We report an eyesafe diffraction-limited single-frequency 1617 nm Er:YAG laser transmitter for coherent laser radar applications. The transmitter utilizes a master oscillator/power amplifier architecture, enabling the production of high peak power output. The pulsed oscillator is Q-switched and cavity-dumped, resulting in a 1.1 ns pulsewidth. The pulsed oscillator is injection-seeded by a commercial 1617 nm CW distributed feedback laser diode, resulting in single longitudinal mode output. The oscillator and amplifier are directly pumped into the Er:YAG laser upper state by commercial diode-pumped CW 1533 nm Yb,Er-doped fiber lasers. The injection-seeded pulsed oscillator produces an average output power of 2.2 W at 10 kHz pulse repetition frequency (PRF) with a pulsewidth of 1.1 ns (0.20 MW peak power) with a beam quality 1.1 times the diffraction limit. The oscillator has a slope efficiency of 47% in the CW mode, and a conversion efficiency of 85% from CW mode to injection-seeded pulsed mode. The power amplifier produces 20 W in the CW mode with an optical-to-optical conversion efficiency of 34% and a beam quality 1.1 times the diffraction limit, and 6.5 W in the pulsed mode at 10 kHz PRF with 1.1 ns pulsewidth (0.59 MW peak power).
We report the development of an eyesafe YAG laser for coherent laser radar wind sensing applications. The upper-state pumped 1.6 mm Er:YAG laser produces high pulse energies with diffraction-limited beam quality.
A novel high time-bandwidth product waveform lidar has been developed. The lidar operates at the eyesafe 2 micrometers wavelength and produces a sequence of two or more cavity- dumped pulselets with a controllable intra-pulse spacing. The number of and spacing for the individual pulselets is adjusted to match the target and atmospheric characteristics. This waveform agility enables the sensor to operate at very long stand-off ranges. Performance predictions and results from recent field demonstrations are described.
A CW Tm:YAG laser with a tuning range from 1.86 to 2.08 micrometers was used to create thermal lesions on chicken breast, calf liver, and porcine cornea. All tissue types were exposed to a constant irradiance (450 mW, 0.92 mm spot diameter, 0.5 and 1.0 second exposures) at five different wavelengths about the 2 micrometers water absorption peak. We estimated tissue absorption coefficients from the thermal history recorded by a 8 - 12 micrometers thermal camera. Our data confirmed that the absorption of all tissue types tested followed the water absorption curve. The effect of these differences in absorption upon the coagulation lesion size was evaluated by histologic measurements.
Broadly tunable cw laser emission is demonstrated at room temperature in the 1.85 - 2.15 micrometers and 2.20 - 2.45 micrometers regions from Tm:YALO solid-state laser with 795 nm diode laser pumping. Also efficient cw laser operation at room temperature is demonstrated from the Er<SUP>3+</SUP> in a garnet host at 2.8 microns, which is resonantly pumped with the 970 nm diode laser, resulting in a laser slope efficiency of 36%.
The 2.8-micrometers Er<sup>3+</sup>:YL<sub>F</sub> <sup>4</sup>I<sub>11/2</sub>yields<sup>4</sup>I<sub>13/2</sub> laser is shown to have higher efficiency for resonant pumping into the 970-nm absorption band than for the 800-nm pump band. The improved efficiency is due to the lower energy of the 970-nm pump radiation, and the avoidance of the self-quenching process <sup>4</sup>I<sub>9/2</sub>+<sup>4</sup>I<sub>15/2</sub>yields<sup>4</sup>I<sub>13/2</sub>+<sup>4</sup>I<sub>13/2</sub> which partially bypasses the upper laser state for 800-nm pumping. These advantages result from the direct pumping of the <sup>4</sup>I<sub>11/2</sub> upper laser state in the 970-nm pumping scheme.
Solid state lasers based on the trivalent thulium ion which operate
within the strong water absorption band in the 2zin region are
discussed. This water band has maximum absorption in the range 1.92-
1.94pm. The relative merits of thulium lasers in the crystalline
hosts YAG, YSGG, and YLF which operate in this wavelength region are
The 2-micron spectral region containing several strong molecular absorption bands such as carbon dioxide and water is reviewed. Tunable CW-laser action from resonantly pumped trivalent thulium is considered. A thulium-laser operating scheme is presented, and attention is given to the laser transition and laser cavity. The tuning range of a CW Tm:YAG laser at room temperature is analyzed, along with its output spectrum. Tunable laser performance in YAG codoped with trivalent thulium and trivalent holmium is investigated, and it is concluded that the output efficiency is better for the codoped laser than for the singly doped Tm(3+) laser in the range of 2.09 - 2.12 micron, but the overall tuning range and efficiency is better for the singly doped laser