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Mode-medium instability and its correction with a Gaussian reflectivity mirrorA high power CO2 laser beam is known to deteriorate after a few microseconds due to a mode-medium instability (MMI) which results from an intensity dependent heating rate related to the vibrational-to-translational decay of the upper and lower CO2 lasing levels. An iterative numerical technique is developed to model the time evolution of the beam as it is affected by the MMI. The technique is used to study the MMI in an unstable CO2 resonator with a hard-edge output mirror for different parameters like the Fresnel number and the gas density. The results show that the mode of the hard edge unstable resonator deteriorates because of the diffraction ripples in the mode. A Gaussian-reflectivity mirror was used to correct the MMI. This mirror produces a smoother intensity profile which significantly reduces the effects of the MMI. Quantitative results on peak density variation and beam quality are presented.
Document ID
19900016357
Acquisition Source
Legacy CDMS
Document Type
Technical Publication (TP)
Authors
Webster, K. L. (NASA Marshall Space Flight Center Huntsville, AL., United States)
Sung, C. C. (Alabama Univ. Huntsville., United States)
Date Acquired
September 6, 2013
Publication Date
June 1, 1990
Subject Category
Optics
Report/Patent Number
NAS 1.60:3023
NASA-TP-3023
Accession Number
90N25673
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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