Impact of the Kerr effect on FM-to-AM conversion in high-power lasers.

In order to smooth the focal spot of high-power energetic lasers, pulses are phase-modulated. However, due to propagation impairments, phase modulation is partly converted into power modulation. This is called frequency modulation to amplitude modulation (FM-to-AM conversion).

Interference filters and their impact on FM-to-AM conversion: a method for investigation and characterization.

High-power nanosecond laser pulses are usually spectrally broadened via temporal phase modulations to tackle the issue of stimulated Brillouin scattering and to achieve optical smoothing of the focal spot. While propagating along the beamline, such pulses can undergo frequency modulation to amplitude modulation (FM-to-AM) conversion. This phenomenon induces modulations of the optical power that can have a strong impact on laser performance.

Nonlinear FM-AM conversion due to stimulated Brillouin scattering.

We report an effect potentially harmful occurring in regenerative amplifiers due to stimulated Brillouin scattering (SBS). Most high energy laser facilities use phase-modulated pulses to prevent the transverse SBS effect in large optical components and to smooth the focal spot on target. However, this kind of pulse format may undergo a detrimental effect known as frequency modulation to amplitude modulation (FM-AM) conversion in the presence of spectral distortions.

Random and pseudo-random phase modulations for FM-to-AM reduction in high power lasers.

Frequency modulation to amplitude modulation (FM-to-AM) conversion is an important issue that can prevent fusion ignition with high power lasers such as with the Laser Megajoule (LMJ). A way to reduce FM-to-AM conversion is to change the phase modulation (currently sinusoidal). In this paper, we study the case of random phase modulation.

Laser-induced damage of fused silica optics at 355 nm due to backward stimulated Brillouin scattering: experimental and theoretical results.

Forward pump pulses with nanosecond duration are able to generate an acoustic wave via electrostriction through a few centimeters of bulk silica. Part of the incident energy is then scattered back on this sound wave, creating a backward Stokes pulse. This phenomenon known as stimulated Brillouin scattering (SBS) might induce first energy-loss, variable change of the temporal waveform depending on the location in the spatial profile making accurate metrology impossible, and moreover it might also initiate front surface damage making the optics unusable.