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Spectral Beam Combining (SBC) of fiber lasers provides a simple, robust architecture for high brightness power scaling beyond the limit of a single fiber. We review recent progress in power scaling and describe what we believe is the highest power SBC fiber demonstration and largest number of fiber lasers combined to date. Here we report results on a fiber SBC system where we achieved > 30 kW by combining 96 individual fiber lasers into a single high brightness beam with a beam quality of M2 = 1.6 x 1.8. The potential for further power scaling at the system level is highlighted with examples of beam combinable fiber laser power scaling.

The MErcury, Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission will send the first spacecraft to orbit the planet Mercury. A miniaturized set of seven instruments, along with the spacecraft telecommunications system, provide the means of achieving the scientific objectives that motivate the mission. The payload includes a combined wide- and narrow-angle imaging system; γ-ray, neutron, and X-ray spectrometers for remote geochemical sensing; a vector magnetometer; a laser altimeter; a combined ultraviolet-visible and visible-infrared spectrometer to detect atmospheric species and map mineralogical absorption features; and an energetic particle and plasma spectrometer to characterize ionized species in the magnetosphere.

Elevations from the Mars Orbiter Laser Altimeter (MOLA) have been used to construct a precise topographic map of the martian north polar region. The northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5-kilometer-deep hemispheric depression that is contiguous with the area into which most outflow channels emptied. Polar cap topography displays evidence of modification by ablation, flow, and wind and is consistent with a primarily H 2 O composition. Correlation of topography with images suggests that the cap was more spatially extensive in the past. The cap volume of 1.2 × 10 6 to 1.7 × 10 6 cubic kilometers is about half that of the Greenland ice cap. Clouds observed over the polar cap are likely composed of CO 2 that condensed out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography.

The transient theory of stimulated Brillouin Scattering (SBS) in optical fibers is used to investigate the effects of weak feedback of an incident broadband laser field. When the linewidth of the laser approaches the Brillouin frequency shift, a weak reflection of the laser field overlaps with the SBS gain and can be amplified in the fiber resulting in an apparent reduction in SBS threshold. We show that a reflection of 0.01% (-40 dB) of a laser field with a linewidth equal to the Brillouin shift can reduce the SBS threshold by a factor of 2. These results have implications on the design of high power fiber laser systems that utilize spectral broadening to suppress SBS.

We report a master-oscillator/power-amplifier laser system featuring a polarizing and coilable 40-micron-core Yb-doped photonic crystal fiber as the final-stage amplifier. The laser source generates 3.4 ns pulses at a repetition rate 19 kHz, with maximum pulse energy 1.2 mJ, maximum average power 22.8 W, near diffraction-limited (M 2 < 1.1) beam quality, and 20% electrical to optical efficiency in a compact package. This pulsed-fiber laser flight system provides high pulse energy, average power, peak power, diffraction limited beam quality, and high efficiency all in a thermally and mechanically stable compact package.

Spectrally Beam Combined fiber laser provide a superior architecture for power scaling laser to high power. We present experimental results where we achieved < 3 kW, M2 = 1.35 with < 39% E-O efficiency by combining 12 individual fiber lasers into a single high brightness beam.

We describe our work on Spectral Beam Combining geometries and design implementations using multilayer dielectric gratings. With appropriate designs, power scaling beyond the single fiber limit can be achieved while maintaining near diffraction limited beam quality.

We have demonstrated and characterized a Q-switched Nd:YAG laser under continuous operation for over 7 billion shots. Through periodic monitoring of the laser's 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.

Simple modifications were made to a commercial microscope to enable injection of light from a diode laser, and demonstrate optical tweezers action. The basic properties of microscope optics are presented together with discussion of principles to be followed in arranging the external optics for achieving useful tweezers. Procedures using a single‐mode diode laser along with experimental results are presented in enough detail to permit readers to make their own system for trapping and manipulating single cells. It is surprisingly easy to demonstrate tweezers action once some basic concepts are understood.

We have observed ring structure formation on a dye laser beam (5850 A) propagating through ruby. We also present, to our knowledge, the first observation of transverse beam encoding by two-beam coupling where spatial rings form on a probe beam copropagating with an argon laser beam in ruby.

