The current generation of laser diodes suffers from poor thermal management. Typically, Cu-W is used as a submount material. Although it offers a good CTE match with GaAs, thermal conductivity is very limited (160 W/mK). A new approach to improving the thermal management of laser diodes was developed involving the use of hybrid CC/graphite foam composites.

We also have a novel technology developed for LIDAR optical structures consisting of SiC-SiC composite material which exhibits excellent fracture toughness and homogeneous CTE.

There is a need in NASA for development of mid-infrared (mid-IR) lasers, such as Quantum Cascade (QC) lasers, for in-situ and remote laser spectrometers. Mid-IR, compact, low power consumption laser spectrometers have a great potential for detection and measurements of planetary gases and biological important biomarker molecules such as H2O, H2O2, CH4, and many additional chemical species on Mars and other planets of Solar systems. Other applications of mid-IR QC lasers are in high power remote Laser Reflectance Spectrometer (LRS) instruments for future NASA outer solar system explorations. In LSR instruments, QC lasers will act as the illumination source for conducting active mid-IR reflectance spectroscopy of solidsurfaced objects in the outer Solar System. LRS instruments have the potential to provide an incredible amount of information about the compositions of surfaces in the outer Solar System. In this work, we will discuss our current effort at JPL to develop and improve the mid-IR QC lasers to a level that the laser performance, operational requirements and reliability will be compatible with the instruments demands for space exploration applications.

An all-fiber coherent laser radar system capable of high-resolution range and line of sight velocity measurements is under development with a goal to aid NASA's new Space Exploration initiative for manned and robotic missions to the Moon and Mars. Precision range and velocity data are key parameters to navigating planetary landing pods to the pre-selected site and achieving autonomous safe soft-landing. By employing a combination of optical heterodyne and linear frequency modulation techniques [1-3] 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.

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 directly measure the platform velocity by extracting the Doppler shift generated by the platform motion. The Doppler velocity measurement is about two orders of magnitude more accurate than the velocity estimates obtained by laser altimeters using the rate of change in range [4]. Another advantage is continuous-wave operation that allows the use of highly efficient and reliable commercial off-the-shelf fiber optic telecommunication components. This paper will describe the design and operation of this laser radar sensor and discuss its projected performance. A laboratory breadboard system has already been developed as a step toward a flight prototype. The experimental data representing the potentials of this laser radar system will be reported.

Compact, robust, high power fiber lasers have been demonstrated. In fiber lasers of only a few cm length we obtained up to 10 W of cw output power, diffraction limited beam profiles at 4 W cw operation, 1.6 W output with single frequency operation, and more than 150 mW output with a spectral linewidth of a few kHz. The potential of active microstructured fibers for further improvements in fiber laser performance has been shown. We also demonstrated Q-switching and mode-locking of these compact fiber lasers.

NASA remote sensing missions involving laser systems and their economic impact are coutlined. Potential remote sensing missions include: green house gasses, tropospheric winds, ozone, water vapor, and ice cap thickness. Systems to perform these measurements use lanthanide series lasers and nonlinear devices including second harmonic generators and parametric oscillators. Demands these missions place on the laser and nonlinear optical materials are discussed from a materials point of view. Methods of designing new laser and nonlinear optical materials to meet these demands are presented.

Future planetary exploration missions will require safe and precision soft-landing to target scientifically interesting sites near hazardous terrain features, such as escarpments, craters, slopes, and rocks. Although the landing accuracy has steadily improved over time to approximately 35 km for the recent Mars Exploration Rovers due to better approach navigation, a drastically different guidance, navigation and control concept is required to meet future mission requirements. For example, future rovers will require better than 6 km landing accuracy for Mars and better than 1 km for the Moon plus 100 m maneuvering capability to avoid hazards. Laser Radar or Lidar technology can be the key to meeting these objectives since it can provide highresolution 3-D maps of the terrain, accurately measure ground proximity and velocity, and determine atmospheric pressure and wind velocity. These lidar capabilities can enable the landers of the future to identify the pre-selected landing zone and hazardous terrain features within it, determine the optimum flight path, having atmospheric pressure and winds data, and accurately navigate using precision ground proximity and velocity data. This paper examines the potential of lidar technology in future human and robotic missions to the Moon, Mars, and other planetary bodies. A guidance and navigation control architecture concept utilizing lidar sensors will be presented and its operation will be described. The performance and physical requirements of the lidar sensors will be also discussed.

