FREQUENCY-ASYMMETRIC GAIN PROFILE IN A SEEDED RAMAN AMPLIFIER

This paper examines the effect of index guiding on Raman gain. The slo wly varying Maxwell wave equation including both the real and imaginar y parts of the Raman susceptibility for a seeded Raman amplifier is ex plored. Using a Gauss-Laguerre mode expansion for the Stokes field, th e output Stokes energy is numerically studied as a function of gain an d detuning from the Raman resonance. The calculations indicate that th e real part of the Raman susceptibility causes the Raman medium to act as a lens when the Stokes seed is detuned from the Raman resonance. T his focusing effect leads to higher peak Stokes energy when the Stokes seed is tuned to the blue side of the Raman resonance. Specifically f or Raman scattering in H-2 with a pump laser at 532 nm and an input se ed near 683 nm, the peak Stokes energy can shift by as much as 300 MHz from the Raman resonance. An experiment which confirms these predicti ons is also presented.