George E. Busch

First operation of a photocathode radio frequency gun injector at high duty factor

Tests of the electron beam injector for the Boeing/Los Alamos Average Power Laser Experiment have demonstrated first time operation of a photocathode radio frequency gun accelerator at 25% duty factor, exceeding previous photocathode operating parameters by three orders of magnitude. The macropulse format was 30 Hz and 8.3 ms with a micropulse frequency of 27 MHz. Average beam currents of up to 32 mA have been accelerated to 5 MeV for an average beam power of 160 kW. The macropulse peak current was 128 mA. The 32 mA average beam current exceeds previous cathode performance by a factor of 1000. Emittance measurements demonstrate excellent electron beam quality.

Utilization of 3-D Imaging Flash Lidar Technology for Autonomous Safe Landing on Planetary Bodies

NASA considers Flash Lidar a critical technology for enabling autonomous safe landing of future large robotic and crewed vehicles on the surface of the Moon and Mars. Flash Lidar can generate 3-Dimensional images of the terrain to identify hazardous features such as craters, rocks, and steep slopes during the final stages of descent and landing. The onboard flight comptuer can use the 3-D map of terain to guide the vehicle to a safe site. The capabilities of Flash Lidar technology were evaluated through a series of static tests using a calibrated target and through dynamic tests aboard a helicopter and a fixed wing airctarft. The aircraft flight tests were perfomed over Moonlike terrain in the California and Nevada deserts. This paper briefly describes the Flash Lidar static and aircraft flight test results. These test results are analyzed against the landing application requirements to identify the areas of technology improvement. The ongoing technology advancement activities are then explained and their goals are described.

Processing of 3-Dimensional Flash Lidar Terrain Images Generated From an Airborne Platform

Data from the first Flight Test of the NASA Langley Flash Lidar system have been processed. Results of the analyses are presented and discussed. A digital elevation map of the test site is derived from the data, and is compared with the actual topography. The set of algorithms employed, starting from the initial data sorting, and continuing through to the final digital map classification is described. The accuracy, precision, and the spatial and angular resolution of the method are discussed.

High-speed random access laser tuning

We have developed a technique for laser tuning at rates of 100 kHz or more using a pair of acousto-optic modulators. In addition to all-electronic wavelength control, the same modulators also can provide electronically variable Q-switching, cavity length and power stabilization, chirp and linewidth control, and variable output coupling, all at rates far beyond what is possible with conventional mechanically tuned components. Tuning rates of 70 kHz have been demonstrated on a radio-frequency-pumped CO2 laser, with random access to over 50 laser lines spanning a 17% range in wavelength and with wavelength discrimination better than 1 part in 1000. A compact tuner and Q-switch has been deployed in a 5-10-kHz pulsed lidar system. The modulators each operate at a fixed Bragg angle, with the acoustic frequency determining the selected wavelength. This arrangement doubles the wavelength resolution without introducing an undesirable frequency shift.

The Los Alamos FEL photoinjector drive laser

The drive laser system of the photoelectric injector for the Los Alamos free-electron laser (FEL) is described. This system consists of a 1.053 mu m mode-locked Nd:YLF oscillator, a grating-rhomb pulse compressor, a fast electrooptic shutter to reduce pulse repetition frequency, a pulsed Nd:YLF amplifier chain, and a KTP frequency doubler. The bright electron beams required for high performance FELs demand stringent specifications on drive laser output levels, beam quality, and stability. The design specifications, laser architecture, and operating performance following the most recent round of upgrades are presented. >

Up conversion measurements in Er:YAG; comparison with 1.6 μm laser performance

Up conversion significantly affects Er:YAG lasers. Measurements performed here for low Er concentration are markedly different than reported high Er concentration. The results obtained here are used to predict laser performance and are compared with experimental results.

Comprehensive system model for CO2 DIAL

The Simulation and Optimization Numerics for DIAL (SONDIAL) code is described. An overview of the code structure is given consisting of individual models for the lidar hardware linked to a set of models for the natural environment through which the laser energy must traverse. The affects of the environment are contained in the field models. A detailed description of the field models is given including the effects of the atmosphere, plume and target on the return statistics of the radiation. The atmosphere attenuates and scatters the laser light. Atmospheric extinction has both spectral and temporal structure that can cause bias and correlation in the DIAL measurements. The results of FASCODE calculations utilizing the HITRAN database are used to assess the magnitude of these effects. Atmospheric turbulence spatially modulates the intensity footprint at the target and modifies the statistics of the return light collected by the receiver aperture. The roughness of the target produces speckle at the receiver, the statistics of which are given by the intensity distribution on the target surface. An albedo model that includes the effects of (macroscopic) spatial reflectivity variations of typical natural targets on the system single-shot signal-to-noise ratio is described. To address the effect of footprint size and position on effluent detection sensitivity, an overlap calculation between a Gaussian plume model and the optical footprint is performed. Validation comparisons between the model and experimental data are given.

Measurement of Up Conversion in Er:YAG and Influence on Laser Performance

Up conversion significantly affects Er:YAG lasers, particularly when Q-switching. Measurements performed here using low Er concentration materials are significantly different than those reported using high Er concentrations. Analytical results are compared with experimental data and used to predict laser performance.

Acousto-optically tuned isotopic CO2 lasers for long-range differential absorption lidar

We are developing 2-100 kHz repetition rate CO2 lasers with milliJoule pulse energies, rapid acousto-optic tuning and isotopic gas mixes, for differential absorption LIDAR applications. We explain the tuning method, which uses a pair of acousto-optic modulators and is capable of random access to CO2 laser lines at rates of 100 kHz or more. The laser system is also described, and we report on performance with both normal and isotopic gas mixes.

Progress of the Average Power Laser Experiment (APLE) program

Abstract The Average Power Laser (APLE) is a high power free-electron laser demonstration. This paper summarizes progress in the design and selected component testing for a 10 kW oscillator, which is the precursor to a 100 kW oscillator-amplifier system.