Overview and future direction for blackbody solar-pumped lasers

A review of solar-pumped blackbody lasers is given which addresses their present status and suggests future research directions. The blackbody laser concept is one system proposed to scale to multimegawatt power levels for space-to-space power transmissions for such applications as onboard spacecraft electrical or propulsion needs. Among the critical technical issues are the scalability to high powers and the laser wavelength which impacts the transmission optics size as well as the laser-to-electric converter at the receiver. Because present blackbody solar-pumped lasers will have laser wavelengths longer than 4 microns, simple photovoltaic converters cannot be used, and transmission optics will be large. Thus, future blackbody laser systems should emphasize near visible laser wavelengths

Large volume multiple-path nuclear pumped laser

Large volumes of gas are excited by using internal high reflectance mirrors that are arranged so that the optical path crosses back and forth through the excited gaseous medium. By adjusting the external dielectric mirrors of the laser, the number of paths through the laser cavity can be varied. Output powers were obtained that are substantially higher than the output powers of previous nuclear laser systems

A Remote Laser-mass Spectrometer for Determination of Elemental Composition

Determination of the elemental composition of lunar, asteroid, and planetary surfaces is a major concern for science and resource utilization of space. The science associated with the development of a satellite or lunar rover laser-mass spectrometer instrument is presented here. The instrument would include a pulsed laser with sufficient energy to create a plasma on a remote surface. Ions ejected from this plasma travel back to the spacecraft or rover, where they are analyzed by a time-of-flight mass spectrometer, giving the elemental and isotope composition. This concept is based on the LIMA-D instrument on board the former Soviet Union Phobos-88 spacecraft sent to Mars. A laser-mass spectrometer placed on a rover or satellite would substantially improve the data return over alternative techniques. The spatial resolution would be centimeters, and a complete mass spectrum could be achieved in one laser shot. An experiment is described that demonstrates these features. A 400 mj Nd:YAG laser is focused, to an intensity of 10(exp 11) w/sq cm, onto a Al, Ag, Cu, Ge, or lunar simulant target. A plasma forms from which ions are ejected. Some of these ions travel down an 18-m evacuated flight tube to a microchannel plate detector. Alternatively, the ions are captured by an ion trap where they are stored until pulsed into a 1-m time-of-flight mass spectrometer, giving the elemental composition of the remote surface. A television camera monitors the plasma plume shape, and a photodiode monitors the temporal plasma emission . With this system, ions of Al, Ag, Cu, Ge, and lunar simulant have been detected at 18 m. The mass spectrum from the ion trap and 1-m time-of-flight tube will be presented

Lasant Materials for Blackbody-Pumped Lasers

Blackbody-pumped solar lasers are proposed to convert sunlight into laser power to provide future space power and propulsion needs. There are two classes of blackbody-pumped lasers. The direct cavity-pumped system in which the lasant molecule is vibrationally excited by the absorption of blackbody radiation and laser, all within the blackbody cavity. The other system is the transfer blackbody-pumped laser in which an absorbing molecule is first excited within the blackbody cavity, then transferred into a laser cavity when an appropriate lasant molecule is mixed. Collisional transfer of vibrational excitation from the absorbing to the lasing molecule results in laser emission. A workshop was held at NASA Langley Research Center to investigate new lasant materials for both of these blackbody systems. Emphasis was placed on the physics of molecular systems which would be appropriate for blackbody-pumped lasers

A blackbody-pumped CO2-N2 transfer laser

A compact blackbody-pumped CO2-N2 transfer laser was constructed and the significant operating parameters were investigated. Lasing was achieved at 10.6 microns by passing preheated N2 through a 1.5-mm-diameter nozzle to a laser cavity where the N2 was mixed with CO2 and He. An intrinsic efficiency of 0.7 percent was achieved for an oven temperature of 1473 K and N2 oven pressure of 440 torr. The optimum laser cavity consisted of a back mirror with maximum reflectivity and an output mirror with 97.5-percent reflectivity. The optimum gas mixture was 1CO2/.5He/6N2. The variation of laser output was measured as a function of oven temperature, nozzle diameter, N2 oven pressure, He and CO2 partial pressures, nozzle-to-oven separation, laser cell temperature, and output laser mirror reflectivity. With these parameters optimized, outputs approaching 1.4 watts were achieved

A Remote Laser Mass Spectrometer for Lunar Resource Assessment

The use of lasers as a source of excitation for surface mass spectroscopy has been investigated for some time. Since the laser can be focused to a small spot with intensity, it can vaporize and accelerate atoms of material. Using this phenomenon with a time-of-flight mass spectrometer allows a surface elemental mass analysis of a small region with each laser pulse. While the technique has been well developed for Earth applications, space applications are less developed. NASA Langley recently began a research program to investigate the use of a laser to create ions from the lunar surface and to analyze the ions at an orbiting spacecraft. A multijoule, Q-switched Nd:YAG laser would be focused to a small spot on the lunar surface, creating a dense plasma. This plasma would eject high-energy ions, as well as neutrals, electrons, and photons. An experiment is being set up to determine the characteristics of such a laser mass spectrometer at long flight distances. This experiment will determine the character of a future flight instrument for lunar resource assessment

The White Pine-Hardwood Vegetation Types of the Great Smoky Mountains National Park

