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 ###. | ||
6.1.1 Interaction of Light and Electrons; Inversion
© H. Föll (Semiconductors - Script)