Far-infrared superradiance in methyl fluoride

Dicke superradiance, that is, cooperative spontaneous emission, has been observed in methyl fluoride, which is optically pumped by a pulsed carbon dioxide TEA laser operated on the P(20) line at 9.55 ~m. The far-infrared (FIR) super-radiant pulses, at a wavelength of 496 microns, were identified by the pressure (p) dependence of their widths and delays (inversely proportional to p) and their intensities (as p2). These pulses were observed by a fast, sensitive Si:P photoconductor calibrated to give absolute intensity, and were recorded for a range of pressures from .44 to .01 torr in each of several sample lengths from 168 to 1021 cm. This was done for <emission in both the forward and the backward directions. The full complex Maxwell-Bloch equations, including degeneracy and sources for polarization and population which synthesized the pump pulse, were solved numerically for the experimental conditions. One parameter, the initial Bloch vector tipping angle, was treated as quasifree and varied to try to fit the data. By choosing the proper fUnctional dependence of the tipping angle on cell length and pressure, a good fit was obtained to all the forward-wave data. (The backward~wave case was not considered here.) It was necessary to include emission on FIR transitions with values of K = 1, 2, and 3 for the case of linear polarization perpendicular to that of the pump to get this agreement, which explained a disGontinuity in the slopes of the width and delay vs. p-l and of the intenslty vs. p. These discontinuities had been previously attributed to the onset of swept superradiance or to the onset of Doppler broadening, and were shown to be due to changes in the dominant value of K. The question of the form of the tipping angle was left unsolved, as our values vary between the two cases, theta= 2N-1/2 and () 0 = 2 (uN)-1/2. The delay was found to vary more nearly as lnN than as (lnN)2 i possibly supporting the assumption that completely full inversion of the superradiant transition was not achieved, due to Raman scattering, and that the process observed is properly called superradiance rather than super-fluorescence. A review of previous experiments and major theoretical work on superradiance is also given, with a consistent notation used throughout. The semiclassical theory is developed and several limiting cases are noted and solved.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Rosenberger, Albert Thomas

Contributors dc:contributor

• DeTemple, Thomas A.

• far-infrared superradiance
• methyl fluoride
• Dicke superradiance
• cooperative spontaneous emission

Statement dc:rights

• 1979 Albert Thomas Rosenberger

Language dc:language

en

Identifier

360827

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25564