The Nd:YAG laser is now being employed in a number of cost effective applications in semiconductor manufacture. Three of these are briefly reviewed: (1) the use of the CW-pumped, repetitively Q-switched Nd:YAG laser for dicing of circular die for power devices, (2) the application of a small, passively Q-switched, pulse-pumped Nd:YAG laser for repair of defects in hard-surface photomasks and (3) the use of a CW-pumped, Nd:YAG laser with internal second-harmonic-generator, for direct diffusion of dopants to produce back-side ohmic contacts.

The conventional method of dieboard manufacture is described and compared with the laser dieboard process. Consideration is given to savings achievable as a result of the precision die produced by laser cutting in combination with numerical control. The development of machines is briefly discussed and modern laser die-board cutters are described. Some points on laser job shops are also covered.

A Nd:YAG laser-based microprocessor-controlled marking system has been developed for commercial use. It can mark a variety of metallic, semiconductor, plastic, and coated materials with letters, numbers, special symbols, and company logos. The alpha-numeric information is presented in a standard 5 by 7 dot matrix format, with continuously adjustable character height up to 7 mm. Programming features of the control system allow for either automatic or manual serializing, editing of messages during laser marking, "reverse-video" marking, among others. Depending upon the marked material or the required marking rate, either a CW pumped Q-Switched laser or a flash-pumped pulsed laser is used. Examples of marked materials are shown.

Pulsed laser drilling and welding of nuclear reactor fuel rods has been demonstrated to be a simple and reliable process for injecting helium into fuel rods at specified pressures and providing an absolute seal. Fuel rods can be pressurized to high pressures, if required, with tight pressure tolerances. The accuracy and reliability of the laser pressurization process represents an attractive technology. The capabilities and limitations of the laser pressurization process are discussed as well as the station design for efficiently pressurizing production quantities of fuel rods. Production welding experience of over 100,000 nuclear reactor fuel rods will be discussed.

The Exxon Nuclear Company, Inc. acting as a Subcontractor to EG&G Idaho Inc.3 Idaho National Engineering Laboratory, Idaho Falls, Idaho, has developed a welding process to attach titanium sheathed thermocouples to the outside of the zircaloy clad fuel rods. The fuel rods and thermocouples are used to test simulated loss-of-coolant-accident (LOCA) conditions in a pressurized water reactor (LOFT Reactor, Idaho National Laboratory). The design goals were to (1) reliably attach thermocouples to the zircaloy fuel rods, (2) achieve or exceed a life expectancy of 6,000 hours of reactor operation in a borated water environment of 316°C at 2260 psi, (3) provide and sustain repeatable physical and metallurgical properties in the instrumented rods subjected to transient temperatures up to 1538°C with blowdown, shock, loading, and fast quench. A laser beam was selected as the optimum welding process because of the extremely high energy input per unit volume that can be achieved allowing local fusion of a small area irrespective of the difference in material thickness to be joined. A commercial pulsed laser and energy control system was installed along with specialized welding fixtures. Laser room facility requirements and tolerances were established. Performance qualifications and detailed welding procedures were also developed. Product performance tests were conducted to assure that engineering design requirements could be met on a production basis. Irradiation tests showed no degradation of thermocouples or weld structure. Fast thermal cycle and heater rod blowdown reflood tests were made to subject the weldments to high temperatures, high pressure steam, and fast water quench cycles. From the behavior of these tests, it was concluded that the attachment welds would survive a series of reactor safety tests.

The Exxon Nuclear Company, Inc., acting as a subcontractor to EG&G Idaho Inc., Idaho National Engineering Laboratory, Idaho Falls, Idaho, conducted a laser beam welding study to attach internal stainless steel thermocouples into stainless steel upper end caps in nuclear fuel rods. The fuel rods and thermocouples are used to test simulated loss-of-coolant-accident (LOCAL) conditions in a pressurized water reactor (LOFT reactor, Idaho National Laboratory). The objective of this study was to determine the feasibility of laser welding a single 0.063 inch diameter stainless steel (304) sheathed thermocouple into a stainless steel (316) upper end cap for nuclear fuel rods. A laser beam was selected because of the extremely high energy input in unit volume that can be achieved allowing local fusion of a small area irrespective of the difference in material thickness to be joined. A special weld fixture was designed and fabricated to hold the end cap and the thermo-couple with angular and rotational adjustment under the laser beam. A commercial pulsed laser and energy control system was used to make the welds. Process tests were performed and evaluated. Results indicated that successful welds could be made using the laser system. A process qualification was written specifying laser energy, spot size and weld overlay. This program was successfully concluded by welding seventeen (17) centerline fuel rods for the LOFT reactor.

