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NASA NTRS1973

High-power broadly tunable difference-frequency generation in proustite.

High-power wavelength-tunable coherent radiation has been produced by generating the difference frequency between the output from a tunable narrow-linewidth ruby-pumped infrared dye laser and a Q-switched ruby laser in a proustite crystal. Peak infrared powers in the kilowatt range and wavelength tunability from 3.20 to 5.65 microns have been achieved. The experimentally determined infrared power tuning curves are compared to those predicted by theory for interacting Gaussian light beams.

Decker, C. D.↗

NASA NTRS1974

Laser system to detonate explosive devices

Detonating system is not affected by electromagnetic interference. System includes laser source, Q-switch, and optical fiber connected to explosive device. Fiber can be branched out and connected to several devices for simultaneous detonation.

Menichelli, V. J.↗

NASA NTRS1973

Investigation of laser holographic interferometric techniques for structure inspection

The application of laser holographic interferometric techniques for nondestructive inspection of material structures commonly used in aerospace works is investigated. Two types of structures, composite plate and solid fuel rocket engine motor casing, were examined. In conducting the experiments, both CW HeNe gas lasers and Q-switched ruby lasers were used as light sources for holographic recording setups. Different stressing schemes were investigated as to their effectiveness in generating maximum deformation at regions of structural weakness such as flaws and disbonds. Experimental results on stressing schemes such as thermal stressing, pressurized stressing, transducer excitation, and mechanical impact are presented and evaluated.

Chu, W. P.↗

NASA NTRS1974

Optically detonated explosive device

A technique and apparatus for optically detonating insensitive high explosives, is disclosed. An explosive device is formed by containing high explosive material in a house having a transparent window. A thin metallic film is provided on the interior surface of the window and maintained in contact with the high explosive. A laser pulse provided by a Q-switched laser is focussed on the window to vaporize the metallic film and thereby create a shock wave which detonates the high explosive. Explosive devices may be concurrently or sequentially detonated by employing a fiber optic bundle to transmit the laser pulse to each of the several individual explosive devices.

Yang, L. C.↗

NASA NTRS1973

Cautionary note concerning the CuSO4 X-ray laser

For the so far unconfirmed lasing action claimed by Kepros et al. (1972) to have been obtained by focusing a 1.06-micron radiation of a q-switched Nd(3+) glass laser to a small cylindrical volume inside a CuSO4-doped gelatin medium supported between two glass plates, an alternate explanation is proposed that does not depend on the assumption of laser action in copper. The proposed explanation shows how collimated X-ray beams might be created under the experimental conditions described by Kepros et al.

Billman, K. W.↗

NASA NTRS1974

A lidar system for remote probing of the lower atmosphere

The development and characteristics of a lidar system for atmospheric measurements are discussed. The lidar system employs a Q-switched ruby laser that radiates an intense pulse of light into the atmosphere to illuminate aerosol particles in the laser beam. Light backscattered from the particles is received by a Cassegrain telescope equipped with a sensitive photomultiplier tube. The output signal of the photomultiplier tube is displayed on an oscilloscope and recorded on polaroid film.

Craig, C. D.↗

NASA NTRS1974

Laser technology for high precision satellite tracking

Fixed and mobile laser ranging stations have been developed to track satellites equipped with retro-reflector arrays. These have operated consistently at data rates of once per second with range precision better than 50 cm, using Q-switched ruby lasers with pulse durations of 20 to 40 nanoseconds. Improvements are being incorporated to improve the precision to 10 cm, and to permit ranging to more distant satellites. These include improved reflector array designs, processing and analysis of the received reflection pulses, and use of sub-nanosecond pulse duration lasers.

Plotkin, H. H.↗

NASA NTRS1975

Pulse modulation effect on velocity fringes

The degradation of a hologram caused by object motion can be utilized to measure the rate of change of the length of an object beam. A rectangular shaped laser pulse is ordinarily used to illuminate the object in such an investigation. The velocity fringes obtained are considered in the calculation. There are no velocity fringes for Gaussian shaped pulses or for the pulses produced by a Q-switched ruby laser. It is shown with the aid of a mathematical analysis that a pulse of oscillating intensity or a pulse train will yield velocity fringes regardless of the shape of an individual pulse.

Decker, A. J.↗

NASA NTRS1975

Inherent time delay for dielectric breakdown in shock-loaded x-cut quartz

Dielectric breakdown in shock-loaded x-cut quartz is examined under conditions of both impact loading and Q-switched laser-irradiation loading. It is observed that breakdown is characterized by an inherent time delay which depends on the magnitude of the electric field. For pulse duration less than about 30 ns, dielectric breakdown is not observed.

Graham, R. A.↗

NASA NTRS1975

A 10.6 micron ladar for space rendezvous and docking

The paper describes a 10.6 micron ladar (a laser detection and ranging device) which is considered as a baseline sensor for space rendezvous and docking applications. The sensor uses a passively Q-switched CO2 laser as the transmitter active element, and a four-quadrant photodiode array, operated as a coherent receiver element in the heterodyne mode. The aperture will be about 3 inches, and the telescope will be able to steer the beam in a 40 by 40 degree window. Various aspects of the ladar system are examined in detail, including the laser control loop, the transmitter, the local oscillator, the telescope, and the output beam scanning.

