The He-Ne laser has seen a developmental renaissance in recent years. Whereas ten years ago technologists had predicted its extinction by today, it has in fact become all the more ubiquitous and survived strong threats from solid state sources, unfolded a broad rainbow of new lines, and reformed itself into more useful envelopes. Today, the He-Ne laser appears to be well entrenched to survive and proliferate into the 1990's and the end of the second millennium. The historical development of the He-Ne laser is revisited emphasizing critical techno-logical paths enroute to today's device. Hard-sealing introduced during the last decade has been the primary factor extending tube life into the tens of thousands of hours range. The availability of higher quality optics has been critical to the construction of resona-tors capable of sustaining the low-gain green (543nm), yellow (594nm), and orange (612nm) lines at useful powers. An overview of multiline, infrared, and color selectable (tunable) devices is presented. New applications for He-Ne lasers, especially the non-red wavelengths, are discussed. Particular focus is given to 633nm resonator cavity structures which have come to dominate airborne particle size measurements and ring laser gyros (RLG). The close proximity of the green (543nm) and yellow (594nm) lines to excitation of prominent fluorescent dyes is seen to potentially open numerous medical markets. Other applications in photochemistry, micro-surgery, photolithography, and the visual arts are also emerging. When combined with several new infrared He-Ne lines, there promises to be a strong future for tomorrow's He-Ne laser.
The development of HeCd (helium cadmium) lasers with wavelengths at 442nm and 325nm is reviewed from the earliest commercial versions to the most recent developments. Particular emphasis is placed on design features introduced by LiCONiX, a developer and supplier of HeCd lasers for fifteen years. The early problems of short lifetime, power instabilities and high noise are discussed and the preferred solutions described in some detail. The emphasis is historical and leads to the design goals and the implementation thereof in the most recent HeCd laser, the LiCONiX model 4300. Although the detailed physics of the discharge is avoided, stress is placed on the multiparameter dependence of key operating specifications and useful advice for system designers is included. Some key applications are mentioned and the trend of future development of this unique laser indicated.
Since its introduction in 1971, the air-cooled argon ion laser has evolved to become the primary output light source in color separation systems and in some computer printing applications. Recently, air-cooled ion lasers have also been designed into chemical and medical analysis equipment. As a result of the widespread acceptance of this type of laser into systems environments, laser manufacturers have made significant investments in order to improve lifetime and reliability characteristics, and to reduce the product costs. This article describes the air-cooled ion laser and discusses the changes that have been made, both to the design and to the manufacturing process, with the consequent improvement in laser lifetimes and reliability. In addition, the advantages and disadvantages of this type of laser in systems environments are noted throughout.
The first semiconductor lasers, based on simple p-n junctions formed in gallium arsenide, were demonstrated in 1962 . It was not until 1970, however, that continuous oper-ation at room temperature could be demonstrated. This was achieved by using double hetero-junctions of GaAlAs and GaAs in which the carriers are confined in the potential well formed by sandwiching a thin, narrower energy-gap material between higher energy-gap n- and p-type materials [2,3]. Since then there has been worldwide extensive research and development efforts in improving the operation characteristics as well as the reliability of the laser diodes. For the past fifteen years the main driving force behind these efforts have been applications in optical communications. Some attractive features of using laser diodes as light sources in fiber optic communications include narrow emission linewidths, excellent directionality, and very high bandwidth of direct modulation. Such features enable good coupling efficiency into the transmitting medium and make laser diodes particularly attractive for long haul communication. Extensive research of the optical fiber in the late 70's revealed the 1.3 um and 1.55 um wavelength regions to be the regions of lowest loss for silica based fiber. Development of GaInAsP/InP laser diodes with these wave-lengths soon followed. At present, GaAlAs/GaAs laser diodes in the 0.83 um region and GaInAsP/InP laser diodes in the 1.3 um and 1.55 um regions are "mature" for fiber optics communications.
This paper is an historical and tutorial review that examines the product development life cycle of a single laser product: the IBM 3687 Supermarket Bar Code Scanner. The intent of this paper is to reveal to the reader the manner in which this product progressed from the conceptual stage to the design and development of the final product. We will begin with a brief review of the UPC bar code and the basic concepts involved in scanning the code. We will then discuss the early IBM scanner products in order to lay the groundwork for the introduction of the 3687 scanner. The major portion of the paper will be devoted to a discussion of the technical factors involved in the design of the product once the marketing decision was made to develop the product. The discussion will include those factors that influenced the decision to use holography, the problems encountered in the use of this relatively new (to bar code scanning) technology, and the solutions of those problems. In fact, the major emphasis in our discussion of the various stages of this product development life cycle will be on the development and implementation of a holographic optical element as a key component in the 3687 bar code scanner. By 1977, when this product development began, the low-power Helium-Neon laser was already a tried and tested, well established component in supermarket bar code scanners. The holographic deflector disk was, on the other hand, completely untested in any low-cost, high-volume, commer-cial product. The unique capabilities and problems associated with the use of this device will be discussed. Note that most of the dimensions in this paper will be in inches instead of in metric units. This is consistent with the units generally used by the supermarket industry in the design and installation of supermarket check-stands, and with the units generally used by the UPC standards committees.