We have developed a KCl:Li (F+2)A color center laser which produces more than 1.2 W of cw laser power, over a factor of 3 greater than the highest power previously reported. This paper contains the results of this study, and presents guidelines for preparing laser crystals to routinely and reproducibly generate these high powers.

We have demonstrated an efficient, compact, passively Q-switched single-mode diode-pumped Nd:YAG laser that uses Cr4+:YAG as a saturable absorber. Linear- and ring-cavity configurations were demonstrated. Pulse energies and widths were, respectively, 1.5 mJ and 3.9 ns for the linear cavity and 2.1 mJ and 12 ns for the ring cavity.

Solid-state lasers have been in use for space applications since the early days of the space program. To date most of the lasers have been pulsed Nd:YAG lasers and with the development of diode laser technology as pump sources, performance improvements in lifetime, weight and efficiency have been the key drivers to enable space missions. This paper will review the lasers used on various missions and discuss their designs and performance in light of their mission requirements.

The Geoscience Laser Altimeter System (GLAS), launched in January 2003, is a laser altimeter and lidar for the Earth Observing System's (EOS) ICESat mission. The laser transmitter requirements, design and qualification test results and in-flight performance for this space-based remote sensing instrument is summarized and presented.

A compact, passively Q-switched Nd:YAG laser has been developed for the Mercury Laser Altimeter, an instrument on the Mercury Surface, Space Environment, Geochemistry, and Ranging mission to the planet Mercury. The laser achieves 5.4% efficiency with a near-diffraction-limited beam. It passed all space-flight environmental tests at subsystem, instrument, and satellite integration testing and successfully completes a postlaunch aliveness check en route to Mercury. The laser design draws on a heritage of previous laser altimetry missions, specifically the Ice Cloud and Elevation Satellite and the Mars Global Surveyor, but incorporates thermal management features unique to the requirements of an orbit of the planet Mercury.

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.

We present tests of 100 W/bar quasi-CW laser diode arrays conducted, at SDL Inc. (at various deratings with constant junction temperature) and NASA Goddard, to assist in designing lasers for use in space.

Interest in lasers for space applications such as active remote sensing in Earth orbit, planetary science, and inter-satellite laser communications is growing. These instruments typically use diode-pumped solid state lasers for the laser transmitter. The mission specifications and constraints of space qualification, place strict requirements on the design and operation of the laser. Although a laser can be built in the laboratory to meet performance specifications relatively routinely, tile mission constraints demand unique options and compromises in the materials used, and design to ensure the success of the mission. Presently, the best laser architecture for a light weight, rugged, high peak power and efficient transmitter is a diode laser pumped ND:YAG laser. Diode lasers can often obviate the need for water cooling, reduce the size and weight of the laser, increase the electrical to optical efficiency, system reliability, and lifetime. This paper describes the in-space operation and performance of the Mars Orbiter Laser Altimeter (MOLA) laser transmitter, representing the current state-of-the-art in space-based solid- state lasers.

NASA's 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. Cr 4+ :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 Cr 4+ :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/cm 2 . 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 Cr 4+ :YAG in this pulse energy regime.

NASA is embarking on a new era of laser remote sensing instruments from space. This paper focus’ specifically on the laser technology involved in two present NASA missions. The first is a current mission, the Mars Orbiter Laser Altimeter and the second is the Geoscience Laser Altimeter System scheduled to launch in 2001. The laser transmitters in these space-based remote sensing instruments are discussed in the context of requirements of these two missions.

We have demonstrated a 150 mj, 4 ns, 40 Hz, M2 ≈ 2, diode-pumped Nd:YAG laser as a breadboard for the GLAS laser transmitter.

As part of NASA's suite of Earth Observing Satellites, Goddard Space Flight Center is developing a laser altimeter for measuring the polar ice sheet mass balance. The Geoscience Laser Altimeter System (GLAS) requires a diode pumped, Q-switched, Nd:YAG laser transmitter producing 150 mJ, 4 ns pulses at a 40 Hz repetition rate in a single transverse mode. The mission lifetime goal is five years (6.3 billion shots). The projected performance of the GLAS laser can be limited by a number of failure sources including optical damage to the components and degradation of the pump laser diodes. To the authors' knowledge, no data exists describing the multi-billion shot accumulative exposure effect Q-switched, 4 ns pulses have on intracavity optical components. To obtain multi-billion shot results in a reasonable time, an accelerated repetition rate (500 Hz) version of the GLAS oscillator was built with modifications for thermal management. An Accelerated GLAS Exposure System (AGES) was developed to autonomously monitor the laser's vital signs. Upon analysis of the stored data, the system dynamics were decoupled to identify the sources of degradation. Over 7 billion shots were accumulated during AGES' non-stop 5.5 month operation.

