Sodium Guidestar Lasers (SGLs) are an important element of adaptive-optics (AO) image correction techniques for astronomical observatories. In recent years, the astronomy community has employed Raman shifted fiber lasers to meet the need. However, emerging applications would greatly benefit by a reduction in the cost per Watt of on-sky power and the Size Weight and Power (SWAP) required by the laser. Small (meter-class) observatories seek to incorporate AO systems to meet space situational awareness and free space laser communication applications. Simultaneously, large (10 meter class) observatories require larger numbers of lasers on-sky to implement multi-conjugate AO systems. Optically pumped semiconductor lasers (OPSLs), also referred to as Vertical External Cavity Surface Emitting Lasers (VECSELs), represent a technology pathway to realizing Sodium Guidestar Lasers (SGL)s with high performance, compact size, high reliability, and low acquisition and maintenance costs. In pursuit of the next generation of SGL, we demonstrate <15W of single-frequency power at 589 nm based on in intracavity frequency doubling of 1178 nm fundamental wavelength VECSEL. Our work characterizes laser performance with an emphasis on suitability for guidestar laser applications. We examine, wavelength stability, linewidth, tuning and tuning agility and the ability to lock the laser to the sodium transition. In addition, we demonstrate simultaneous generation collinear beams with a frequency spacing of approximately 1.7 GHz.
The Mount Stromlo LGS facility includes two laser systems: a fiber-based sum-frequency laser designed and built by EOS Space Systems in Australia, and a Semiconductor Guidestar Laser designed and built by Aret´e Associates in the USA under contract with the Australian National University. The Beam Transfer Optics (BTO) enable either simultaneous or separate propagation of the two lasers to create a single LGS on the sky. This paper provides an overview of the Mount Stromlo LGS facility design, integration and testing of the two sodium guidestar lasers in the laboratory and on the EOS 1.8m telescope.
Over the last 30 years, Sodium Guidestar Lasers (SGLs) have proved to be an important element of adaptive-optics (AO) image correction techniques for astronomical observatories. In recent years, the astronomy community has employed Raman shifted fiber lasers to meet the need. However, emerging applications would greatly benefit by a reduction in the cost per Watt of on-sky power and the Size Weight and Power (SWAP) required by the laser. Small (meter-class) observatories seek to incorporate AO systems to meet space situational awareness and free space laser communication applications. Simultaneously, large (10 meter class) observatories require larger numbers of lasers on-sky to implement multi-conjugate AO systems, Further, techniques such as re-pumping and frequency-chirping are being developed to increase returns from the sky for a given laser power. The next generation of SGLs (Sodium Guidestar Lasers) must be suited for such modes of operation while reducing cost and SWAP. Optically pumped semiconductor lasers (OPSLs), also referred to as Vertical External Cavity Surface Emitting Lasers (VECSELs), represent a technology pathway to realizing SGLs with high performance, compact size, high reliability, and low acquisition and maintenance costs. In pursuit of the next generation of SGL, we demonstrate 8W of single-frequency power at 589 nm based on in intracavity frequency doubling of 1178 nm fundamental wavelength VECSEL. Our work investigates the key challenges of the laser design; especially frequency selection, tuning, and locking the laser to sodium resonance, laser power, and gain-mirror lifetime.
We demonstrate 104 Watts of in-band output power from a cascaded Raman fiber laser operating around 1.7 μm with a spectral purity of over 90% operating in both continuous wave and pulsed regimes. Through the use of a filter fiber with its cutoff wavelength designed between the 6th and 7th Stokes orders, output above 1.8 μm is suppressed below threshold values. In the pulsed regime the laser produces output pulses ranging from 11.5 mJ pulses with 100 μs pulse width to 10 J pulses with 100 ms pulse width.
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