Search NASA⌕ Search

SEARCH · Search NASA

Results for “Q-SWITCHING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Calculations of laser cavity dumping for optical communications

For deep-space pulse-position modulation (PPM) optical communication links using Nd:YAG lasers, two types of laser transmitter modulation techniques are available for efficiently producing laser pulses over a broad range of repetition rates: Q-switching and cavity dumping. The desired modulation scheme is dependent on the required pulse repetition frequency and link parameters. These two techniques are discussed, theoretical and numerical calculations of the internal energy of the laser cavity in cavity dumping are described, and an example of cavity dumping is applied to a link for a proposed experiment package on Cassini.

Robinson, D. L.↗
NASA NTRS1989

Development of mid-infrared solid state lasers for spaceborne lidar

The laser performance of a Ho(3+):Tm(3+):Cr(3+):YAG crystal was measured under flashlamp pumping at various operating temperatures. The normal mode laser thresholds of a Ho(3+)(0.45 at. percent):Tm(3+)(2.5 at. percent):Cr(3+)(1.5 at. percent ):YAG crystal were found to range from 26 to 50 J between 120 and 200 K with slope efficiencies up to 0.36 percent with a 60 percent reflective output mirror. From the Q-switched operations a slope efficiency corresponding to 90 percent of the normal mode operation was observed. Laser wavelengths were measured for various operating conditions and fluorescence spectra were obtained at various temperatures in order to help understand the dynamic energy processes among the Ho(3+), Tm(3+), and Cr(3+) ions. A pulse forming network for a flashlamp pumped Cr:GSAG laser, which is to be used as a high power laser diode simulator in rare earth laser pumping, was completed and tested. The network provided critically damped, 1 ms FWHM, square pulses with a rise time of about 160 micrometers at an input electrical energy of 300 J.

Whitney, Donald A.↗
NASA NTRS1988

Laser action in chromium-activated forsterite for near infrared excitation

This paper reports on laser action in chromium-doped forsterite (Cr:Mg2SiO4) for 1064-nm excitation of the crystal's double-hump absorption band spanning the 850-1200-nm wavelength range. The cavity arrangement used for obtaining laser action in Cr:Mg2SiO2 was similar to that described by Petricevic et al. (1988). The fundamental and second harmonic emissions from a Q-switched Nd:YAG laser operating at a 10-Hz repetition rate were used for excitation of the NIR and visible bands, respectively. Pulsed laser action was readily observed for both the 1064-nm and 532-nm pumping at or above the respective thresholds. The laser parameters of the 532-nm and 1064-nm excitations were similar, indicating that the IR band is responsible for laser action for both excitations.

Petricevic, V.↗
NASA NTRS1988

Modulation techniques for deep-space pulse-position modulation (PPM) optical communication

The extremely energy-efficient pulse-position modulation (PPM) format is being actively developed as a basis for optical communications with deep-space probes. Attention is presently given to different modulation schemes for the efficient production of laser pulses over a broad range of repetition rates. Both Q-switching and cavity dumping modulation methods are available for the envisioned diode-pumped Nd:YAG laser source. Numerical calculation results are presented for cavity-dumping.

Rayman, Marc D.↗
NASA NTRS1989

Solid-state lasers for the mid-infrared region

Developmental results for solid-state lasers for the mid-IR region are reviewed. Good slope efficiency and reasonable thresholds have been demonstrated for multiply doped mid-IR lasers. Laser efficiency increases as the operating temperature is decreased, due to both reduced threshold and a higher slope efficiency. Good slope efficiencies have been achieved even at room temperature. While Q-switching has been demonstrated at room temperature, it is not nearly as efficient as it is at reduced temperatures.

Barnes, Norman P.↗
NASA NTRS1990

Absolute and relative nonlinear optical coefficients of KDP, KD(asterisk)P, BaB2O4, LiIO3, MgO:LiNbO3, and KTP measured by phase-matched second-harmonic generation

Both absolute and relative nonlinear optical coefficients of six nonlinear materials measured by second-harmonic generation are discussed. A single-mode, injection-seeded, Q-switched Nd:YAG laser with spatially filtered output was used to generate the 1.064-micron fundamental radiation. The following results were obtained: d36(KDP) = 0.38 pm/V, d36(KD/asterisk/P) = 0.37 pm/V, (parallel)d22(BaB2O4)(parallel) = 2.2 pm/V, d31(LiIO3) = -4.1 pm/V, d31(5 percentMgO:MgO LiNbO3) = -4.7 pm/V, and d(eff)(KTP) = 3.2 pm/V. The accuracy of these measurements is estimated to be better than 10 percent.

