# 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 ###.

With frame

6.1.1 Interaction of Light and Electrons; Inversion

© H. Föll (Semiconductors - Script)