Temperature Dependence of the Fine Structure Mixing Induced by 4He and 3He in K and Rb Diode Pumped Alkali Lasers

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A critical evaluation of the experimental and theoretical literature regarding the rates for fine structure mixing in the first excited 2P3/2,1/2 states of potassium and rubidium induced by collision with 4He is performed. The evaluation is used to develop a recommendation for the fine structure mixing rates as a function of temperature. The rate coefficient for transitions from Rb 5 2P3/2 to 52P1/2 induced by helium ranges from 1.2 to 4.6 × 10–12 cm3 s−1 as temperature increases from 300–600 K. Remarkable agreement for the thermally average cross-sections is observed between the empirical, semi-classical perturbative, and quantum scattering theory approaches. In addition to collisions with 4He, new energy-dependent cross-sections for the K 42P mixing induced by 3He are reported using time-dependent channel packet scattering theory. The 3He rates are faster than for 4He due to both increased relative speed and more impulsive interactions. The fine-structure mixing rates in high-power Diode Pumped Alkali Lasers limit intensity scaling and are the primary source of heating. This heating induces spatial and temporal optical phase variations and accurate values for mixing rates as a function of temperature are critical for high fidelity laser modeling and simulation.


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Applied Physics B