Joseph L. Dallas

The Geoscience Laser Altimeter System (GLAS) Laser Transmitter

The Geoscience Laser Altimeter System (GLAS), launched in January 2003, is a laser altimeter and lidar for the Earth Observing Systems (EOS) ICESat mission. GLAS accommodates three, sequentially operated, diode-pumped, solid-state, Nd:YAG laser transmitters. The laser transmitter requirements, design, and qualification test results for this space-based remote-sensing instrument is summarized and presented.

Efficient, diode-laser-pumped, diode-laser-seeded, high-peak-power Nd:YLF regenerative amplifier.

Optical amplification of 11 orders of magnitude in a microlens-collimated, diode-laser-pumped regenerative amplifier has been demonstrated. The amplifier was seeded with 20-ps pulses from an FM mode-locked oscillator and with 0.9-ns pulses from a modulated diode laser. Seed pulses from both sources were amplified to energies exceeding 2.5 mJ. With the thermoelectric coolers and the Pockels cell electronics neglected, the diode-seeded system exhibited an electrical-to-optical efficiency of 2.2%.

Demonstration and characterization of a multibillion-shot, 2.5-mJ, 4-ns, Q-switched Nd:YAG laser

We have demonstrated and characterized a Q-switched Nd:YAG laser under continuous operation for over 7 billion shots. Through periodic monitoring of the lasers vital signs, the system dynamics were decoupled to identify the sources of degradation. The initial and the final pump-laser diode wavelengths and powers were measured and compared. No evidence of an accumulative effect leading to optical damage at a fluence lower than the single-shot threshold was observed.

The Geoscience Laser Altimeter System laser transmitter

Summary form only given.The Geoscience Laser Altimeter System (GLAS) scheduled to launch in 2001, is the sole instrument for the ICESat (Ice, Cloud and Land Elevation Satellite) mission. GLAS will be a satellite laser altimeter and atmospheric lidar whose primary mission is the global monitoring of the earths ice sheet mass balance. GLAS will also provide high precision land topography and global monitoring of aerosols and cirrus cloud heights. The current state-of-the-art in space based solid-state lasers is the Mars Orbiting Laser Altimeter (MOLA), on the Mars Global Surveyor spacecraft collecting topography data of Mars. The GLAS laser will generally have an order of magnitude higher performance than MOLA in power, beam quality, etc., and represents the next generation of space-based remote sensing laser transmitters.

Modeling of a diode-side-pumped Nd:YAG laser

We have developed a unique numerical laser model by use of a commercial physical optics software package. The experimentally measured lasing threshold, slope efficiency, power output distribution, and phase front have been derived. This model is particularly powerful for monitoring the effects caused by thermal distortions encountered in power scaling lasers. Extrapolations have been made through parametric studies to predict changes required in the laser design that would optimize the performance of the laser.

Frequency-modulation mode-locking performance for four Nd 3+ -doped laser crystals

To determine an optimum host for simultaneous short-pulse-width and large-slope-efficiency generation, the performance of Nd:YAG, Nd:YLF, Nd:YVO(4), and Nd(3+):Sr(5)(VO(4))(3)F [Nd:strontium fluorovanadate (S-VAP)] was characterized under a variety of end-pumped and frequency-modulation mode-locking conditions. The slope efficiency, threshold pump power, and pulse width were recorded for each laser and compared with theory. A figure of merit was defined, yielding Nd:YLF and Nd:YVO(4) as the experimentally determined crystals of choice.

Quasi-cw laser diode bar life tests

NASAs Goddard Space Flight Center is developing technology for satellite-based, high peak power, LIDAR transmitting requiring 3-5 years of reliable operation. Semi-conductor laser diodes provide high efficiency pumping of solid state lasers with the promise of long-lived, reliable operation. 100-watt quasi-CW laser diode bars have been baselined for the next generation laser altimeters. Multi-billion shot lifetimes are required. The authors have monitored the performance of several diodes for billions of shots and investigated operational modes for improving diode lifetime.

Space qualification of the Geoscience Laser Altimeter System (GLAS) laser transmitters

Summary from only given. We have completed the manufacture, space-qualification and delivery of three flight, diode pumped solid-state lasers for the Geoscience Laser Altimeter System (GLAS), the sole instrument for the ICESat (ice, cloud and land elevation satellite) mission scheduled to launch in early 2002.

Narrow band volume holographic 532 nm optical filter

We describe a narrow band (16 pm FWHM), passive, holographic 532 nm optical filter for use with frequency stabilized doubled Nd:YAG lasers.

Multibillion shot high-influence exposure of Cr4+:YAG passive Q-switch

NASAs Goddard Space Flight Center is developing the Geoscience Laser Altimeter System (GLAS) employing a diode pumped, Q-switched, Nd:YAG laser operating at 40 Hz repetition rate. To meet the five-year mission lifetime goal, a single transmitter would accumulate over 6.3 billion shots. Cr4+:YAG is a promising candidate material for passively Q- switching the laser. Historically, the performance of saturable absorbers has degraded over long-duration usage. To measure the multi-billion shot performance of Cr4+:YAG, passively Q-switched GLAS-like oscillator was tested at an accelerated repetition rate of 500 Hz. The intracavity fluence was calculated to be approximately 2.5 J/cm2. The laser was monitored autonomously for 165 days. There was no evidence of change in the material optical properties during the 7.2 billion shot test. All observed changes in laser operation could be attributed to pump laser diode aging. This is the first demonstration of multi-billion shot exposure testing of Cr4+:YAG in this pulse energy regime.