In many industrial branches a continuous scaling down of parts and products is observed. For example in the fields of micro-mechanics new sensors and actuators can be produced which offer the possibility of making self acting micro- systems. Other micro-components for medicine, chemistry or optics allow minimal invasive surgery and inspection. In every case conventional fabrication technologies such as turning and milling have to be carefully investigated: their appropriateness for the production of micro-parts is not always guaranteed. On the other hand new technologies such as the LIGA-process (German acronym for lithography, galvano forming and plastic molding process) open new ways to inexpensive mass-production. The following paper describes the potential of DUV-lasers (laser wavelength: lambda equals 200 - 280 nm) for micro-machining specific applications. Using excimer-lasers the machining of ceramics, glass and polymer materials is presented. The excellent beam properties of a self developed quadrupled Nd:YAG-laser are used for the repair of photolithographic masks. The mask repair using ablation and deposition of chromium on glass substrate is described.
In the paper we consider the process of local welding between different layers induced by pulsed laser radiation. The effect of laser radiation on solids is accompanied by a number of physical phenomena that can be successfully used in various modern technologies.
The article describes a computer model of laser welding with a deep penetration base on unification of solution heat-mass transfer problem and the problem of irradiation propagation in cavity in approximation of geometrical optics.
Laser technology is one of the technologies the most highly developed at present; however, its wide introduction is constrained, on the one hand, by complexity and the high cost of the equipment, and, on the other hand, by complexity and insufficient knowledge about processes of laser welding, cutting and surface processing, as well as shortages of qualified staff. In spite of these reasons the technologies of laser processing of materials have reached such a level of development that their further perfection on the basis of accumulation of the empirical information has become impossible, whereas technological opportunities of such ways of laser processing, such as welding, cutting, melting and marking, are not completely used. For their successful realization it is necessary to choose the optimum mode of processing, but it is impossible because of the shortage of knowledge about the physical nature of given technological processes, as practically all existing information on these processes has qualitative character. On the other side, to provide the high quality and stability of treatment results it is necessary to have realization of the current monitoring and control during the most technological processes. For this purpose CAD and CAM systems are necessary, the absence of which is explained by the fact that for the present the physically adequate theoretical descriptions of laser technological processes are missing, and the experimental data, by virtue of non-systematic use of experimental work, does not give a complete experimental picture of the physical phenomena, proceeding at laser processing of materials.
Reported is the observation of laser treatment processes of materials by the brightness amplifier based upon the copper laser. Provided is an experimental investigation of melting stainless steel under the laser radiation. Real time monitored is the process of surface heating, melting, spreading a melting boundary and the progress of turbulent movement in the melting container.
As a result of kinetics of computer simulation of soldered joints forming, practical investigations of soldering modes influence at the joints' strength and analysis of micro section metalographic specimens fulfilled with the aid of electronic microscope, the possibility of three-five fold enhancement of soldered joints strength in comparison with manual soldering. Technological process and automated equipment are developed for laser soldering of electronic components with planar leads at the printed circuit boards.
The many-phase structure phase concentration of which depends on the concentration of mixture components forms in the alloy synthesized from powder mixture by laser irradiation. The maxima of phase concentration corresponds to values of the stoichiometric composition. Under the heating up to 800 K, the structure and the properties of the alloy become stable. The nanocrystalline structure distinguished for its hyperparamagnetic properties is formed in the synthesized alloys.
The article describes the characteristics and areas of application of laser technological complexes for marking, engraving and assay mark marking materials, developed by Laser Technology Center (LTC, St. Petersburg, Russia) and Central Research and Development Institute of Robotics and Technical Cybernetics (CR&DIR&TC, St. Petersburg, Russia).
Rapid prototyping, tooling and manufacturing are spread very quickly now and promise to accomplish radical changes in design and production. Laser-assisted rapid prototyping and manufacturing (RPM) processes, such as laminated object manufacturing (LOM), powders sintering (PS), and stereolithography (SL) occupy the first place among the above-mentioned techniques. The selection of laser radiation delivery system is a central question of laser-assisted 3D- process realization. Two principal ways are possible -- scanner and plotter systems. Scanners provide relatively higher rates of processing, but their use is restrained from optical distortions and limitations increasing with the increasing of processing field. Both plotter and scanning systems also have fundamental mechanical limitations at high speed of motion.