Lowrey, D. O.↗

NASA NTRS1975

A wide angle search technique for a 10.6 micron ladar

A ladar (laser radar) sensor designed around a pulsed passively Q-switched CO2 laser, capable of a efficient and rapid scans with a narrow beam over a wide field of view, is considered for surveillance and tracking applications in space. The output is a train of narrow pulses with a controllable pulse repetition rate. A resonant vibrating mirror in back of a classical Gregorian telescope, and a plane pointing mirror in front for beam steering, are used in scanning. Scan pulse sequences are described and illustrated. The 10.6 micron ladar set is under consideration as baseline sensor for various space rendezvous and docking applications.

Levinson, S.↗

NASA NTRS1976

Laser fiber optics ordnance initiation system

Recent progress on system development in the laser initiation of explosive devices is summarized. The topics included are: development of compact free-running mode and Q-switched lasers, development of low-loss fiber optic bundles and connectors, study of nuclear radiation effects on the system, characterization of laser initiation sensitivities of insensitive high explosives, and the design methods used to achieve attractive system weight and cost savings. Direction for future work is discussed.

Yang, L. C.↗

NASA NTRS1977

High-accuracy range measurements to the moon

The lunar ranging station at the University of Texas McDonald Observatory has made more than 1800 range measurements to the four lunar retroreflectors during the first six years of its operation. Each range consists of a normal point constructed of from 5 to 20 single photoelectron returns. Normal point accuracies to about four parts in 10 to the tenth plus or minus 10 cm have become routine. The availability of excellent commercial timing equipment means that the error for such a measurement is primarily dependent on the width of the transmitted laser pulse. Second generation systems using mode-locked subnanosecond lasers can probably achieve routine normal point accuracies approaching one part in 10 to the tenth plus or minus 2 cm. High speed pockel cells may permit such accuracies to be realized with conventional Q-switched lasers.

Silverberg, E. C.↗

NASA NTRS1979

Nd:YAG development for spaceborne laser ranging system

The results of the development of a unique modelocked laser device to be utilized in future NASA space-based, ultraprecision laser ranger systems are summarized. The engineering breadboard constructed proved the feasibility of the pump-pulsed, actively modelocked, PTM Q-switched Nd:YAG laser concept for the generation of subnanosecond pulses suitable for ultra-precision ranging. The laser breadboard also included a double-pass Nd:YAG amplifier and provision for a Type II KD*P frequency doubler. The specific technical accomplishment was the generation of single 150 psec, 20-mJ pulses at 10 pps at a wavelength of 1.064 micrometers with 25 dB suppression of pre-and post-pulses.

Harper, L. L.↗

NASA NTRS1979

Internal photoemission in Ag-Al2O3-Al junctions

The magnitude of the photon-induced current in Ag-Al2O3-Al metal-oxide-metal junctions has been studied as a function of photon energy and angle of incident radiation. Photocurrents were theoretically analyzed on the basis of a modified vacuum photoemission model (Jain, 1975; Slayman et al., to be published). Optical constants previously reported in the literature (Irani et al., 1971; Ehnrereich et al., 1963) were used to calculate the true spatial generation rate in Ag and Al as a function of the angle, polarization of incident radiation, and film thickness. Results were found to be in very good agreement with experimentally determined values for a tunable dye laser with a KDP doubling crystal pumped by a Q-switched Nd:YAG laser with a LiIO3 doubling crystal. The system provided risetimes of 50 ns or less and peak powers of 10 W. Under short circuit conditions, the photoresponse to incident power was linear up to available power densities of 10 kW/sq cm. Quantum efficiencies of about 0.1% at zero-bias, near 3.8 eV under P polarization, were typically observed.

Guedes, J. M. P.↗

NASA NTRS1978

Pulse compression inside an actively AM mode-locked Nd:YAG laser using a liquid Kerr cell

A mode-locked Nd:YAG laser capable of generating pulses substantially shorter than the present limit of 30-50 ps, while retaining the stability of active mode locking, would be a useful development. This study presents a simplified theoretical analysis and a preliminary experimental verification of the use of an optical Kerr cell as a passive lossless pulse compressor inside a Q-switched and actively mode-locked YAG laser. The theoretical model indicates possible compression to as short as about 5 ps in a typical low-power Nd:YAG laser. The preliminary experimental results show substantial pulse compression via the predicted mechanism, though still not below about 30 ps. The technique appears capable, however, of pulse compression to substantially shorter values without the instabilities, statistical fluctuations, or energy losses associated with saturable-absorber mode locking.

Duerinckx, A. J.↗

NASA NTRS1979

Ultrashort pulse solid-state transmitter development

A pulsed, actively mode-locked, pulse-transmission-mode (PTM) Q-switched Nd:YAG laser has been developed for a planned NASA spaceborne precision ranging system. The laser emits single, 150-psec, 20-mJ pulses at 10 pulses per second at 1.064 micrometers.

Harper, L. L.↗

NASA NTRS1980

Ion beams from laser-generated plasmas

The paper describes the space-charge-limited beams produced by the plasma blowoffs generated by 20-MW bursts of 1.06-micron radiation from an active Q-switched Nd:YAG laser. Laser power densities near 10 to the 11th/sq cm on solid targets generate thermalized plasma plumes which drift to a 15-kV gridded extraction gap where the ions are extracted, accelerated, and electrostatically focused; the spatially defined ion beams are then magnetically analyzed to determine the charge state content in the beams formed from carbon, aluminum, copper, and lead targets. This technique preserves time-of-flight (TOF) information in the plasma drift region, which permits plasma ion temperatures and mass flow velocities to be determined from the Maxwellian ion curve TOF shapes for the individual charge species.

Hughes, R. H.↗