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A number of aqueous systems including acids, bases, salts, and some organic materials were irradiated with a Co-60 gamma-source, and then examined by ESR spectroscopy. H-atoms were found in sulfuric, phosphoric, perchloric and hydrochloric acid and in a number of phosphates. The H-atoms are unstable at 77 K in HC1 solutions. In H2SO4 and H3PO4 solutions there is an initial fast decay over a period of 20 to 40 hours, after which the sample is stable or decays very slowly. The H-atoms in perchloric acid solutions are stable at 77 K. A number of adsorbants were irradiated and examined by ESR both in the 'activated' state and when loaded with various materials. A Corning porous glass, various molecular sieves and some mixed silica alumina catalyst gave stable H-atoms when loaded with H2O. The yields are generally lower than in the aqueous systems described above. (Author)

The simultaneous Q-switching and mode-locking of a 1-meter-long glass laser rod has produced a pulse having an energy content of 44 joules with a peak power of 4 gigawatts and time duration of approximately 1.5 x 10 to the -9th power sec. A 47-joule pulse has been obtained using a 45-cm-long glass rod as a simultaneous Q-switched and mode-locked oscillator and a 1-meter-long glass rod as an optical amplifier. The time duration of individual mode-locked pulses for this case was 0.75 x 10 to the 9th power sec. Use of a 16.5-cm-long oscillator and 1-meter-long amplifier resulted in generation of pulses with a peak power between 3.7 x 10 to the 10th power and 9.4 x 10 to the 10th power watts and time durations of 2 x 10 to the -11th power to 8 x 10 to the -12 power sec, respectively. These measurements are believed to represent the highest peak power pulses reported in literature to date. Experimental techniques for generating single, subnanosecond pulses having peak powers in the hundreds of megawatts range have been devised and made operative. A 600-megawatt peak power pulse of 0.4 x 10 to the -9th power sec time duration was obtained with a 45-cm-long oscillator. Using such an oscillator plus a 1-meter rod as an amplifier a single 0.5 x 10 to the -9th power sec pulse has been generated with an energy content of 1.8 joules. A Marx-Bank pulse generator was designed, constructed, and utilized in generation of these single, ultrashort optical pulses. These measurements represent the shortest single, optical pulses reported in the literature to date.

A number of aqueous systems including acids, bases and some organic materials were irradiated at 77 degrees K with a Co-60 gamma-source, and then investigated by ESR spectroscopy. Hydrogen atoms were found in sulfuric and hydrochloric acid solutions. In H2SO4, at low concentrations, the hydrogen atoms were quite stable at 77 degrees K. At higher concentrations there was a noticeable decrease after storage at 77 degrees K. Preliminary data indicate that hydrogen atoms are much less stable in HCl than in H2SO4. (Author)

An experimental research program is being carried out to investigate two particular aspects of the thermal blooming problem. Thermal blooming is the self-induced effect which results from refractive index variations in the path of a laser beam caused by absorption of laser beam energy. The two aspects being investigated are the effect of transonic flow and also dead zones on the thermal distortion. When heat is added to flow at near sonic velocities severe density gradients and even shock waves can result. An experiment involving a CO2 laser and a blow down wind tunnel are being used to investigate this problem and a pulsed schlieren system is used to observe the density gradients., Report on Laser Propagation.

The report reviews briefly the application of ultrashort pulses to imaging radars, and shows the need for an alternate signal processing scheme. A mathematical description and physical interpretation of frequency domain sampling is presented and its application to time scaling and matched filtering is discussed. An experiment to demonstrate the technique is outlined and will be carried out during the next reporting period., See also AD0758059. Sponsored in part by DARPA.

The long range objective of this program is to develop an efficient and practical ultra-wideband thin film modulator for CO2 lasers useful for optical image radars and high-data-rate optical communication systems. During the present contracting period (25 May 1973 to 25 December 1973), the goal of this program is aimed at the demonstration of efficient sideband generation of a 10.6 micrometer CO2 laser carrier at microwave frequencies (X-band) in a nonlinear GaAs thin film optical modulator element which is interfaced with a microwave ridge guide structure. Electrooptic interaction in a GaAs thin film between an optical guided-wave and either a traveling or a synchronous standing microwave signal can produce a sideband at the sum and difference frequencies. By using a frequency modulated microwave field, a chirped optical signal in the sideband is generated. This signal can be separated from others by a proper optical filtering technique such as a diffraction grating or a narrow bandpass interferometer., See also report dated Mar 1973, AD0757792.

The feasibility of producing stimulated in the 3-5 wavelength band by exciting hydrogen chloride vibrational levels by electron impact is being investigated theoretically and experimentally. Theoretical interpretation of available transport data predicts large vibrational excitation rates. A high current density electron gun capable of sustaining a high electron density discharge has been developed and is described. The pulsed hydrogen chloride laser experiments in progress are also described., See also report dated 30 Nov 1972, AD0752631.

An experimental program was conducted using a small-scale, arc- augmented gas-dynamic laser with the objective of obtaining comprehensive data for evaluating theoretical predictions of optical gain for such devices over a wide range of potential operating conditions. Included among the program results were attainment of stagnation temperatures higher than those possible in ordinary combustion-driven gas-dynamic lasers, experimental evaluation of the homogeneity of the flow in this device and theoretical determination of the plenum gas composition from the experimentally measured stagnation temperature and pressure. A number of experimental difficulties were encountered during this program which limited the scope of the gain measurements obtained and thereby partially compromised the overall program objective., Sponsored in part by DARPA.

Measurements were made of the unsteady normal force and pitching moment on an NACA 0012 airfoil model oscillated both sinusoidally and nonsinusoidally over a range of incidence angles, including a substantial penetration into stall. The sinusoidal normal force and pitching moment data were reduced and tabulated as functions of the angle of attack, the angular velocity parameter, and the angular acceleration parameter. This generalized form of the data was used to reconstruct the measured sinusoidal aerodynamic response of the model airfoil with excellent results. Additional correlations were made using nonsinusoidal pitch schedules which included periodic ramp changes in angle of attack and a flexured angular blade response to a one-per- rev sinusoidal incidence angle change typical of that for a helicopter blade. The agreement between predicted and measured normal force and moment loops was very good for the ramp motion.

A CO2 waveguide laser was operated with an intracavity electro-optic polarization modulator. Coupling modulation at 48 and 120 MHz was observed which represents a significant step towards the contract goal to investigate the feasibility of linear ramp frequency modulation (500 MHz in 300 microsec.) of a stable CO2 oscillator. This master oscillator is of interest for a high resolution optical radar application.

The deposition of aluminum nitride was studied by comparing results obtained by reactive rf sputtering in nitrogen and ammonia ambients. Physical and optical properties of the films were measured. Charge storage characteristics of MIS capacitors employing a composite insulator structure of SrTiO3-SiO2 were studied. The strontium titanate was deposited by rf sputtering. Field effect transistors using SrTiO3-SiO2 gate insulation were fabricated and evaluated., Sponsored in part by DARPA.

The report discusses the investigation of the frequency stability characteristic of single-frequency Nd:YAG lasers. Technical Results reported include the locking of a single-frequency Nd:YAG laser to the bandpass of a high finesse Fabry-Perot interferometer, the unification of etalon thermal tuning of the laser for course frequency control, the construction of a second single- frequency laser, and the heterodyning of the two single-frequency YAG lasers at a variable frequency offset., See also report dated 31 Jul 1971, AD729030.

The report covers work under Contract N00014-66-C0344 for the period 1 August 1967 to 31 July 1968. Topics discussed include theoretical and experimental work on the propagation of ultrashort pulses, measurement of nanosecond fluorescent decay times, light amplification in saturable absorbers, adiabatic inversion of quantum states, optical rectification and mode-locking of organic dye lasers., See also Annual rept. no. 1, AD0657210. Sponsored in part by DARPA.

