When an optically rough surface is illuminated by a coherent laser beam, speckles are created due to multiple interference of the reflected (or transmitted) wavelets. They fill a volume in front of the illuminated surface. By suitably choosing a "plane" of speckles to photograph before and after they are displaced by the surface deformation via double exposure or time-average, the resulting speckle interferogram can yield a variety of information for engineering measurement. Speckles can also be created in the interior of a body by scattered light if it is made of transparent material and a laser beam is sent through it. In this way one can also probe the stress distribution inside a general three dimensional object. In this presentation two types of applications of the basic principle of one-beam laser speckle interferometry will be discussed: one is in the realm of nondestructive quantitative evaluation such as stress analysis of plane problems of elasticity, flexure of plates, vibration, and general three-dimensional problems; and the other is qualitative evaluation such as detection of crack in structure and debonding of laminated composites.
The capability to visualize, at a single moment, the full surface, or large areas, of engineering components has provided a strong impetus to the development and application of interferometric holography as a metrological tool. At the United Technologies Research Center, its adaptation to the nondestructive evaluation and analysis of structures has continued to expand. As examples, the practical implementation of interfero-metric holography for the optical analysis of rotating objects has recently been demonstrated, and a new swept frequency acoustic stressing technique for HNDT is under development. Both of the above, which utilize pulsed laser illumination, are reviewed herein, together with additional holographic test work conducted at the operating divisions of United Technologies Corporation, to demonstrate the tolerance of interferometric holography to levels of ambient illumination and vibration well above those sometimes felt to restrict its practi-cal application in industrial facilities.
The design of a special purpose configuration. recognition system is described. briefly from problem statement through .s,ecification. The system, inspects assemblies for correct part placement and part type. A variety of uses for such an on-line inspection device are described based on its particular three dimensional measurement capabilities.
An improved gauging precision was achieved with a laser extensometer by adding a spatial modulation to the scanning beam with phase detection signal processing. This laser extensometer demonstrated an electronics limited gauging precision of ±45 x 10-6 inch for diametral measurements on 0.430-inch reactor fuel cladding samples.** An analysis of the projected accuracy, limited by the optical detector noise and phase detection error, indi-cated a theoretical resolution limit of 1 x 10-6 inch. The modulation of the scanned beam produces an extensometer response with a reduced sensitivity to the sample optical sharpness and beam spot size, and allows sample motion in the 0.1 inch range with no loss of gauging precision. Since the modulation is essentially an electro-optical vernier on the interrogating/scanning beam, it can be applied to any gauging or sensing problem where edge sensing is the basic concept. This paper presents a description and analysis of this modulation concept.
Several years ago a new era in streak, cameras began with the introduction of an x-ray sensitive proximity mfocused streak tube. This device displayed. better than 3 ps resolution and a large dynamic range, making it a fundamental laser-fusion. diagnostic. The new tube is based upon parallel-photoelectron trajectories, rather than cross-over or pinhole electron optics used in virtually all other streak tubes. This eliminates a most of problems due to space charge buildup effects at the electron pinhole such as low dynamic resolution, limited dynamic range and unpredictable instrumental field distortion. In the old, tube instrumental errors are relate to distribution of photocathode illumination. in picosecond temporal application. Recently a visible variant of the proximity-focused tube design has been constructed. This camera displays all the advantages of its predecessor including high sensitivity, large dynamic range and a flat format making it ideal for digital readout. In addition, picosecond streaks of high statistical quality indicate the design limit has yet to be reached. TLe. new camera has already uncovered laser oscillator problems proving its utility as a basic laser diagnostic. Using this new "photon micrometer", a myriad. of new optical techniques such as high-accuracy three dimensional imaging are now possible.
Battelle, Pacific Northwest Laboratories has developed an advanced cartridge case measurement/eject system (CCMES) which automatically inspects and rejects cases at up to 1200 per minute. The system consists of a mechanical handler, measurement instruments, and a dedicated computer. System operation is monitored and controlled while the product is being measured. Five case dimensions are measured by an electro-optical system using diode arrays to measure a case image at unity magnification. By scan averaging, measurement standard deviations as small as 2.5 microns are obtained at a throughput of 1200 cases per minute. Measurements made with the system fall within the uncertainties of hand-gauged values for the same cases. Four zones on each case are examined for surface flaws, such as dents and scratches, by detecting light scattered from the surface. The system can detect these surface flaws at inspection rates of 1200 cases per minute. Using electro-optic methods, two additional measuring stations detect vent hole presence and gross size deviations to prevent mechanical jams. A third station employs an eddy current technique to detect splits and folds in critical regions of the cartridge. The overall system has passed quality assurance tests administered by the sponsor and will soon be installed at the Lake City Army Ammunition Plant.
