Precision spectral sculpting for narrow-band amplification of broadband frequency-modulated pulses

Amplification of broadband frequency-modulated (FM) pulses in high-efficiency materials such as ytterbium-doped strontium fluorapatite results in significant gain narrowing, leading to reduced on-target bandwidths for beam smoothing and to conversion from frequency modulation to amplitude modulation (AM). To compensate for these effects, we have applied precision spectral sculpting, requiring both amplitude and phase shaping, to the amplification of broadband FM pulses in narrow-band gain media. We have demonstrated sculpting for centerline small-signal gains of 10(4), producing amplified pulses that have both sufficient bandwidths for on-target beam smoothing and temporal profiles that have no potentially damaging AM.

Entirely reflective slit spatial filter for high-energy laser systems

An entirely reflective slit spatial filter is proposed to provide spatial filtering, gain isolation, and ASE mitigation for high-energy laser systems. The traditional circular pinhole is replaced by two orthogonal slits, which lowers the intensity at the spatial filter plane by up to two orders of magnitude, and by using reflective optics we reduce spatial dispersion and eliminate B-integral effects. A ray trace model of the spatial filter shows excellent transmitted wavefront, but also indicates aberrations at the foci from using cylindrical optics at 45°. It is expected that the use of off-axis parabolic mirrors would mitigate this issue but comes at the cost of more complicated, expensive optics and more complex alignment. We created a numerical model based on Fourier optics to explain this effect and guide design requirements to mitigate it. High-quality imaging and filtering capabilities are demonstrated experimentally.