Pulse compression of cw mode-locked dye and Nd:YAG lasers has provided several new pico-second and femtosecond sources. In this paper, we describe pulse compression techniques and present several scientific applications to illustrate their utility.

For several years now picosecond dye laser technology has served researchers in the investigation of ultra-short phenomena. While becoming more and more sophisticated, synchronously pumped dye lasers today are a standard research tool in many laboratories. There exists however a substantial range of applications - mainly for instance in the short wavelength range or in non-linear applications - where these lasers do not provide sufficient pulse energy or peak powers. The answer to this problem has been the develop-ment of picosecond pulse amplifiers which can bring the low intensity pulses from a mode-locked laser to high intensities followed possibly by frequency doubling and maybe even further amplification after the doubling stage. While such systems have led to excellent results they have at the same time excluded experimenters who are not interested in spending time and energy in the development of such comparatively complex laser systems from doing research in this area. To these researchers, the Lambda Physik PSL 4000 makes available for the first time a turn-key laser of modest complexity which can deliver pulses in the ultraviolet spectral region at 248 and 308nm with durations of the order of a few 10 picoseconds and energies of the order of 10 mJ or more. With this instrument focussed intensities which exceed 1014Wcm^-2 can be achieved using standard optics.

A brief review of the operating specifications of CW mode-locked Nd:YAG lasers including Q-switching, frequency-doubling (SHG) and frequency-tripling (THG) is followed by a discussion of amplitude stabilization schemes. Experimental results of noise reduction using feedback to the pump lamp are presented.

We report the design of a dye laser capable of producing 20 picosecond pulses at repetition rates of up to lk Hz with energies of up to 50 μJ. The problems associated with the design of this laser will be discussed. In recent years the synchronously pumped dye laser has evolved into one of the most widely used sources of tunable picosecond and sub-picosecond pulses. The typical output of these systems is at most a few tens of nanojoules. If higher energy is required the output is amplified. Recently Wisoff et all reported the development of a dye laser designed to be pumped by the output of a mode locked and Q-switched Nd:YAG laser that produced pulses from 10^-30 picoseconds duration at repetition rates of 6-10 Hz. The laser described in this paper has been designed to use an acousto-optic cavity dumper. Figure 1 shows the optical layout of the laser. A telescope configuration (M₂ and M₃) allows selection of the appropriate beam waist sizes in the dye cell and acousto-optic Bragg cell. The prism beam expander is used to select the spot size at the grating thereby allowing the user to generate a Fourier transform pulse with given duration.

Color center lasers in alkali halide crystals span the entire spectral range from 0.8 to 4 micrometers.^1,2 This spectral region encompasses the vibrational excitation range of many novel molecular species such as: free radicals, dimers and molecular ions; Rydberg transitions in atoms; and sub-band gap excitations in semiconductors. As a spectroscopic tool color center lasers offer powers from ten to several hundred milliwatts, good beam quality, and passive frequency stability on the order of a megahertz.³ In mode-locked operation they produce pulses in the 5 to 20 picosecond range. Color center lasers also have been operated in the pulsed mode with both flash lamp and pulsed laser pumping.4^,5 The most powerful pulsed sources have produced several hundred kilowatts of peak power. At this level they are close to the threshold of being able to produce stimulated Raman scattering, and thus extend their tunability significantly farther into the infrared.

Following the demonstration of the second harmonic generation in 1961 by Franken, numerous non linear methods have been used associated with pulsed lasers to generate U.V. radiation in the range 200-300 nm. The corresponding sources are now widely used in the spectroscopic studies, but their limited monochromaticity makes them of poor interest in high resolution spectroscopy. There is for a long time now a pronounced interest to have at one's disposal a radiation source which provides extremely narrow bandwidth, convenient intensity and tunability, but it is only recently, with the advent of powerful CW dye lasers, and the development of enhancement techniques that the first reliable sources have been demonstrated, and the first high resolution spectroscopy studies performed. We give in this paper a brief and then certainly incomplete review of the different progress that has been made in the generation of highly monochromatic U.V. radiation. We mainly deal with the use of non linear crystals in second harmonic generation and sum frequency mixing schemes.

Excimer lasers form a group of pulsed high-pressure gas lasers which emit at four wave-lengths, namely at 193nm (ArF*), 248nm (KrF*), 308nm (XeCl*) and 351nm (XeF*) in the ultraviolet spectral region. Unlike the infrared radiation from lasers like e.g. Nd:YAG and CO₂, the high energy photons from excimer lasers typically interact with the electronic excitation levels of an absorber and this can lead to chemical bond breaking, ionization or electronic excitation. The excellent focusability of their short wave-length radiation can further be exploited to generate submicron structures.

