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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Theoretical simulation of a 2 micron airborne solid state laser anemometer

In the near future, military aircraft will need to know precisely their true airspeed in order to optimize flight conditions. In comparison with classical anemometer probes, an airborne Doppler lidar allows measurement of the air velocity without influence from aircraft aerodynamic disturbance. While several demonstration systems of heterodyne detection using a CO2 laser have been reported, improvements in the technology of solid state lasers have recently opened up the possibility that these devices can be used as an alternative to CO2 laser systems. In particular, a diode pumped Tm:Ho:YAG laser allows a reliable compact airborne system with an eye safe wavelength (lambda = 2.09 microns) to be achieved. The theoretical study of performances of a coherent lidar using a solid state diode pumped Tm:Ho:YAG laser, caled SALSA, for measuring aircraft airspeed relative to atmospheric aerosols is described. A computer simulation was developed in order to modelize the Doppler anemometer in the function of atmospheric propagation and optical design. A clever analysis of the power budget on the detector area allows optical characteristic parameters of the system to be calculated, and then it can be used to predict performances of the Doppler system. Estimating signal to noise ratios (SNR) and heterodyne efficiency provides the available energy of speed measurement as well as a useful measurement of the alignment of the backscattered and reference fields on the detector.

Imbert, Beatrice↗
NASA NTRS1992

A study of atmospheric optical scattering parameters at 1.5 and 2 micron region for solid state Doppler lidar applications

The increasing interest in the development of an eye-safe, solid state, Doppler lidar for avionic applications has created the need for a quantitative evaluation of atmospheric effects on performance. Theoretical calculations were completed for optical scattering parameters to be compared with the field measurements. Computer codes were developed for the required calculations and designed to be interactive and user friendly in order to support comparison with experimental results and, thus, provide the basis for evaluation of eye-safe Doppler lidar over a wide range of atmospheric conditions and geographical locations. A holmium Doppler lidar operating at 2.09 microns was constructed for atmospheric backscattering, attenuation, and wind velocity measurements. Theoretical calculations and field studies were performed for backscatter coefficients. The selected wavelengths correspond to Er:glass, Tm:YAG, and Tm,Ho:YAG solid state lasers that are suitable for use in an eye-safe Doppler lidar system.

Margalit, Eli↗
NASA NTRS1992

Emerging solid-state laser technology by lidar/DIAL remote sensing

Significant progress has been made in recent years in the development of new, solid-state laser sources. This talk will present an overview of some of the new developments in solid-state lasers, and their application toward lidar/DIAL measurements of the atmosphere. Newly emerging lasers such as Ho:YAG, Tm:YAG, OPO, and Ti:Sapphire will be covered, along with the spectroscopic parameters required for differential operational modes of atmospheric remote sensing including Doppler-Windshear lidar, Tunable laser detection of water/CO2, and broad linewidth OPO's for open path detection of pollutant hydrocarbon gases. Additional considerations of emerging laser technology for lidar/DIAL will also be covered.

Killinger, Dennis↗
NASA NTRS1991

Gain and energy storage in holmium YLF

It is demonstrated that Q-switched holmium lasers are capable of high-gain and high-energy operation at 300 K. Small-signal gain coefficients of 0.50 and 0.12/cm have been measured in YLF and YAG, respectively. Small-signal gains of 0.50/cm are comparable to those achievable in Nd:YAG and are not typical of low-gain materials. This large gain in the Ho:YLF material is made possible by operating the amplifier in the ground state depletion mode. The amplifier performance data and associated analysis presented demonstrate that efficient energy storage is possible with very high excited state ion densities of the Ho 5I7 upper laser level. This is an important result since upconversion can limit the 5I7 population. Although upconversion was still present in this experiment, it was possible to achieve efficient energy storage, demonstrating that the problem is manageable even at high excitation densities in YLF.

