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 .
We present analytical solutions for the populations of the D 1 transition line of 85 Rb atoms. The time evolution of the populations of the magnetic sublevels in the excited state at the weak intensity limit exhibits several kinds of homogeneous or inhomogeneous second-order differential equations. General solutions of the differential equations result in an analytical form of the population in each magnetic sublevel as a function of the elapsed time, laser intensity, and laser frequency detuning.
Теоретически исследован новый метод генерации лазерного излучения без инверсии населённостей в «красном» крыле D1-линии атомов щелочных металлов при резонансном поглощении широкополосного излучения лазерных диодов накачки на переходе D1. Причиной возникновения лазерной генерации является то обстоятельство, что в красном крыле спектральной линии вероятность вынужденного испускания превышает вероятность поглощения, если однородное уширение из-за взаимодействия активных частиц с буферным газом существенно превышает естественное (при больших давлениях буферного газа). Получены аналитические формулы, представляющие работу лазера на парах щелочных металлов при поперечной диодной накачке. Выяснено, что наиболее перспективным объектом для наблюдения лазерной генерации без инверсии населённостей в красном крыле D1-линии атомов щелочных металлов являются атомы цезия. В достаточно длинной активной среде (длина среды в 50 раз превышает её ширину) эффективность преобразования излучения накачки в лазерное излучение может достигать 57 % при давлении буферного газа 5 атм, интенсивности излучения диодов накачки 5 кВт/см2 и полуширине его спектра 1 см-1. Частота лазерного излучения может перестраиваться на несколько десятков см-1. A new method for generating laser radiation without population inversion in the «red» wing of the D1 line of alkali metal atoms under resonant absorption of broadband radiation from pump laser diodes at the D1 transition has been theoretically investigated. The reason for the occurrence of laser generation is the fact that the probability of stimulated emission in the red wing of the spectral line exceeds the probability of absorption if the uniform broadening due to the interaction of active particles with the buffer gas significantly exceeds the natural one (at high pressures of the buffer gas). Analytical formulas that describe the operation of an alkali metal vapor laser under transverse diode pumping are derived. It has been found that the most promising objects for observing laser lasing without population inversion in the red wing of the D1 line of alkali metal atoms are cesium atoms. In a sufficiently long active medium (the length of the medium is 50 times greater than its width), the conversion efficiency of pump radiation into laser radiation can reach 57% at a buffer gas pressure of 5 atm, a pump diode radiation intensity of 5 kW/cm2, and a half-width of its spectrum of 1 cm-1. The frequency of laser radiation can be tuned by several tens of cm-1.