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© 2012 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., An electrically tunable system for the control of optical pulse sequences is proposed and demonstrated. It is based on the use of an electrooptic modulator for periodic phase modulation followed by a dispersive device to obtain the temporal Talbot effect. The proposed configuration allows for repetition rate multiplication with different multiplication factors and with the simultaneous control of the pulse train envelope by simply changing the electrical signal driving the modulator. Simulated and experimental results for an input optical pulse train of 10 GHz are shown for different multiplication factors and envelope shapes. © 2006 IEEE.

A high-power Q-switched Nd:YAG/Cr:YAG laser mounted in a silicon microbench is presented. It reaches an average output power well above 2 W and the pulse width is in the order of 1.4 ns. The use of microstructure silicon carriers provides efficient thermal control, compact integration and alignment of active and passive optical components., QC 20100901

The domain wall regions in periodically poled KTiOPO4 crystals were examined and found to give rise to phasematched second harmonic generation in the Cerenkov directions. This phenomenon is caused by the nonlinear coefficients d(11) and d(12), which are not present in single domain regions, but are nonzero at and close to domain walls. The appearance of these nonlinearities is attributed to strain, produced by the domain inversion process and results in the creation of a dc piezoelectric field., QC 20100525 QC 20110926

In this work we demonstrate low-threshold oscillation in the mid-infrared spectral region with periodically poled KTiOPO4 (PPKTP) pumped at 1064 nm by a single-frequency Nd:YAG laser. The compact pump laser had a diode-pumped passively Q-switched monolithic ring cavity configuration and could generate up to 70 μJ, 2 ns pulses. With two PPKTP crystals having ferroelectric domain inversion periods of 37.8 μm and 38.5 μm, the temperature tuning bands for the signal (idler) of 1720-1750 nm (2790-2717 nm) and 1850-1920 nm (2510-2390 nm) have been obtained. The lowest oscillation threshold of 8.3 μJ was obtained in a cavity using two mirrors reflecting 99% at the signal and the idler wavelengths. The maximum OPO output power of 6 mW and the pump depletion of 39% was achieved by driving cavity close to stability limit for the idler field. The output power was substantially increased to 36 mW (6 μJ) by using output mirror with 90% reflectivity only in the signal band and optimizing pump focusing conditions. The external OPO efficiency in this case reached 21%., QC 20150323

A laser is end pumped by laser diodes and is repetitively Q-switched using an intracavity variable speed moving aperture. The aperture apparatus includes a precision motor which drives a pair of matched aperture blades and produces efficient Q-switched operation over a wide range of output powers and repetition rates. Each aperture blade may contain an identical number of transmissive and opaque regions, and two aperture blades may be mounted onto the motor in a manner that allows continuous adjustment of the aperture width. In a preferred embodiment the aperture blades are shaped as circular discs. The laser resonator mode is nearly hemispherical, and the aperture blade is located at or near the laser resonator mode waist. When pumped with the optimum pump flux, efficient repetitively Q-switched operation is obtained as long as the Q-switch opening time is shorter than the pulse build-up time. The pulse build-up time can be calculated, and the Q-switch opening time is defined in accordance with this inventive concept. The Q-switch opening time is a function of the laser resonator mode diameter at the location of the aperture blade and the velocity of the aperture blade as it moves through the resonator mode. The Q-switch opening time is a fraction of the time required for the edge of the aperture blade to traverse the entire resonator mode diameter., Supersedes PAT-APPL-389 463-95.

The use of compound total internal reflection prisms rather than Porro prisms in polarisation coupled lasers is proposed. Performance advantages resulting from the use of these prisms include higher output without the need to bias the Pockels cell, ability to give a larger range of output coupling and independence of performance on the refractive index of the prism. In conventional Q-switched lasers the use of the prism at the Pockels cell end of the resonator instead of the usual 100% reflecting mirror also leads to some advantages including better hold-off, elimination of the need to bias the Pockels cell and insensitivity in one plane to angular misalignment.

