Measuring single-shot, picosecond optical damage threshold in Ge, Si, and sapphire with a 5.1-μm laser

Optical photonic structures driven by picosecond, GW-class lasers are emerging as promising novel sources of electron beams and high quality X-rays. Due to quadratic dependence on wavelength of the laser ponderomotive potential, the performance of such sources scales very favorably towards longer drive laser wavelengths. However, to take full advantage of photonic structures at mid-IR spectral region, it is important to determine optical breakdown limits of common optical materials. To this end, an experimental study was carried out at a wavelength of 5 μm, using a frequency-doubled CO₂ laser source, with 5 ps pulse length. Single-shot optical breakdowns were detected and characterized at different laser intensities, and damage threshold values of 0.2, 0.3, and 7.0 J/cm², were established for Ge, Si, and sapphire, respectively. The measured damage threshold values were stable and repeatable within individual data sets, and across varying experimental conditions.