Mark E. Storm

Single-longitudinal-mode lasing of Ho:Tm:YAG at 2.091 μm

This Communication demonstrates that single-longitudinal-mode operation of Ho:Tm:YAG at 2.091 Am using a laser diode pumped, monolithic crystal.

Blackbody absorption efficiencies for six lamp pumped Nd laser materials

Utilizing high resolution spectra, the absorption efficiency for six Nd laser materials was calculated as functions of the effective blackbody temperature of the lamp and laser crystal size. The six materials were Nd:YAG, Nd:YLF, Nd:Q-98 Glass, Nd:YVO(4), Nd:BEL, and Nd:Cr:GSGG. Under the guidelines of this study, Nd:Cr:GSGGs absorption efficiency is twice the absorption efficiency of any of the other laser materials.

Thulium YAG laser operation at 2.01 μm

Variable temperature laser experiments were performed with two compositions of Tm:Cr:YAG (5.0:1.0 and 1.5:2.0 percent substitutions), with special attention given to the spectroscopic details of energy transfer and quasi-3 level lasing. Differences in laser threshold and flashlamp degradation were found in lasing the two compositions, and it is suggested that the difference is due to the 1.5:2.0 rod having much less efficient energy transfer than the 5.0:1.0 Tm:Cr crystals. To first order, the thermal occupation factor is found to dominate laser threshold determination at temperatures betwen 120 and 240 K.

Solid state UV laser development for the remote sensing of ozone from space

Development of a UV laser transmitter capable of operating from a space platform is a critical step in enabling global earth observations of aerosols and ozone at resolutions greater than current passive instrument capabilities. Tropospheric chemistry is well recognized as the next frontier for global atmospheric measurement. Moreover, global measurement of tropospheric ozone with high vertical resolution (2.5 km) from space were endorsed for the EX-1 Mission by NASAs Post2002 Mission Planning Workshop. At this workshop, held in Easton, Maryland, in August 1998, it was recognized that a space-based UV Differential Absorption Lidar (DIAL) system was necessary in order to obtain this high- resolution capability for measurements of ozone and aerosols. The results of this workshop can be found at http:llwww.hq.nasa.gov/office/ese/nra/RFldodgelPanelrev.html. For the EX-1 Mission, the UV DIAL measurement would be complemented with passive measurements of ozone precursor gases and pollutant tracer species. Langley Research Center (LaRC) and the Canadian Space Agency (CSA) have jointly studied the requirements for a satellite based, global ozone monitoring instrument. The study, called Ozone Research using Advanced Cooperative Lidar Experiment (ORACLE) has defined the DIAL instrument performance, weight and power, and configuration requirements for a space based measurement. In order to achieve the measurement resolution and acceptable signal-to-noise from lidar returns, 500mJ/pulse (10 Watts average power) is required at both, 308nm and 320nm wavelengths. These are consecutive pulses, in a 10 Hz, double-pulsed format. The two wavelengths are used as the on- and off-lines for the ozone DIAL measurement.1 5 NASA Langley is currently developing technology for a UV laser transmitter capable of meeting the ORACLE requirements; this development effort is focused on improving the efficiency of converting 1im laser energy to the 308 and 320nm energies needed for the DIAL measurement. Our approach includes making maximum use of existing, space-qualified optical components to reduce risk, cost and development time. Our experimental efforts to date have shown that our UV generation scheme is viable, and that energies greater than lOOmJ/pulse are possible. Future work will focus on improving efficiency and on addressing reliability, size and scalability issues. Our goal is to improve the optical conversion efficiency from the current state of the art, currently at 5%, to a minimum of 12%. We will accomplish this by using OPO/OPA and sum frequency mixing technology to generate the required UV wavelengths. The technology being developed has undergone an extensive peer review and down-select process from 20 possible UV generation schemes through in-house and industry trade studies and by experimental investigations. By using the selected technique and a diode pumped laser, a wall plug efficiency (electrical to optical) of greater than 2% is expected. In this paper, we will briefly discuss the study effort to date, the overall system design, and the down select process for the proposed laser design. We will describe UV laser technology that minimizes the total number of optical components (for enhanced reliability) as well as the number of UV coated optics required to transmit the light from the laser (for enhanced optical damage resistance). While the goal is to develop a laser that will produce 500 mJ of energy, we will describe an optional design that will produce output energies between 100-200mJ/unit and techniques for combining multiple laser modules in order to transmit a minimum of 500mJ of UV energy in each pulse of the on- and off-line pulse pairs. This modular laser approach provides redundancy and significantly reduces development time, risk and cost when compared to the development of a single, 500mJ double-pulsed laser subsystem. Finally, we will describe the common source for seeding the OPOs such that the absolute wavelength and linewidth of each transmitter module will be controlled and summarize the laser development effort to date, including results that include the highest known UV energy ever produced by a solid-state laser operating in this wavelength region.