The wavelength switching probe laser as described in this paper is the key component in a "J-line scan" diagnostic system, that was developed during the past year at Rocketdyne. Typically, the J-line scan experiment consists of performing small signal gain measurements at a set of wavelengths, that correspond to different rotational transitions of the CO2 molecule. From these gain measurements the rotational temperature of the CO2 (001) state may be computed, which in turn yields the amount of specific optical energy available in the active medium. The significance of being able to measure this quantity is substantial. A low power wavelength switching CO2 laser was designed and constructed, that allows scanning of up to 8 individual, selected wavelengths in rapid sequence. This probe laser incorporates several novel features. The wavelength scan of the probe laser is accomplished by a galvo controlled mirror, switching 8 prealigned gratings in sequence into the optical cavity of the probe laser. Accurate and rapid angular registration of the switch-mirror is achieved by using control loops. After the laser is switched to the next wavelength (in less then 10 milliseconds) the laser cavity length is then rapidly readjusted to lock cavity resonance to line center. An electronic control center was also developed, that provides fully automatic operation. This system is now fully operational. The present paper describes the system together with experience gained by using it on a medium scale Gas Dynamic Laser (GDL) device.
In a variety of laser applications there are requirements for devices which shorten laser pulses, emphasize the peaks, or act as a limiter to suppress peaks in the intensity. In this paper we consider several types of devices which can perform all these functions with subnanosecond response times. The emphasis in this paper is on the limiting function, however. All the devices are based on the concept of a dual-beam interferometer with a nonlinear element in one or both beams. The nonlinear component can be either a saturable absorber or a medium exhibiting the optical Kerr effect. In the former case, the transmission of the absorber increases with increasing incident intensity; in the latter case, a phase shift is introduced as the intensity increases. By combining both beams at the out-put port of the interferometer with an appropriate static phase difference, these nonlinear effects can be made to produce either pulse peaking or limiting. In the same way, using two orthogonal polarizations and one beam, rather than two physically separated beams, one can construct a nonlinear polarization interferometer with the same characteristics but with reduced sensitivity to vibration and temperature changes. Theoretical and experimentally determined characteristics of several nonlinear interferometers are presented here. Of particular interest is a simple, inexpensive limiter with excellent shaping characteristics which we have demonstrated using a Nd:YAG laser at 1064 nm. This device operates for days without adjustment and can be designed for use with a wide range of laser wave lengths.
The second harmonic of the Nd:YAG output wavelength (1,064 nm) can be produced with both CD*A and KD*P with efficiencies approaching 50% when the crystal indices of refraction are equal at the fundamental and second-harmonic frequencies -- the so called "phase-matching" condition. For Type I doubling processes, this condition can be satisfied by allowing the ordinary index of refraction at the fundamental wavelength to be equal to the extraordinary index at the doubled frequency. For Type II doubling, the necessary condition is that the extraordinary index at the second harmonic be the average of the extraordinary and ordinary indices at the fundamental. For CD*A, phase matching can be accomplished via the Type I process with 0m=90° by elevating the crystal temperature to -100°C, depending on the deuteration level of a specific crystal. For a 21-mm-long CD*A crystal, the width of the temperature versus efficiency curve is 3.25°C FWHM. Ninety-degree phase matching allows efficient doubling with incident beam divergences an order of magnitude greater than dif-fraction limited and does not introduce walkoff resulting from double refraction. Data are presented showing doubling efficiency as a function of crystal length and incident average power density, including considerations of efficiency and average power saturation. Type II KD*P phase matches at room temperature with 0111=53°36'. To obtain efficient doubling in this case, the incident fundamental beam divergence must be close to diffraction-limited. The angular halfwidth of a 25-mm crystal is 1 mr FWHM for rotation about the ordinary axis. Compared to CD*A, the use of KD*P is advantageous because of its ready availability, high damage threshold, high saturation levels and usefulness at room temperature. Using a 3.0-J pulsed Nd:YAG laser with a repetition rate of 10 pps, 10.5 W of 532-nm power has been achieved.
