Analytic approximations for key parameters of passively
Q
-switched (PQS) lasers, such as pulse energy and duration, were developed and widely tested in particular for microchip lasers with semiconductor saturable absorbers. However, the same approach can be readily extended to PQS lasers using Cr:YAG as the saturable absorber, including excited-state absorption (ESA) in the model. ESA causes a reduction of pulse energy and an increase in pulse duration. Interestingly, performances of many previously reported PQS lasers using Cr:YAG, from microchips to more powerful multi-millijoule lasers, are correctly predicted by this simple model. Unlike energy estimation, which is intrinsically robust, pulse width requires a more careful evaluation of the influence of the ratio (total linear loss)/(saturable loss) as a correction of the asymptotic result.
A compact diode-pumped Nd:YVO ring laser was developed for generation of relatively long (few tens nanoseconds) single-frequency pulses for high-spectral-resolution LIDAR applications. Exploiting the feedback from an external mirror and Cr:YAG passive Q-switching with pulsed pump, unidirectional single-frequency operation with high quality ∼50-ns, 80-µJ TEM pulses was achieved from 100 Hz to 10 kHz. Amplitude, duration and repetition rate stability of the pulses was better than 1%.
A stable, narrow-bandwidth (274 MHz) backward wave optical parametric oscillator (BWOPO) generating mJ-level backward signal at 1885nm and forward idler at 2495 nm is presented. The BWOPO was pumped by a single-longitudinal mode, Q-switched Nd:YAG high-energy laser at 1064 nm. We show that multi-transversal mode pumping leads to the spectral broadening of the BWOPO backward signal and the generation of nanosecond pulses 2.7 times above the Fourier transform limit. We demonstrate over 100 GHz continuous tuning of the parametric output by adjusting the temperature of the BWOPO crystal, showcasing the significant role of thermal expansion in tuning performance. The BWOPO signal was used as a seed for a single-stage PPRKTP optical parametric amplifier (OPA) to boost the narrowband signal and idler energies to 20 mJ. This combination of mJ-level BWOPO seed with a single-stage PPRKTP OPA comprises a simple concept that would benefit long-range differential absorption lidar (DIAL) in the near and mid-infrared regions.
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