Eckardt, Robert C.↗
NASA NTRS1989

Optical limiting in solutions of metallo-phthalocyanines and naphthalocyanines

Optical limiting measurements have been made on solutions of several metal containing phthalocyanines and naphthalocyanines. Measurements at 532nm using nanosecond pulses from a Q-switched Nd:YAG laser show limiting throughputs of 1-10 millijoules with mild focussing in alcohol solutions with nominal transmissions of 30-70 percent. Measurements on chloro-aluminum-phthalocyanine solutions utilizing individual 30 psec pulses or trains (spanning about 100nsec) of modelocked pulses have shown even lower limiting throughputs. Thus, the dynamic range of the limiting behavior has been shown to cover at least three orders of magnitude. Prompt limiting is attributed to strong singlet-singlet (S1-Sn) absorption, whereas the longer time limiting behavior is postulated to result from strong triplet-triplet (T1-Tn) absorption. In addition to these studies, efforts have been underway to identify materials with reduced limiting throughput and improved optical transmission characteristics.

Coulter, Daniel R.↗
NASA NTRS1991

High-resolution measurements of surface topography with airborne laser altimetry and the global positioning system

Recently, an airborne lidar system that measures laser pulse time-of-flight and the distortion of the pulse waveform upon reflection from earth surface terrain features was developed and is now operational. This instrument is combined with Global Positioning System (GPS) receivers and a two-axis gyroscope for accurate recovery of aircraft position and pointing attitude. The laser altimeter system is mounted on a high-altitude aircraft platform and operated in a repetitively-pulsed mode for measurements of surface elevation profiles at nadir. The laser transmitter makes use of recently developed short-pulse diode-pumped solid-state laser technology in Q-switched Nd:YAG operating at its fundamental wavelength of 1064 nm. A reflector telescope and silicon avalanche photodiode are the basis of the optical receiver. A high-speed time-interval unit and a separate high-bandwidth waveform digitizer under microcomputer control are used to process the backscattered pulses for measurements of terrain. Other aspects of the lidar system are briefly discussed.

Garvin, James B.↗
NASA NTRS1989

Phase conjugation by degenerate four wave mixing in disodium fluorescein solution in methanol

Organic dyes are known to show the resonant type of nonlinear optical properties, including phase conjugation. In the present work, disodium fluorescein in methanol is used as an organic nonlinear medium for degenerate four wave mixing at 532 nm to see the intensity dependence of the phase conjugate signal at different concentrations of the solution. It is observed that the maximum reflectivity of the signal occurs in a concentration range of 5 x 10(exp -3)/cu cm to 1.2 x 10(exp -2) g/cu cm. It is also observed that the intensity of the signal drops suddenly to less than half of its maximum outside the concentration range mentioned above. An investigation of the phase conjugate signal intensity by changing the delay time between probe signal and the forward pump is also examined. Briefly discussed is the possibility of population grating in dye liquids as a source of enhancing the third order susceptibility besides the other techniques mentioned in reference. The experiment is done by beam splitting the second harmonic (532 nm) of Nd:YAG laser, Q-switched at 20 pulses/sec (pulse width is approximately 8 and 200 mJ per pulse).

Abdeldayem, Hossin↗
NASA NTRS1991

In situ extraction and analysis of volatile elements and molecules from carbonaceous chondrites

A laser microprobe mass spectrometer was used to measure volatiles released, on a scale of 30-50 microns, from freshly broken, sawed, and weathered surfaces in fragments of the Allende, Murchison, Coolidge, Felix, and Orgueil carbonaceous chondrites. Samples were heated to about 120 C under a vacuum of 200 ntorr and illuminated with the focused beam of a Q-switched Nd:glass laser of variable energy output (0.1-1.0 J); the gases released were analyzed using a computer-controlled mass-selective detector. The results are presented in tables and graphs and discussed in detail, with particular attention to aqueous alteration; weathering; thermal metamorphism; the distribution of sulfur-bearing phases; and differences in the amounts of volatiles in matrix, inclusions, and chondrules.

Hartmetz, C. P.↗
NASA NTRS1991

Ultrafast IR detector response in high Tc superconducting thin films

The response from a high Tc superconducting multielement optical detector made of a laser deposited Y-Ba-Cu-O thin film has been evaluated. Several microscopic and spectroscopic techniques were used to establish the presence of the correct phase of the thin film. Optical pulses from a laser diode at 830 nm and from a Q-switched CO2-laser at 10.6 microns were used. The detector responded to 50 ps (FWHM) pulses. A comparison between dR/dT of the film and the response amplitude as a function of temperature indicated a bolometric response.

