Two-line phase-matched raman amplifier

Abstract

To provide a solution of the problem of medium dispersion in a two-line Raman amplifier which may increase the intensity-length product requirement and limit the conversion efficiency. By adjusting the angles between the input beams, the four-wave mixing phase mismatch due to medium dispersion may be eliminated. This couples together the Raman gains of the two lines so that the effective pump intensity for each is the total pump intensity. Since both lines convert in about the same amplifier length, independent of the relative power in each, the conversion efficiency is not limited by the inability to optimize the length for both lines simultaneously.

What is claimed is: 
     
       1. A method for a Raman amplifier having a pump laser with two spectral lines used as input beams, and a Raman medium in which Raman gains of two lines in Stokes-shifted output are coupled together by a four-wave mixing process, said method comprising adjusting the angles between the input beams, so that the four-wave mixing phase mismatch due to medium dispersion is substantially eliminated; whereby the Raman gains of the two Stokes shifted lines are coupled together so that the effective pump intensity for each is the total pump intensity: and since both lines convert in about the same amplifer length, independent of the relative power in each, the conversion efficiency is not limited by the inability to optimize the length for both lines simultaneously.   
     
     
       2. The method according to claim 1, wherein a Raman amplifier is used to transfer energy from a pump laser having two spectral lines with poor beam quality into a Stokes beam having two spectral lines of good quality, thereby creating a beam cleanup device. 
     
     
       3. The method according to claim 1, wherein a Raman amplifier is used to transfer the energy from a pump laser having two spectral lines into a Stokes beam of shifted frequency, said frequency being either lower than the pump laser frequency (Stokes) or higher than the pump laser frequency (anti-Stokes) thereby creating a frequency shifting device. 
     
     
       4. The method according to claim 1, wherein a Raman amplifier is used to transfer the energy from a pump laser having two spectral lines into a Stokes beam of shifted frequency, said Stokes beam being generated from a small seed beam which has a desired wavefront impressed upon it by a linear or nonlinear adaptive optic in order to provide Raman lookthrough device. 
     
     
       5. The method according to claim 1, wherein a Raman amplifier is used to transfer the energy from two coherent pump lasers into a Stokes beam of shifted frequency, thereby creating a beam combining device.