useful for remote sensing.
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