The effect of temperature as a function of time in laser welding of similar and/or dissimilar materials was evaluated experimentally and by finite element analysis. Three cases = copper-copper, copper-aluminum, and aluminum-aluminum welded joints - were analyzed by simulation. There were four tests evaluations: tensile strength, relative impact strength, resistance versus temperature variation, and an electron microprobe analysis. Good tensile strength and low electrical resistance results were obtained for welding ETP copper with a neodymium (Nd)-glass laser. Copper-aluminum conductors responded with good tensile and impact strengths to laser welding.

The development of a system for pricing diamonds, whose price differs greatly for gems of equal weight, must be matched by the development of the techniques of quality control. Until the present time, most of the control relied on human perception. The interaction of laser light, in controlled conditions, with the gem gives enough data to quantify all the commercialized gems.

The CW ring dye laser is capable of high-power, single mode operation in the visible and near infrared spectral region. This laser's performance is enhanced by frequency stabilizing the laser to an external reference Fabry-Perot yielding a jitter-induced linewidth of about 150 kHz rms. Systems of this type may mode hop due to bubbles in the dye laser jet stream or other perturbations and lock to another fringe of the reference Fabry-Perot. Locking to another fringe means that laser frequency has changed by at least one equivalent free spectral range of the reference Fabry-Perot. We will describe the properties of a stabilized CW, ring dye laser system which has the feature of automatically reacquiring lock to the original fringe of the reference in the presence of mode hopping.

The history and development of mini-TEA CO₂ lasers is presented, beginning with longitudinally pulsed waveguide lasers and leading up to the current state-of-the-art mini-TEA devices (less than 20 cm overall length) which produce more than 20 mjoules per pulse, single-mode, with an operating life of more than 2 x 106 pulses.

Waveguide CO₂ lasers are being developed into reliable, low cost, fieldable and versatile devices with applications ranging from surgical to military to industrial. The attractiveness of waveguide lasers lies in a number of features including: a) the ability to obtain long sealed-off lifetimes, b) the ruggedness of its construction, c) the good mode quality without suffering from loss, d) the high wall-plug efficiency, e) the compactness, f) the scalability in output powers up to at least 30 Watts, g) the capability of the laser to be line and frequency stabilized, h) the large line and frequency tunability, i) the "safeness" of the device, and j) the relative simplicity and hence inexpensiveness. A review of waveguide CO₂ lasers, including pulsed and CW, is presented. Also presented is a comparison between RF excited devices and DC excited devices.

Free electron lasers (FELs), based on stimulated emission of radiation by a relativistic electron beam, show potential as a new class of coherent radiation sources that are characterized by continuous tunability, high average power, and electrically efficient operation. Exploratory computer simulations of an FEL oscillator are presented for experimental conditions appropriate to a repetitively-pulsed Van de Graaff accelerator. A program to establish the feasibility of a continuously-tunable IR laser is also described, including discussions of two-stage and optically-pumped devices that promise attractive efficiency and power levels.

The optically pumped far infrared (FIR) laser is a simple, reliable source of coherent radiation for the spectral region from 40 µ to 1.8mm. A theoretical description is presented and compared with state-of-the-art performance. System design is also discussed.

There are several different types of one electron color centers in alkali halide crystals which have produced tunable laser action in the near infrared. The combined tuning range of all of the color center lasers is from .8µm to 3.3µm, although at present only lasers operating in the 2.2μm to 3.3μm range have proved to be sufficiently stable to be offered commercially. The single mode version of this laser has a frequency stability of about 1MHz and has been used in high resolution molecular spectroscopy. Multimode versions, on the other hand, have been extensively used in applications such as photoacoustic spectroscopy and laser induced chemical reactions. In more recent developments the color center laser has been operated both as a mode locked system and as a high power pulsed laser.

The method of mounting laser diodes between thin metal plates for more efficient heat sinking is discussed. The principles involved in making the double-sided heat sink ope rate over a large temperature range without stressing the laser diode are explained. Double-sided heat sink diodes both single heterostructure and stripe geometry double heterostructure configuration can be operated at higher average power output, higher duty factor, and greater efficiency than with a standard single heat sink.

The method of using the double-sided heat sink diodes in linear array configurations is explained. The method and efficiency of air cooling the array when arranged for diode packing of 40 diodes per centimeter is given. Data on 20 diode array operation to over 500 mW CW at 10% power efficiency is given. Also included are the initial selection criteria, burn in procedure, and final selection criteria for very long life high power array operation. Modulation data for the array is given which proves that each laser diode in the array can be current modulated in exact RF phase with the others so that the entire laser diode array is 100% amplitude modulated at frequencies to several hundred megahertz. Data is given for wavelength matching the laser diodes as in the diode pumping of Nd:YAG. Linear diode arrays with up to 100 diodes in an inch have been fabricated.

