We report on the cause and corrective actions of three amplifier crystal fractures in the space-qualified laser systems used in NASA Goddard Space Flight Center’s (GSFC) Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2). The ICESat-2 lasers each contain three end-pumped Nd:YVOO4 amplifier stages. The crystals are clamped between two gold plated copper heat spreaders with an indium foil thermal interface material, and the crystal fractures occurred after multiple years of storage and over a year of operational run-time. The primary contributors are high compressive loading of the NdYVO4 crystals at the beginning of life, a time dependent crystal stress caused by an intermetallic reaction of the gold plating and indium, and slow crack growth resulting in a reduction in crystal strength over time. An updated crystal mounting scheme was designed, analyzed, fabricated and tested. Thee fracture slab failure analysis, finite-element modeling and corrective actions are presented.
We present the results of a three-year operational-aging test of a specially designed prototype flight laser operating at 1064 nm, 10 kHz, 1ns, 15W average power and externally frequency-doubled. Fibertek designed and built the q-switched, 1064nm laser and this laser was in a sealed container of dry air pressurized to 1.3 atm. The external frequency doubler was in a clean room at a normal air pressure. The goal of the experiment was to measure degradation modes at 1064 and 532 nm separately. The external frequency doubler consisted of a Lithium triborate, LiB3O5, non-critically phase-matched crystal. After some 1064 nm light was diverted for diagnostics, 13.7W of fundamental power was available to pump the doubling crystal. Between 8.5W and 10W of 532nm power was generated, depending on the level of stress and degradation. The test consisted of two stages, the first at 0.3 J/cm2 for almost 1 year, corresponding to expected operational conditions, and the second at 0.93 J/cm2 for the remainder of the experiment, corresponding to accelerated optical stress testing. We observed no degradation at the first stress-level and linear degradation at the second stress-level. The linear degradation was linked to doubler crystal output surface changes from laser-assisted contamination. We estimate the expected lifetime for the flight laser at 532 nm using fluence as the stress parameter. This work was done 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.
We report on the completion of the space qualification testing program for NASA Goddard Space Flight Center’s
(GSFC) Ice, Cloud, and Land Elevation Satellite 2 (ICESat-2) program. This paper describes the final performance
results of the fully integrated (laser and electronics) flight laser system with an emphasis on the system design evolution
from a breadboard demonstration to a fully space-qualified laser system. The 532 nm ICESat-2 laser transmitter
generates diffraction limited pulse energies of 1 mJ, pulsewidths of < 1.5 ns, and 10 kHz pulse repetition frequency and
has minimum lifetime of 1 trillion pulses on-orbit. A combination of engineering design units and correlated structural
thermal optical analysis was used to systematically improve reliability and performance over the operating environment.
The laser system qualification and acceptance test programs included electromagnetic interference (EMI), vibration, and
thermal vacuum (TVAC) testing. This paper presents key laser performance results and lessons learned on the multi-year
laser development to facilitate future space-qualified laser developments, improve reliability, and increase performance.
Fibertek is under contract from NASA Goddard to build four space qualified laser transmitters for the ICESat-2 (Ice, Cloud, and Land Elevation Satellite) program, a second generation orbiting laser altimeter. Pertinent laser parameters driving the design included laser wall plug efficiency, laser reliability, a relatively narrow linewidth with wavelength tunability, high beam quality (M2<1.6), short pulsewidths (<1.5ns), and energy scalable from 250 μJ to 900μJ in predefined steps. The laser design employs fiber coupled 880nm diodes and end-pump Nd:YVO4 slabs as the gain medium in a master oscillator/power amplifier (MOPA) architecture with an LBO second harmonic generator (SHG). Following the SHG is a telescope that sets the final beam size and divergence requirements. The first laser built will be the Integration and Test Laser (ITL) used for qualification of the design. The ITL will set the baseline parameters for the flight laser builds. The ITL will also validate the design for the telescope and will be subjected to the full environmental testing required for a space hardened flight laser. Environmental testing includes vibration, thermal vacuum conditions, and electromagnetic interference (EMI). Our presentation will address the measured laser parameters from ITL as compared to the as designed laser.
The design of space-flight hardware is typically required to be at a Technology Readiness Level (TRL) of 6 before the build of the actual flight hardware can begin. At the early design phase the "relevant environment" for TRL-6 is frequently not well defined. For the ICESat-2 laser relevant environment was defined as the qualification levels in GEVS (General Environmental Verification Standard, GSFC-STD-7000). Our approach to dealing with the high-frequency content of the 14.1 grms random vibration levels in GEVS was a flexure mounted canister design that filtered the highfrequency content. In our talk we will discuss the program and system level implications of this design approach.
A number of ICESat-2 system requirements drove the technology evolution and the system architecture for the laser transmitter Fibertek has developed for the mission.. These requirements include the laser wall plug efficiency, laser reliability, high PRF (10kHz), short-pulse (<1.5ns), relatively narrow spectral line-width, and wave length tunability. In response to these requirements Fibertek developed a frequency-doubled, master oscillator/power amplifier (MOPA) laser that incorporates direct pumped diode pumped Nd:YVO4 as the gain media, Another guiding force in the system design has been extensive hardware life testing that Fibertek has completed. This ongoing hardware testing and development evolved the system from the original baseline brass board design to the more robust flight laser system. The final design meets or exceeds all NASA requirements and is scalable to support future mission requirements.
Fibertek has developed an environmentally hardened Technology Readiness Level-6 laser transmitter system for the NASA Ice, Cloud and land Elevation Satellite-2 (ICESat-2). The laser transmitter generates over 9 W of 532 nm output with a pulse repetition rate of 10kHz and a FWHM pulse width of < 1.5 ns with an expected lifetime of > 1 trillion shots. This paper presents the results of the Structural, Thermal and Optical analysis, details on the NASA General Environmental Verification Specification testing requirements, and the success of the laser transmitter performance through vibration and thermal vacuum testing.
The increasing use of lidar remote sensing systems in the limited power environments of unmanned aerial vehicles and
satellites is motivating laser engineers and designers to put a high premium on the overall efficiency of the laser
transmitters needed for these systems. Two particular examples upon which we have been focused are the lasers for the
ICESat-2 mission and for the Laser Vegetation Imaging Sensor-Global Hawk (LVIS-GH) system. We have recently
developed an environmentally hardened engineering unit for the ICESat-2 laser that has achieved over 9 W of 532 nm
output at 10 kHz with a wall plug efficiency to 532 nm of over 5%. The laser has a pulse width of <1.5 ns and an M2 of
<1.5. For the LVIS-GH lidar, we recently delivered a 4.2 W, 2.5 kHz, 1064 nm laser transmitter that achieved a wall
plug efficiency of 8.4%. The laser has a pulse width of 5 ns and an M2 of 1.1 We provide an overview of the design and
environmental testing of these laser transmitters.
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