Spaceborne laser instruments for high-resolution mapping

Anthony W. Yu, Michael A. Krainak, David J. Harding, James B. Abshire, Xiaoli Sun, Susan Valett, John Cavanaugh, Luis Ramos-Izquierdo, W. Andrew Clarkson, Norman Hodgson, Ramesh K. Shori
2010 Solid State Lasers XIX: Technology and Devices  
We report ytterbium-based disk amplifier for USPL using edgepumped architecture and offering excellent scalability to high-average power in kW-range. Edge-pumping [1] allows for reduced doping of crystals with laser ions, which translates to lower lasing threshold in quasi-3 level materials. The disk has a composite construction with undoped perimetral edge designed to channel pump light while efficiently outcoupling amplified spontaneous emission (ASE). Thermal management of the disk is
more » ... d by an innovative active heat sink with ultra-low thermal resistance. Uniform extraction of waste heat together with uniform pumping offers very low optical path distortion and allows for amplification of near diffraction limited beams. This work discusses modeling of the disk amplifier performance using a time-dependent 2-dimensional model for dynamic pumping and extraction. The model tracks tempral evolution of the upper level and ground state population density maps, ASE losses, amplification by chirped seed pulses in a multi-passed extraction, and optical distortions. Use of the model for determining optimum configuration the edge pumping array is discussed. Simulations of thermal performance of the disk and the heat sink are also included. This We report on the results of an experimental and theoretical investigation of the relevant performance attributes of Yb:YAG thin disk gain elements for use in high brightness resonators. We compare the laser operation, under extremely high pump and laser power densities, of crystalline thin disks to ceramic disks with and without undoped, amplified spontaneous emission (ASE) suppressing caps. The thin disks had between 120um and 150um thick doped regions, and the 1mm thick undoped caps were applied using chemically activated diffusion bonding. The disks were operated with impingement cooling either directly on the back (high Conference 7578: Solid State Lasers XIX: Technology and Devices Return to Contents The laser is capable of emitting more than 10 W of output power in a single-frequency, near-diffraction-limited beam. The output of this laser is frequency doubled using periodically poled MgO:LiNbO3 to generate in excess of 1.5 W of output power at 531 nm in a single-frequency, near-diffraction-limited beam. We investigate different configurations for generation of the green light and will present the use of the green light source for different applications. Red (631 nm), green (532 nm), and blue (448 nm) continuous-wave (CW) lasers have been developed by Evans & Sutherland (E&S). These multiwatt RGB lasers are used as light sources in E&S' laser projector (ESLP), which delivers ultrahigh-resolution content (8192 × 4096 pixels) to largesurface-area venues (e.g., planetariums, simulators, visualization centers, etc.). Efficient visible wavelength generation is obtained by coupling single-frequency near-infrared (NIR) beams into free-space enhancement cavities containing critically phase-matched lithium triborate (LBO) crystals. The NIR energy is produced by a master-oscillator-poweramplifier (MOPA) system which is fiber-based, thus yielding Gaussian beams which are near-ideal for efficient fundamental-to-harmonic conversion. Both polarization-maintaining (PM) fibers and non-PM fibers have been employed with non-PM fiber systems requiring polarization sensing and control. Green laser light is produced by a second-harmonic generation (SHG) process with a 1064 nm fundamental. Red laser light is produced by a sum-frequency mixing (SFM) process with 1064 nm and 1550 nm as fundamentals. Blue laser light is produced by an SFM process with 1064 nm and 775 nm as fundamentals, where 775 nm is first produced by an SHG process with a 1550 nm fundamental. All resulting visible lasers are single-axial-frequency with FWHM bandwidths less than 200 kHz, and are spatially pure with M² values less than 1.05. At least 18 W of CW optical power has been generated at all three visible wavelengths, with available NIR amplifier power as the primary limiting factor. A frequency-doubled disk laser emitting at 589 nm has a high potential for realising laser guide stars, which are useful for adaptive optics based telescopes. This wavelength range has been reached by using gain mirrors based on GaInAs quantum wells with a fundamental emission at 1178 nm. However, GaInAs-based quantum wells (QWs) possess high amount of lattice strain, potentially reducing the laser lifetime. The quantum well strain can be reduced by using dilute nitride, GaInNAs, where a small amount of nitrogen is added to the lattice. In this paper, we report progress towards demonstration of multi-watt 589-nm radiation based on high-power dilute nitride disk laser emitting at 1178 nm. The gain mirror was grown using a molecular beam epitaxy reactor and comprised 10 GaInNAs QWs and a 27-pair GaAs/AlAs distributed Bragg reflector. A 2.5 mm × 2.5 mm gain chip was attached to a wedged diamond heat spreader, which was also anti-reflective coated to reduce reflection at the air-diamond interface. The gain chip was first characterized in a V-shaped cavity without wavelength selective elements. Next, the gain chip characterized by forcing the operation wavelength to 1178 nm by an intra-cavity birefringent filter (BF). The maximum output powers in the free-running mode and with the BF were 7 W and 5 W, respectively, both limited by the cooling capacity of the gain chip mount. Using the BF, a continuous tuning range of more than 30 nm was achieved.
doi:10.1117/12.843191 fatcat:6ouzsdkdknh63ordfsktdz3lqq