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Goddard Technology Efforts to Improve Space Borne Laser Reliability
In an effort to reduce the risk, perceived and actual, of employing instruments containing space borne lasers NASA initiated the Laser Risk Reduction Program (LRRP) in 2001. This program managed jointly by NASA Langley and NASA Goddard and employing lasers researchers from government, university and industrial labs is nearing the conclusion of its planned 5 year duration. This paper will describe some of the efforts and results obtained by the Goddard half of the program.
Independent Reliability Assessment of the Laser Transmitter for the ESA-NASA Laser Interferometer Space Antenna (LISA) Program
As part of the laser development process, NASA’s Goddard Space Flight Center (GSFC) requested support from the NASA Engineering and Safety Center (NESC) to independently assess the Technology Readiness Level (TRL) of the LISA Laser System (LS). The independent assessment included the following tasks: (a) assess the design for weaknesses and suggest improvements to mitigate risks, (b) assess the laser reliability plan for weaknesses and suggest improvements to mitigate risks and improve effectiveness, and (c) assess the current redundancy plan on laser subsystems for weaknesses and suggest improvements to mitigate risks and improve effectiveness. The presentation will focus on the assessment findings and the current development progress of the LISA laser to meet the mission requirements with a delivery of a form, fit, and functional TRL6 laser to the LISA mission by late 2023.
Reliable, laser-welded packaging of a Nd:YAG laser for spaceflight application
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Reliable, laser-welded packaging of a Nd:YAG laser for space application
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High Power Laser Diode Arrays for 2-Micron Solid State Coherent Lidars Applications
Laser diode arrays are critical components of any diode-pumped solid state laser systems, constraining their performance and reliability. Laser diode arrays (LDAs) are used as the pump source for energizing the solid state lasing media to generate an intense coherent laser beam with a high spatial and spectral quality. The solid state laser design and the characteristics of its lasing materials define the operating wavelength, pulse duration, and power of the laser diodes. The pump requirements for high pulse energy 2-micron solid state lasers are substantially different from those of more widely used 1-micron lasers and in many aspects more challenging [1]. Furthermore, the reliability and lifetime demanded by many coherent lidar applications, such as global wind profiling from space and long-range clear air turbulence detection from aircraft, are beyond the capability of currently available LDAs. In addition to the need for more reliable LDAs with longer lifetime, further improvement in the operational parameters of high power quasi-cw LDAs, such as electrical efficiency, brightness, and duty cycle, are also necessary for developing cost-effective 2-micron coherent lidar systems for applications that impose stringent size, heat dissipation, and power constraints. Global wind sounding from space is one of such applications, which is the main driver for this work as part of NASA s Laser Risk Reduction Program. This paper discusses the current state of the 792 nm LDA technology and the technology areas being pursued toward improving their performance. The design and development of a unique characterization facility for addressing the specific issues associated with the LDAs for pumping 2-micron coherent lidar transmitters and identifying areas of technological improvement will be described. Finally, the results of measurements to date on various standard laser diode packages, as well as custom-designed packages with potentially longer lifetime, will be reported.
Laser Holder Aids Centering of X-Ray Head
Laser holder used when alining X-ray head makes procedure safer and more reliable. Laser holder assembly attached to X-ray head to enable head to be alined optically before X-ray exposure. When laser in operating position laser beam shines on spot later illuminated with X-rays. New holder grips laser securely, maintains alinement, does not interfere with head placement, and requires only one 110-V power cord.
Power beaming research at NASA
NASA's current research activities to evaluate laser power beaming systems are summarized with regard to their applications of greatest interest. Key technical certainties and uncertainties pertaining to laser power beaming systems appropriate for space applications are quantified. A path of development is presented that includes maturation of key technology components for reliable laser and millimeter wave power beaming systems during the 1990s.