Scaling presently available excimer laser systems to lasers designed to operate at high average power and high pulse repetition rates for long periods of time requires advances in many areas of engineering technology. For economical application to industrial processes, the efficiency must be increased. This leads to more stringent requirements on preionization techniques, energy delivery systems, and system chemistry. Long life operation (>10⁹-10¹⁰ pulses) requires development of new pulse power components, optical elements and flow system components. A broad-based program underway at the Los Alamos Scientific Laboratory is addressing these key technology issues, with the help of advanced component and systems development programs in industry. A prototype XeCl laser meeting all requirements for efficiency, system performance and life is scheduled for completion in 1984.

The state-of-the-art for laser materials for miniaturized laser systems are to be discussed. New materials, such as neodymium pentaphosphate, will be evaluated as to their potential in miniature laser systems for ranging applications. A comparison of these systems to the currently developed miniature Nd:YAG laser rangefinders is to be given. The design goals, as well as the range performance goals for the miniaturized systems, will be covered. We will present the system performance of two Nd:YAG miniaturized laser rangefinders which have recently been designed and constructed. Two different design approaches have been used in these systems: one system uses a tri-axial design whereas the other has discrete optical channels. Finally future performance predictions and future requirements will be given.

The electro-optical (E-0) community has long sought a neodymium doped yttrium aluminum garnet (Nd:YAG) laser system that provides short duration pulses and high peak powers at repetition frequencies in excess of 10 kilohertz (kHz). Previous attempts to develop such a laser implemented Pulse Transmission Mode (PTM) modulation using E-0 modulators. Because of insertion loses, these modulators were adversely affected by high average powers. A new approach to implementing the PTM technique has been investigated using a combination of an Acousto-Optic (A-0) and a Frustrated Total Internal Reflectance (FTIR) modulator. These devices were selected because their operation is independent of the direction of polarization of the laser energy and they provide a low insertion loss. The new PTM configuration provided significant increases in peak power and a reduction in pulsewidth in comparison to conventional A-0 Q-switching. Preliminary laboratory tests indicated that, if the FTIR can be optimized for PTM operation, narrow pulsewidths at high pulse repetition frequencies (PRF) can be obtained from an Nd:YAG resonator.

Alexandrite is a laser crystal which is unique in that it is broadly tunable, is four-level, and has a long storage time making Q-switched operation possible. In addition the crystal is surpassed only by ruby in desirable strength and thermal properties of all practical laser crystals. A simple four-level model that describes the laser operation in alexandrite is presented. The terminal laser level in this model is a set of vibrational states well above the ground state. The initial laser level is a level 800 cm-1 above a long-lived storage level and in thermal equilibrium with it. Experimental results of Q-switched operation and tuned long pulse operation are presented, both as a function of temperature. In Q-switched operation, pulsewidths from 70 ns to 300 ns have been measured and laser efficiency increases with temperature. In tuned operation, the increase in gain with temperature is accompanied by a shift of the tuning curve to the red. Both observations are consistent with the simple model. Some laser design parameters are discussed.

An array of twenty GaAlAs laser diodes was fabricated and RF and pulse modulation tests were conducted over a wide range in frequencies and pulse repetition rates. Measurements were made on the arrays to determine the dc voltage-current characteristics, optical output versus dc current, optical output beam distribution with off-axis angle, RF impedance versus frequency, RF optical waveform phase variation with off-axis angle, RF modulated optical output versus the RF drive voltage, RF modulated optical output for individual diodes in the array, optical waveform spectrum analyzer measurements, emission wavelength spectrum with and without modulation, effect of failed diodes on array performance, and the effects of long-term operation on array performance. All tests confirmed that the concept of requiring modulated diode arrays in applications requiring high optical power is acceptable.

A Md:YAG laser using CW room temperature injection lasers as pump sources was constructed, and proved capable of 100 mW polarized output at 1.06 μm when prime power input to the injection laser arrays was 25 W. The potential for stable long-life operation, together with its low power consumption, makes this laser an ideal source for spaceborne applications.

A giant-pulse laser R4man probe, suitable for gas concentration detection below loo ppm with high local (o.6 mm³)and temnoral (pulse width 2o ns) resolution, is presented. Concen-tration values of some selected gaseous pollutants have been detected in pure gases and in adjusted gas mixtures ranging from the pure component (106 ppm) down to measured 65 ppm. Concentration values of loo ppm were measured with an accuracy of ±l00%. When the local resolution was not required to be so high - measurement volume about 5oo mm3 - concentration values of 65 ppr cou3d be detected with an accuracy of about ±3o%.