Storm, Mark E.↗
NASA NTRS1991

Spectral performance of monolithic holmium and thulium lasers

Fabry-Perot resonators have been used to demonstrate single-mode lasing of holmium and neodymium YAG. The previous demonstration in the holmium laser required TE cooling the crystal to -15 C in order to achieve threshold. The present study extends that result, demonstrating +25 C operation in a 1-mm thick plano/plano resonator. The experimental configuration of lasing both the holmium and thulium lasers used a 500-mW diode laser which was collimated, circularized, and focused into a beam radius of 60 microns. The single-frequency lasing spectrum of the holmium laser is shown. By adjusting the mirror reflectivity, the ability to control the laser's wavelength is demonstrated. This laser operated with 11 mW of optical power, a 57-percent slope efficiency, and 120-mW threshold vs absorbed diode power laser for the 60-micron beam radius. The thulium laser operated very efficiently at room temperature, but on seven longitudinal modes. The Tm:TAG laser exhibits typical characteristics of spatial hole burning not seen in the Ho:Tm:YAG for flat/flat resonators.

Storm, Mark E.↗
NASA NTRS1991

Solid state lasers for planetary exploration

Design and performance data for two laser transmitters for spaceborne laser ranging are presented. The first laser uses a master oscillator/power amplifier configuration consisting of a diode pumped Nd:YAG slab ring and a multipass diode pumped slab amplifier which can operate at 40 Hz for more than ten to the ninth shots. The other laser is a diode pumped Nd:YAG slab standing wave oscillator which operates at 10 Hz for more than 0.6 x 10 exp 9 shots. The lasers were specifically developed for reliability, for use in space exploitation of the Earth and nearby planets. Applications include planetary altimetry of Mars (MOLA) and Earth (GLRS), as well as space geodesy, navigation, and tracking.

Greene, Ben↗
NASA NTRS1992

Performance of a 1-micron, 1-joule Coherent Launch Site Atmospheric Wind Sounder

The paper describes the design and performance of the Coherent Launch Site Atmospheric Wind Sounder (CLAWS), which is a test and demonstration program designed for monitoring winds with a solid-state lidar in real time for the launch site vehicle guidance and control application. Analyses were conducted to trade off CO2 (9.11- and 10.6-microns), Ho:YAG (2.09 microns), and Nd:YAG (1.06-micron) laser-based lidars. The measurements set a new altitude record (26 km) for coherent wind measurements in the stratosphere.

Hawley, James G.↗
NASA NTRS1993

An improved light source for laser ranging

The development of a new laser material, Cr-doped LiSAF, makes possible the development of a laser source for satellite ranging systems that is more superior in performance capabilities than current Nd:YAG-based laser sources. This new material offers the potential of shorter pulses and more preferable wavelengths (850 and 425 nm) than multiwavelength Nd:YAG systems, leading to superior ranging resolution and greater detection sensitivity. We are embarking on a feasibility study of a two-wavelength, mode-locked laser system based on Cr:LiSAF, providing shorter pulses for improved ranging resolution.

Hamal, Karel↗
NASA NTRS1993

Space Applications Industrial Laser System (SAILS)

A program is underway to develop a YAG laser based materials processing workstation to fly in the cargo bay of the Space Shuttle. This workstation, called Space Applications Industrial Laser System (SAILS), will be capable of cutting and welding steel, aluminum, and Inconel alloys of the type planned for use in constructing the Space Station Freedom. As well as demonstrating the ability of a YAG laser to perform remote (fiber-optic delivered) repair and fabrication operations in space, fundamental data will be collected on these interactions for comparison with terrestrial data and models. The flight system, scheduled to fly in 1996, will be constructed as three modules using standard Get-Away-Special (GAS) canisters. The first module holds the laser head and cooling system, while the second contains a high peak power electrical supply. The third module houses the materials processing workstation and the command and data acquisition subsystems. The laser head and workstation cansisters are linked by a fiber-optic cable to transmit the laser light. The team assembled to carry out this project includes Lumonics Industrial Products (laser), Tennessee Technological University (structural analysis and fabrication), Auburn University Center for Space Power (electrical engineering), University of Waterloo (low-g laser process consulting), and CSTAR/UTSI (data acquisition, control, software, integration, experiment design). This report describes the SAILS program and highlights recent activities undertaken at CSTAR.