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

We have demonstrated an efficient, compact, 1.5-mJ, 3.9-ns, passively Q-switched, single mode, diode pumped Nd:YAG laser using Cr4+:YAG as a saturable absorber.

The Geoscience Laser Altimeter System (GLAS) is being developed by NASA/GSFC to measure the dynamics of the ice sheet mass balance, land, cloud, and atmospheric properties. An instrument altimetric resolution of 10 cm per shot is required. The laser transmitter will be a diode-pumped, Q-switched, Nd:YAG laser producing 1064 nm, 100 mJ, 4 ns pulses at 40 Hz repetition rate in a TEM(infinity) mode. A minimum lifetime goal of 2 billion shots is required per laser transmitter. The performance of the GLAS laser can be limited by physical damage to the optical components caused by the interaction of intense laser energy with the optical coatings and substrates. Very little data exists describing the effects of long duration laser exposure, of 4 ns pulses, on an optical component. An Accelerated GLAS Exposure Station (AGES) is being developed which will autonomously operate and monitor the GLAS laser at an accelerated rate of 500 Hz. The effects of a large number of laser shots will be recorded. Parameters to be monitored include: laser power, pulsewidth, beam size, laser diode drive current and power, Q-switch drive voltage, temperature, and humidity. For comparison, one set of AGES sister optical components will be used in the nonaccelerated GLAS laser and another will be evaluated by a commercial optical damage test facility.

The Goddard Visible and Near IR Lidar(VIRL) 1 has been modified to the 2.1um region by replacing the Raman cell previously used to generate the 1.54 um pulse with an Optical Parametric Oscillator (OPO) 2 that can efficiently convert the 1.064um output of the system Nd:YAG laser to generate a pulse at 2.1um. The initial test and application of the 2.1um measurements was during a deployment of the lidar on the NASA DC-8 for the TOGA/COARE project in January-February 1993. For T/C, the DC-8 was flown to and out of Townsville, Queensland. The T/C flights were north to the region of the equator and back. From the transit and local flights, a data set of significant coverage is to be generated.

The Mars Observer Laser Altimeter utilizes a space qualified diode laser pumped Q-switched Nd:YAG laser transmitter. We present a simple numerical model of the laser energetics predicting the pulse energy, pulse width and temperature dependence.

The design, calibration, and performance of the Mars Orbiter Laser Altimeter (MOLA) receiver are described. The MOLA measurements include the range to the surface, which is determined by the laser-pulse time of flight; the height variability within the footprint determined by the laser echo pulse width; and the apparent surface reflectivity determined by the ratio of the echo to transmitted pulse energies.

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.

A simple, efficient diode-laser-pumped Q-switched Nd:YAG laser is described that produces 2.25-mJ, TEM(00), 4-ns pulses up to 90 Hz with only 20 mJ of pump power. The laser has a zigzag slab geometry, side pumped with only one high-power quasi-cw diode bar. This performance approaches that of longitudinal pumping, demonstrating TEM(00) mode operation with long-pulse and Q-switched slope efficiencies of 28% and 19%, respectively. Secondand fourth-harmonic efficiencies of >50% and >20% from 1064 nm without the use of external focusing optics were also demonstrated.

The Mars Observer Laser Altimeter utilizes a space-qualified diode-laser-pumped Q-switched Nd:YAG laser transmitter. A simple numerical model of the laser energetics is presented, which predicts the pulse energy and pulse width. Comparisons with the measured data available are made. The temperature dependence of the laser transmitter is also predicted. This dependence prediction is particularly important in determining the operational temperature range of the transmitter. Knowing the operational temperature range is especially important for a passive, thermally controlled laser operating in space.

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%.

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained.