Pumping mechanism of CO2 laser and formation rate of CO2 from CO and O
Time delay in pulsed optical carbon dioxide laser pumping mechanism in high current gaseous discharge
Chen, C. J.↗
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Results for “optical pulses”
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.
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X-ray observations of pulsars.
The X-ray pulsations from NP 0532, discovered by Fritz et al. (1969), have been studied. The detectors in the investigations had wide fields of view, and the entire Crab Nebula NP 0532 radiation was detected. The power density spectrum of X-radiation observed is presented together with the shapes of X-ray and optical pulses. Searches for X-ray pulsations from other X-ray sources have also been carried out. The summarized results are shown in a table.
Bradt, H. V.↗
Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation
Work continued on a number of projects aimed at the generation of tunable visible, infrared, and ultraviolet light; and on the control of this light by means of novel mode-locking and modulation techniques. Progress is summarized for the following projects: (1) the transient modelocking of the Nd:YAG laser and application of short optical pulses; (2) studies of the sodium-xenon excimer laser; (3) development of techniques for vacuum ultraviolet holography; and (4) studies of multiple photon pumped xenon and argon excimer lasers.
Harris, S. E.↗
Investigation of laser dynamics, modulation and control by means of intra-cavity time varying perturbation
Projects aimed at the generation of tunable visible, infrared, and ultraviolet light, and on the control of this light by means of novel mode-locking and modulation techniques are discussed. During this period the following projects have been active: (1) studies of transient mode-locking of the Nd:YAG laser and the application of short optical pulses; (2) experimental investigations of the Na-Xe excimer laser system; (3) further development of techniques for vacuum ultraviolet holography; and (4) theoretical and initial experimental studies of a new device which should prove very useful for both infrared up-conversion and generation of tunable UV radiation - a two-photon resonantly pumped frequency converter.
Harris, S. E.↗
Nonlinear optical response of metal-barrier-metal junctions
The optical response of metal-barrier-metal (MBM) junctions is discussed, with emphasis on the nonlinearity of response associated with reversal of polarity as optical intensity is increased. This nonlinear behavior can be used to measure correlation functions of optical pulses or to generate ultrashort electrical pulses. Expressions for the current flowing through the insulating barrier (junction), and for the rectification current, are given. Pulse signal and polarity of the electrical pulse evolves as the junction bias is varied about the null-signal bias. The apparatus used to obtain rectification pulse signals is described; the calculated evolution of the rectified pulse shape is found to correspond to that of pulse signals obtained experimentally. The generation of pulses six orders of magnitude smaller than a previously-obtained instrument-limited 1.6 nanosecond pulse has been observed.
Fan, B.↗
A comparative study of optimum and suboptimum direct-detection laser ranging receivers
A summary of previously proposed receiver strategies for direct-detection laser ranging receivers is presented. Computer simulations are used to compare performance of candidate implementation strategies in the 1- to 100-photoelectron region. Under the condition of no background radiation, the maximum-likelihood and minimum mean-square error estimators were found to give the same performance for both bell-shaped and rectangular optical-pulse shapes. For signal energies greater than 100 photoelectrons, the root-mean-square range error is shown to decrease as Q to the -1/2 power for bell-shaped pulses and Q to the -1 power for rectangular pulses, where Q represents the average pulse energy. Of several receiver implementations presented, the matched-filter peak detector was found to be preferable. A similar configuration, using a constant-fraction discriminator, exhibited a signal-level dependent time bias.
Abshire, J. B.↗
Studies of laser and laser devices
The generation of tunable, infrared, and ultraviolet light, and the control of this light by mode-locking and modulation techniques are discussed. Particular emphasis is given to energy storage and extraction using atomic levels, the development of a tunable narrowband vacuum ultraviolet light source, and to the generation and applications of ultrashort optical pulses.
Harris, S. E.↗
Rapid oscillations in cataclysmic variables. V - H2252-035, a single-sideband X-ray and optical pulsar
Photometric and spectroscopic observations of the optical counterpart of the X-ray source H2252-035 reveal the existence of stable periodicities of 3.59 hr and 14.31 min. Both radial velocity and photometric variations occur at the longer period, suggesting that it is the true orbital period of the underlying cataclysmic binary. The shorter period appears as a 10% modulation in the light curve, superposed on the 3.59 hr variation. The frequency is the lower orbital sideband of the X-ray pulsation frequency, suggesting that the optical pulses arise from reprocessing in the atmosphere of the secondary. Unlike the majority of X-ray pulsars, H2252-035 appears to contain a white dwarf rather than a neutron star.
Patterson, J.↗
Capacity and cutoff rate of (M+1)-ary decision rules for noisy M-ary optical PPM channel
The channel capacity C and the cutoff rate R sub o of two (M + 1)-ary decision rules for noisy M slots/symbol optical pulse position modulation (PPM) with ideal photon counting are computed and compared. Also the values of the optimum thresholds needed to minimize the signal requirements are given. With a minor increase in hardware complexity, the symbol by symbol threshold decision rule is shown to be superior to the slot by slot threshold detection and decision rule in two aspects: first, it saves more than 0.5 dB in signal energy for the very noisy cases of more than one noise photon per slot (for low noise cases it also saves signal energy, but a negligibly small amount). Second, it is more robust to variations in the noise level.
Lee, P. J.↗
The NASA Thunderstorm Overflight Program (TOP): Research in atmospheric electricity from an instrumented U-2 aircraft platform
An overview of the NASA Thunderstorm Overflight Program (TOP) is presented. The various instruments flown on the NASA U-2 aircraft, as well as the ground instrumentation used to collect optical and electronic signature from the lightning events, are discussed. Samples of some of the photographic and electronic signatures are presented. Approximately 6400 electronic data samples of optical pulses were collected and are being analyzed.