A theoretical model is proposed for a laser system with two types of active ingredients--one with three energy levels that is capable of population inversion and a second that transfers energy to the former to aid in this inversion. Some properties of the model are examined under continuous-wave and Q-switched operations, to establish a theoretical insight regarding the behavior of multiply doped systems such as LiYF4 doped with Ho, Tm, and Er. Concentration, temperature, and cavity Q dependences are introduced in simple, nontrivial ways, but are not fully explored in this preliminary report.

A laser cartridge has been developed which incorporates a Nd:YAG laser rod, passive Q-switch and resonator mirror into an integral bonded assembly. The laser rod is 3 millimeters diameter and 15 or 16 millimeters long. Output energy is over 0.5 millijoule when pumped with 1 joule into a Xenon flash lamp. The key elements of the program were: development of a total process for manufacturing nickel-complex dyed polymethylmethacrylate (PMMA) with accurate control of optical density in a high purity damage resistant material; selection of an optical adhesive with necessary dimensional stability and strength while bonding materials with widely different temperature expansion coefficients; the development of alignment and assembly procedures for consistently obtaining good laser cartridges. The program has demonstrated the feasibility and applicability of the ECOM laser cartridge concept.

A novel laser design is given that uses a special polarising device to generate unpolarised Q-switched laser energy with a conventional electro- optic Pockels cell. The special polarising device, which replaces the linear polariser normally used in conventional Q-switched resonators, allows solid state lasers to operate efficiently at high repetition rates. Other features of the design include the elimination of the beam non-uniformities that normally occur at high repetition rates, the elimination of the need to bias the Pockels cell and the ability to produce, by a simple mirror realignment, a plane polarised output with high efficiency.

This report was written to demonstrate how a pulsed Q-switched ruby laser provides an excellent light source for use in various areas of holography and photoelasticity. The present investigation was undertaken in order to develop a ruby laser system suitable for photomechanics research.

Contents: Laser technology and propagation - A. Propagation-- (Laboratory experiment on phase correction for thermal blooming, Phase compensation for multiple-pulse thermal blooming, Phase compensation for turbulence, Fog hole boring and propagation study), B. Pollution studies - Atmospheric CO monitoring over long paths in the 1975 regional air pollution study (RAPS) in St. Louis--(Introduction, Site 108 - Granite City, Illinois, Site 105 - Downtown St. Louis, Missouri)., See also report dated 30 Jun 1975, ADA020339.

Laser target designator performance criteria are established from past Pave Way program - related mission analyses. With these criteria as performance standards, parametric design studies are performed in four areas of investigation - laser resonators, flashlamps, coolant systems, and Q-switches. These parametric studies are combined with other design factors and a complete laser target designator integration is postulated. After describing methods for designing a laser resonator with beam divergence being the motivating factor, the report substantiates best choices of flashlamps, coolant systems, and Q-switches. These choices are as follows: flashlamp - krypton for less than 10 J/p and xenon for greater than 10 J/p; coolant system - liquid to air heat exchanger using ethylene glycol/distilled water; and Q-switch - LiNbO3. These approaches along with other design factors are summarized and integrated into one optimum design taking into account cost-effectiveness, reliability, maintainability, and producibility.

This report describes a continuation of research efforts to prepare high purity rare earth fluorides, grow single crystals of Er, Ho, and Tm doped YLiF4, and test fabricated laser rods for operation at 2.06 micrometers. All fluorides were prepared by hydrofluorination of of 99.99 + % commercial oxides at 800 - 1200C in a platinum reactor. Single crystal growth was performed in a N2-HF atmosphere using a top seeded solution method. A platinum furnace was developed along with a diameter control device based on continuous crystal weighing. High quality scatter-free single crystals were grown in 10 - 15 mm diameter and 6 - 10 cm length. Laser rods of (3 x 30) mm size and a axis orientation were finished for several compositions. Both long pulse and Q-switch tests were run on five rods. These indicate that a favorable composition may lead to room temperature operation. Some damage occurred during the Q-switch tests but is not unique to the preparation or growth., See also report dated Jan 75, AD-A009 895.

