Large-format Spatial Light Modulators for High Peak Power Lasers

Laser plasma accelerators and associated light sources, including high brightness x-ray generation through Compton backscattering, offer the potential for transformative applications in science, industry, medicine, homeland security, and future particle colliders. The beam power and efficiency of such systems is limited by our ability to correct for phase imperfections during amplification. Liquid Crystal on Silicon (LCoS) Spatial light modulators (SLMs) have the millions of pixels of phase control and 100 Hz speeds required for phase correction, but is currently unable to handle the average powers, fluences, and beam diameters of current and next-generation kW- class lasers. MLO already manufactures the largest and highest frame rate SLMs in the world. Building on this experience, we will build new large-area SLMs that can handle average powers at the few kW-level and energy densities of 250 mJ/cm2 for 30 fs pulses. Our strategy will use a combination of efficient active cooling, custom liquid crystal, improved construction, and increasing SLM size (30.7 x 30.7 mm in Phase 1, and 100 x 100 mm in Phase 2) to reduce peak fluence and average power density. Our high (>600 Hz) frame rates will allow for closed-loop control of the ~100 Hz perturbations from air turbulence and ground motions. We will perform peak power testing of our SLM materials using a 50 fs Ti:Sapphire laser (5 mJ/pulse), in collaboration with Prof. Jeff Squier of the Colorado School of Mines (a member of the ADAPT industry manufacturing consortium). We will focus on the liquid crystal itself, evaluating formulations customized to withstand high peak power. The best-performing material combination will be built into a working SLM design and peak power tested. In parallel with our peak power testing, MLO will redesign the SLM housing for improved heat dissipation. Using the optimum material construction identified in our peak power tests, we will build a fully working SLM and test its average power handling using a 400 W CW laser at 1070 nm. In Phase 2 we will design an SLM with active area up to 100 x 100mm, and test it at both high average powers and at high peak fluences. The SLMs developed in this work will find a broader market in pulsed laser machining/micro-milling applications, particularly those that rely on high peak fluences. SLMs are used in this field to produce custom beam profiles that can adapt as the machining process proceeds. Long-range communications and defense applications are also target markets for this design, which can be adapted for wavelengths from visible to mid-wave IR.