The fundamental physical processes taking place in lasers are discussed. The methods of achieving the necessary conditions to produce laser light, and the characteristics which distinguish it from light emitted by ordinary sources, are reviewed. The applications of laser light and the way they relate to the characteristic properties are examined in a general way.
Relative to all other types of lasers the Helium-Neon gas laser has outstanding characteristics which make it a prime target for the OEM user: it is rugged and reliable and is now available in mass produciable inexpensive designs. Most of this can be attributed to its simple construction. Other advantages to the OEM, who must incorporate the laser in his own equipment, lie in the small size of the laser and its portability. Also of interest to the OEM is the fact that multiple sources are now available with plug-in compatible products.
This tutorial paper contains a general description of laser safety considerations which should be applied both to the laser product and its use. The authors outline major laser hazards which include a survey of the dangers of optical radiations as they affect the human eye and skin. The biological effects of laser radiations upon these tissues are described in detail based upon appropriate references. The paper also briefly discusses the potential electrical and toxic dangers associated with laser use. Two main approaches to achieve laser safety are: 1) guidelines or standards which govern the emission characteristics and performance features of the laser product itself, and 2) user controls to minimize human radiation exposure levels. As specific examples of laser radiation protection, the authors present a brief analysis of the effectiveness of laser protective eyewear as one user-oriented means and a summary of the salient requirements of the Federal regulatory performance standard for laser products.
Surveys conducted in several regions of the country indicate a current shortage of technicians who are well trained in lasers and electro-optics; this shortage is expected to increase significantly by 1980. Needs exist in these regions for educational programs at schools and in employer facilities for preparing new employees and retraining existing employees. A government sponsored program has developed curricula and instructional materials which are available and can be adapted into a variety of learning environments. Six schools are currently teaching Laser Electro-Optics Technology and twelve more anticipate programs beginning this fall or next year. Several employers have adopted the instructional materials for use in "in-house" training programs.
The advent of the laser has had a profound effect in most areas of scientific and technological research. A particularly fertile area of application is in the measurement of the optical, thermal, and mechanical properties of materials. This paper discusses the application of laser measuring techniques in the fields of Raman spectroscopy, optical surface scatter, interferometry and optical testing, dimensional stability measurements, microyield and microcreep studies, thermal expansion coefficient measurements, and transient thermal phenomena in optical materials. In these areas of materials measurement, all of the laser's characteristics-temporal and spatial coherence, frequency tunability, collimation, polarization, and high brightness--have been usefully exploited at wavelengths from the ultraviolet to the far infrared.
An optical device has been developed that passively compensates for certain instrumental angular and/or translationalbeam misalignment errors internal to a laser beam projector. This device insures that centroid of the projected beam remains centered with the optic axis of the projection optics in spite of these errors. Several concepts for such a compensator are mentioned, and the performance of one concept that has been reduced to functional hardware form is summarized. The intended application of this device in an alignment subsystem that senses relative translational errors of separated components in an optical instrument is briefly described.
The technology of the laser gyro has advanced to where production of this unique gyro with low cost and high performance is now possible. The technology of lifetime and its factors have now shown operating lifetime capability in excess of 50,000 hours. The performance variation with wavelength and size shows the wide range of parameters which must be considered. The performance of the laser gyro in scale factor linearity varies from 0.1% in the small 9.8 cm 1.15μ gyro to better than 0.0001% in the 43 cm 0.63μ gyro. In similar fashion the null stability and performance also varies over a range of 10°/hr to 0.01°/hr for the same gyros, respectively. Other factors such as gas pressure and multi-mode effects are also discussed.
The use of short-duration laser pulses in both two-beam and multiple-beam interferometry, and a new interferometer configuration adapted for short-pulse usage are described. Avoidance of spurious phase shifts due to nonlinearities in the propagation of the short pulses, and the relationship between finesse and pulse duration are discussed. Experimental data is shown to demonstrate time-integrated and time-resolved short-pulse interferometry.
A new standardized bar code specification for identification of shipping containers was published in June, 1976 by Distribution Codes, Inc. (DCI) at the request of the Distribution Research and Education Foundation (DREF) who selected the unique symbology for use by members of the National Association of Wholesaler Distributors. Intended for automated scanning, the symbol enables a computer to identify products and control the handling and storage of these products. The new bar code symbol, called the Distribution Symbol, is a variant of the well known U.P.C. symbol for supermarket use. Scanning approaches for the Distribution Symbol will be discussed, and a comparison to U.P.C. scanning will be shown.