Optical restrictions on the design of a solar pumped laser are related to the collection of the sunlight and the required opto-mechanical assembly to provide end pumping of a small Nd:YAG laser rod. Solar pumping influences affect the laser operation. Simultaneous mode-locking and frequency-doubling are additional complications.
Remote analytical sensing requires a high pulse energy tunable infrared source for detection of molecular species(1)This paper describes progress made in a Nd:YAG pumped, computer controlled LiNb03 parametric oscillator with a tuning range of 1.4 - 4.0 μm.
The application of high average power frequency doubling for dye laser pumping is discussed. The desirable features of using the frequency doubled output of a Nd:YAG laser for pumping dye lasers are described and this technique is compared with flash lamp pumping. Two techniques to overcome the deleterious thermal effects of high average power on the FD crystal are described. These are electro-optical tuning (EOT), which compensates for thermal loading, and beam shaping, which reduces thermal gradients. Results of EOT experiments are presented. The use of beam shaping to obtain reasonably uniform phase-matching across the beam-crystal interface, previously unattainable with high average power, is explained.
This paper presents the phenomenology of different approaches to the frequency-shifting (upconversion) of infrared radiation into the visible and discusses the practical aspects of designing systems to up-convert IR images. The recently discovered process of upconverting infrared radiation into the visible or the ultraviolet using two-photon-pumped alkali-metal vapors and the more familiar method of frequency-mixing using single-photon-pumped nonlinear crystals are described and compared. In addition to these coherent processes, the use of quantum-counter action in certain crystals to convert an IR photon into a visible photon by an incoherent process is discussed. The important performance parameters of an IR imaging system are briefly discussed and the considerations and constraints involved in the design of coherent and incoherent image upconverter systems are presented. Using this background, practical system designs are developed for both active and passive imaging. The expected performances of these systems are compared with those of IR imaging systems based on direct-detection of IR photons with semiconductor detectors.
This paper deals with certain nonlinear effects that,can directly generate a wavefront which is the phase conjugate of the incident field. These phenomena can be exploited in pulsed laser systems to remove aberrations in the optical train as well as aberrations arising from turbulence in the atmosphere. We discuss our measurements of the effectiveness of this conjugation process using a ruby laser and stimulated Brillouin scattering in a CS2 waveguide device. Measurements are made of the divergence angle of the beam after correction as a function of interaction length. The application of conjugate processes realizable in SBS, SRS, parametric down conversion, and four-wave mixing is considered for typical CO2 laser systems. System gain, backscatter limitations and parasitic oscillation are discussed for typical pulsed amplifier systems. Amplified spontaneous emission and unwanted glint returns from optical defects appear to be the most serious limitations.
The design and performance of optical cables, connector hardware and communication systems are governed by the light transmission and coupling characteristics of waveguide fibers. These characteristics depend upon waveguide design and materials as well as manufacturing tolerances. Measurement methods and limitations are discussed and use and interpretation of waveguide specifications in designing optical links and predicting over-all performance are shown.
Progress in optical fiber technology has been rapid in recent years and usage is now expected to grow rapidly. The design of a fiber optic system requires that all component specifications be consistent with those of the overall system. This paper describes many of these specifications and some of the trade-offs inherent in the technology today. The components of most importance are the optical cable, optical connectors, and electro-optic modems. Such specifications as cable attenuation/dispersion, connector loss, modem outputs and input sensitivities, and various environmental factors are discussed.
Although the capability of dielectric fibre to guide optical energy has been known for centuries, it has been only since about 1970 that this capability has begun to be exploited for long distance transmission of information. Before that time, the absorption of materials used to fabricate fibres was too high to consider the long distance application. In 1972 sufficient purity of optically transparent materials was obtained so that the transmission losses of laboratory fibres were lowered to 4 dB/km. Because of these advances and the ability of fibres to transmit extremely high data rates, industries (and the military) throughout the world are heavily investing in the vast potential of this "new" technology.
Single mode guided light data transfer systems offer greatly expanded capabilities over multimode optical fiber systems. An overview of the status and capabilities of present single mode devices will be given with emphasis on sources, switches and couplers. Discussion will center on single mode coupling problems because low loss rugged couplers and splicers represent the most significant technological barrier to be overcome. A single mode fiber optic switching terminal presently under development at NRL will be described.
