Laser Generation without Population Inversion in the Red Wing of the
D1-Line of Alkali Metal Atoms under Resonant Diode Pumping
A new method of laser radiation generation without population inversion in the red wing of the
D1 -line of alkali metal atoms under resonant absorption of broadband radiation of pump laser diodes at the
D1 transition is studied theoretically. The appearance of laser generation is caused by the fact that the probability of stimulated emission in the red wing of the spectral line exceeds the probability of absorption if homogeneous broadening due to interaction between active particles and the buffer gas significantly exceeds the natural broadening (under high pressures of the buffer gas). Analytical formulas representing the operation of a transversely diode-pumped alkali metal vapor laser are obtained. It is found that cesium atoms are the most promising object for observation of laser generation without population inversion in the red wing of the
D1 -line of alkali metal atoms. In a sufficiently long active medium (the length of the medium is 50 times its width), the efficiency of pumping radiation conversion into laser radiation can reach 57% at a buffer gas pressure of 5 atm, a pump diode radiation intensity of 5 kW/cm
2 , and a half-width of its spectrum of 1 cm
−1 . The laser radiation frequency can be tuned by several tens of cm
−1 .
The resonance radiation trapping in alkaline-earth metal atomic lasers were investigated according to Holstein's theory. The threshold temperature, ground-state density and resonant level effective lifetime of the resonance radiation trapping were calculated for Ca, Sr, and Ba atomic vapor lasers with different tube radii. The calculated threshold temperature is found to be in good agreement with the experimental laser-starting temperature, which indicates the resonance radiation trapping is a significant factor in establishing the population inversion of the resonance to metastable transition lasers.