While developing a fiber diameter measuring instrument that is based on lateral interferometry (LI), we became aware of another application which opens up exciting opportunities - the automatic-noncontact detection and monitoring of imperfections in high quality surfaces. Quality assurance for such surfaces has become a major problem in the semiconductor industry where such surfaces are regularly produced on silicon disks. Comparable, or higher surface quality requirements also exist in other branches of the laser optics industry. The proposed surface quality monitor utilizes a high precision optical interference pattern which is projected onto a target surface to determine the presence and size of imperfections. The measurement technique involves the use of a low power laser beam which is split into two beams of slightly different frequency us,ng an acoustic-optical (A-0) device. When the split beam is again merged, a small (in the order of lmm2), accurate optical interference pattern is produced on the test surface. This interference pattern consists of a large number of fringes that move rapidly in a direction perpendicular to the fringe planes. The AC component of the optical radiation, back scattered from the exposed (illuminated) portion of the test surface contains the information on the surface quality of that segment of the surface. By using conventional raster scan techniques, the whole test surface is scanned systematically. The paper describes analytical and experimental results together with a brief review of potential applications.
A simplified theoretical model for the interpretation of the double-exposure holographic interference fringe loci due to the general three-dimensional displacements has been derived for the specific composite mobile holographic non-destructive test system. The model, representing a good approximation to a more tedious theoretical result, predicts that a combination of in-plane and out-of-plane displacements of the surface will produce concentric circular-shaped fringe patterns.
This paper briefly reviews some of the concepts involved in optical coherence, and discusses selected applications where the laser has either led to dramatic improvements or it has made something feasible for the first time. Implications as to noise and optical receivers, improvements in remote monitoring and distance measurement, and new capabilities in data processing are some of the topics discussed in connection with the use of lasers. The references represent a fairly comprehensive and worthwhile reading list for those who are interested in gathering additional information on the whole field of lasers as well as just coherence.
The potential high data rate handling capabilities, coupled with loss cost, low loss, and noise immunity, make integrated optical communications an exciting emerging technology. Recent advances in hybrid fiber optics and integrated optical circuits and results of recent commercial and military demonstrations will be presented.
Space laser communications with the Nd:YAG laser offers the most efficient means for transfering wideband data from one satellite to another. A space test in 1980 of the Nd:YAG laser system operating at a rate of 1000 megabits per second will establish the basis for future systems. The present state of the art of low power Nd:YAG lasers has been demonstrated by the space laser. The principles of operation and design of the space Nd:YAG laser are discussed. The laser is operated conductively cooled, mode-locked and frequency doubled. The space system uses both solar and lamp pumped lasers.
Characteristics, fabrication, and write-read-erase procedure of a thermoplastic data recording medium are presented with experimental results describing diffraction efficiency, signal to noise ratio, residual image, sample surface condition, fatiguing, and infrared spectrum.
The microwave terminals, satellite ground stations, and CATV industries demand wideband, high-frequency communication links. A very-low-mesa-stripe Ga1-xAlxAs-Ga1-yAlyAs double-heterostructure (DH) injection laser diode (ILD), and a silicon avalanche photodetector (APD) have been utilized in a 500-MHz fiber-optic system to demonstrate high-frequency feasibility. The ILD, capable of being modulated up to 700 MHz with 1.25-dB/octave rolloff, coupled 4.9 mW into a single Corning low-loss fiber with microlens formed at the input end. Above 700 MHz, the distortion becomes severe due to relaxation oscillation. The frequency-dependent nonlinearity of ILD, which can be compensated by a special circuit design, has been analyzed by Volterra series. Using a gain equalization circuit in both the ILD transmitter and APD receiver, the system has very flat response up to 270 MHz and usable response to 500 MHz (S/N = 56 dB). Above 270 MHz, the gain is reduced due to the characteristics of the APD. With two tones (90 and 125 MHz), the system has an S/N (each tone) of 58 dB in 100-kHz bandwidth measurements. Without nonlinear compensation, the second- and third-order intermodulation products (IMP's) are 24 dB below the carrier. Presently, with special compensation network, IMP's of 33 dB below the carriers are obtained.
