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Abstract

The conversion efficiency of a cascaded Raman laser (CRL) can be significantly improved if it comprises one or more of the below recited design features. The CRL comprises an intracavity section between an input section and an output section. The CRL is adapted for receiving pump radiation of wavelength .lambda..sub.p, and for emitting output radiation of wavelength .lambda..sub.n >.lambda..sub.p, and each of the input section and output section comprises fiber Bragg gratings of center wavelengths .lambda..sub.1, .lambda..sub.2 . . . .lambda..sub.n, where n.gtoreq.2 and .lambda..sub.1 <.lambda..sub.2 < . . . .lambda..sub.n-1. Among the efficiency-increasing features is ordering of the fiber Bragg gratings such that in the input section and the output section the gratings of center wavelengths .lambda..sub.1 . . . .lambda..sub.n and .lambda..sub.1 . . . .lambda..sub.1-1, respectively, are disposed in sequence according to center wavelength, with center wavelengths increasing with increasing distance from the intracavity section. In a preferred embodiment the fiber Bragg grating of center wavelength .lambda..sub.n of the output section is disposed between the intracavity section and the grating with center wavelength .lambda..sub.1. Other efficiency-increasing features are choice of the .lambda..sub.n grating in the output section such that it has a reflectivity in the range 10-25%, disposition of a grating of center wavelength .lambda..sub.p in the output section downstream of the .lambda..sub.n-1 grating, choice of at least some of the fiber Bragg gratings such that their reflectivity has full width at half maximum in the range 0.8-2.0 nm, selection of the fiber Bragg gratings such that the center wavelength spacing between successive gratings corresponds to a frequency shift in the range 11.7-14.9 THz, choice of a specified optical fiber refractive index profile, and use of an intracavity section of length in the range 300-1200 m.

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