Spectra-Physics recently introduced the Model 750 SL scanner for use in the European point-of-sale market, to meet the European requirement for a scanner of less than 13 cm height. The model 750 SL uses a higher density computer designed scan pattern with a retrodirective collection system to scan and detect UPC, EAN, and JAN bar codes. The scanner "reads" these bar codes in such a way that the user need not precisely align the bar code symbol with respect to the window in the scanner even at package speeds up to 100 inches per second. By using a unique geometrical arrangement of mirrors, a polygonal mirror assembly, and a custom-designed plastic bifocal lens, a design was developed to meet these requirements. This paper describes the design of this new low cost scanner, the use of computer-aided design in the development of this scanner, and some observations on the future of bar code scanning.
Two systems serve as examples of surface evaluation by means of laser scanners. One utilizes conventional image-processing methods in a hazardous environment. The other uses analysis of scattered light to extract the signature of the surface flaws. A general check list for optical design questions illustrates similarities and differences in the two applications.
We describe studies on the scanning optical system for compact and inexpensive Canon laser beam printer (which we call LBP). Based on Canon's historically accumulated laser scanning optical technologies, our originally developed scanning optical system has the two functions of fθ-characteristic and deflection error compensation (we call the scanning optical system fθ-DEC), comprising a polygonal mirror scanner and toric lens as key components. As for the design, compactness and inexpensiveness of the fθ-DEC scanning optical system was investigated based on our theoretical and analytical study on fθ-lens for LBPs. On the manufacturing side, exclusive manufacturing equipment was developed for each of the above mentioned key components for effective mass production. In this paper, the theory, design, and manufacturing technologies for our fθ-DEC scanning optical system are presented. In addition, as an application example, Canon LBP-CX is introduced, where the above technologies have been integrated.
A review is presented of the design and performance of an electro-optical scanning system for direct transfer of raster data to recording media. The system uses either a semiconductor laser diode or a HeNe laser to record rasterized bit map images, and features a grating clock scheme for exact beam positioning at high speed, high resolution, and extremely small cross scan error.
The design of a write-once-read-multiple optical disc drive head using an 780 nm 20 mW diode laser is presented. To achieve high density data storage, the laser is collimated and aberration corrected before it is focused by a .50 NA objective lens onto the disc. The light diffracted back from the disc is used to generate an RF data signal as well as error signals for focusing and tracking. Detailed design requirements and considerations are discussed.
Instruments incorporating low power He-Ne lasers are used in construction and agriculture for rapid and accurate leveling and alignment. The optical systems used in these instruments must meet extremely high accuracy requirements yet be low cost and function reliably in a rugged environment. This paper is a case study of the optical design used in one of these instruments. The overall operation of the instrument is presented with emphasis on accuracy and environmental requirements. The general design criteria for the optical system are reviewed and the major components described. Using a recently developed product as an example, a detailed design of the optical system is developed. The various design alternatives that were considered during development to achieve high performance, low cost and efficient manufacturing are discussed.
In the past, radial grating optical shaft encoders have generally provided the highest attainable resolution and precision for the measurement of angular rotation. These encoders employ relatively coarse gratings, and use incoherently illuminated Moire-type grating readout heads. A 24-bit version of such an encoder has an angular resolution of 0.4 microradians, is about 18-inches in diameter and generally somewhat fragile, and can be a major perturbation to the shaft to which it is attached. A precision laser-based angular measurement system has recently been developed in which the encoder is a cylindrical diffraction grating, and the readout head is replaced by a moving interference fringe pattern formed by beams from a stabilized 2-frequency HeNe laser. The sensor head is small, stable, and capable of angular resolution appreciably in excess of that provided by other currently available techniques. In this paper we describe a configuration in which a 600 line/mm grating on a 3 cm diameter shaft is used with two laser readout heads to independently measure both angular rotation and cross-axis wobble with a resolution and precision of better than 0.5 microradians. The sensor head is less than 2 cubic inches (30cm3) in volume. The laser beam is brought. to the sensor by polarization-preserving monomode fiber, and the optical signals are carried to detectors by multimode fibers. The maximum update rate and angular velocity are 225 KHz and 5 rad/sec respectively. By increasing the diameter of the cylindrical grating, the angular resolution can be increased proportionally: using the same grating and readout head with a 12-inch diameter shaft, a 28-bit incremental encoder can be achieved--having art angular resolution on the order of 20 narioradians.
Frequency stability plays a crucial role for laser metrological applications. This paper first reviews the laser as a measurement tool in metrology. The techniques of laser frequency stabilization for metrological applications are then discussed from physical and engineering points of view. Finally, an example of recent advance in laser frequency stabilization is presented.