Mccay, T. D.↗
NASA NTRS1994

Solid state laser systems for space application

Since the last report several things have happened to effect the research effort. In laser metrology, measurements using Michelson type interferometers with an FM modulated diode laser source have been performed. The discrete Fourier transform technique has been implemented. Problems associated with this technique as well as the overall FM scheme were identified. The accuracy of the technique is not at the level we would expect at this point. We are now investigating the effect of various types of noise on the accuracy as well as making changes to the system. One problem can be addressed by modifying the original optical layout. Our research effort was also expanded to include the assembly and testing of a diode pumped\Nd:YAG laser pumped\Ti sapphire laser for possible use in sounding rocket applications. At this stage, the diode pumped Nd:YAG laser has been assembled and made operational.

Kay, Richard B.↗
NASA NTRS1994

Computational modelling of Er(3+): Garnet laser materials

The Er(3+) ion has attracted a lot of interest for four reasons: (1) Its (4)I(sub 13/2) yields (4)I(sub 15/2) transition lases in the eyesafe region near 1.5 micron; (2) the (4)I(sub 13/2) transition lases near 2.8 micron, an important wavelength for surgical purposes; (3) it displays surprisingly efficient upconversion with lasing observed at 1.7, 1.2, 0.85, 0.56, 0.55, and 0.47 micron following 1.5 micron pumping; and (4) it has absorption bands at 0.96 and 0.81 micron and thus can be diode pumped. However, properties desirable for upconversion reduce the efficiency of 1.5 and 3 micron laser operation and vice versa. Since all of the processes are influenced by the host via the crystal field induced stark splittings in the Er levels, this project undertook modelling of the host influence on the Er lasinng behavior. While growth and measurement of all ten Er(3+) doped garnets is the surest way of identifying hosts which maximize upconversion (or conversly, 1.5 and 3 micron performance), it is also expensive - costing approximately $10,000/material or approximately $100,000 for the materials computationally investigated here. The calculations were performed using a quantum mechanical point charge model developed by Clyde Morrison at Harry Diamond Laboratories. The programs were used to fit the Er:YAG experimental energy levels so that the crystal field parameters, B(sub nm) could be extracted. From these radial factors, rho (sub n) were determined for Er(3+) in garnets. These, in combination with crystal field components, Anm, available from X-ray data, were used to predict energy levels for Er in the other nine garnet hosts. The levels in Er:YAG were fit with an rms error of 12.2/cm over a 22,000/cm range. Predicted levels for two other garnets for which literature values were available had rms errors of less than 17/cm , showing the calculations to be reliable. Based on resonances between pairs of calculated stark levels, the model predicts GSGG as the best host for 1.5 micron laser operation, GSGG or YSAG as the best host for a 2.8 micron operation, and LuGG as the best host for an upconversion material.

