MULTI-WAVELENGTH RAYLEIGH AND SODIUM BEACON

Ground-based satellite-imaging requires adaptive optics to mitigate atmospheric distortion. These systems utilize a laser guide-star in the upper atmosphere to produce a point source which can be used to measure the atmospheric distortion to the target of interest. Closed-loop correction requires sampling the atmospheric phase distortion at a Pulse Repetition Frequency (PRF) from ~2 to 4 kHz and at sufficient spatial resolution. Laser Beacons can be based on Rayleigh Scattering or excitation of the Sodium layer. Sodium guide-stars perform best due to the height of the sodium layer (80 to 100 km). However, sodium beacons require narrow-line excitation at the sodium D line. Rayleigh beacons are based on measuring non-resonant molecular or aerosol backscatter from the atmosphere. Due to the lambda-4 scaling of the scattering cross-section, Rayleigh beacons are most efficient in the ultraviolet. We developed a Master Oscillator/Power Amplifier architecture utilizing the new Distributed Gain Technology for diode-pumped solid-state lasers. Prior operation of a kW class, compact Distributed Gain Laser system capable of pulsed or CW operation demonstrates feasibility for the system proposed here. Specifically, we have developed a Conceptual Design of a Master Oscillator/Power Amplifier Distributed Gain laser capable of function as both a Rayleigh Beacon Laser at 532 and 355 nm or a Sodium Guidestar Laser at 589 nm. Rayleigh Beacon operation produces 10 nsec pulses at a user selectable pulse repetition frequency with a M2<1.3 for both 532 and 355 nm. The laser enables operation at the Sodium D-line with either pulsed or CW format by changing the master oscillator and sum frequency conversion module. Detailed simulations predict more than 10x increase in the average power (over 300 W) as either a Rayleigh Beacon or Sodium Guidestar beyond the current state of the art. Such an increase in brightness of the laser guidestar enables improved resolution and greater operational capability for both Ground Based Observatories and Space Situational Awareness. The Final Design, development, fabrication, assembly and test of a laboratory prototype of this Multi-wavelength Guidestar Laser will be conducted during this Direct to Phase II Program. The prototype shall include the electric power, thermal management and control systems for a complete laser system. We shall work with AFRL to integrate and test the system at the Starfire Optical Range (SOR) or other designated facility.