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High Power Raman Converter with no Beam Trapping

IP.com Disclosure Number: IPCOM000092402D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Vanderslice, JT: AUTHOR

Abstract

A Raman laser having minimal beam trapping of the laser pump beam is shown. Beam trapping within a Raman active medium causes the laser pump beam to be trapped into fine filaments. This is due to a second order refractive index induced by the strong electric field of the pump laser. Thus, n = n(0) + (delta n)E/2/ describes the increase in refractive index n of a Raman medium whose (delta n) is a coefficient specific to the Raman medium and E represents the strength of the electric field of the laser pump beam.

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High Power Raman Converter with no Beam Trapping

A Raman laser having minimal beam trapping of the laser pump beam is shown. Beam trapping within a Raman active medium causes the laser pump beam to be trapped into fine filaments. This is due to a second order refractive index induced by the strong electric field of the pump laser. Thus, n = n(0) + (delta n)E/2/ describes the increase in refractive index n of a Raman medium whose (delta n) is a coefficient specific to the Raman medium and E represents the strength of the electric field of the laser pump beam.

Beam trapping is eliminated if the electric field gradient within the Raman medium is eliminated. Raman medium 1 is pumped by a laser whose output 2 is modified so that it has a flat-topped intensity distribution over the effective diameter of Raman cell 3. A normally exponential or Gaussian intensity of laser output 2 is collimated and focused by lens 4 on square slit 5 to generate a Fraunhofer intensity distribution. Laser beam 2 is then recollimated by lens 6. The latter produces a far field z>>f intensity which is the Fourier transform of the Fraunhofer pattern.

Cell 3 has Raman active material 1. Laser output 2 has a uniform intensity distribution within Raman medium 1. Cell 3 includes thick walls 7 of material that has a refractive index similar to that of Raman medium 1. Also, the (delta n') of walls 7 is zero or <<(delta n), so that beam trapping does not occur. Glasses are suitable materials. It is d...