Source: http://aoot.osa.org/oe/abstract.cfm?uri=oe-27-7-9676
Timestamp: 2019-04-26 12:00:48+00:00

Document:
Accurate modeling of the operation of diode-pumped alkali lasers is a critical step toward the design of high-powered devices. We present precision measurements for the Cs-CH4 62P3/2 → 62P1/2 mixing cross section and the 62P3/2,1/2 → 62S1/2 quenching cross section, which are important parameters in understanding the operation and, in particular, the heat generated in a cesium vapor laser. Measurements are carried out using ultrafast laser pulse excitation and observation of fluorescence due to collisional excitation transfer in time is done using the technique of time-correlated single-photon counting. Mixing rate measurements are acquired over methane pressures of 10 – 40 Torr, resulting in a Cs-CH4 62P3/2 → 62P1/2 mixing cross section of (1.40 ± 0.08) × 10−15 cm2, while quenching rate measurements are carried out over methane pressures of 500 – 4000 Torr, resulting in a 62P3/2,1/2 → 62S1/2 quenching cross section of (1.57 ± 0.03) × 10−18 cm2. These results suggest only a slight contribution to the heating of a cesium vapor laser is due to Cs 62P quenching, contrary to previous studies. We also discuss additional possible sources of energy transfer from upper excited states of Cs.
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Fig. 1 (a) Cesium energy level diagram, illustrating the states involved in these experiments. (b) Schematic of the experimental setup used to carry out cesium 62P mixing rate and quenching rate measurements in methane gas.
Fig. 2 The time evolution of 894 nm fluorescence induced by collisional excitation transfer with methane gas at the pressures listed. Also shown is the excitation laser pulse at 852 nm. The solid lines are fits to the data according to Eq. (4) and are used to extract the mixing rates. The inset shows the mixing rates as a function of methane gas pressure and a linear fit to the data is used to extract the mixing cross-section.
Fig. 3 The decay in time of 894 nm fluorescence induced by collisional excitation transfer in the high pressure regime. The solid lines are fits to the data according to Eq. (8) and are used to extract the quenching rates. The inset shows the quenching rates as a function of the methane gas pressure and a linear fit to the data is used to extract the quenching cross-section.
Fig. 4 Fluorescence emitted by upper atomic states of Cs after laser pulse excitation at 852 nm for various methane pressures. The peaks at 602, 620, 673 and 698 nm correspond to Cs 8D → 62P1/2, 8D → 62P3/2, 7D → 62P1/2 and 7D → 62P3/2 transitions, respectively.

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