Lindgren, Mikael↗
NASA NTRS1990

High Tc superconducting IR detectors from Y-Ba-Cu-O thin films

A thin-film high-Tc superconducting multielement optical detector made of Y-Ba-Cu-O has been designed and evaluated using optical pulses from a diode laser (830 nm) and a Q-switched CO2-laser (10.6 microns). Different thin films have been tested. A laser deposited film showed the strongest response amplitude for short pulses and responded to an ultrafast, 50 ps wide pulse. Comparisons between dR/dT and response as a function of temperature indicated, however, a bolometric response.

Lindgren, M.↗
NASA NTRS1991

Tunable 2.1-micron Ho lidar for simultaneous range-resolved measurements of atmospheric water vapor and aerosol backscatter profiles

An eye-safe tunable differential-absorption lidar system has been developed for the range-resolved measurement of aerosol backscatter and water vapor in the atmosphere. The lidar uses a flash-lamp-pumped, Q-switched, 10-mJ solid-state Ho:YSGG laser that is continuously tunable over a 20/cm wavelength range near 2.084 microns. Both path-averaged and range-resolved measurements were performed with the Ho differential-absorption lidar system. Preliminary measurements have been made of the temporal variation of atmospheric aerosol backscatter and water-vapor profiles at ranges out to 1 km. These results indicate that the Ho lidar has the potential for the eye-safe remote sensing of atmospheric water vapor and backscatter profiles at longer ranges if suitably enhanced in laser power and laser linewidth.

Cha, Sungdo↗
NASA NTRS1992

Summer graduate research program for interns in science and engineering

The goal of the 10 week graduate intern program was to increase the source of candidates for positions in science and engineering at the Goddard Space Flight Center. Students participating in this program submitted papers on the work they performed over the 10 week period and also filled out questionnaires on the program's effectiveness, their own performance, and suggestions on improvements. The topics covered by the student's papers include: microsoft excel applications; fast aurora zone analysis; injection seeding of a Q-switched alexandrite laser; use of high temperature superconductors; modifications on a communication interface board; modeling of space network activities; prediction of atmospheric ozone content; and applications of industrial engineering.

Lee, Clinton B.↗
NASA NTRS1992

Laser Transmitter Module (LTM) for LITE

In Dec. 1991 TITAN SPECTRON successfully completed its six year effort to design, build, space qualify, test, and deliver the Laser Transmitter Module (LTM) for NASA LaRC's LITE program. The delivered LTM is a three color Q-switched flashlamp pumped Nd:YAG laser that is described as the first true world-class lidar in space. The preliminary design and verification tests results were first presented at the 14th International Laser Radar Conference (ILRC) in 1988. This paper describes not only the delivered product but also the verification and space qualification processes that resulted in the world's first space qualified high powered laser system for environmental exploration from space. Video of the laser operating in a Class 100 clean room and subsystems undergoing 10 G vibration tests will provide a vivid illustration of the key elements that separate a space qualified system from its laboratory counterpart. Flight laser performance measurements form the baseline in post-delivery test results to be presented at this conference.

Chang, John↗
NASA NTRS1992

System Testing and Performance Characterization of the LITE Laser Transmitter Module at NASA

The Laser Transmitter Module (LTM) is a three-color Q-switched flashlamp pumped Nd:YAG laser. The original design concept was to package commercially available optics and flashlamp electronics for spaceflight with a power consumption goal of 2200 W and a weight goal of 600 lbs. The optical output was to exceed 200 mJ of IR, 400 mJ of green, and 150 mJ of UV per pulse at 10 Hz. The new space qualified laser exceeds the optical output requirements by 188 percent, 50 percent, and 13 percent in the UR, green, and UV respectively. This output needs only 1500 W at a weight of only 500 lbs. The LTM was delivered to the NASA Langley Research Center in December 1991. Optical characterization is now being completed.

Cimolino, Marc C.↗
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 NTRS1992

One joule output from a diode-array-pumped Nd:YAG laser with side-pumped rod geometry

Output of 1.25 J per pulse (1.064 micron) with an absolute optical efficiency of 28 percent and corresponding electrical efficiency of 10 percent was demonstrated in a diode-array-pumped Nd:YAG laser using a side-pumped rod geometry in a master-oscillator/power-amplifier configuration. In Q-switched operation, an output of 0.75 J in a 17-ns pulse was obtained. The fundamental laser output was frequency doubled in KTP with 60 percent conversion efficiency to obtain 0.45 J in a 16-ns pulse at 532 nm. The output beam had high spatial quality with pointing stability better than 40 microrad and a shot-to-shot pulse energy fluctuation of less than +/-3 percent.

Kasinski, Jeffrey J.↗