High speed videography and photography have been limited by insufficient illumination from conventional light sources. The properties of the copper vapor laser as a very short pulse, high-repetition rate, visible light source are discussed and its applications with high speed video and film cameras described.

The characteristics of high power laser diode arrays which make them a useful pump source for solid state laser systems are described.

A 10-kW CO₂ laser has been developed with design emphasis on the output beam quality. The laser is of a fast transverse-flow type, wherein the discharge takes place along the gas flow. Both stable and unstable resonators were used and compared in their output and beam properties. Results show that diffraction inside the unstable resonators plays an important role in determining their beam characteristics. Near diffraction limited beams have been obtained from the unstable resonators.

Laser processing has become increasingly competitive with conventional methods for cutting and welding three-dimensional metal and non-metal parts. Major productivity increases have been reported by the growing numher of users of industrial multiaxis carbon dioxide (CO₂) laser systems. For example, in replacing conventional machining, laser cutting has increased throughput in trimming a deep drawn gas turbine engine component from 18 pieces per day to 18 pieces in 30 minutes. For another, laser cutting has replaced hand methods for cutting intersecting tubing used in aerospace applications. With the hand method, one assembly was produced every 1 1/2 hours. With laser cutting, the rate has been increased to one assembly every minute.

High power laser systems and high pressure waterjet systems are both emerging as non-conventional cutting tools, capable of increasing productivity and quality in the manufacture of a great number of products employing diverse material. It is often a confusing issue for the manufacturing engineer or production manager to decide which system would be most suited for his applications. This paper is intended to provide some insights into the engineering and economic aspects of laser systems versus waterjet systems.

A review of the Nd:YAG laser rangefinder/designator is presented. General operation of the laser rangefinder and its use by the military are discussed. Comparisons between conventional laser designs and ruggedized stable configurations show the folded crossed porro resonator is a successful approach. Designing a laser rangefinder in a small package that will meet performance specifications in a military environment requires many unique features. Size, weight, and volume reductions in military laser rangefinders have progressed over the last ten years. Comparable airborne systems have been reduced from 50 lbs. to less than 7 lbs. Handheld rangefinders are available in packages slightly greater than 1 lb. Future trends for the Nd:YAG laser rangefinder are referred to in closing.

Designed and developed as a commercial product designated the KEI Model LH-83, the hand-held eyesafe laser rangefinder was refined and "hardened" for the full military field environment under a competitive Army advanced development contract for the MELIOS (Mini-Eyesafe-Laser-Infrared-Observation-Set) program which is also designated the AN/PVS-6 ( ). The Model LH-83 currently has a weight of 2 kg and is about the size of a pair of binoculars. The monocular device displays system status and range data in the eyepiece. Operation is powered by self-contained AA-sized alkaline, rechargeable NiCd, or long-life Lithium batteries. A major feature of the KEI Model LH-83 and MELIOS design is compartmentalization into three field-replaceable modules (i.e., power supply, range/control and transceiver). From built-in tests, a possible field malfunction can be diagnosed and, by module replacement, the system can be returned to operational status in a matter of minutes. The overall system design is discussed. Subsystem design and performance is detailed in a manner that will enable possible fire control system users to incorporate the modules into various system configurations where an eyesafe laser rangefinder would be advantageous. The Army is in the process of conducting extensive evaluations, which include environmental and field testing. It is expected that these evaluations will be completed by the First Quarter of FY 1986.

Improvements in alexandrite laser technology have led to lasers with improved efficiency, higher brightness, more energy per pulse and higher average power. These improvements have come about because of understanding and solving the "problems" of low emission cross section, high damage probability, short fluorescence lifetime, and high thermal lensing in alexandrite together with improvement in alexandrite crystal quality.

The development of Nd,Cr:GSGG has progressed rapidly over the past few years. Two inch diameter and larger boules have been grown core free with flat interfaces. The early problems of attaining low loss at 1.06 μm, the cost and availability of scandium, and growth problems have been alleviated. The crystal composition and trace impurities in starting materials must be controlled rigidly. Active laser testing of 1/4 x 3 inch rods has demonstrated slope efficiencies of greater than 7%. Wavefront distortions at 1.06μm with a Zygo interferometer are A/4 PV along [111] for 3 inch lengths or comparable to Nd:YAG. Loss factors at 1.06Pm are typically <0.006 cm^-1 or several times that of the best Nd:YAG. This may be caused by impurities, crystal quality, or intrinsic loss of the gallium garnets. The size of present boules has yielded 1/4 x 4 inch cylindrical rods and 6 x 20 x 100 mm3 slabs. These may possess growth striae which introduce a noticeable birefringence when viewed normal to the growth axis. Striae can be minimized by more stringent temperature control but their effects are governed by the stress optic coefficients. The latter must be measured accurately. The growth of 2 inch boules is discussed along with problems associated with the growth of larger crystals.

