Lasers three-level

The efficiency of a ruby laser is less than 0.1 per cent, typically low for a three-level laser. 

Three-electrode system, 9 573 300-series stainless steels, 13 510-511 Three-level lasers, 14 666, 696 inversion in, 14 669 3M Corporation... 

Figure 2.6 An energy-level scheme for (a) four- and (b) three-level lasers, transition =, laser transitions , fast nonradiative transitions.

The active medium also determines the pumping scheme. Commonly, two types of operational schemes are used to describe laser operation /oMr-/cvc/ and three-level laser systems ... 

As early as 1982, a diode laser-pumped miniature NdtYAG laser with a linewidlh of less lhan 10 kHz. was demonstrated. The research in this area continued apace at Stanford University and by a numher of commercial electronics limis. w ith emphasis placed on ihe development of three-level lasers. Q-switched and mode-locked operation, single-frequency operation (monolithic nonplanar ring oscillator), visible radiation by harmonic generation, and array-pumped solid-slate lasers. See Fig. ft. 

The mechanism consists of using a conventional energy source (flash-lamp or other) to excite atoms or molecules from the ground state to some excited state, so that an inversion of population occurs in the Arrhenius55 sense this is usually best understood in a three-level laser, although two-level lasers are also discussed (see Problem 10.10.1), and many are four-level lasers (see Fig. 10.14). 

Fig. 7.10 Transitions and energy levels in a three-level laser.

Population inversion cannot be achieved in a two-level system, a material with two electronic states. At best, a nearly equal population of the two states is reached, resulting in optical transparency, when absorption by the ground state is balanced by stimulated emission from the excited state. An indirect method of populating the emitting excited state must be used. In a three-level laser (Figure 3.6, left), irradiation of the laser medium pumps an upper level 2, which is rapidly depleted by a nonradiative... 

Figure C2.15.4. (a) A three-level laser energy level diagram and (b) the ruby system.

Note that the levels are numbered. 1 => 3 is the excitation transition while 3 => 2 and 4 = 1 are relaxation transitions. Let us take the simpler case of the three level laser. Let N i be the number of activator sites in the ground state, N3 in the excited state, etc. We can then set up a series of differential equations involving ooij and the number of sites changing per unit of time. This is shown as follows in 6.8.77., presented on the next page. 

Fig. 3.31. The ruby three-level laser. The pumping nansiiion is 1, the lasing transition 3. The nonradiaiive transition 2 is fast relative to the radiative inverse of 1. The level notations are for Cr +. The orders of magnitude of the relevant rates are p( T2 - Aj) = 10 s .

It is energetically costly to obtain a population inversion in a three-level laser because one must... 

It is widely accepted that the room temperature spectroscopic properties of Yb-doped ceramic materials could offer nearly pure four-level emission on the transition of F5/2(l) and quasi-three-level laser emission on the much... 

Other modes are possible with a Nd YAG laser (other output wavelengths). They correspond to transitions to the higher " I/ states (represented in gray in Figme 6), or to the ground state if working as a three-level laser. 

We have already mentioned the difficulties involved with a three-level laser in which the laser transition is terminated in the continuously well populated ground state. The successful operation of the ruby laser relies on the very favourable combination of broad absorption bands and the long upper-state lifetime allowing the storage of energy. In a 4-level laser., a final level, which is not the ground state, is used. The basic diagram is shown in Fig. 8.9a. 

Photochromic materials change their color upon illumination. In some cases, a quasi-stationary concentration of an exdted state has strong absorption bands, such as triplet-triplet transitions in many aromatic hydrocarbons, or the doublet-doublet transitions of chromium(in) in ruby operating as a three-level laser. In other cases, the color is due to exdted states of the reversible or irreversible product of a photochemical reaction. Many organic molecules can undergo such reactions, like rearrangement between cis- and iran -isomers around double... 

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