Pulsed green lasers offer a very promising technique for conducting airborne coastal hydrographic surveys. When used as the transmitter of an airborne optical radar system, such lasers can chart miles of coastline quickly and accurately. The frequency-doubled Nd:YAG laser, operated in pulse transmission mode (PTM), can provide the required performance characteristics (wavelength, pulse duration, and repetition frequency) for this application. This paper describes a PTM Nd:YAG laser operating reliably at pulse repetition frequencies (PRF) of up to 400 Hz. Technical problems encountered include thermal effects in the laser rod, design of suitable Q-switch driving circuitry, and the problem of doubler lifetime. A stable resonator designed to correct thermal lensing and birefringence is described. A differential Q-switch driver for high PRF operation is described. A power output of 2.4 watts at 1.06 micrometers was obtained in PTM operation; at 400 Hz. Frequency doubling in DCDA at 400 Hz produced 0.176 watts at 532 nm. Thermally induced birefringence in the index-matched Q-switch imposed a limit on the average power of the PTM laser.

This paper describes an instrument which is capable of monitoring both the twist and lateral motion of a microwave tower. The Microwave Tower Deflection Monitor (MTDM) gives designers the capability of evaluating towers, both for troubleshooting purposes and comparison with design theory. The MTDM has been designed to operate on a broad range of tower structures in a variety of weather conditions. The instrument measures tower motion by monitoring the position of two retroreflectors mounted on the top of the tower. The two retroreflectors are located by scanning a laser beam in a raster pattern in the vicinity of the reflector. When a retroreflector is struck its position is read by a microprocessor and stored on a magnetic tape. Position resolution of better than .5 cm at 200 ft. has been observed in actual tests.

A laser surface finish gauge has been developed to measure the roughness of the entire inside surface of hemishells in the range of 4 to 10 microinches roughness average (Ra). Standards have been fabricated that allow for traceability of the gauge's measurements to the National Bureau of standards. The gauge employs the principles of angular scatter from a laser beam and was designed to eliminate errors introduced by varying degrees of part reflectance and changes in laser intensities. A microprocessor is used to extract data from the standards and manipulate the scatter information from test parts to produce a continuous trace of the part surface roughness on a strip chart. The gauge has been installed in a product certification laboratory and a statistical evaluation made which indicates a repeatability of +0.5 microinch Ra. The principles and theories under which the gauge was developed can easily be adapted to other part configurations and roughness ranges.

An airborne laser tracker was designed around a two-level beam deflection system. An xy acoustooptic beam deflector provides high angular rate control of the l-mrad divergeBce helium-neon laser beam over a 0.8 degree square field of view. Wide angle pointing (20 azimuth and 50 elevation) is accomplished with a 2-axis mirror beam deflector. The out-going and return beams are coaxial. The angular accuracy is <.5 milliradian. The track-loop angular velocity is greater than one radian/second.

The developed measuring device is a noncontacting system utilizing a He-Ne laser, which permits rapid measurement of interior dimensions of automobiles, based on the principle of optical triangulation. Laser beam is projected from the head of the device to a point to be measured as a spot and this spot is automatically searched by means of a mirror, a lens and a two-element photodetector to measure the length along the projection axis. The head of the device including optical parts is rotated by a motor and the rotating angle is measured by a rotary encoder. Thus, the measured length and rotating angle are calculated into rectangular coordinate values with a microcomputer, and the coordinate values can be represented on a panel and also punched out on a teletypewriter. The values thus obtained with this device have been successfully utilized for a computer aided design system for automobiles.

This Calibrator-Compensator System was developed at Farrand Controls to satisfy a need for a practical measuring system with a long term accuracy of a few parts in ten million over distances up to 1.9 meters (75 inches). The inherent high accuracy of laser interferometers is limited by changes in the wavelength of light as a function of atmospheric temperature, pressure, and composition. The errors can exceed 13 PPM in air under constant temperature conditions. The best commercially available automatic compensator measures atmospheric variations with separate transducers, digitizes the data, and calculates the required correction factor. Since the remaining errors, typically 3 PPM, did not meet requirements, an improved compensation technique had to be developed. A reference optical path of known fixed length is used to determine the initial wavelength and to track changes in wavelength as they occur. The true wavelength of light is determined by evacuating the optical path to a modest vacuum and measuring the apparent path length change. The same optical path, open to the atmosphere, monitors the aggregate effect of all atmospheric changes without the use of separate transducers. The relative velocity of light is servoed to the reference path length, and the outputs of all axes of an Option 450 Hewlett-Packard laser interferometer are corrected. There is no cumulative error, and full accuracy is maintained over indefinitely extended intervals. Test runs of 50 to 90 hours have consistently shown total errors less than 3 parts in 10 million over path lengths of 0.25 to 1.9 meters (10 to 75 inches).