This paper discusses the advances in CO2 waveguide laser technology and compares the output characteristics of the waveguide laser with those of the conventional CO2 laser both operating at 10.6 micron. Since the first demonstration of the waveguide laser in 1972 significant strides have been made towards the achievement of an operational unit that can be used for many electro-optical systems application. Especially due to operation at high pressures a large tunability (>1 GHz) can be obtained and applications such as tunable sources for satellite communication and doppler tracking radar appear now feasible. Beam confinement of the mode to narrow capillaries made of high strength dielectric materials gives the laser a new dimension in terms of rigidity and miniaturization. Applications appear now feasible that have thus far been a domain of conventional light sources. Sealed-off lasers are now available that do not require a gas supply and a vacuum pump. High stability waveguide lasers have been built with both excellent short-term and long-term stabilities comparable to the best conventional lasers. Thus, compact coherent receivers can be built which are superior to straight detection receivers. With this potential it is no surprise that the waveguide laser is finding every day many new applications for which lasers have not been considered.
The use of tunable lasers for isotope separation and selective photochemical reactions is a field or rapidly growing research. Many economic and scientific benefits of this research can be identified. A number of basic methods of laser isotope separation have been successful. Examples of each are compared and the laser requirements discussed. The advantages of using lasers to enrich various isotopes or to separate the elements using photochemistry are described. The uses of lasers and specific laser wavelengths are outlined.
Low power gas lasers are nearly ideal light sources for particle size spectrometers. Particle size spectrometers involving imaging and light scattering have proven most satisfactory and are described in detail. The imaging spectrometers use 2 - 5 mW He-Ne lasers and a photodiode array to size and provide particle shape information on particles 1 - 10,000 μm diameter. Airborne spectrometers designed for hydrometeor measurements have 128 MHz data rate capabilities and provide full data compression. The light scattering spectrometers developed use 1 - 2 mW He-Ne lasers in both open and closed cavity sensing configurations. These instruments typically size particles with diameters less than 0.1 μm to greater than 30 μm. Methods of combining an imaging system with the light scattering methods to define the sample volume are detailed. Some possible advantages of short and multiwavelength lasers are discussed.
Soon after the development of the laser in 1960, a number of medical applications of the new device were. undertaken. Thus, by 1963 there were important steps taken in photocoagulation of the eye, in cellular studies, in surgery, and in cancer research. It is apparent that the medical profession is quick to incorporate new developments in its forefront research, particularly in difficult problem areas. Although, the introduction of the laser in medical and biological applications were made widely and with great enthusiasm, the results have been rather disappointing in some areas. At present, there still is only one major clinical application of the laser in medicine, i.e., in ocular photocoagulation, however, there are numerous exciting areas that are being currently investigated and unquestionably, the laser is proving to be an exceptional tool in many areas of research.
Methods are described for exciting tissue fluorochromes by means of a He-Cd laser (325 nm). A laser micro-fluorimeter was used to measure emission spectra of tissue fluorochromes and to record the fluorescence by means of photographic and vidicon techniques. The results show previously undescribed fluorochromes in brain and adrenal tissues.
The potential use of the laser as a heat source in preventive dentistry is very promising. However, the tooth is a very complex organism which is easily damaged. This paper surveys several factors that are known regarding the interaction of lasers with human teeth. The status of two of the more promising preventive techniques currently under development is discussed: the enhancement of fluoride uptake and the application of durable pit and fissure sealants. Areas where additional work is required to bring the laser into the dental clinic are outlined.
Various facets of the printing industry have been making practical use of laser-operated equipment for the past few years, although developmental work dates back more than 10 years. Main applications today include optical character readers for the inputting of copy; phototypesetting machines; exposure and processing of black-and-white and color photographs; reading and recording devices in facsimile-transmission systems; and the direct exposure of photosensitized printing plates. This paper reviews the existing practical applications of low-power lasers in equipment for the graphic arts and reports on the extent of use by printing plants of each of the products. Where possible, actual numbers of installations or names of users are given. Brief technical descriptions are included to explain certain unique methods of operation.
Over the past 16 years, the state of laser technology has advanced from the level of the initial demonstration to the myriad of uses that exist today. What the future holds for the uses of lasers can only be guessed at by extrapolation. Lasers have already become an integral part of modern technology, and their number of uses is still expanding rapidly. This paper presents an in-depth overview of laser technology -past, present, and future. The history of the laser and its applications are covered, from the original demonstration to the present, with emphasis on the influence that basic laser studies and laser applications has had on each other.