The development of optical modulators and switches is reviewed with emphasis placed on the comparison of conventional bulk modulators and thin film devices. It is shown that the primary motivation for such a development is the major reduction in the electrical drive power requirements for high bandwidth devices. The thin film devices are first discussed with acousto-optic and electro-optic devices in LiNb03 and LiTa03 given primary emphasis. The application of these devices to high speed scanning is shown to be quite promising. The problems of efficient coupling and optical power handling are shown to be important areas where improvements have been made. The development of directional couplers is then discussed with stress placed on the cross-talk performance and speed of the devices. The problem area of fiber-to-channel coupling is also discussed.
In 1964, Dr. William Bridges of Hughes Aircraft Company discovered the noble gas ion laser family. Thir-teen years later, this type of laser - principally argon and krypton ion systems - has beL.ome a commonplace laboratory instrument used to generate many types of scientific data. Some new applications, which are taking the ion laser out of the laboratory and into industry, include platemakers, graphic systems, holo-graphic testers, blood analyzers, and photocoagulators. More than 1,000 ion laser systems are in use in these applications.
The problem of obtaining high yields in the manufacture of HeNe lasers is compounded as the number of specified performance parameters is increased. This problem is especially difficult when lasers have a low noise specification. Some common kinds of noise encountered in HeNe lasers are discussed along with ways of eliminating or reducing such noise. A case history describing improvements in performance and production yields of one laser model is given.
The AN/GVS-5 Hand Held Laser Rangefinder was designed by RCA for the U.S. Army Electronics Command. The development contract required that it be designed for high-rate production with Design to Unit Production Cost (DTUPC) and Producibility Engineering and Planning (PEP) invoked throughout the design phase. The stringent performance and environmental specifications, a five pound weight limit, human engineering, safety, reliability and maintainability constraints, combined with the low design to cost goal posed some challenging production engineering problems. This paper describes how these problems were defined and solved, starting with the pro-posal, through the design and development phase, to implementation of production. Specific examples are given of how production process, tooling and test requirements were developed and woven into the product design during development. Emphasis is placed on novel approaches to the manufacture of the optics, laser transmitter, and electronic circuitry. Highlights of the methods used to conduct the DTUPC/PEP program, and lessons learned, are also given.
In characterizing a laser intensity distribution, accepted practice has fallen behind the capabilities of modern image analysis techniques. We have significantly narrowed this technological gap with the development of a Laser Intensity Profile System (LIPS). The LIPS provides real time displays of either near field or far field energy distributions, as an aid in resonator alignment, and accurate calculations of the integrated far field intensity ("energy in the bucket") and the angular position of the laser centroid. The electronic interface with the laser allows individual laser pulses to be recorded, providing the only quantitative way of determining, for example, the shot-to-shot variation in beam divergence during transient laser warmup. The LIPS building blocks are drawn from available video equipment, including a silicon-target vidicon for linear response and sensitivity in the near infrared, a video disc for image storage and convenient instant replay, and an image analyzer which develops both isometric and color-coded intensity level contour displays of the laser pulse. Analysis is performed using a micro-processor. After initial setup, very little operator expertise is required, making the system ideal for production line performance tests as well as laboratory diagnostic studies. The LIPS is described in detail, and several applications to laser evaluation and characterization are presented. In addition, some areas are discussed where performance improvement may be expected in the near future.
There is a need for test equipment to evaluate tracking systems which work in conjunction with laser designated targets. The simulators, which have been built to evaluate the tracking system performance, require pulse laser sources (manufactured by Hughes) in order to achieve the required range of peak pulse power. The simulation includes syntillation, intensity zoom, delayed pulses with amplitude adjustment relative to the main pulse and discrete calibrated power levels of approximate 1 dB increments from 1 to 10-10 peak watts/cm2. The major concern of this paper is to describe a method of simulating the low power levels and a method of determining the calibration error associated with these levels. Brief descriptions are given of the simulator and the operational procedures employed to compensate for the laser source output power drift. Also included are the methods of calibrating the radiometers and attenuation filters. The calibration errors are examined to determine the accuracy of the low power levels. Test results of the correlation between several simulators is given to verify the validity of the accuracy predictions.