Diode-pumped alkali metal vapor lasers (DPAL) offer significant promise for high average power. The DPAL system has high gain and will high output coupling and an unstable resonator to achieve excellent beam quality. We analyze the Rb-He system using average equations for the pump, laser and populations, including amplified spontaneous emission. We extend the formulation to include flow and temperature release and study its effects on the laser efficiency and beam quality. The design and analysis of the DPAL resonator and the influence of spatial variations in gain medium on far field beam quality are developed. A systematic study of the influence of gain medium aberrations, flow geometry, and resonator design on far field beam quality is reported. The relative advantages of longitudinal and transverse flow geometries to beam quality are evaluated. Finally, coupling of the pump and laser radiation fields is dramatic in the DPAL system. The standard approaches to merging CFD analysis of the gain medium with wave optics resonator simulations will require new techniques.
The high gain Diode Pumped Alkali Laser (DPAL) system will require an unstable resonator with high Fresnel number and high output coupling to achieve excellent beam quality. Coupling of the diode pump and laser radiation fields is dramatic in the DPAL system. Merging flow field analysis of the gain medium with wave optics resonator simulations requires new techniques. We develop a wave-optics simulation of confocal, positive-branch unstable resonators for the DPAL gain media to assess the limitations on far field beam quality. The design and analysis of the DPAL resonator and the influence of spatial variations in gain medium on far field beam quality are developed. The relative advantages of longitudinal and transverse flow geometries to beam quality are evaluated. A systematic study of the influence of gain medium aberrations, flow geometry, magnification, and resonator design on far field beam quality is reported.
Studies of the ultrafast (< 100 fs) interactions of infrared, sub-100 fs laser pulses with IR, photosensitive semiconductor materials InGaAs, InSb, and HgCdTe are reported. Both the carrier dynamics and the associated Terahertz radiation from these materials are discussed. The most recent developments of femtosecond (< 100 fs) Optical Parametric Oscillators has extended the wavelength range from the visible to 5.2 micrometers . The photogenerated semiconductor free carrier dynamics are determined in the 77 to 300 degree(s)K temperature range using the Transmission Correlation Peak (TCP) method. The electron-phonon scattering times are typically 200 - 600 fs. Depending upon the material composition and substrate on which the IR crystalline materials are deposited, the nonlinear TCP absorption gives recombination rates as fast as 10's of picoseconds. For the HgCdTe, there exists a 400 fs electron-phonon scattering process along with a much longer 3600 fs loss process. Studies of the interactions of these ultrashort laser pulses with semiconductors produce Terahertz (THz) radiative pulses. With undoped InSb, there is a substantial change in the spectral content of this THz radiation between 80 - 260 degree(s)K while the spectrum of Te-doped InSb remains nearly unchanged, an effect attributed to its mobility being dominated by impurity scattering. At 80 degree(s)K, the terahertz radiation from undoped InSb is dependent on wavelength, with both a higher frequency spectrum and much larger amplitudes generated at longer wavelengths. No such effect is observed at 260 degree(s)K. Finally, new results on the dependence on the emitted THz radiation on the InSb crystal's orientation is presented.
The performance of a repetitively pulsed, 70 joule, closed cycle 1.3 (mu) M photolytic atomic iodine laser with excellent beam quality (BQ equals 1.15) is presented. This BQ was exhibited in the fundamental mode from a M equals 3.1 confocal unstable resonator at a 0.5 Hz repetition rate. A closed cycle scrubber/laser fuel system consisting of a condensative- evaporative section, two Cu wool I2 reactor regions, and an internal turbo-blower enabled the laser to operate very reliably with low maintenance. The fuel system provided C3F7I gas at 10 - 60 torr absent of the photolytic quenching by-product I2. Using a turbo- molecular blower longitudinal flow velocities greater than 10 m/s were achieved through the 150 cm long by 7.5 multiplied by 7.5 cm2 cross sectional photolytic iodine gain region. In addition to the high laser output and excellent BQ, the resulting 8 - 12 microsecond laser pulse had a coherence length greater than 45 meters and polarization extinction ratio better than 100:1. Projections from this pulsed photolytic atomic iodine laser technology to larger energies, higher repetition rates, and variable pulse widths are discussed.
The recent development of femtosecond optical parametric oscillators has extended the wavelength range over which ultrafast lasers are available (visible to 3.5 micrometers has been demonstrated). The options in cavity configurations, phase matching, and nonlinear optical crystals used with a Ti:sapphire pump laser are discussed. Results of an OPO using the nonlinear crystal KTiOAs4, which is potentially tunable to 5 micrometers , are presented.
The performance of a repetitively pulsed, high energy, closed cycle photolytic atomic iodine lasers at 1.315 microns is presented. Using an I2 removal system for the photolyzed C3F7I laser fuel, more than 70 joules/pulse was acquired in the fundamental mode from a M equals 3 confocal unstable resonator at a 0.5 Hz repetition rate. The closed cycle chemical scrubber system consisted of a condensative-evaporative section, two Cu wool I2 reactor sections, and an internal turbo-blower. This closed cycle system provided C2F7I gas at 10 - 60 torr absent of I2. The turbo-blower produced longitudinal flow velocities greater than 10 m/s through the 150 cm long by 7.5 X 7.5 cm2 cross sectional photolytic iodine gain region. In addition to the high energy output, the resulting 10 - 12 microsecond(s) ec laser had a beam quality of less than 1.5 times diffraction limited with a coherence length greater than 45 meters, and a polarization extinction ratio better than 100:1. Projections from this pulsed photolytic atomic iodine laser technology to larger energies, high repetition rates, and variable pulsewidths are discussed. In addition, the performance of cw photolytically excited atomic iodine laser at 1.315 micrometers is reported which has excellent scaling potential. Volumetric extractable cw powers of 55 watts/liter are reported with a small signal gain coefficient of 2%/cm. The potential of enhancing the cw powers to kilowatt levels plus producing variable pulsewidth, repetition rate iodine laser using an internal electro-optical modulator are also discussed.
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