Hughes Aircraft has been developing a hand-held eye-safe laser rangefinder fo1r the Army utilizing Stimulated Raman Scattering technology. The device uses the 2915 cm^-1 vibrational mode of methane (CH₄) to wavelength shift the Nd:YAG pump laser's 1.064 micron to an eye-safe 1.543 micron. The result is a lightweight BRH Class I eye-safe tactical device. A brief description of Raman wavelength shifting basics is followed by description of the Hughes system.

The optics in a laser rangefinder must perform three separate functions: transmitter divergence control, receiver energy collection, and aiming sensor imaging. In addition, boresight may need to be monitored. The design of these optics is driven primarily by the rangefinder packaging constraints, which limit both the external window size and the internal space available. System considerations such as range, target, propagation, package, and safety are used to determine the required optical apertures, fields, divergence, and resolution. Often, the total area of the transmitter, receiver, and sensor apertures cannot be accommodated by the front of the package, in which case functions must be combined. Sensor optics depend somewhat on the specific sensor (eye, TV, FLIR), but usually require the biggest possible aperture with near diffraction-limited performance. Laser beam expanders are usually some form of Galilean telescope, and often present serious Narcissus and damage problems. Receiver optics look simple, but narrow filters and small detectors can make them quite sophisticated. Boresight optics are sometimes required to monitor the alignment of the laser beam to the sensor reticle. Some specific design suggestions are made, with emphasis on those problems which are peculiar to laser range-finders. These designs emphasize high-power pulsed lasers and diffuse targets, since they are the most common and present some of the greatest challenges.

As the telecommunications and data communications marketplaces demand higher rates of information transfer, the need for high performance optical transmitter and receiver components becomes clear. High performance integrated optical transmitter and receiver products that span the spectrum of data rates from 20 Mb/s to in excess of 600 Mb/s will be presented. All components are available utilizing long wavelength LED or laser source and PINFET detector technology. The DTLtm product series is comprised of transmitters and receivers paired as data links. All electronic functions are integrated into custom bipolar silicon integrated circuits. The optical components are 1300 nm light emitting diodes and PIN photodiode detectors (short wavelength versions are available as options). Three data link products are currently available: DTL-13-50: 20 to 50 Mb/s Manchester coded with both ECL data and clock at the receiver output DTL-13-125: Up to 125 Mb/s NRZ operation for transmission of ECL data signal only DTL-13-200: Up to 200 Mb/s NRZ operation for transmission of ECL data signal only For higher data rates, a series of 1300 nm or 1550 nm laser transmitters and PINFET receivers is under development. Currently available is the DTX-13-417 1300 nm laser transmitter, suitable for 417 Mb/s NRZ operation. A 565 Mb/s transmitter, the DTX-13/15-565, at either 1300 nm or 1550 nm is being developed. The complementary PINFET receiver products for 417 and 565 Mb/s operations, are also being developed. All of the DTX/DRX series are available in compact modular packaging, with fiber pigtails for easy coupling to the transmission fiber. An option for design as a standard line card is also available.

The need for mass produced, reliable light sources for fiber-optic communications systems is growing rapidly. Currently the market for these sources is focused on 1.3 μm lasers for long haul telecommunications, with an additional growing need for fast 1.3 μm LEDs to be used in high performance (to 200 Mb/s) data links. In order to address these market needs, Lytel is producing a line of high quality, high reliability emitters.

Buried heterostructure window lasers have been developed, offering conservatively rated powers to 30 mW at 840 nm. Output beams are single spatial and multi-longitudinal mode. Accelerated aging tests project lifetimes greater than 105 hours.

The fabrication, performance and application of indexed guided proton bombarded DH lasers emitting at .8, 1.3 and 1.5 microns are described. The devices are fabricated by single step LPE and utilize double current confinement configuration in order to minimize current leakage and also achieve very good lateral and optical confinements. In the 1.3 micron devices, threshold currents as low as lOmA have been achieved and coupling efficiency as high as 43% has been obtained, enabling us to linearly drive the devices up to 5mW power output from a singlemode fiber.

In the last years, high quality silica optical fibers have been developed where a reduction in the OH content resulted in a transmission loss lower than 0.5 db/km at a wave length range of 1.3 µm. At M/A-COM LASER DIODE INC., edge emitting InGaAsP/InP double heterostructure LEDs have been developed for this wavelength range that are efficiently coupled to single and multimode optical fibers. Optical Fiber Communication systems employing 1.3 µm edge light emitting diodes (ELEDs) as transmitting sources offer advantages over lasers for both multi and single mode applications. Their reliability is higher, they are less sensitive to changes in temperature or variations of the drive current. Also, their driver circuits are simpler because they do not require optical power monitors. LEDs are not susceptible to external feedback. That is, small feedback signals from coupled fibers or from connectors within the fibers, will not induce any noise. This allows the ELEDs to be desirable sources in the competitive areas of local area networks (LANs), tele-communications systems and local loop distribution networks.