In the present paper the laser beams with Cartesian symmetry having the minimum diffraction divergence in near and far fields are synthesized. The spatial sizes of these beams in near field as well as the angular size in far field have been defined on the share of total beam energy that could be transmitted within this size. It is shown that the laser beams with minimum near-field diffraction divergence are well approximated by coherent superposition of a few number of lowest symmetric Hermite-Gaussian modes. The transverse distributions of light waves with minimum far-field divergence are described by prolate spheroidal functions.
Laser setup for flat optical components fabrication with submicron resolution has been developed at the Technological Design Institute of Scientific Instrument Engineering in cooperation with the Institute of Automation and Electrometry, Siberian Branch of the Russian Academy of Sciences and can be delivered to buyers on individual orders. Laser pattern generators in polar coordinate system are optimum for the fabrication of masks, angular scales, optical memory and diffractive optical elements. Accuracy and spatial resolution of recorded structures are comparable with analogous parameters of E-beam pattern generators. However cost of the first one is significantly smaller and it is more simple to work with such equipment.
SiOxNy for micro- and optoelectronics is obtained from low-pressure vapor deposition reaction induced by a novel flash lamp which irradiates a precursor mixture NH3/SiH4/N2O in deep ultraviolet (160 - 260 nm) and IR. Amorphous thin films are resulted within the composition of silicon oxynitride. Flow ratio of precursors and flashtubes were varied to produce a range of x and y. The detailed properties have been investigated using ellipsometry, infrared absorption, auger electron spectroscopy, and atomic force microscope. The hydrogen concentrations, as N-H bonds, were low, in the range (2 - 5)1023 H atoms.cm-3. All samples deposited at 400 degrees Celsius are isotropic and homogeneous in hydrogen content. No absorption bands of O-H, Si-H and H2O are detected in the range of the FTIR spectra. A Monte Carlo type model is well adapted to simulate the morphology tendencies for SiOxNy film isotropy improvement.
The method of the thickness and temperature field measurement in Si wafers is discussed. Laser excitation of thermal waves and their diffusion in depth and lateral directions are used. Thermal wave is detected by IR radiometry. The pulsed laser illumination of wafers under testing are discussed. The investigation of depth and lateral diffusion of heat processes to determine the thickness and thermal diffusivity separately. The accuracy, reliability and resolution of the method proposed are discussed.
Principles of the integrated optical noninvasive inspections (or nondestructive testing) of the material quality are considered. It is well known, that different optical methods allow us to obtain 2-dimensional spatial distributions of parameters most required for tested materials. The aim of this contribution is to elaborate ways of comprehensive using of optical techniques (photometry, reflectivity, scattering, interferometry, holography, polarization, luminescence and so on). The special feature of proposed set up is the modular construction and high flexibility in design, i.e. it is possible to adapt our equipment to different kinds of automated testing techniques. Considered methods and setup were applied to the investigation of wide range of subjects, e.g. solid natural or artificial materials, liquid crystals, microporous or fractal matrix, solutions, biological specimens. In this paper the only results, concerned with semiconductor wafers of film- structures, are discussed. The experimental verifications and arbitrary electrophysical measurements are included.
A three dimensional volumetric display system utilizing a rotating helical surface is described. The rotating helix system permits images to be displayed in a three-dimensional format that can be observed without the use of special glasses. Its rotating helical screen sweeps out a cylindrical envelope, providing a volumetric display medium through which scanned laser pulses are projected. The light scatters from the surface of the helix so that each voxel appears to emanate from specific points in space. Each point has x-y-coordinates determined by the laser scanner and a z- coordinate determined by the intersection of the laser beam and the helix surface. Display images are created by synchronizing the interaction of the laser pulses and the moving screen to address a full three-dimensional volume that gives the viewer true depth cues (binocular parallax, accommodation, convergence) without the need for any special viewing aids. We describe recent work on the development of mechanical, optical, electronic, and software engineering for a display system based on a 36-inch diameter helix using high speed, multichannel, random access laser scanners. Color images are created using red, green and blue laser sources. The system is capable of displaying 800,000 voxels per second, per color. A portable, 12-inch diameter, translucent helix system is also presented.