Linear FMCW Laser Radar for Precision Range and Vector Velocity Measurements
An all fiber linear frequency modulated continuous wave (FMCW) coherent laser radar system is under development with a goal to aide NASA s new Space Exploration initiative for manned and robotic missions to the Moon and Mars. By employing a combination of optical heterodyne and linear frequency modulation techniques and utilizing state-of-the-art fiber optic technologies, highly efficient, compact and reliable laser radar suitable for operation in a space environment is being developed. Linear FMCW lidar has the capability of high-resolution range measurements, and when configured into a multi-channel receiver system it has the capability of obtaining high precision horizontal and vertical velocity measurements. Precision range and vector velocity data are beneficial to navigating planetary landing pods to the preselected site and achieving autonomous, safe soft-landing. The all-fiber coherent laser radar has several important advantages over more conventional pulsed laser altimeters or range finders. One of the advantages of the coherent laser radar is its ability to measure directly the platform velocity by extracting the Doppler shift generated from the motion, as opposed to time of flight range finders where terrain features such as hills, cliffs, or slopes add error to the velocity measurement. Doppler measurements are about two orders of magnitude more accurate than the velocity estimates obtained by pulsed laser altimeters. In addition, most of the components of the device are efficient and reliable commercial off-the-shelf fiber optic telecommunication components. This paper discusses the design and performance of a second-generation brassboard system under development at NASA Langley Research Center as part of the Autonomous Landing and Hazard Avoidance (ALHAT) project.
Interchange for Joint Research Entitled: Miniature Laser Spectrometer for Stable Isotope Measurements
As a first step in successfully measuring carbon isotopes optically we have previously demonstrated the measurement of C-13/C-12 to a precision of 0.1% using a tunable diode laser and CO2 spectral lines in the 2300/cm spectral region. This precision of 0.1% (1 per mil) for carbon isotopes is a value sufficiently precise to provide important isotopic data of interest to astrobiologists. The precision presently attainable in gases is sufficient to permit our instrument to be used in the measurement of isotopic ratios of interest to astrobiologists as well as geologists and planetary scientists. A small stable isotope laser spectrometer with a 10 cm path gas cell was designed and constructed. The cell was integrated with a liquid nitrogen cooled tunable diode laser and indium antimonide detector for evaluation. Using the small gas cell, preliminary measurements of 13C/12C in CO2 were made employing single-beam sequential acquisitions of the required spectral data. The results indicate an accuracy of 0.1% which is sufficiently high to make meaningful measurements of martian samples. In addition, improvements in the spectrometer gas handling system have been made to markedly reduce C-13/C-12 isotopic fractionation during sample gas cell loading which we expect will lead to further improvements in precision and accuracy. An important part of making isotopic ratio measurements in solid samples using diode lasers is the conversion of the elements of interest to molecules that have absorption spectra in the mid-ir spectral range accessible by tunable diode lasers. In this project we have investigated the necessary sample preparation procedures to extract carbon, an element of astrobiological importance, from model soil compounds and to convert it to CO2, a molecule with appropriate optical absorption characteristics for reliable laser spectrometer isotopic ratio measurements of 13C/12C. We have considered calcium carbonate as a model for a component of the martian regolith, and we have formulated a simple heating protocol for extracting carbon in the form of CO2.
Laser Oscillator Incorporating a Wedged Polarization Rotator and a Porro Prism as Cavity Mirror
A laser cavity was designed and implemented by using a wedged polarization rotator and a Porro prism in order to reduce the parts count, and to improve the laser reliability. In this invention, a z-cut quartz polarization rotator is used to compensate the wavelength retardance introduced by the Porro prism. The polarization rotator rotates the polarization of the linear polarized beam with a designed angle that is independent of the orientation of the rotator. This unique property was used to combine the retardance compensation and a Risley prism to a single optical component: a wedged polarization rotator. This greatly simplifies the laser alignment procedure and reduces the number of the laser optical components.
Reliability of scanning laser acoustic microscopy for detecting internal voids in structural ceramics
The reliability of 100 MHz scanning laser acoustic microscopy (SLAM) for detecting internal voids in sintered specimens of silicon nitride and silicon carbide was evaluated. The specimens contained artificially implanted voids and were positioned at depths ranging up to 2 mm below the specimen surface. Detection probability of 0.90 at a 0.95 confidence level was determined as a function of material, void diameter, and void depth. The statistical results presented for void detectability indicate some of the strengths and limitations of SLAM as a nondestructive evaluation technique for structural ceramics.
Reliability of scanning laser acoustic microscopy for detecting internal voids in structural ceramics
The reliability of 100 MHz scanning laser acoustic microscopy (SLAM) for detecting internal voids in sintered specimens of silicon nitride and silicon carbide was evaluated. The specimens contained artificially implanted voids and were positioned at depths ranging up to 2 mm below the specimen surface. Detection probability of 0.90 at a 0.95 confidence level was determined as a function of material, void diameter, and void depth. The statistical results presented for void detectability indicate some of the strengths and limitations of SLAM as a nondestructive evaluation technique for structural ceramics.