Q-Peak has been developing solid state laser and nonlinear optical systems applied to remote sensing for nearly 20 years. Our first devices were based on the use of gas-discharge lamps to optically pump the laser crystals, a standard technology that traces back to 1960 with the first laser demonstration, using ruby (Cr3+:Al2O3) as the laser material. In later and most current systems we have employed the newer and more efficient use of semiconductor diode lasers as pump sources, which has allowed operation at higher levels of performance and makes practical the deployment of satellite-based, active remote-sensing systems.

Low duty cycle, high peak power, conductively cooled laser diode arrays have been manufactured for several years by a number of different vendors. Typically these packages have been limited to a few percent duty cycles due to thermal problems that develop in tight bar pitch arrays at higher duty cycles. Traditionally these packages are made from some combination of copper and BeO or Tungsten/copper and BeO. Trade-offs between thermal conductivity and CTE matching are always made when manufacturing these devices. In addition, the manufacturability of the heat sinks plays a critical role in creating a cost effective, high performance solution. In this discussion we examine several different exotic materials that have been manufactured and tested as heat sinks for laser diode arrays.

Strain-balanced InxGa1-xAs/InyGa1-yAs superlattices and fractional monolayer In0.532Ga0.468As/InAs superlattices were grown by solid-source molecular beam epitaxy (SSMBE) in order to extend the photodetection wavelength range beyond 1.7μm. Material qualities were characterized by transmitted electron microscope (TEM), X-ray diffraction (XRD), roomtemperature photoluminesecence (RTPL) and optical absorption measurement.

This paper provides an overview of novel single frequency and broadly tunable laser technology being developed at Coherent Technologies, Inc. (CTI) for long-range remote sensing of hard targets and distributed targets from ground based and airborne platforms. In all these applications, the need for high beam quality and efficient high power operation is paramount. For many of the applications, it is also critical to control and measure frequency content of the emitted and collected light to a high degree of accuracy. For example, a sub-kHz linewidth is typically required for velocity and vibration imaging, and sub-MHz linewidth for some differential absorption lidar (DIAL) type measurements.

After several decades of observations from space, direct measurements of the global threedimensional wind field remain elusive, however crucial to weather predictions. The ALADIN instrument, payload of the AEOLUS satellite (figure 1), will provide measurements of atmospheric wind profiles with global Earth coverage for the climatology and meteorology users. The AEOLUS programme is sponsored by the European Space Agency with a launch planned in 2008.

ALADIN belongs to a new class of Earth Observation payloads and will be the first European Lidar in space. The instrument comprises a diode-pumped high energy Nd:YAG laser and a direct detection receiver operating on aerosol and molecular backscatter signals in parallel. In addition to the Flight Model (FM), two instrument models are developed: a Pre-development Model (PDM) and an Opto-Structure-Thermal Model (OSTM). The OSTM integration has been completed and the flight equipments are under manufacturing. This paper describes the instrument design as well as the development status. The ALADIN instrument is developed under prime contractor EADS Astrium SAS with a consortium of thirty companies.

Tm, Ho codoped YLF, LuLF,and LuAG and GdVO4 crystals are very attractive for diode pumped 2-μm lasers. A comparison study of laser performance was made using a diode-pumped, quasi-end-pump scheme at various pulse repetition frequencies and temperatures. At 5 Hz and at an operating temperature of 300 K, normal mode laser output energies of 15.7 mJ (YLF) with a slope efficiency of 7.3%, 26.8mJ (LuLF) with that of 12.6% and 20.0 mJ (LuAG) with that of 10.8% were achieved using 5%Tm and 0.5%Ho, respectively. A Tm,Ho:GdVO4 laser was also investigated. It was found, in the case of GdVO4, that optimum Tm and Ho dopant concentrations were slightly lower than those for garnet and fluoride crystals. Using a 3% Tm,0.3% Ho:GdVO4 crystal, an output energy of 31.2 mJ with a slope efficiency of 14.5% was obtained in normal mode operation at room temperature.

In this note, lidar materials, ready and waiting, will be discussed. Most lidar applications depend upon “Ready” materials, conventional materials that are part of a design solution to the application. Lidar systems already operating and serving the needs of communities in atmospheric, earth and planetary sciences, include airborne terrain mapping, airborne bathymetric mapping, ground-based imaging rangefinding and ceilometry are included in this category. Even in space application, “Ready” spaceborne applications include orbital rendezvous and docking, precision landing/hazard avoidance and Martian atmospheric evaluation. Other applications, however, have particular materials needs and constitute “Waiting” systems. These include in particular spaceborne differential absorption lidar (DIAL) for the measurement of important trace species such as ozone and water vapor in the Earth's atmosphere (ORACLE, WALES). An evaluation of critical issues facing mission-enabling lidar materials development will be presented, based upon Optech Incorporated's direct experience in these areas.

