History of the Laser

	Lasers are one big success story – and an embodiment of Feynmans famous sentence:
		"There are certain situations in which the peculiarities of quantum mechanics can come out in a special way on a large scale."
		It is not necessary to to emphasize how important lasers are to all of us – to the scientist, the patient in a hospital, the consumer listening to her discs, the supermarket cashier, the geometer – and just about everybody else. It should be quite clear.
		It is, however, quite necessary to emphasize that lasers – and, of course, all of solid state electronics – are purely quantum mechanical devices, because this is simply not known to the "people in the street" (including those in suits; and this says something about the state of general eduction in this country).
	Here are a few milestones in the development of the laser.

	The first major date is 1916, when Albert Einstein introduced the concept of stimulated emission.
		The first experimental verification of stimulated emission was obtained in 1928 (by W. R. Ladenburg).
	It took till 1953 to experimentally demonstrate not only stimulated emission but amplification of radiation. This was achieved by Gordon, Zeiger and Townes.
		The researchers used the two lowest vibrational energy levels of ammonia molecules and obtained a very narrow emission line at 12.6 mm, i.e., in the "micro"wave region.
		This is where the name "maser" comes from.
		Follow-up on the "maser" finally led to the 1964 Nobel prize in physics being shared between Townes and, for their contributions to the underlying theory, the Russians Basov and Prokhorov .
	Meanwhile, however, Maiman produced the first optical maser, as the laser was originally called in 1960.
		The light came from Cr³⁺ ions fixed in an Al₂ O₃ crystal – in other words, a ruby – at a wavelength of 694.3 nm.
		Pumping took place with an intense light source, and the laser only emitted a short pulse.
	The first semiconductor lasers started working in 1962: Three different research groups achieved lasing ##from different devices##.
		The light came ### at a wavelength of 694.3 nm.
		Pumping took place ###.