This report describes fluoride preparation and single crystal growth of the solid state crystal laser of composition Y(.45)Er(.499) Tm(.05)Ho(.001)LiF4. The respective component fluorides were prepared from 5-9's oxides by hydrofluorination at 800-1200C in a platinum reactor. Single crystal growth was performed by a seeded-solution method utilizing platinum apparatus under a N2-HF atmosphere. Techniques were developed for core drilling and fabricating (3 x 30 mm) or (3 x 50 mm) a-axis cylindrical rods. Passive optical tests have demonstrated high quality and freedom from scattering sites. Infrared analyses on 5-10 cm paths have shown low ppm trace molecular impurities. Active laser tests in long pulse and Q-switch operation are not completed but preliminary data indicate threshold above 10 joules due to compositional effects., See also report dated Feb 74, AD-775 211.

The light shutter uses in part a conventional laser triggered spark gap but adds a 'tail biter' to terminate the pulse, thus closing the shutter. There are two Pockels cells and two polarizers. When either switch is in the 'off' condition the entire switch is off. In the initial static condition the first Pockels cell (PC) polarizer combination causes the switch to be in the 'off' condition while the second PC polarizer is 'on' due to the fact that the polarizers are crossed. One of the features of the invention includes the use of a spark gap to ground the high voltage electrode of a Pockels cell. Another feature is the use of a second Pockels cell polarizer combination to terminate the light passing through the light switch ('tail biter'). Still another feature permits the selection of light pulse duration in the picosecond region., Supersedes AD-D000 418.

A standard cavity, Q switched laser is used to initiate and sustain submicrosecond pulses in a long laser. Short pulses from the standard cavity laser are directed onto the remote reflector of a long laser and are then reflected back through the lasing material of the long laser. Properly timed activation of the long laser lasing material causes amplification and oscillation of the pulses in the long laser cavity. Beam expanding telescopes are used to focus the laser pulses on the long laser's remote reflector. By way of a specific example, the generation of submicrosecond pulses in a long laser has been accomplished using neodymium doped yttrium aluminum garnet (Nd:YAG) as the lasing material perating at 1.06 micrometers., Supersedes AD-D002 613.

A configuration of a pair of crystalline quartz wedges used as polarizers is combined with an electro optic switch to constitute a laser Q-switch. The two wedges are identical and are positioned on either side of the switch and oriented such that one compensates the angular deviation and dispersion of the other., Supersedes AD-D000 676.

The patent application concerns a very fast optical shutter, or Q-switch, using an acousto-optic diffraction cell and associated optics such that a fast chirp wave in the cell diffracts the light so that it will be matched by the transfer function of the optics. This is used for laser beam Q switching.

A Q-switched and cavity dumped laser system is provided in which a 45 degree Faraday rotator and an auxiliary cavity mirror are disposed in the beam path to compensate for the polarization change caused by thermally stresses laser rods., Supersedes AD-D000 496.

Multiphoton absorption in semiconductors was investigated with emphasis on the III-V compounds. It was shown that this mechanism can set an intrinsic upper limit to the power density transmittible through semiconductors. Laser action in a large volume of GaAs was excited by double-photon pumping using a Q-switched neodymium laser, yielding output power of the order of a megawatt/sq cm at 8365A at liquid nitrogen temperature. A new temperature anomaly of the threshold for stimulated Raman emission in liquid benzene was discovered and investigated. The first observation of infrared stimulated emission associated with optical phonons of a liquid was reported. This was seen at 5 micrometers from benzene. In addition, induced transparency by coherent optical phonons was observed. A new technique of frequency-modulated spectroscopy was developed which enables one to readily obtain the first or higher derivatives of any optical spectra., Spnsored in part by the DARPA.