Topics discussed include analytical results on the propagation of ultrashort optical pulses, experimental results on tunable mode-locked organic dye laser and investigations of stimulated scattering process in absorbing liquids. (Author), See also AD673858.

Research plan: Analysis of the propagation of ultrashort optical pulses; Measurement of nanosecond fluorescence decay time; Light amplification in absorbing media; Adiabatic inversion of quantum states; Optical rectification of mode-locked laser pulses at microwave frequencies; and Mode-locking of organic dye lasers.

The focused high-intensity optical frequency beam from a Q-spoiled ruby or neodymium laser is used to cause electrical breakdown in a test gas, and the ionization produced is examined as a function of the gas, pressure, volume within which the breakdown occurs, and frequency of radiation. With both ruby and neodymium radiation, for the gases studied breakdown in air was observed to require the highest field strength with successively lower field strengths required for breakdown in neon, helium, and argon. Studies have been carried out to examine the attenuation of the laser beam by the breakdown plasma. For beam intensities slightly above the breakdown threshold, it is observed with both ruby and neodymium incident radiation that more than half of the laser beam energy can be absorbed in the plasma produced by the breakdown and that over 90% attenuation of the laser beam can occur at later times in the optical pulse. Measurements of the attenuation of an optical beam by the breakdown plasma at times subsequent to the incident giant pulse have been made using the cw beam from a helium-neon laser., See also AD428206.

Research is directed toward obtaining laser host materials with structures having cubic centrosymmetric sites in which trivalent laser activating ions can be substituted. Powders of perovskite-type compounds having the general formula Ba(B(3+) sub 0.5Ta sub 0.5) 03 with B(3+) = rare earth Y(3+) , Sc(3+) and In(3+) ions were prepared and their structures analyzed by means of X-ray diffraction. The studies showed that the most suitable host materials for this program were Ba(Y sub 0.5Ta sub 0.5)03, Ba(Lu sub 0.5Ta sub 0.5)03, Ba(Sc sub 0.5Ta sub 0.5)03 and Ba(In sub 0.5a sub 0.5)03 because they had cubic unit cells and contained ions with appropriate electronic configurations. These compounds have been prepared with Cr(3+) and Nd(3+) doping, and the fluorescence spectra of the Nd(3+) doped phases have been recorded and analyzed. Studies involving flux growth of crystals also have been made during this period.

Aluminum reinforced by up to 60 volume per cent boron fiber has been fabricated in the form of flat panels by a plasma spray technique. This material exhibited strengths in excess of 130,000 psi at room temperature and 100,000 psi at 500 C in the direction of fiber orientation and less than 10,000 psi in the transverse direction. A modulus of 34 x 10 to the 6th power psi was measured for aluminum containing 50 v/o boron fiber. 2024 Al alloy containing 41 v/o boron fiber was found to exhibit an apparent endurance limit at 10 to the 7th power cycles of 70,000 psi. Boron-aluminum has been shown to have excellent creep resistance and exhibit a 100 hr rupture life above 30,000 psi at 400 C and above 50,000 psi at 300 C. It was found that boron-titanium composites could not be fabricated without degradation of the fiber. Nickel plating the fiber eliminated this situation; however, reaction with the nickel was found to be deleterious. (Author)

An investigation of fires within a typical aircraft wing structure resulting from simulated battle damage has been conducted at sea level conditions and varying approach velocities in the United Aircraft Corporation Jet Burner Test Stand. The purpose of this program was two-fold: (1) To evaluate the Jet Burner Test Stand and test techniques for simulation and investigation of aircraft wing fires resulting from battle damage; and (2) To investigate the extinguishing of internal wing fires by a variation in airspeed. In addition to the work required to satisfy the above two objectives, tests were made to determine the effects of battle damage hole size, air leakage out of the wing, and fuel flow. The effects of combined battle damage and the variation of wing temperatures with time were also investigated, and an indication of wing fire heat release was obtained. Typical results are presented primarily in the form of temperature patterns on the wing surface and along the spars. Motion pictures taken during the tests have been assembled into a film to supplement the information presented in this report.