Spangler, Lee H.↗
NASA NTRS1993

Non-intrusive measurements in a rocket engine combustor

In recent years analytical tools to characterize combustor flow have been developed in order to support design. To facilitate anchoring of combustion related physical models and the CFD codes in which they are incorporated, considerable development and application of non-intrusive combustion diagnostic capabilities has occurred. Raman spectroscopy can be used to simultaneously detect all polyatomic molecules present in significant concentrations and to determine gas temperature. This is because all molecules possess a distinct temperature dependent Raman spectrum. A multi-point diagnostic system for non-intrusive temperature and species profiling in rocket engines has been developed at Rocketdyne. In the present effort, the system has been undergoing validation for application to rocket engine component testing. A 4 inch diameter windowed combustor with a coaxial gas-gas injector was chosen for this series of validation experiments. Initially an excimer-pumped tunable dye laser and later a solid state Nd-Yag laser served as excitation sources. The Raman signal was dispersed by a monochromator and detected by a gated, intensified Charged Coupled Device (CCD) array. Experiments were carried out prior to each series of hot fire tests to ensure that the Raman signal detected was due to a spontaneous rather than a stimulated Raman emission process. Over sixty hot fire tests were conducted during the first series of tests with the excimer/dye laser. All hot fire testing was at a mixture ratio of 0.5 and chamber pressures of approximately 100 and approximately 300 psia. The Raman spectra of hydrogen, water vapor and oxygen recorded during single element hot fire tests were reduced and analyzed. A significant achievement was the attainment of single shot Raman spectra in cold flow tests. Unfortunately, the single shot signal-to-noise ratio deteriorated to an unacceptable level during the hot fire testing. Attempts to obtain temperature data from the hydrogen Q1-branch profiles obtained in hot fire tests suggest that potentially complicating factors may render the approach of averaging data on the photodiode array invalid. A second series of hot fire tests was conducted with a 4 element coaxial injector using the Nd-Yag laser. A very compact and portable diagnostics set up was assembled for ease of alignment, relocation and flexibility. Measurements were made at several regions in the chamber in order to map concentration profiles. High spatial resolution and improved signal to noise characteristics were demonstrated.

Farhangi, S.↗
NASA NTRS1995

Design and development of an all-solid-state laser unit for microgravity combustion applications

The laser-induced fluorescence (LIF) technique is a sensitive and noninvasive method for imaging of flames and for monitoring of temperature and the presence of transient molecular species in flames. Our research effort has two major objectives: (1) to use LIF to study the fundamentals of microgravity combustion via spectroscopic characterization of free radicals, and (2) to design and develop an all-solid-state portable laser unit for combustion studies in a microgravity environment. Well-characterized free radicals, namely hydroxyl (OH) and methoxy (CH3O), have analytically convenient bands that can be laser-excited in the 280-298 nm spectral region with the newly discovered solid-state tunable laser, which is based on the LiCaAIF6:Ce3+(LiCAF:Ce) single crystal pumped by the quadrupled (266 nm) output of a Q-switched YAG:Nd laser. The 266 nm YAG radiation (of about 10 mJ pulse energy) was split into two beams of about equal intensity, one used for photolysis of the free radical precursor and the other used for pumping the laser crystal. Tunability of the LiCAF:Ce laser was provided by a step-motor-driven Littrow-mounted diffraction grating. Laser excitation spectra of the CH3O radical was recorded in the 291.5-296.5 nm region with 0.15 cm(exp -1) resolution. Laboratory experiments have thus successfully shown that the idea of using the LiCAF:Ce laser as a dual-purpose photolysis and excitation source can pay rich dividends and that such a laser can be the center piece of an all-solid-state portable device that can be used for routine analytical investigations of microgravity combustion phenomena.

Kamal, Mohammed M.↗
NASA NTRS1995

Space Applications of Industrial Laser Systems (SAILS)

A program is under way to develop a YAG laser based materials processing workstation to fly in the cargo bay of the Space Shuttle. The system will be capable of cutting and welding steel, aluminum, and Inconel alloys of the type planned for use on Space Station Freedom. As well as demonstrating the ability of a YAG laser to perform remote (fiber-optic delivered) repair and fabrication operations in space, fundamental data will be collected on these interactions for comparison with terrestrial data and models. The flight system, scheduled to fly in 1995, will be constructed as two modules to fit into the standard Get Away Special (GAS) canisters. The first can holds the laser and its power supply, to be constructed by our industrial partner, Lumonics Industrial Processing Division. The second canister has the materials processing workstation and the command and data acquisition subsystems. These components will be provided by groups at the University of Tennessee Space Institute (UTSI) and the University of Waterloo. The cans are linked by a fiber-optic cable which transmits the beam from the laser head to the workstation.