Cometary particulate analyzer design definition study
A concept for remotely determining the relative abundance of elements contained in cometary particulates collected by a spacecraft was conducted with very encouraging results. The technique utilizes a short high intensity burst of laser radiation to vaporize and ionize collected particulate material. Ions extracted from this laser-produced plasma are analyzed in a time of flight mass spectrometer to yield an atomic mass spectrum representative of the relative abundance of elements in the particulates. A prototype analyzer system was designed, constructed, and tested. Results show that: (1) energy-time focus performs as predicted in improving resolution; (2) power densities sufficient to produce usable ionization efficiencies can be obtained; (3) complex alloys such as stainless steel can be analyzed; and (4) a tiny, simple and reliable laser used in the demonstration easily meets spacecraft power and mass limitations. A mass resolution of 150 was experimentally demonstrated at mass 108, and an analytical extrapolation predicts a resolution sufficient to separate masses 250 and 251.
AlGaAs heterojunction lasers
The characterization of 8300 A lasers was broadened, especially in the area of beam quality. Modulation rates up to 2 Gbit/sec at output powers of 20 mW were observed, waveform fidelity was fully adequate for low BER data transmission, and wavefront measurements showed that phase aberrations were less than lamda/50. Also, individually addressable arrays of up to ten contiguous diode lasers were fabricated and tested. Each laser operates at powers up to 30 mW CW in single spatial mode. Shifting the operating wavelength of the basic CSP laser from 8300 A to 8650 A was accomplished by the addition of Si to the active region. Output power has reached 100 mW single mode, with excellent far field wave front properties. Operating life is currently approx. 1000 hrs at 35 mW CW. In addition, laser reliability, for operation at both 8300 A and 8650 A, has profited significantly from several developments in the processing procedures.
Three Year Aging of Prototype Flight Laser at 10 Khz and 1 Ns Pulses with External Frequency Doubler for the Icesat-2 Mission
We present the results of three year life-aging of a specially designed prototype flight source laser operating at 1064 nm, 10 kHz, 1ns, 15W average power and external frequency doubler. The Fibertek-designed, slightly pressurized air, enclosed-container source laser operated at 1064 nm in active Q-switching mode. The external frequency doubler was set in a clean room at a normal air pressure. The goal of the experiment was to measure degradation modes at 1064 and 532 nm discreetly. The external frequency doubler consisted of a Lithium triborate, LiB3O5, crystal operated at non-critical phase-matching. Due to 1064 nm diagnostic needs, the amount of fundamental frequency power available for doubling was 13.7W. The power generated at 532 nm was between 8.5W and 10W, depending on the level of stress and degradation. The life-aging consisted of double stress-step operation for doubler crystal, at 0.35 J/cm2 for almost 1 year, corresponding to normal conditions, and then at 0.93 J/cm2 for the rest of the experiment, corresponding to accelerated testing. We observed no degradation at the first step and linear degradation at the second step. The linear degradation at the second stress-step was related to doubler crystal output surface changes and linked to laser-assisted contamination. We discuss degradation model and estimate the expected lifetime for the flight laser at 532 nm. This work was done within the laser testing for NASA's Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) LIDAR at Goddard Space Flight Center in Greenbelt, MD with the goal of 1 trillion shots lifetime.
Optimized Biasing of Pump Laser Diodes in a Highly Reliable Metrology Source for Long-Duration Space Missions
Optical metrology system reliability during a prolonged space mission is often limited by the reliability of pump laser diodes. We developed a metrology laser pump module architecture that meets NASA SIM Lite instrument optical power and reliability requirements by combining the outputs of multiple single-mode pump diodes in a low-loss, high port count fiber coupler. We describe Monte-Carlo simulations used to calculate the reliability of the laser pump module and introduce a combined laser farm aging parameter that serves as a load-sharing optimization metric. Employing these tools, we select pump module architecture, operating conditions, biasing approach and perform parameter sensitivity studies to investigate the robustness of the obtained solution.
Reliability of High Power Laser Diode Arrays Operating in Long Pulse Mode
Reliability and lifetime of quasi-CW laser diode arrays are greatly influenced by their thermal characteristics. This paper examines the thermal properties of laser diode arrays operating in long pulse duration regime.