Scintillation averaging and fade statistics.

This work develops expressions for the variance and power spectral density (PSD) of atmospherically induced amplitude fluctuations of a propagating beam of light, also known as scintillation. This extends a recently published analytic approach for atmospheric propagation studies, previously applied to the phase properties of a propagating beam. In addition to laying out the general principles for manipulating log-amplitude expressions, this work develops novel expressions for scintillation under aperture, path, wavelength, and temporal averaging, first separately and then as a unified expression.

Diffractive anisoplanatism and tracker bandwidth limitations.

This work develops the concept of "diffractive anisoplanatism," a phenomenon that limits tracker performance for directed-energy applications by introducing differences between point-source-beacon tilt measurements and scoring-beam centroid motion. Our theoretical analysis of this phenomenon, checked against wave-optics simulations, highlights two relevant effects: diffractive conversion of phase to amplitude in the beacon light, and diffractive spreading of the scoring beam into regions outside of the geometric cone sampled by the beacon. In this work, we derive expressions for the variance and power spectral density of the differential jitter between beacon tilt and scoring-beam centroid motion.

Analytic propagation variances and power spectral densities from a wave-optics perspective.

This work presents an approach for constructing equations describing the effects of atmospheric turbulence on propagating light based on equations and concepts that will be familiar to those with a background in paraxial wave-optics modeling. The approach is developed and demonstrated by working through three examples of increasing complexity: the variance and power spectral density of the aperture-averaged phase gradient (G tilt) on a point-source beacon, the variance of the Zernike tilt difference between two physically separated point-source beacons, and the irradiance-weighted average phase gradient (centroid tilt) and target-plane jitter variance for a generic beam. The first two results are shown to be consistent with the existing literature; the third is novel, and it is shown to agree with wave optics and to be consistent with the literature in the special case of a Gaussian beam.

Analytic propagation variances and power spectral densities from a wave-optics perspective: publisher's note.

This publisher's note explains corrections to J. Opt. Soc.

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG.

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps.