Growing applications of CO2-lasers in many cases demand transmission optical elements (widows, lenses, etc.) which could reliably operate at high beam powers. In the present work we propose to produce CVD diamond transmissive diffractive optics. To realize this idea surface microstructuring by laser ablation was applied. Computer controlled selected area ablation of preliminary polished (plane) diamond plates with thickness of 0.3 mm was performed by scanning focused beam of KrF laser. As a test sample for radiation with (lambda) equals 10.6 micrometers a cylindrical lens with the aperture of 4 X 4 mm2 and focal length of 25 mm was produced. Numerical simulation of the lens was made for the fundamental mode TEM00. For tests of the diamond lens 20 W CO2 laser was used.
Micromachining of hard materials such as fused silica and GaN by hybrid laser processing, in which interaction of the conventional pulsed laser beam and another medium on the material surface leads to effective ablation, is reviewed. Simultaneous irradiation of VUV and UV laser beams emitted from a VUV Raman laser presents great potential for precision microfabrication of the hard materials (VUV-UV multiwavelength excitation process). In addition, another hybrid laser processing of glass materials using a conventional UV or visible laser, referred to as `laser- induced plasma-assisted ablation', is introduced. The mechanisms and the advantages of each technique are discussed in comparison with the conventional single wavelength laser ablation.
The ablation of thin films by single laser pulse is a well known technique with widespread industrial applications. Ablation occurs in a well defined power density region if a supported thin film is illuminated by a single laser pulse. In the literature there are a number of theoretical description of ablation, but a very few based on in-situ experiments. In our study we have directly visualized the ablation processes with fast photography based on application of dye laser probe pulses. The ablation of chromium and tungsten layers supported onto glass substrates with pulses of ArF excimer laser was investigated. The ablated area was illuminated by a delayed short pulse of a fluorescein dye laser or a Rhodamine6G dye laser. Snapshots of initial phase of ablation and the forthcoming material transport were recorded by an optical system and a video camera. Blowing-off mechanisms and thermo-mechanical mechanisms are considered to take place during ablation. Pressures formed during laser ablation were calculated and compared with experimental data. It was found that thermo- desorption of gas adsorbed on to the substrate surface, substrate materials evaporation and film exfoliation by its longitudinal thermal enlargement may be acting during laser ablation of thin films.
The present work contains results of the investigations of the master disks manufacturing process and the following stamp plating process for compact disk duplication. The salient feature of the process under consideration is the use in a master disks as a photosensitive material of the vacuum deposited organic dye layer, the relief image on which is formed directly in the irradiation-recording process. In the work are considered the master disks manufacturing process. An organic dye is deposited by the thermal vacuum evaporation method. This provides the thickness test of a coating directly during the manufacturing process, the high purity of a photosensitive layer and its very high uniformity in thickness.
The one-pulse intracavity processing of the solid-state surface by the radiation of the 150-ns TEA carbon dioxide laser allowed to form the system of supernarrow (less than 0.3 micrometer) equidistant parallel grooves on thin metallic films, evaporated on glass substrates. Later, the more complicated structures, looking as the grids and the regular systems of submicron hollows, were formed by means of only one laser pulse on the basis of the modified laser resonator. The final view of the system of microstructures, which can be formed by the intracavity method, substantially depends on the laser resonator parameters as well the characteristics of the laser impulse (energy, wavelength, duration, mode structure, etc.).
The film formation thinner than a few ten nano-meters, called ultra-thin films, has been the indispensable technology to develop various electronic devices. This paper describes the ultra-thin film forming process and properties of an Al2O3 film deposited mainly. The films of a few nano-meter thickness and nearly mono-atomic layer were formed by the excimer laser ablation. The ceramics film and multi-layer film were deposited on a Si wafer and a plate glass substrate at room temperature in the extremely high vacuum atmosphere. Surface roughness of the film was less than 1 nm and no defects of small holes and micro-cracks were found in the film of 2.6 nm thickness by measuring tunneling current at liquid N2 temperature.
Two methods for the formation of semiconductor films were proposed: (1) laser chemical vapor deposition was based on the deposition of elements owing to the photodissociation of iron carbonyl (Fe(CO)5) vapors while irradiating Si substrate surface with focused Ar+-laser radiation ((lambda) L equals 488 nm) followed by focused YAG:Nd+3-laser radiation ((lambda) L equals 1064 nm) treatment of the deposited film at the power density of 105 W/cm2 resulted in the formation of semiconductor phases: (beta) -iron disilicide ((beta) -FeSi2) and silicon carbide (SiC) which formed carbide-silicide phase with such stoichiometric composition FeSi2-XCX and bandgap about 0.1 eV; (ii) electron beam sputtering was based on pure iron sputtering on Si substrate surface followed by focused YAG:Nd+3-laser radiation treatment of the deposited film at the power density ranging from 1.35 X 105 W/cm2 to 2.1 X 105 W/cm2 resulted in the formation of semiconductor phase ((beta) -SiFe2) with maximum bandgap about 0.05 eV and metal phase ((alpha) -FeSi2).
Plasma plume expansion and crater formation in the interaction of Nd-YAG laser beam (TEMoo-mode, 532 nm, 6 ns pulse duration and 10 micrometers waist at FWHM) with various metal targets in air were investigated. The craters formed at the surfaces were measured with 0.1 micrometers longitudinal and 0.5 micrometers transversal resolutions. Laser plasma expansion during laser pulse/surface interaction was measured by ICCD camera with 3 micrometers spatial and 1 ns temporal resolutions. These measurements were performed with different optical filters in the following spectral ranges (250< (lambda) <400 nm, 300<(lambda) <600 nm, 600< (lambda) <800 nm).
Today the laser technologies are widely used in the processing of materials, including also the technologies of the precise micromachining. UV and X-ray lasers have very good prospects in the lithography, used for fabrication of chips, while the femtosecond pulsed lasers open the new horizons for the micro- and submicroscribing. But these are the prospects. As for today state-of-the-art, contributing to the application of lasers for these purposes are the numerous advantages of the laser techniques over the traditional methods, such as wide variety of materials separated, possibility of achieving narrow cuts and practically waste-free separation, small heat-affected zone, minimal mechanical effect and minimal thermal deformations, possibility of fast and precise process switch-on and off, possibility of separation along a complex profile in two, or even three, dimensions.
UV laser microdrilling of high aspect ratio holes requires a low numerical aperture and intense beam. It does not produce any thermal or mechanical damage on the target. In some particular experimental conditions, it is shown that long deep holes are obtained with reproducible aspect ratio ((Phi) /d approximately equals 600) in a variety of materials. Generally speaking the more absorbing the polymer is, the better is the resolution. However highly absorbing materials exhibit a low ablation rate. These promising results on laser microdrilling can be extended to new applications when beam and target relative movement is computer driven. For instance this approach can applied to cutting micro-objects with complicated shape or machining of fragile or brittle materials.
In very large scale of integration processing photolithographic techniques control the patterning of thin film and the deposition of dopant used to make transistor gates and metal contacts. Microelectromechanical systems (MEMS) processing uses the same techniques to create structural components that are essentially submillimeter- sized machines parts. These parts usually require post- fabrication processing or assembly in order to become finished devices. MEMS technology can generally be categorized into two groups as bulk and surface micromachining. These categories respect not only different fabrication processes but different post fabrication techniques for finishing the mechanical subsystem.
Laser heating of glass samples is a simple and versatile method for obtaining polished surfaces of optical quality. Since laser beam intensity non-uniformity can translate into significant variations in the induced surface temperature, the success of the laser surface-polishing process strongly depends on obtaining uniform intensity profiles or flat-top distributions at the sample plane. In this paper we present a comparison between large-area CO2 laser-polishing experiments carried out in optical glass substrates following two different approaches: (1) A reshaped beam obtained by an active integration method is swept over the glass surface. (2) A static beam reshaped by means of both a multifaceted mirror and a square pipe light guide is applied.
This paper describes two processes for the 3D microstructuring of metallic/metal-matrix composite parts by using pulsed Nd-YAG laser. (1) In the first part, laser microcladding process is discussed. The effect of beam interaction time and the relationship between various layers are considered. The results show that in this case the beam interaction time greatly affect the structural development of the product with respect to its strength and quality. (2) In the second part, selective laser sintering with the one and two components metallic powders shall be discussed. The results show that due to the surface contact only, the feature size obtained with the one component solid state sintering is smaller compared to the two metal liquid phase sintering of the metallic powder, comprising of high and low melting point. The influence of the processing conditions on the type of phases and the microstructure evaluation are considered. Successful attempts were also made in creating the fine structures with the metal-matrix composite powder materials. A few examples are demonstrated briefly.
Surface modification experiments on aluminum were performed using CO2 laser beam irradiation on a surface on which an alloying powder had been pre-placed. Using TiO2 particles coated with Ni as a new material for laser alloying, a hard and uniformly-structured alloyed layer was achieved on the Al substrate. The effects of additive Ni on the hardness and structure of the alloyed layer were then investigated. With an increase in Ni content in the alloying powder, the hardness of the alloyed layer increased. This hardening in the alloyed layer was caused by the crystallization of intermetallic compounds. The optimum alloyed layer was obtained, when the weight ratio of TiO2 to Ni was about 1:1. The thickness of the alloyed layer was 0.6 - 0.7 mm, and the surface roughness about Rz 70 micrometers. It mainly consisted of Al+Al3Ni eutectic matrix and Al3Ti dendrites. The micro Vickers hardware of the alloyed layer was Hv200+/- 50. According to the sliding friction test, and specific wear volume was smaller than that of tempered carbon steel under high sliding speed and heavy load conditions.
Ablation of submicron structures on metals and semiconductors is presented using subpicosecond laser pulses at 248 nm. Morphology changes as a function of pulse duration have been investigated. The dynamics of the surface modification has been studied using a pump-probe technique. Diffracted signals of a probe beam on laser induced gratings provide information on the dynamics of the electron phonon interaction, melting and material removal simultaneously. For metals, in the first 5 - 10 ps following irradiation the electron-phonon relaxation dominates the process, followed by melting, expansion and violent material ejection. For semiconductors, rapid amorphization of the surface occurs within a couple of hundred femtoseconds following irradiation, with less pronounced indication for the development of molten material.
Current commercially available diode lasers with output powers above a few watts lack beam quality, i.e. the ability to be precisely focused. Recent advances in coherent coupling 1,2 of such lasers open view to a new generation of high power, high beam quality, low cost lasers suitable for a wide range of technical applications such as microshaping or cutting. Therefore, we couple bars of 25 diode lasers with total output powers of 25-40 Watts and specially coated lowreflection front facets. Mutual coherence is achieved in external resonators as opposed to the internal resonator absent in our case. Additional elements like mode stops can improve beam quality. Here we present results on the coupling of gain-guided broad-area diode lasers in external resonators, both of single emitters and bars of 25 emitters. Also numerical simulations concerning the mutual coherence of the single emitters have been performed.
Dependence of the negative nonlinear absorption effect (NNA effect) on modulation frequency was investigated in an erbium-doped lutetium aluminum garnet (Er:LuAG) crystal at the wavelength of 787.8 nm. When the intensity of the incident laser irradiated on Er:LuAG and Er:YAG crystals was wavy, those crystals were observed NNA effect that the transmitted laser intensity shows opposite phase of the incident laser at the wavelength of about 788 nm. The transmitted waveforms changed to the opposite phase of the incident waveform for modulation frequencies up to 1 GHz. For 1 GHz, the peak of the reversed-phase waveform was shifted by approximately 250 ps.
In this paper we report on the development program of an original intracavity Q-switch for CO2 lasers, called Integrated Mirror Optical Switch (IMOS). The IMOS is based on the optical plasma resonance effect in a GaAs- semiconductor when the refractive index of a tens of nm's thin MBE grown n-GaAs (5-8X1018cm-3) layer is modulated by electronically controlling the electron density in the thin n-GaAs layer. A heterostructure diode is conceived to keep the power dissipation low. 15 to 30% modulation depth can be achieved for a depletion voltage of 15 V at 1 W power dissipation. Switching frequencies of more than 1 MHz were measured. These driving characteristics are very promising to turn a CO2 laser into an easily computer controlled and flexible-machining tool. In order to achieve this, the structure of the Q-switch needs to be adapted for intracavity usage. Q-switches operating in reflection and transmission are compared and discussed. Highly efficient coupling mechanisms are suggested. Special attention will be paid to the design of diffraction gratings.