The report summarizes the results during the reporting period of a program whose goal is the development of a flash-pumped, Q-switched, mode- locked, cavity-dumped, amplitude-stabilized laser operating at approximately 1. 06 micrometer in the fundamental transverse (TEM(oo)) mode. System design and test results are presented., See also AD0719931. Sponsored in part by DARPA.

Processes that can produce optical damage in transparent insulators are studied in the present work. A general discussion is given of laser induced damage which distinguishes between breakdown from intrinsic processes and damage from absorbing contaminants called inclusions. New and previously published techniques for identifying damage from inclusions are discussed and applied. A detailed summary of self-focusing theory is given. A series of controlled experiments are described which represent the first unambiguous measurements of an intrinsic damage mechanism at near-infrared and visible frequencies. Finally, a summary of avalanche breakdown theories is presented, and the implications of the experimental data for avalanche theory are discussed.

The bibliography is a selection of references to unclassified and unlimited reports which were processed into the AD data bank from January 1953 through March 1972. Corporate Author-Monitoring Agency, Subject, Title, Personal Author, Contract, and Report Number indexes are included., Supersedes report dated Aug 1970, AD710460.

The report describes studies of photoconductivity in single crystal GaAs via two-photon absorption of light quanta from either a Q-switched or mode- locked Nd: glass laser. The results obtained with nanosecond light pulses are compared with those obtained with picosecond case. In the latter case, the transient response of the induced charge carrier accounts for the observed effects.

This report presents the results of a detailed study conducted by the Advanced Systems Laboratory on weapon system concepts incorporating Laser Techniques. The study consists of two parts. The first considers Laser kill mechanisms, and the second investigates guidance and control approaches. Conclusions drawn from the study are presented.

The output beam uniformity of a Q-switched Nd:YAG laser, using four different flashlamp-laser rod pump cavity coupling configurations, is described. The test apparatus and test procedure used to establish the beam uniformity quantitatively are given. A newly defined beam uniformity parameter M, the ratio of maximum-to-average peak power density, is shown to vary significantly for the pump cavities tested. The data presented on beam uniformity is applicable toward improving laser pump cavity design, interpreting particular missile and seeker tracking behavior, comparing techniques for measuring laser beam divergence and is an aid in establishing the damage threshold level for retinal tissues and laser resonator components at 1.06 micrometers.

The feasibility determination and design for an experimental, pulsed laser, diffuse target, remote crosswind measurement system is described. The system consists of a laser transmitter, a diffuse target and a receiver. A unique scheme using a double-pulsed, Q-switched ruby laser is used to measure the slope of the time delayed autocovariance function at zero time delay which under appropriate conditions is proportional to the weighted average crosswind along the laser propagation path. The receiver consists of two silicon vidicons, a spinning disk for directing alternate pulses to the vidicons and appropriate scanning circuitry for generating a 10 x 10 array of apertures on each vidicon.

The theory for steady state operation of a saturable absorber was developed starting with the treatment of a Fabry-Perot interferometer with nonsaturable loss. Resonance characteristics of the interferometer were obtained in terms of mirror reflectivity and cavity loss. With this result it was then possible to replace the unsaturable loss with a saturable loss. In order to do this is was necessary to first develop models for the saturable absorbers used. A model with excited state absorption previously developed by Huff and DeShazer was extended to include both excited singlet and triplet level absorption. A second model, which was applicable to the semiconductor saturable absorber, was also developed. With a mathematical expression for the saturable absorber, it was possible to solve the saturable resonator problem. With this solution a set of criteria were established for operation of the saturable resonator in a bistable regime.