Novel highly efficient laser transmitter design for a spaceborne ozone differential absorption lidar (DIAL)

Development of a UV laser transmitter capable of operating from a space platform is a critical step in enabling global earth observations of aerosols and ozone at resolutions greater than current passive instrument capabilities. Tropospheric chemistry is well recognized as the next frontier for global atmospheric measurement. NASA Langley Research Center (LaRC) and the Canadian Space Agency (CSA) have jointly studied the requirements for a satellite based, global ozone monitoring instrument. The study, called Ozone Research using Advanced Cooperative Lidar Experiment (ORACLE) has defined the Differential Absorption Lidar (DIAL) instrument performance, weight and power, and configuration requirements for a space based measurement. In order to achieve the measurement resolution and acceptable signal-to-noise from lidar returns, 500mJ/pulse (5 Watts average power) is required at both 305-308nm and 315-320nm wavelengths. These are consecutive pulses, in a 10 Hz, double-pulsed format. The two wavelengths are used as the on- and off-lines for the ozone DIAL measurement. NASA Langley is currently developing technology for a UV laser transmitter capable of meeting the ORACLE requirements. Experimental efforts to date have shown that the UV generation scheme is viable, and that energies greater than 100mJ/pulse are possible. In this paper, we will briefly discuss the down select process for the proposed laser design, the study effort to date and the laser system design, including both primary and alternate approaches. We will describe UV laser technology that minimizes the total number of optical components (for enhanced reliability) as well as the number of UV coated optics required to transmit the light from the laser (for enhanced optical damage resistance). While the goal is to develop a laser that will produce 500 mJ of energy, we will describe an optional design that will produce output energies between 100-200mJ/unit and techniques for combining multiple laser modules in order to transmit a minimum of 50

Compact Ti:Sapphire laser with its Third Harmonic Generation (THG) for an airborne ozone Differential Absorption Lidar (DIAL) transmitter

A compact and high-pulse-energy Ti:Sapphire laser with its Third Harmonic Generation (THG) has been developed for an airborne ozone differential absorption lidar (DIAL) to study the distributions and concentrations of the ozone throughout the troposphere. The Ti:Sapphire laser, pumped by a frequency-doubled Nd:YAG laser and seeded by a single mode diode laser, is operated either at 867 nm or at 900 nm with a pulse repetition frequency of 20 Hz. High energy laser pulses (more than 110 mJ/pulse) at 867 nm or 900 nm with a desired beam quality have been achieved and utilized to generate its third harmonics at 289nm or 300nm, which are on-line and off-line wavelengths of an airborne ozone DIAL. After experimentally compared with Beta-Barium Borate (b-BaB2O4 or BBO) nonlinear crystals, two Lithium Triborate (LBO) crystals (5520 mm3) are selected for the Third Harmonic Generation (THG). In this paper, we report the Ti:Sapphire laser at 900nm and its third harmonics at 300nm. The desired high ultraviolet (UV) output pulse energy is more than 30mJ at 300nm and the energy conversion efficiency from 900nm to 300nm is 30%.

Gain measurements in Ho:Tm:YLiF4

The small signal gain coefficients of Ho:Tm:YLiF4 (Ho:Tm:YLF) have been measured as a function of pump energy fluence and Ho concentration, in order to determine the optimum conditions for efficient pulse amplification. The results show that, for Ho:Tm:YLF amplifier systems, the available pump energy fluence ultimately dictates the Ho concentration.

Future technologies for lidar/DIAL remote sensing

In response to NASA thrusts in Mission to Planet Earth, this paper outlines several technology needs for future space-based lidar/DIAL applications. Several technological tall poles in flight systems are identified, including the technology for laser transmitters; systems technology; and major electro-optical, structural, mechanical, and thermal subsystems. Technologists must address the key questions associated with deploying these lidar systems in medium-class satellite and aircraft platforms. This involves demonstrating engineering parameters for long duration missions which are affordable in terms of weight, power, and volume. The question of affordability must be tied to simplicity in engineering design and to simplicity in the testing and verification of the instrument performance parameters. This requires sufficient testing and demonstration in laboratory systems to avoid the need for changes in engineering design late in the project life cycle.