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Proceedings Paper

Diode-pumped alkali laser-bleached wave dynamics
Author(s): Glen P. Perram; Wooddy Miller; Ed Hurd
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Paper Abstract

A three level analytic model for optically pumped alkali metal vapor lasers is developed by considering the steady state rate equations for the longitudinally averaged number densities of the ground 2S 1/2 and first excited 2P3/2, and 2P1/2 states. The threshold pump intensity includes both the requirements to fully bleach the pump transition and exceed optical losses, typically about 200 Watts/cm2. Slope efficiency depends critically on the fraction of incident photons absorbed. For efficient operation, the collisional relaxation between the two upper levels should be fast to prevent bottle-necking. By assuming a statistical distribution between the upper two levels, the limiting analytic solution for the quasi-two level system is achieved. The highly saturated pump limit of the recently developed three-level model for Diode Pumped Alkali Lasers (DPAL) is also developed. The model is anchored to several recent laser demonstrations. A rubidium laser pumped on the 5 2S1/2 – 5 2P3/2 D2 transition by a pulsed dye laser at pump intensities exceeding 3.5 MW/cm2 (< 1000 times threshold) has been demonstrated. Output energies as high as 12 μJ/pulse are limited by the rate for collision relaxation of the pumped 2P3/2 state to the upper laser 2P1/2 state. More than 250 photons are available for every rubidium atom in the pumped volume during each pulse. For modest alkali atom and ethane spin-orbit relaxer concentrations, the gain medium can only process about 50 photons/atom during the 2 – 8 ns pump pulse. At 110° C and 550 Torr of ethane, the system is bottlenecked. The system efficiency based on absorbed photons approaches 36% even for these extreme pump conditions. Furthermore, at 320°C with 2500 torr of helium, a pulsed potassium laser with 1.15 MW/cm2 peak intensity and 9.3% slope efficiency has been demonstrated.

Paper Details

Date Published: 8 November 2012
PDF: 8 pages
Proc. SPIE 8547, High-Power Lasers 2012: Technology and Systems, 854709 (8 November 2012); doi: 10.1117/12.972308
Show Author Affiliations
Glen P. Perram, Air Force Institute of Technology (United States)
Wooddy Miller, Air Force Institute of Technology (United States)
Ed Hurd, Air Force Institute of Technology (United States)

Published in SPIE Proceedings Vol. 8547:
High-Power Lasers 2012: Technology and Systems
Harro Ackermann; Willy L. Bohn, Editor(s)

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