An experimental investigation was conducted to determine the feasibility of directly detonating secondary explosives by means of radiation from a ruby laser (6943A). The secondary explosives included PETN, HMX, RDX, and tetryl. Most of the effort was devoted to a statistical evaluation of the initiation energy required for PETN. For the most part, powdered explosives were used; however, a limited effort also was expended on large single crystals. The use of a light guide as a means of transporting energy was also examined. It was established that although a highly sensitive mixture can be detonated through a light guide, the attenuation of the radiation is too great to make this method practical for secondary explosives. A bivariate dependence of the probability of initiation on both power and energy is indicated. The effectiveness of the experimental techniques of power evaluation was, however, limited by the speed of the equipment used.

The paper reports on studies on the spatial uniformity and time characteristics of the Kerr cell. It analyzes the optimal construction and electrical parameters of a Kerr cell designed to form light pulses with minimal rise time. The analysis shows it is possible to build a shutter giving a series of light pulses of approximately 10 to the - 11th power sec duration. A Kerr cell with which a light monopulse of 0.4-nsec duration can be obtained is described. Ruby laser light of such duration was used in a design for seven- frame shadow photography of high-speed processes., Trans. of Akademiya Nauk USSR, Moscow. Fizicheskii Institut. Laboratory of Quantum Radiation Physics, Report, Preprint no. 53 31p 1969, by Richard S. Relac, and John M. McMahon.

The Research and Development program which resulted in the development of a Nd(3+) DOPED Self Q-Switching Glass Laser Illuminator Oscillator is described. Research studies undertaken in this program included an evaluation of some new self Q- switching glass compositions, a study of the effects of relatively high input powers on the laser output beamspread and efficiency, and a study of the temperature dependence of the characteristics of the laser self Q- switching train of spikes and efficiency over the temperature range 12 C through 50 C. In another study it was found that the thermal fracture point of untreated self Q- switching glass laser rods is roughly about a factor of 1.7 times less than that for the untreated conventional laser glass of similar composition. The laser illuminator oscillator developed and delivered to Fort Belvoir is described. Included is a description of the highly efficient and flexible imaging type water cooled laser cavity structure. The laser self Q-switching oscillator developed utilizes an 0.8 cm diameter, 61 cm long rod of self Q-switching laser glass. At the train repetition rate of 8 TPS an average output power of about 14 watts is obtained at the laser wavelength of 1.06 microns at the recommended operating point. The slope efficiency above threshold was measured to be 2% and the full beamspread was found to be about 6 degrees at -TPS. A typical train contains 17 smooth Gaussian-type self Q-switching spikes with a minimum time interval of about 12 microseconds between any two successive spikes. (Author-PL)

Evaluations and remedial modifications to laser photography systems have resulted in a 30-percent increase in reliability for optimum performance. Another unique modification to the laser photographic technique has added the capability for flow visualization when desired. A 70-percent increase in spatial resulution has resulted from refinements to photopyrometry systems. Investigations of schlieren-related flow visualization techniques resulted in the selection of a focused shadowgraph arrangement for detection of boundary- layer transition on conical models. Preliminary designs for photographic instrumentation systems for use during erosion testing were completed., Prepared in cooperation with ARO, Inc., Tullahoma, Tenn. Rept. no. ARO-VKF-TR-72-105.

The objective of this program was to develop the techniques necessary to implement a multiple pulse laser. The particular multiple pulse device chosen for the effort was a 1.06 micrometer, Nd:YAG, electro optically modulated laser that could generate bursts of 1 millijoule, Q-switched pulses at average rates up to 10 bursts per second. The pulses in each burst were to be 1 microsecond apart and a burst was to last for 100 microseconds. As a further goal, it was required that the bursts would be generated upon command using an external trigger, and the first pulse of each burst should be transmitted not later than 3 to 5 microseconds after receiving the external trigger pulse. The baseline, guide system chosen is the TVR (Time Variable Reflection) cavity. Although TVR lasers had been built previously, the stringent requirements of the multiple pulse format demanded the solution of three major technical problems: Controlled pumping, high speed modulator driving, and modulator crystal acoustic damping.