Light and general radiation laws. Coherence and incoherence. Emission, absorption and amplification of radiation. Units and physical constants

Solid-state lasers

The world's first laser was created in 1960 by the American physicist T. Meiman. When it was created, all the basic ideas of quantum electro- nics, expressed by this time, were used. Basov, A.M. Prokhorov and C. Townes, i.e. the need for an inverted population of the level of the active medium, a three-level method with external pumping, the use of open resonators to enhance the effect of stimulated radiation, and obtaining a positive feedback.

As the active substance in the Meiman laser, a ruby ​​crystal (Al₂O₃) was used, in the crystal lattice of which about 0.05% of the Al atoms are replaced by Cr^{3 +} ions. A simplified diagram of Cr^{3 +} levels in the ruby ​​crystal is shown in Fig. 3.1, a. Here, E₁ is the main energy level, the transition from which to two broad energy bands E₃ and E₃' is realized with the help of green and blue (respectively) light emitted by a pulsed xenon flash lamp (pumping). The duration of the impulse is rolling . In the states E3 and E₃', the atoms are not long ( ) and quickly pass into the less excited but longer-lived ( ) metastable state E₂ in a nonradiative manner, i.e. giving off excess energy to the crystal lattice (heating it). With sufficiently powerful pumping, the number of particles at the metastable level may turn out to be greater than on the ground, i.e, there is an inverse population, for a sufficiently large (threshold) value, a laser transition with a wavelength (red light) becomes possible.

In the Meiman laser a ruby ​​crystal with a diameter of 5 mm was used. The open (by the principle of action) and the "bulk" (by design) resonator were the strictly parallel polished and silvered ends of the crystal, one of which was made partially transparent in order to ensure the emergence of the emerging radiation. To pump a pulse lamp was used, fed from a battery of capacitors with a capacity of 400 F at a voltage of 4 kV. We give more precise time and other characteristics of the first laser: the duration of the pump pulse ; coherent radiation consists of individual flashes of duration with intervals between them for a few microseconds and a total duration of ~ 10^-3 s. The peak radiation power was about 10 kW. Coefficient of efficiency is about ~ 1%.