A laser opto-acoustic system for measuring 3-D objects surface topology has been described. The main principle of operation consists in excitation of a short acoustic pulse by irradiation of surface under test by short laser pulse and in measuring the time of acoustic pulse traveling to the detector. A laser pulse with nanosecond scale duration and liquid immersion medium with high enough sound speed was used to increase the measurement precision. The examples of system applications including aircraft turbine blade measuring have been presented.
In this research, time-resolving opto-acoustic fiber sensor for registration of acousto-optical signal parameters in devices with fiber-optic delivery systems of pulsed laser radiation and feedback systems has been advanced and investigated for the first time.
Last year laser medicine received high recognition as an effective means of treatment and preventative maintenance of processing of various tissues. The use of fiber-optical systems in laser medical installations allows us to produce a lot of operations without surgical insertions and treatment in difficult locations. Application of such systems assumes the formation of laser spot in the processing area by special technique. It is possible to be reached using the various optical elements, however the use of conventional microlenses and elements leads to the essential increase of tool dimensions. A lot of methods enabling us to form the microlenses on the ends of fibers by the methods of fusion of fiber material are known. We already offer the method of formation of microlenses by means of co-actions of carbon dioxide laser radiation and various mechanical forces. In this report we present a lot of fiber-optical elements for the formation of laser radiation, produced by such method, and some of their optical parameters being measured by special technique. The list of designed elements is submitted in Table 1. The above-mentioned elements can be formed on the optical fibers of the quartz-quartz, quartz-polymer types, glass and sapphire fibers.
We have designed a laser complex which is a combination of a YAG:Er laser operating in the free-running mode, a radiation delivery system based on a chalcogenide fiber with uniquely high damage threshold, and a diagnostic optical coherent tomography (OCT) device for in situ monitoring of surface layers of the tissue under treatment. A flexible chalcogenide glass multimode fiber operates with pulse energy 150 mJ at a repetition rate of 3 Hz. Neither degradation nor laser damage were observed after transmission of 104 laser pulses through the fiber delivery instrument. This complex was employed to study the effect of YAG:Er laser radiation on a cataract-suffered human lens. The laser ablation process has been monitored by OCT. During the lens treatment the image of ablation crater and inner layers with a scanning depth of several millimeters and spatial resolution of 15 micrometers was available. The kinetics of pulse-to-pulse ablation crater growth a well as of the adjacent thermally damaged zone formation were investigated.
Elaboration and application to clinical practice of new laser technologies, based on use of high intensity radiation, provided by IR solid-state lasers on the crystals YAG:Nd (1.06 mm and 1.32 mm) and YAG:Ho (2.09 mm), whose surgery action is different, is one of the most important fields of laser surgery. Our experiments, which were carried out on animals, have shown that the treatment methods, based on the use of radiation of these lasers provide the best covering of surgery (general and endoscopic) necessities. The reasons are as follows. On the one hand, one has the possibility to organize loss-free transport of radiation of YAG:Nd/Ho lasers via the fused silica fiber optical waveguide to practically any place in the patient's body. On the other hand, various ranges of penetration depths -- from much less than 1 mm to 1 cm -- provides variety of surgery effects. The action of these lasers emission onto the surgery field is well controllable and differential and thus makes it possible to vary its effect just in the course of operation.
This paper is targeted to define optimum Nd:YAG laser radiation parameters causing the best hemostatic and cytotoxic effect on an area of tumor tissue coagulated and heperemied over. Experimental data form the basis of a method of endoscopic laser operations with airway malignant formations.
The description of experimental installation for investigation fractal structure of dental tissues light scattering is presented. The installation includes light source (He-Ne laser), beam transformer based on microlens array, light polarization control unit and registrating device (which represented computer interfaced CCD-camera). The experimental installation provides the estimation of different kinds of light scattering in the enamel and dentin. The joint computer processing of images corresponding to different states light polarization allows us to separate the effects of light scattering caused by different scattering object as well as by relief junctions. The results of research may be useful for dental restorations, because fractal dimension defined adhesion properties of dentin.
The description of experimental set-up for investigation of light scattering in dental tissue and dental restorative material is presented. The set-up includes the light source (He-Ne laser), beam shaping light polarization control unit and registration device. The latter represents the computer interfaced CCD-camera. The experimental results of side light scattering in enamel/dentin and in double-layer porcelain are represented. The results of this research may be useful for aesthetic dental restorations.