The Coastal Zone Mapping and Imaging Lidar (CZMIL) system1 aims to expand bathymetric lidar performance in shallow water conditions, where high spatial and temporal data resolutions are required. This must be achieved without sacrificing performance in deep water. Very high frequency data collection (as high as 70KHz) utilizing a hybrid flash-point lidar approach is utilized, which places high demands on the transmitted laser beam, namely high pulse power with short duration with very high fidelity beam characteristics. To meet these requirements, we have developed a compact, high-power, short pulse length, high repetition rate laser with beam quality acceptable for use with the hybrid lidar approach employed in CZMIL. The short pulse length is achieved using a CW-pumped Q-switched oscillator, and the required power is achieved by using multiple amplifiers employing fiber coupled, CW end-pumped Nd:YVO4 crystals
prior to doubling the 1064 nm beam. The resulting output power is ~ 30W at 10 kHz with a pulse length of < 2.5 ns FWHM at 532 nm and ~ 20W of residual power at 1064 nm.
We report an optical parametric oscillator (OPO) system operating at 1574 nm using KTP crystals, with output peak
power of more than 5 megawatts, output pulse energy of up to 30 mJ per pulse, and pulse width of less than 6
nanoseconds at full width half maximum (FWHM). The OPO was pumped by a diode pumped Nd:YAG Q-switched
laser, with pump energy of about 95 mJ and pulse width of approximately 7 ns. The conversion efficiency from 1064 nm
Nd:YAG laser to OPO output at 1574 nm is more than 30%. The complete Nd:YAG / OPO system, compactly packed
inside a case with foot print measuring 15" × 9" × 5.3", was tested over an operating temperature range of -20 °C to +35
°C and a storage temperature range of -40 °C to +50 °C without significant power or performance variations.
We report the operation of an optical parametric oscillator (OPO) at 1574 nm using KTP, with output peak power of
more than 5 megawatts, output pulse energy of up to 30 mJ per pulse, pulse width of less than 6 nanoseconds at full
width half maximum (FWHM) and operating frequency of 30 Hz. The OPO was pumped by a diode pumped Nd:YAG
Q-switched laser, with pump energy of about 95 mJ and pulse width of approximately 7 ns. The conversion efficiency
from 1064 nm Nd:YAG laser to OPO output at 1574 nm is more than 30%. The whole system including the Nd:YAG
laser was compactly packed inside a case measuring 15" x 9" x 5.3". The complete OPO system was tested over an
operating temperature range of -20 °C to +35 °C and a storage temperature range of -40 °C to +50 °C without significant
power or performance variations, which makes it suitable for field operation.
We have developed a highly efficient Nd:YLF oscillator- amplifier operating at 10 Hz. The design of both the oscillator and amplifier is based on conduction-cooled QCW diode bar stacks and a total internal reflection pumping geometry. The oscillator is designed as a gain guided confocal unstable resonator. Maximum electrical to optical efficiencies of 8.3% and 8.8% are demonstrated in the oscillator and amplifier, respectively.
We have demonstrated the highest long-pulse efficiency and highest Q-switched energy reported to date for a Yb:S-FAP laser. THe Yb:S-FAP laser was pumped with a flashlamp pumped, free-running Cr:LiSAF laser. Threshold pump energy was extremely low, typically 30 mJ. Maximum output energy was 370 mJ at 1.047 micrometers with 650 mJ of pump incident on the Yb:S-FAP crystal. We obtained total optical-to-optical conversion efficiency of up to 57 percent in the long pulse mode. This is the highest conversion efficiency ever reported for this material in high energy, pulsed mode. Three samples of Yb:S-FAP of differing dimensions, doping, and crystal quality were tested. Two of the Yb:S-FAP crystals showing crystal defects experienced bulk damage during Q-switched mode of operation. The remaining crystal had the lowest dopant concentration of all the crystals, limiting the stored energy. Up to 65 mJ of output was obtained in this high-quality crystal, the highest ever reported in Q-switched mode with this laser material. Conversion efficiency at this energy level was 11.8 percent. However, the maximum efficiency obtained was 16.3 percent before pump bleaching effects started to occur due to low dopant concentration in this crystal sample.
The technique of Type I quadrature doubling has been used to generate 266 nm output from 532 nm input. Using a simple flashlamp pumped Nd:YAG laser doubled in KTP, the best conversion efficiency from the second harmonic to the fourth harmonic was 42% using two KDP crystals. With a second harmonic conversion efficiency of 60%, the total conversion efficiency from 1.064 micrometers to 266 nm was 25%. Output energies at 266 nm of up to 11.5 mJ in a nearly diffraction-limited beam, and 22 mJ in a multimode beam, were obtained, limited by the pump laser. The transient nonlinear absorption of 266 nm induced in the KDP crystals was measured in our samples, and the effect was accurately modelled to predict performance of a harmonic conversion system using improved nonlinear crystals.
A narrow band, tunable Cr:LiSAF laser oscillator using self injection- locking for line narrowing was developed. With two etalons and one prism in the master oscillator arm of the composite resonator, output energies of up to 75 mJ/pulse were obtained with a linewidth of 1.5 pm FWHM at 830 nm, and a pulsewidth of 70 ns. This linewidth was achieved without the use of a separate injection seed source. Up to 530 mJ output energy was obtained in long pulse, free-running mode. The laser was tuned from 800 nm to 960 nm. the Q-switched laser data was consistent with the performance predicted by our model.
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