We present a record brightness of 0.3 PW/(sr∙cm2) using a passively cooled Nd:YAG/Cr4+:YAG microchip laser at 10 Hz. It delivers a peak power of 26.4 MW, an energy of 10.5 mJ, a pulse duration of 398 ps, and a M2 value of 2.7. The achieved brightness, utilizing an unstable resonator and a Gaussian mirror with a maximal reflection of 60%, exceeds that of a conventional flat-flat resonator by over 20 times at the same peak power. This increase enables a 150 mm long-focusing air-breakdown and a 7-point air-breakdown, suitable for multi-point ignition and multi-point Laser Induced Breakdown Spectroscopy (LIBS).
We present an air-cooled unstable cavity Nd:YAG/Cr4+:YAG ceramic microchip laser generating pulses with an energy of 22.54 mJ, a duration of 313.5 ps, and a beam quality M2 of 5.79 at 100 Hz, corresponding a record peak power of 71.9 MW and a record brightness of 189.5 TW/(sr∙cm2). However, the small but high intensity center peak of Bessel-like far-field beam can increase the brightness effectively up to 884 TW/(sr∙cm2) with a long effective Rayleigh range. No significant degradation of laser characteristics was confirmed during power scaling in contrast to common flat-flat resonators, promising further brightness scale-up without amplifier.
Long-time operation of passively Q-switched monolithic Nd:YAG/Cr4+:YAG ceramic microchip lasers was carried out to test the durability as a laser ignitor of internal combustion engines. The pulse energies of three microchip lasers were monitored, operating at three different configurations of repetition rates and temperatures: 20 Hz/room temperature, 20 Hz/90°C, and 80 Hz/ room temperature. No significant degradation of 3 mJ level output energies was observed over 32,000 hours or 3.6 years for the all operating conditions.
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