Improved laser-beam uniformity using the angular dispersion of frequency-modulated light

TLDR

The method aligns with frequency‑tripling constraints and avoids high‑intensity spikes, making it suitable for high‑power glass lasers in fusion experiments. A new technique is presented for obtaining highly smooth focused laser beams. Smoothing is achieved by imposing a frequency‑modulated bandwidth via an electro‑optic crystal, dispersing the frequencies with a pair of gratings while preserving pulse shape, and splitting the beam into beamlets with a phase plate so each diffraction‑limited spot matches the target size. The time‑averaged interference between beamlets is greatly reduced due to their frequency differences, yielding a relatively smooth diffraction‑limited intensity pattern on target.

Abstract

A new technique is presented for obtaining highly smooth focused laser beams. This approach is consistent with the constraints on frequency tripling the light, and it will not produce any significant high-intensity spikes within the laser chain, making the technique attractive for the high-power glass lasers used in current fusion experiments. Smoothing is obtained by imposing a frequency-modulated bandwidth on the laser beam using an electro-optic crystal. A pair of gratings is used to disperse the frequencies across the beam, without distorting the temporal pulse shape. The beam is broken up into beamlets, using a phase plate, such that the beamlet diffraction-limited focal spot is the size of the target. The time-averaged interference between beamlets is greatly reduced because of the frequency differences between the beamlets, and the result is a relatively smooth diffraction-limited intensity pattern on target.