The white pine-hardwood type was described by Miller in 1938; however, subsequent researchers of the vegetation of the Great Smoky Mountains National Park have not described this type. A field study of white pine-hardwood vegetation was conducted in the Park from June to October, 1977. The objectives were to relocate and plot sample the white pine-hardwood stands to 1) group samples into vegetation types based upon the importance of white pine and its associated taxa, 2) use quantitative vegetation analysis procedures to describe the white pine-hardwood vegetation types, 3) assess the relationship of the vegetation types to environmental characteristics, 4) examine the successional status of the types, and 5) provide a basis for further ecological studies of these types in the Park. Data were analyzed from 144 sample plot locations in the western portion of the Park in Tennessee at low to middle elevations (312 to 716 meters). Circular 0.0406 hectare (1/10 acre) plots were located in areas which had been previously mapped by Miller in 1941. Canopy (over 10 cm), sapling (2.5 to 10 cm), subsapling (2.5 cm diameter and one meter high), and herbaceous data were tallied in each plot. Site properties were collected in each plot. Laboratory determinations of soil pH and texture of both the A and B horizons were made. Canopy data were used to group plots into vegetation types using an agglomerative clustering technique (Orloci, 1967). The seven communities identified were: white pine-Virginia pine, white pine-red maple, white pine-hemlock, white pine-chestnut oak, white pine-white oak, white pine-northern red oak, and white pine types. Relative densities of tree taxa in the canopy, sapling, subsapling, and seedling strata were compared to determine the reproductive success of each type. Disturbance evidence and historical accounts were analyzed to assess the successional status of the types. Most types have been disturbed through cultivation, logging, and fire although portions of the white pine-chestnut oak, white pine-white oak, white pine-northern red oak, and white pine types occurred on sites of limited human disturbance. The absence of chestnut stumps and the low proportion of sprouts indicated that it had a minimal former presence in the white pine-hardwood types. Simple linear correlations among and between site, soil, and vegetation characteristics were computed. Significant correlations among soil characteristics indicated that slope angles increased as microtopographic position increased such that steep slope angles occurred predominately downslope. Site and soil correlations indicated that stone volume was negatively correlated with elevation: lower elevations had an increase in stone material. The increased acidity of litter and the increased leaching due to additional precipitation at higher elevations contributed to a decrease in soil pH. Discriminant analysis of the community types using vegetation data indicated that 95 percent of the types were distinct as classified by the cluster procedure. Discriminant analysis using selected environmental variables indicated that some types were not as distinct environmentally as they were vegetationally. Discriminating factors related to soil moisture conditions such as stone percentages, horizon thickness, and total available water were important on the first discriminant axis. The second discriminant function appeared to be related to both soil moisture phenomena and slope position, which contributed to the concept that the white pine-hardwood types were segregated by available soil moisture. The classification success was low with only 41 percent of the plots correctly classified. The inability of the measured environmental variables to exactly distinguish the types may be attributed to the successional relationships among the types. Canonical analysis was used to display the arrangement of the seven vegetation types along the first two canonical axes. The centroids of each type were arrayed along the first axis in an order which closely corresponded to the first and second axes in the discriminant analysis of the environmental variables. From the canonical analysis, it is inferred that soil moisture was important in segregating the white pine-hardwood types. The diameter distribution of white pine may be of considerable value in inferring the age distribution and stand history of a forest. A direct sampling of white pine increment cores was conducted. Regression analysis was used to determine the best fit of the collective white pine-hardwood type as well as the individual types. The white pine-Virginia pine, white pine-red maple, white pine-hemlock, and portions of the white pine type were represented by relatively even-aged stands resulting from large scale disturbances. The white pine-oak types and portions of the white pine type more closely represented all-aged forests

Nuclear pumped laser II

The first direct nuclear pumped laser using the He-2-(n,p) H-3 reaction is reported. Lasing took place on the 1.79 microns Ar I transition in a mixture of He-3-Ar at approximately 600 Torr total pressure. It was found that the electrically pulsed afterglow He-Ar laser had the same concentration profile as the nuclear pumped laser. As a result, nuclear lasing was also achieved in He-3-Xe (2.027 micron) and He-3-Kr (2.52 micron). Scaling of laser output with both thermal flux and total pressure as well as minority concentration has been completed. A peak output (He-3-Ar) of 3.7 watts has been achieved at a total pressure of 4 atm. Direct nuclear pumping of He-3-Ne has also been achieved. Nuclear pumping of a He-3-NF3 mixture was attempted, lasing in FI at approximately 7000 A, without success, although the potential lasing transitions appeared in spontaneous emission. Both NF3 and 238UF6 appear to quench spontaneous emission when they constitute more than 1% of the gas mixture

A model for the kinetics of a solar-pumped long path laser experiment

A kinetic model for a solar-simulator pumped iodine laser system is developed and compared to an experiment in which the solar simulator output is dispersed over a large active volume (150 cu cm) with low simulator light intensity (approx. 200 solar constants). A trace foreign gas which quenches the upper level is introduced into the model. Furthermore, a constant representing optical absorption of the stimulated emission is introduced, in addition to a constant representing the scattering at each of the mirrors, via the optical cavity time constant. The non-uniform heating of the gas is treated as well as the pressure change as a function of time within the cavity. With these new phenomena introduced into the kinetic model, a best reasonable fit to the experimental data is found by adjusting the reaction rate coefficients within the range of known uncertainty by numerical methods giving a new bound within this range of uncertainty. The experimental parameters modeled are the lasing time, laser pulse energy, and time to laser threshold

Nuclear-pumped lasers 2

The two main research objectives of the contract were to demonstrate high power nuclear lasering (similar to kWatt) and demonstrate nuclear pumping with fission fragments from (U-235)F6. The progress made towards these objectives is discussed