Vaughan, O. H., Jr.↗
A new class of radio pulsars
A new class of spun-up radio pulsars with short periods, long apparent ages, and pulsed optical, X-ray, and gamma ray fluxes significantly below those expected for canonical pulsars with similar periods is reported. Scenarios for the formation of such a pulsar, in which a neutron star accretes from a Keplerian accretion disk initially fed by a companion, are discussed. Because of their long spin-down lifetimes, such pulsars would probably be observable if their birth rate exceeded even 10 to the -4th that of the canonical ones. It is proposed that the recently discovered millisecond pulsar 4C21.53 belongs to this class, together with the binaries PSRs 1913+16, 0820+02, and 0655+64, as well as possibly several isolated pulsars such as PSRs 1952+29 and 1804-08.
Alpar, M. A.↗
Laboratory simulation of Venusian lightning
Evidence of lightning activity in the Venusian atmosphere has been obtained from the Venera 9, 11, and 12 spacecraft, and from the Pioneer Venus Orbiter (PVO). However, a search for optical pulses expected from Venusian lightning using the star sensor on the PVO did not detect any signals. It has been suggested that the star sensor did not detect lightning because Venusian lightning does not radiate in the 500- to 900-nm spectral region detected by the star sensor. In this paper, spectra obtained from a laboratory simulation of Venusian lightning are discussed. Both the laboratory spectrum and the results of a theoretical calculation of line intensities show that Venusian lightning can be expected to radiate strongly in the 600- to 900-nm spectral region. Hence, the failure of the star sensor to detect lightning must be caused by the low flashing rate or by the low intensity of Venusian lightning.
Borucki, W. J.↗
Picosecond measurements using photoacoustic detection
A report is presented of experimental results on picosecond time-resolved photoacoustic measurements of excited-state lifetimes, cross sections, and polarization properties for organic dye molecules in solution, using a new technique in which the total photoacoustic impulse produced by two ultrashort optical pulses with variable time delay between them is detected. The picosecond photoacoustic detection technique reported here appears to be a promising new way to observe weak excited-state cross sections and to perform picosecond lifetime measurements in a large variety of weakly absorbing and/or nonfluorescing atomic and molecular systems.
Heritier, J.-M.↗
NASA thunderstorm overflight program: Atmospheric electricity research. An overview report on the optical lightning detection experiment for spring and summer 1983
This report presents an overview of the NASA Thunderstorm Overflight Program (TOP)/Optical Lightning Experiment (OLDE) being conducted by the Marshall Space Flight Center and university researchers in atmospheric electricity. Discussed in this report are the various instruments flown on the NASA U-2 aircraft, as well as the ground instrumentation used in 1983 to collect optical and electronic signatures from the lightning events. Samples of some of the photographic and electronic signatures are presented. Approximately 4132 electronic data samples of optical pulses were collected and are being analyzed by the NASA and university researchers. A number of research reports are being prepared for future publication. These reports will provide more detailed data analysis and results from the 1983 spring and summer program.
Vaughan, O. H., Jr.↗
Phase locked loop synchronization for direct detection optical PPM communication systems
Receiver timing synchronization of an optical pulse position modulation (PPM) communication system can be achieved using a phase locked loop (PLL) if the photodetector output is properly processed. The synchronization performance is shown to improve with increasing signal power and decreasing loop bandwidth. Bit error rate (BER) of the PLL synchronized PPM system is analyzed and compared to that for the perfectly synchronized system. It is shown that the increase in signal power needed to compensate for the imperfect synchronization is small (less than 0.1 dB) for loop bandwidths less than 0.1% of the slot frequency.
Chen, C. C.↗
Nighttime observations of thunderstorm electrical activity from a high altitude airplane
Observations of nocturnal thunderstorms from three aerial cameras flown at an altitude of 20 km and at an airspeed of 200 m/s are analyzed and compared with previous ground-based observations. Both diffuse illumination in the cloud and unobscured segments of lightning channels a kilometer or longer in clear air around and above the cloud are observed. A similarity is noted to exist between the airborne and the ground-based lightning spectra registered. It is further asserted that discrimination between cloud-to-ground and intracloud flashes and the counting of ground strokes can be achieved through the use of optical pulse pairs identified with leader return-stroke events in the cloud-to-ground flashes studied.
Brook, M.↗
Spectral and temporal characteristics of AlGaAs/GaAs superlattice p-i-n photodetectors
Measurements of the spectral and the temporal response of AlGaAs/GaAs p-i-n photodetectors with superlattice intrinsic regions grown by molecular beam epitaxy are reported. The feasibility for high-speed applications is demonstrated by a time constant limited impulse response of 200 ps (full width at half-maximum) when excited near the band edge with 100 ps optical pulses. The theory-predicted and recently verified voltage tunability of the band edge with clearly resolved excitonic resonances was observed. The responsivity was measured to be 0.2 A/W.
Larsson, A.↗
Performance measurements of a diode laser optical communications link with Q = 4 PPM signaling
The theoretical and measured performance characteristics of a direct detection optical communication system are reported. The system consisted of a semiconductor diode laser, silicon avalanche photodiode detector, and used Q = 4 optical pulse position modulation signaling to transmit binary source data at a rate of 25 megabits/sec. Operation at a receiver bit error probability of 10 to the -6th was demonstrated at received signal energies corresponding to an average of 160 detected photons per PPM symbol, or 80 photons per source bit.
Sun, X.↗