A nonorthogonal theory is used to study the non-Hermitian character of the excess noise in gain-guided transient Raman amplifiers. We calculated the output of the gain-guided transient Raman scattering based on a nonorthogonal mode expansion. We found that the excess noise in a transient gain-guided amplifier increases nonlinearly from 0 (and the Petermann factor nonlinearly from 1) and that the evolution depends mainly on the integrated energy of the pump laser pulse.
© 1999 Optical Society of America
Jianqiu Xu and Qihong Lou, "Gain-guiding effects in transient Raman amplifiers," J. Opt. Soc. Am. B 16, 961-965 (1999)