Dissertation/Thesis Abstract

Collisional dynamics, lasing and stimulated Raman scattering in optically pumped cesium and potassium vapors
by Brown, Kirk C., Ph.D., Air Force Institute of Technology, 2012, 119; 3499667
Abstract (Summary)

This dissertation explores quantum effects and collisional dynamics in optically pumped alkali vapors. In cesium, we study the 7 2P state and remeasure the spin orbit mixing and quenching cross sections in mixtures with helium and methane using time-resolved fluorescence techniques. The cross section of an important laser species, ethane, is measured for the first time. The analysis includes the effects of radiation trapping using the Holstein model in the Doppler and pressure-broadened limit. To aid in the interpretation of data, we employ a rate equation model and compare simulations to experimental data. The fine-structure mixing cross sections for He, CH 4 and C2H6 are 14±3, 35±6 and 73±10 Å2 respectively. The 2P3/2 state is quenched more rapidly than the 2P1/2 state.

Information about the spin orbit relaxation rates and quenching cross sections was used to assist in the demonstration and characterization of a three-level, optically pumped gas laser based on the spin orbit relaxation 72P3/2–72P1/2 transition using a mixture of 550 torr of helium and 100 torr of ethane. This laser is a conventionally pumped three-level system similar to the first infrared DPAL lasers. This method of optical pumping demonstrated that in addition to two-photon pumping schemes, a single photon method provided similar performance. The maximum output energy was 3.3 μJ with a threshold of 10 μJ/pulse and a slope efficiency of 0.45%.

Finally, we demonstrated tunable Raman and hyper-Raman lasing in potassium vapor. The hyper-Raman laser utilized a stable cavity without a buffer gas. The output was tunable from 766–770 nm. The threshold for the hyper-Raman process was 60 mW. The maximum slope efficiency (10.4%) and output power (12 mW) are comparable to previously demonstrated potassium DPAL systems that used several atmospheres of buffer gas. Two separate Raman processes were identified, Stimulated Electronic Raman Scattered (SERS) and Three Photon Stimulated Raman Scattering (TPSRS) during the laser demonstration. The Raman processes were observed to compete with each other over the the full tuning range of the pump laser. We also demonstrated rapid switching between the two processes over a small pump wavelength range, with a corresponding and much larger hop in the output wavelength.

Indexing (document details)
Advisor: Perram, Glen P.
Commitee: Dolson, David A., Holtgrave, Jeremy C.
School: Air Force Institute of Technology
Department: Engineering Physics (ENP)
School Location: United States -- Ohio
Source: DAI-B 73/07(E), Dissertation Abstracts International
Subjects: Physical chemistry, Quantum physics, Particle physics
Keywords: Alkali vapors, Cesium, Collisions, Laser, Potassium, Raman scattering
Publication Number: 3499667
ISBN: 978-1-267-24428-4
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