Mueller, Robert E.↗
NASA NTRS1997

Elucidation of Free Radical and Optogalvanic Spectroscopy Associated with Microgravity Combustion via Conventional and Novel Laser Platforms

Combustion studies under both normal gravity and microgravity conditions depend a great deal on the availability and quality of the diagnostic systems used for such investigations. Microgravity phenomena are specially susceptible to even small perturbations and therefore non-intrusive diagnostic techniques are of paramount importance for successful understanding of reduced-gravity combustion phenomena. Several non-intrusive diagnostic techniques are available for probing and delineating normal as well as reduced gravity combustion processes, such as Rayleigh scattering, Raman scattering, Mie scattering, velocimetry, interferometric and Schlieren techniques, emission and laser-induced fluorescence (LIF) spectroscopy. Our approach is to use the LIF technique as a non-intrusive diagnostic tool for the study of combustion-associated free radicals and use the concomitant optogalvanic transitions to accomplish precise calibration of the laser wavelengths used for recording the excitation spectra of transient molecular species. In attempting to perform spectroscopic measurements on chemical intermediates, we have used conventional laser sources as well as new and novel platforms employing rare-earth doped solid-state lasers. Conventional (commercially available) sources of tunable UV laser radiation are extremely cumbersome and energy-consuming devices that are not very suitable for either in-space or in-flight (or microgravity drop tower) experiments. Traditional LIF sources of tunable UV laser radiation involve in addition to a pump laser (usually a Nd:YAG laser with an attached frequency-doubling stage), a tunable dye laser. In turn, the dye laser has to be provided with a dye circulation system and a subsequent stage for frequency-doubling of the dye laser radiation, together with a servo-tuning system (termed the 'Autotracker') to follow the wavelength changes and also an optical system (called the 'Frequency Separator') for separation of the emanating visible and UV beams. In contrast to this approach, we have devised an alternate arrangement for recording LIF excitation spectra of free radicals (following appropriate precursor fragmentation) that utilizes a tunable rare-earth doped solid state laser system with direct UV pumping. We have designed a compact and portable tunable UV laser system incorporating features necessary for both in-space and in-flight spectroscopy experiments. For the purpose of LIF excitation, we have developed an all-solid-state tunable UV laser that employs direct pumping of the solid-state UV-active medium employing UV harmonics from a Nd:YAG laser. An optical scheme with counterpropagating photolysis and excitation beams focused by suitable lenses into a reaction vacuum chamber was employed.

Misra, Prabhakar↗
NASA NTRS1997

A Dual-Line Detection Rayleigh Scattering Diagnostic Technique for the Combustion of Hydrocarbon Fuels and Filtered UV Rayleigh Scattering for Gas Velocity Measurements

Non-intrusive techniques for the dynamic measurement of gas flow properties such as density, temperature and velocity, are needed in the research leading to the development of new generation high-speed aircraft. Accurate velocity, temperature and density data obtained in ground testing and in-flight measurements can help understand the flow physics leading to transition and turbulence in supersonic, high-altitude flight. Such non-intrusive measurement techniques can also be used to study combustion processes of hydrocarbon fuels in aircraft engines. Reliable, time and space resolved temperature measurements in various combustor configurations can lead to a better understanding of high temperature chemical reaction dynamics thus leading to improved modeling and better prediction of such flows. In view of this, a research program was initiated at Polytechnic University's Aerodynamics Laboratory with support from NASA Lewis Research Center through grants NAG3-1301 and NAG3-1690. The overall objective of this program has been to develop laser-based, non-contact, space- and time-resolved temperature and velocity measurement techniques. In the initial phase of the program a ND:YAG laser-based dual-line Rayleigh scattering technique was developed and tested for the accurate measurement of gas temperature in the presence of background laser glare. Effort was next directed towards the development of a filtered, spectrally-resolved Rayleigh/Mie scattering technique with the objective of developing an interferometric method for time-frozen velocity measurements in high-speed flows utilizing the uv line of an ND:YAG laser and an appropriate molecular absorption filter. This effort included both a search for an appropriate filter material for the 266 nm laser line and the development and testing of several image processing techniques for the fast processing of Fabry-Perot images for velocity and temperature information. Finally, work was also carried out for the development of a new laser-based strain-rate and vorticity technique for the time-resolved measurement of vorticity and strain-rates in turbulent flows.