The Research Laboratories of the United Aircraft Corporation under the subject contract are conducting theoretical and experimental studies of the interaction of high intensity optical frequency radiation with gas atoms. By focusing the radiation from a Q-spoiled neodymium or ruby laser, it was found that for sufficiently high radiation intensity electrical breakdown can be produced in a gas. This phenomena has been investigated in a number of gases, and studies have been made to determine the dependence of the gas breakdown threshold on the frequency of laser radiation, gas pressure, gas species for both pure gases and mixtures, and the volume within which breakdown is formed.

The objective of this program was to conduct experimental and theoretical investigations of laser line profiles. The broadened homogeneous line width of an argon ion laser was studied as a function of pressure and excitation by means of the 'Lamb Dip' technique. Broadened homogeneous line widths of 200 to 400 MHz were recorded. These line widths are much larger than the 100 MHz radiative line width. The most plausible source for the broadened line is nonradiative phase interruptions occurring from small-angle Coulomb scattering in ion-ion collisions. It is shown that the line width decreases with increasing pressure for a certain range of laser oscillation. A simple collision broadening approach is not applicable to the ion system because of the behavior of the ion density as a function of pressure and excitation. Preliminary experiments were also performed with a CO2-N2-He laser and no experimental indication of a Lamb Dip was found for this laser medium. Some aspects of the theory of a gas laser recently developed by W. E. Lamb, Jr. have been recast in a form which more fully displays the role played by the particle dynamics. It is shown that effects due to long range forces are most noticeable at long optical wavelengths and when there is a large difference between the lifetimes of the two-laser levels., Sponsored in part by the DARPA.

A high power Q-switched CO2 laser with an output at 10.6 micron wavelength has been developed. In part II, the results of the previous studies of gas breakdown by optical frequency radiation are described along with an outline of the high-power 10.6 micron Q-switched laser development and the gas breakdown studies carried out with this laser source in the present investigations. In part III, the cw and the Q-switched operation of the CO2 gas laser are described in detail and the output power is examined as a function of the various laser parameters. In addition, in this section the operation of the CO2 laser amplifier required for high power operation is also described. In Part IV, the measurements of gas breakdown with 10.6 micron wavelength radiation are presented and the experimental results obtained are compared with a theoretical model of the breakdown. Part V comprises a discussion of the present degree of understanding of the gas breakdown process, and a summary of the results obtained in the studies accomplished under this contract., Sponsored in part by DARPA.

Some aspects of the theory of a gas laser recently developed by W. E. Lamb, Jr. are recast in a form which more fully displays the role played by the particle dynamics. The Wigner distribution function is used to derive kinetic equations which govern the external center of mass motion of the two-level system as well as their internal dynamics. The effect of long range forces is discussed by treating the collision integral in a manner similar to that employed in plasma kinetic theory. A modification in the criterion for the existence of a dip in the output is obtained. It is also shown that effects due to long range forces are most noticeable at long optical wavelengths and when there is a large difference between the lifetimes of the two laser levels. The experimental system for measuring the line profile of a dc excited argon laser was designed, constructed, and made operative. Preliminary data on the 'Lamb Dip' of an argon ion laser was obtained as a function of pressure and excitation., Sponsored in part by the DARPA.

Experimentally, the focused high-intensity optical frequency beam from a Q-spoiled laser is used to cause electrical breakdown in a test gas, and the ionization produced is examined as a function of gas pressure. Of the gases studied, breakdown in air required the highest field strengths, with lower field strengths required in helium and in argon. Studies were also conducted of the attenuation of the laser beam by the breakdown plasma. With either ruby or neodymium incident radiation, it is observed that more than half of the laser beam energy can be absorbed in the plasma produced by the breakdown and that over 90% attenuation of the laser beam can occur at later times in the optical pulse. Preliminary measurements were made of the effects of diffusion loss on the breakdown threshold by varying the focal volume within which the breakdown is formed. These data show that, in argon at atmospheric pressure, the breakdown threshold electric field strength is inversely related to the dimensions of the breakdown region; i.e., breakdown within small focus volumes requires a greater optical frequency electric field than is necessary with a larger focus region. This implies that, over the range of breakdown volumes studied, at atmospheric pressure diffusion losses play a significant role in the development of optical frequency breakdown.