Si-containing polymers, which act as RIE-resists by generating a passivating SiO2 film on the polymer surfaces, are applied in microlithographic processes. New Si-containing polymers, i.e., Si-containing polycarbonates and polyestercarbonates have been synthesized. Various contents of Si (up to 30 wt%) were incorporated into the polymers. Thin films (about 100 micrometers thick) of the polymers were prepared for ablation and microstructuring at 308 nm. With a pinhole mask and a lens, a 10 X 10 matrix of circular craters was created on the polymer films. The fluence and number of pulses were varied for each crater. Ablation parameters (alpha) eff (effective absorption coefficient) and Fth (threshold fluence) were determined for each polymer. Using a reflecting objective (Schwarzschild type), microstructures with a sub-micron resolution can be produced on the polymer films. The quality of the ablated structures was evaluated by scanning electron microscopy. The incorporation of Si into polymers does not affect the ablation behavior of the polymers. Si-containing polyestercarbonates exhibited good ablation behavior, while surface swelling (incubation) was observed for polycarbonates films. The results from this work includes that Si-containing polyestercarbonates are suitable for laser ablation and microstructuring.
We present a novel use of micro-machining with excimer laser: realization of reflective diffractive optical elements (DOE) for laser marking. The DOE's design is first calculated using the standard Gerchberg-Saxton algorithm associated with optimization procedures. The design takes into account the following parameters for the diffraction efficiency optimization: incident beam angle, M2 quality factor and the modulation transfer function of the fabrication process. We consider here two phase levels elements in Fourier and Fresnel configurations. The fabrication process makes use of excimer laser ablation. We demonstrate the transfer of this design on different materials with two cases: direct and indirect substrate etching.
For realization of the optimum mode of hole drilling the packs of laser pulses of high intensity were used, when average level of intensity of radiation is not too high, that reduces specific energy of destruction, and the peak intensity is reasonably great, that the pulse of pressure of effect at evaporation has completely deleted the liquid from the zone of processing. The high peak intensity of radiation permits in this case to place a target not in focus of a optical system, creating on its surface the image with the help of masks. It permits to receive in metal plates the holes of any section, to execute marking of surfaces and deep engraving of sample material with the help of laser. With the using of focused radiation the cutting of thin materials can be executed without a auxiliary gas. The condition of melt replacement is excess of power of recoil pressure above the power of viscous forces and forces of inertia. The decision of the hydrodynamic problem permits to evaluate the necessary parameters of laser radiation, frequency and longitude of packs of pulses which provide increases of process speed in several times. The conducted experiments confirm the indicated theoretical analysis of process of removing of the material under action of packs of pulses of laser radiation. The given process is realized in laser technological installations for holes drilling and marks of materials.
The purpose of presented work is theoretical and experimental research of the reasons of furrow formation on a cut surface at gas-assisted laser cutting. For experimental study of removal laws of a material from a cutting zone a high-speed filming, and as the temporary control of brightness and temperature on the bottom surface of cutting material in a zone of cut outlet were used. The experiments speak about periodic nature of a material removing from the cut.
Results of experimental studies of efficiency of evaporation cutting by copper vapor laser are presented. One- and multi- pass cutting are explored, including cutting with the high instant velocity (with galvanometer-scanner), as well as holes drilling with a changeable repetition rate of pulses. High cutting efficiency and quality are shown in the multi- pass cutting at a high velocity of a focal spot movement.
The analysis of plotting system trajectories for purposes of rapid prototyping is presented. The methods of regulation for obtaining of best possible accuracy and velocity of trajectory executing are described. The criterions of optimization are offered.
The systems of pulse-periodical pumping of the solid-state lasers with adjustable time-amplitude and frequency parameters as of pulses of pumping currency, as well as laser radiation pulses, intended for power supply of the lasers, operating in the mode of free generation, are presented.
The new optical scheme is built up and is used on the set-up for laser-assisted drawing-out processing (LADOP) and the technique of LADOP for optical fibers are investigated. The probes for SNOM with sizes of aperture about 100 nm were obtained and tested by SNOM. The kinetic model of LADOP is represented.
With the laser process of machining a controlled extraction of material at a superficial level is made. We are investigating this process on metal parts of stainless steel 521. For this purpose a Nd:YAG laser is pulsed way with Q- switch, and the fundamental emission wavelength, 1.06 micrometers , has been used. With high enough moving rates, we can neglect losses by thermal conductivity and convection in the environment. Within this type of experiments two simultaneous physical mechanism are observed that take place: melting and evaporation. The results of this work permit to know the method of searching the optimum parameters for 2D and 3D micromachining.