Abstract

The importance of heat-resistant optics is increasing together with the average power of high-intensity lasers. A silicon carbide (SiC) ceramic with high thermal conductivity is proposed as an optics substrate to suppress thermal effects. The temperature rise of the substrate and the change in the surface accuracy of the mirror surface, which degrades the laser beam quality, are investigated. Gold mirrors on synthetic fused silica and SiC ceramic substrates are heated with a 532 nm wavelength laser diode. The synthetic fused silica substrate placed on an aluminum block shows a temperature increase by ~32 °C and a large temperature gradient. In contrast, the SiC ceramic substrate shows a uniform temperature distribution and a temperature increase of only ~4 °C with an absorbed power of ~2 W after 20 min laser irradiation. The surface accuracy (roughness) when using the synthetic fused silica substrate changes from /21.8 (29.0 nm) to /7.2 (88.0 nm), increasing by a factor of ~3.0. However, that of the SiC ceramic substrate changes from /21.0 (30.2 nm) to /13.3 (47.7 nm), increasing by only a factor of ~1.6. Based on these experimental results, detailed considerations and calculations of actively cooled SiC ceramic substrates for high-average-power laser systems are also discussed.

Highlights

  • Controlling the surface accuracy of optics under high thermal load is crucial for the stable operation of laser systems

  • The surface of the chemical vapor deposition (CVD) silicon carbide (SiC) ceramic is used for the mirror because the smaller grain size of CVD SiC ceramic is suitable for polishing with high surface accuracy

  • High performance of a SiC ceramic substrate is experimentally demonstrated under high thermal load due to laser irradiation

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Summary

Introduction

Controlling the surface accuracy of optics under high thermal load is crucial for the stable operation of laser systems. Chirped pulse amplification (CPA) has allowed lasers with high peak power to be constructed [1]. In CPA systems, optics downstream of the pulse compressor are placed in a vacuum to avoid air dispersion self-focusing effects. Laser facilities with petawatt or higher peak power have been built worldwide to achieve higher peak intensity experiments [2]. Practical applications and efficient data acquisition require a high peak power and high repetition rate. There is recently rapid development of petawatt laser systems with higher repetition rates based on the Ti:sapphire gain medium; examples include the lasers at Colorado State University with a peak power of 0.85 PW at 3.3 Hz [3] and Lawrence Livermore National Laboratory with a planned peak power of 1 PW at

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