Two different micro-optical microphones are presented. The first is based on interferometric read-out of a deflecting membrane, based on the Fabry-Perot principle. The sensing device is produced in Silicon by combining standard CMOS and MEMS processing. This ensures that high accuracy alignment and low cost production can be obtained. Optical sensor elements with a ring structure are included on one of the Fabry-Perot surfaces whereas the other surface is an optically transparent membrane. Light from an uncollimated light source such as a semiconductor laser or a LED, will form a ring pattern when transmitted through the membrane.

The other microphone principle presented is based on a diffractive lens. The structure has a metallic ring pattern separated from a reflecting membrane with an air gap. When the air gap is an odd number of quarter wavelengths of the impinging light, these surfaces form a binary phase diffractive lens. By placing a light source and a detector in the focal plane of the lens, the measured intensity will be highly sensitive to the position of the membrane. Similarly to the first microphone this device can be mass produced at low cost using micromachining techniques.

Results from prototype devices will be presented, proving both principles and showing excellent properties compared to expensive commercially available condenser microphones.

Conventional wisdom contends that high-energy nanosecond UV laser sources operate near the optical damage thresholds of their constituent materials. This notion is particularly true for nonlinear frequency converters like optical parametric oscillators, where poor beam quality combined with high intra-cavity fluence leads to catastrophic failure of crystals and optical coatings. The collective disappointment of many researchers supports this contention. However, we're challenging this frustrating paradigm by developing high-energy nanosecondUVsources that are efficient, mechanically robust, and most important, resistant to optical damage. Based on sound design principles developed through numerical modeling and rigorous laboratory testing, our sources generate 8-10 ns 190 mJ pulses at 320 nm with fluences≤ 1 J/cm2. Using the second harmonic of a Q-switched, injection-seeded Nd:YAGlaser as the pump source, we convert the near-IR Nd:YAG fundamental to UV with optical-to-optical efficiency exceeding 21%.

Space-borne laser remote sensing systems typically rely on conductively cooled, diodepumped solid-state lasers as their transmitter source. Since space-borne instruments incur high developmental and launch costs and are inaccessible for maintenance, their reliability is of great importance. Therefore, it is crucial to address the reliability of high power laser pump arrays, which essentially dictate the reliability and lifetime of the laser systems. The most common solid-state lasers used for remote sensing applications are Neodymium-based, 1-micron lasers and Thulium/Holmium based 2-micron lasers. 2-micron lasers require a pump wavelength of around 10 to 20 nm shorter compared with 1-micron lasers, and require pump pulse durations 5 to 10 times longer. This work focuses on the long pulsewidth laser diode arrays (LDAs) operating at a central wavelength of 792 nm used for optically pumping 2-micron solid-state laser materials. Such LDAs are required to operate at relatively high pulse energies with pulse durations on the order of one millisecond. However, such relatively long pulse durations cause the laser diode active region to experience high peak temperatures and drastic thermal cycling. This extreme localized heating and thermal cycling of the active regions are considered the primary contributing factors for both gradual and catastrophic degradation of LDAs, thus limiting their reliability and lifetime. One method for mitigating this damage is to incorporate materials that can improve thermo-mechanical properties by increasing the rate of heat dissipation and reducing internal stresses due to differences in thermal expansion and thus increasing lifetime. This paper explains the need for long pulsewidth operation, how this affects reliability and lifetime and presents some results from characterization and life testing of these devices.

Many coherent lidar applications, particularly airborne and space-based applications, impose stringent power and size constraints while requiring high levels of sensitivity. For this reason, optimization of the lidar heterodyne photoreceiver is one of the critical steps in ensuring full utilization of limited resources to achieve the required sensitivity. The analysis of 2-micron heterodyne receivers shows that substantial improvement of the order of 3 dB can be obtained by proper optimization of the receiver key control parameters and elimination of its parasitic capacitances by integrating the detector, its bias circuit, and the preamplifier on a single substrate. This paper describes analytical steps for defining optimum heterodyne receiver design parameters and development of experimental devices operating at 2-micron wavelength.