Independent Phase and Amplitude Control of a Laser Beam Using a Single-Phase-Only Spatial Light Modulator
Laser-beam shaping is a rapidly developing field of research driven by both technological improvements of beam-shaping devices and the ever-increasing demands of applications. In high-energy laser chains, efficient beam shaping is successfully achieved in the front ends by passive methods such as beam apodization1 or intracavity mode shaping;2 however, these static techniques are unable to correct dynamic laserbeam profiles caused by alignment drifts or thermal problems. Spatial light modulators (SLM’s) are versatile devices that can modulate the polarization or the phase of laser beams at high refresh rates. It has been demonstrated that a SLM can be used to compensate for the thermal phase distortion occurring in high-energy glass amplifiers.3 Similarly, SLM’s have been used in high-energy laser applications, such as intracavity beam shaping4 or focal-spot control.5 In all these applications, only the phase-modulation capability of the SLM was used; however, there are numerous applications where phase-only modulation can be achieved differently. For instance, deformable mirrors are more attractive when it comes to wavefront correction of a large, high-energy, laser beam. Their scale and damage threshold allow them to be used within the power amplifier, while SLM’s are confined to the front end because of their modest size and low damage threshold. Nevertheless, a corrective device that would address both phase and amplitude simultaneously may be successfully used in high-energy lasers to significantly reduce the alignment procedure time, to improve the amplifier fill factor by injecting a more-adapted beam shape, to reduce the risk of damage in the laser chain by removing hot spots, and to improve the on-target characteristics of the beam by better... [continues]
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