The laser-based printing and information processing markets have shown consistent, and at times dramatic, growth over the past few years. Prospects are even brighter for the future as emerging laser applications achieve increasing market share-- and perhaps market dominance--over more established, non-laser printing and information storage products. Millions of additional devices are likely to be sold for new applications that will closely link lasers to the home and personal computer markets.

Laser beam scanning with holographic grating has the advantage of low cost, vibration and wobble insensitive and simple mechanical construction. However, it requires that the laser operate at single longitudinal mode with good wavelength stability. This is easily achieved in a gas laser but is difficult thus far to obtain with a semiconductor laser. We have specifically developed a high power laser particularly suitable for use in holographic scanning. Its high power and single transverse mode feature are also useful in optical disc recording. The device is called channeled-substrate narrow stripe laser with double current confinement and large optical cavity. In this structure, stable single longitudinal mode is achieved by strong index guiding and special facet coating. Furthermore, single transverse mode is maintained by good lateral electrical and optical confinements. The high power capability is obtained by the use of large optical cavity. The resultant is a buried crescent-shaped active region with an additional reverse-biased p-n junction. Light output up to 50 mW is obtained at 790 nm in CW operation at room temperature. Threshold current as low as 30 mA and differential quantum efficiency as high as 60% are achieved. Furthermore, high quality beam with minimum astigmatism and a diver-gence angle of 320 x 100 (FWHM) is maintained throughout the whole power range. This laser has been incorporated into our Holoscan laser printer which is now commercially available. It is also being used in a variety of prototype disc recording systems.

He-Ne Lasers are used in many applications for the acquisition, processing, and recording or reproduction of information. In many instances, these applications place a high performance demand upon the light source that can only be achieved by utilizing He-Ne lasers. Characteristics and attributes of the He-Ne Laser enabling it to meet these performance demands are presented.

We developed two beam laser diode array as a light source of a laser printer which prints multi-line in a single scan. The device consists of a monolithic two beam laser diode array and a monitoring photo-diode. Each beam can be operated independently. The typical lasing wavelength is 785nm, and the light output power is 5mW at operation current of 50mA. Full angles at half maximum points of far-field patterns in parallel and perpendicular planes are 10° and 30° respectively. The difference of optical characteristics between the two laser beams in one chip are small, ex., the difference of lasing wavelength is typically 1.8nm.

The application of short wavelength helium cadmium lasers to printing and information processing is discussed. Features of these lasers which make them useful in high resolution systems are examined. Recent technical improvements in stability and noise control are noted. The advent of hard seal tube technology to this laser type is also noted. The rapid emergence of semiconductor diode lasers as viable sources is discussed and the problems relating to the incorporation of diode lasers into systems are addressed. A new turnkey cw diode laser system, the LiCONiX Diolite 800, is reviewed and its applicability to R&D and prototype use is pointed out. Custom laser diode drivers (LDD's) are mentioned and a specific example given. Finally, a laser stabilization accessory, the LiCONiX 50SA, designed for extreme power stability and noise reduction is described.

Laser diode for DRAW optical disk systems has to have not only high power characteristics (writing) but also low noise characteristics (reading) at low power. However, few of so-called "high power lasers" have low noise. In this paper, we present a new high power low noise laser, which can be volume produced at low cost. The laser have wavelength of 780nm, power output of 25mW (50% duty cycle), and high S/N ratio of 90dB (f=20kHz, BW=300Hz, opt-ical feedback ratio < 1%) at 3mW CW. In addition, it has a lifetime enough to write an optical disk for 50,000 hours.

Recent advances in air-cooled argon ion laser technology have significantly improved the performance characteristics of these lasers. Smaller size and lower costs, combined with improved reliability and longer plasma tube lifetime, have stimulated the development of important new applications in medicine and communications, as well as information processing. In this article some design considerations of the air-cooled ion laser developed at Spectra-Physics will be highlighted as well as a number of potential applications.

The Laser Marketplace Seminar, held January 23 and 24 in conjunction with O-E/LASE '86, provided accurate marketing data on many of the important application areas of lasers. Marketing experts discussed emerging technologies and marketing trends in the laser industry. According to these experts, the laser industry will experience strong, and at times dramatic, growth in coming years.

Steady technical progress is supporting trends toward higher powers, smaller volumes, shorter pulses, higher repetition rates, and new wavelengths in commercial laser devices. Lasers are finding new applications in semiconductor processing, medicine, and other fields.