Otugen, M. Volkan↗
NASA NTRS1998

Two Wavelength Ti:sapphire Laser for Ozone DIAL Measurements from Aircraft

Laser remote sensing of ozone from aircraft has proven to be a valuable technique for understanding the distribution and dynamics of ozone in the atmosphere. Presently the differential absorption lidar (DIAL) technique, using dual ND:YAG lasers that are doubled to pump dye lasers which in turn are doubled into the UV for the "on" and "off' line lasers, is used on either the NASA DC-8 or P-3 aircraft. Typically, the laser output for each line is 40-mJ and this is split into two beams, one looking up and the other downward, each beam having about 20-mJ. The residual ND:YAG (1.06 micron) and dye laser energies are also transmitted to obtain information on the atmospheric aerosols. While this system has operated well, there are several system characteristics that make the system less than ideal for aircraft operations. The system, which uses separate "on" and "off" line lasers, is quite large and massive requiring valuable aircraft volume and weight. The dye slowly degrades with time requiring replacement. The laser complexity requires a number of technical people to maintain the system performance. There is also the future interest in deploying an ozone DIAL system in an Unpiloted Atmospheric Vehicle (UAV) which would require a total payload mass of less than 150 kg and power requirement of less than 1500 W. A laser technology has emerged that could potentially provide significant enhancements over the present ozone DIAL system. The flashlamp pumped Ti:sapphire laser system is an emerging technology that could reduce the mass and volume over the present system and also provide a system with fewer conversion steps, reducing system complexity. This paper will discuss preliminary results from a flashlamp-pumped Ti:sapphire laser constructed as a radiation source for a UV DIAL system to measure ozone.

Situ, Wen↗
NASA NTRS1998

Efficient Third Harmonic Generation for Wind Lidar Applications

The characterization of atmospheric winds on a global basis is a key parameter required for accurate weather prediction. The use of a space based lidar system for remote measurement of wind speed would provide detailed and highly accurate data for future weather prediction models. This paper reports the demonstration of efficient third harmonic conversion of a 1 micrometer laser to provide an ultraviolet (UV) source suitable for a wind lidar system based on atmospheric molecular scattering. Although infrared based lidars using aerosol scattering have been demonstrated to provide accurate wind measurement, a UV based system using molecular or Rayleigh scattering will provide accurate global wind measurements, even in those areas of the atmosphere where the aerosol density is too low to yield good infrared backscatter signals. The overall objective of this work is to demonstrate the maturity of the laser technology and its suitability for a near term flight aboard the space shuttle. The laser source is based on diode-pumped solid-state laser technology which has been extensively demonstrated at TRW in a variety of programs and internal development efforts. The pump laser used for the third harmonic demonstration is a breadboard system, designated the Laser for Risk Reduction Experiments (LARRE), which has been operating regularly for over 5 years. The laser technology has been further refined in an engineering model designated as the Compact Advanced Pulsed Solid-State Laser (CAPSSL), in which the laser head was packaged into an 8 x 8 x 18 inch volume with a weight of approximately 61 pounds. The CAPSSL system is a ruggedized configuration suitable for typical military applications. The LARRE and CAPSSL systems are based on Nd:YAG with an output wavelength of 1064 nm. The current work proves the viability of converting the Nd:YAG fundamental to the third harmonic wavelength at 355 nm for use in a direct detection wind lidar based on atmospheric Rayleigh scattering.

Mordaunt, David W.↗