Theory of frequency shift, injection-locking, and appearance of sidebands in class-C laser amplifiers

The second-order nonlinear amplification features of an optical signal by a single-mode class-C laser are discussed in detail. Due to a four-wave mixing process, the laser amplifier demonstrates a multiple frequency region in which a spectrum of the new signal and image sidebands is produced; simultaneously the free-running laser intensity is weakened and its frequency is pulled toward the amplified input signal frequency. The main aim is to find the ranges of input signal intensity and frequency detuning for which the four-wave mixing process occurs for class-C laser amplifiers. Our results satisfy the energy conservation law and they are in complete agreement with the previous results derived for class-A and -B laser amplifiers.