Current progress toward establishing the feasibility of reactive rf sputtering as a means of preparing single crystal films suitable for integrated optics and electronics applications is discussed. Single crystal films of aluminum nitride, zinc oxide, rutile and gallium arsenide have been successfully grown by this technique. Epitaxy of aluminum nitride and zinc oxide has been obtained on (0001) and (1,-1,0,2) sapphire substrates, rutile on (1,-1,0,2) sapphire and gallium arsenide on semi-insulating substrates of gallium arsenide. Surface acoustic wave delay lines were fabricated to evaluate the piezoelectric qualities of the zinc oxide and aluminum nitride films. The piezoelectric coupling coefficients determined indicate that the quality of the sputtered films is comparable to the best results reported for films prepared by chemical vapor deposition., Sponsored in part by DARPA. See also report dated 27 Nov 1972, AD0752081.

Research is described on an experimental program to generate short pulses at the 10.6 micrometers wavelength, to study the propagation and interaction of these pulses with amplifying and absorbing media, and to investigate flowing metal vapor lasers as sources of radiation in the blue-green portion of the spectrum. The selection of a single pulse from a train of mode- locked CO2 laser pulses based on the attenuation and reflection of a gas breakdown has been explored. Work with several 'low temperature' metal vapor lasers, led to the practical design for copper vapor laser operation using fast closed-cycle transverse vapor flow., See also AD743491.

The objective of the program is to explore various techniques using GaAs epitaxial thin films as the active elements for electrooptic modulation of the 10.6 micrometer CO2 laser radiation. The advantages as well as the limiting factors concerning the use of thin films to perform phase and polarization modulation or switching of infrared laser radiation are investigated. The results of this program shall provide useful information concerning the possible use of GaAs thin films to replace bulk materials for electrooptic modulation of infrared laser radiation. Furthermore, results of this program may provide a guideline to the design of the master oscillator by taking the advantage of thin film modulator to yield the necessary wave envelope and bandwidth required for the high power pulsed CO2 laser imaging radar system.

The report discusses the application of ultrafast laser pulses to high resolution imaging radar systems. The principal results reported include the successful demonstration of a laboratory scale range Doppler radar, and a discussion of novel ultrafast data processing techniques.

The report discusses the investigation of the frequency stability characteristic of single-frequency Nd:YAG lasers, and of the use of coherent ultrashort pulses for high resolution imaging. Technical Results on the first topic include; the locking of a single-frequency Nd:YAG laser to the bandpass of a high finesse Fabry-Perot interferometer; the use of etalon thermal tuning of the laser for course frequency control; the construction of a second single- frequency laser; and the heterodyning of the two single-frequency YAG lasers at a variable frequency offset. In the area of high resolution imaging, a discussion of the application of microwave synthetic aperture techniques to optical radar is presented as are initial results of an experiment to obtain high optical resolution by doppler processing., See also report dated 25 Feb 1971, AD0719415. Sponsored in part by DARPA.

Al3Ni whisker reinforced aluminum was found to exhibit excellent toughness and little notch sensitivity even though its room temperature tensile elongation is only 2%. This excellent toughness is maintained at liquid nitrogen temperature (-196 C). It is postulated that this remarkable behavior is due to the presence of a continuous metal matrix which provides sufficient localized ductility in the vicinity of the crack tip to absorb considerable energy from the advancing crack. The impact behavior was found to be quite anisotropic. Of six orientations studied, the transverse orientation having the notch normal to the whisker axis was found to exhibit the lowest impact energy; whereas the transverse orientation having the notch parallel to the whisker axis was found to exhibit the highest impact energy. A significant difference was noted between the impact behavior of material containing needle-like whiskers and that containing blade-like whiskers. Only two of the six orientations studied exhibited complete fracture for the material containing needle-like whiskers.