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Advances in excimer laser processing of materials

Description: The use of pulsed excimer lasers to surface processing of materials hinges on an understanding of the nature of the interaction between the laser energy and the material. The application of this understanding of the laser materials interaction to surface modification must also recognize the existence of thermodynamic driving forces and kinetic limitations in light of the short duration of a single pulse event. For species that have higher solubility in the liquid than in the solid phase, segregation by ``zone refinement`` from multiple passes by a solidification front to the surface results in surface enrichment of those species. The most obvious applications for surface processing occur where the bulk properties of a component are not commensurate with the needed surface properties. Improvements in surface mechanical properties have been observed in a number of metal and ceramic alloys. In the microelectronics industry, apart from micromachining or material removal applications, for which excimers are indeed well suited, the same features of the laser-materials interaction that are used to modify the mechanical or electrochemical properties of a surface can be used to advantage. Further advances, such as those demonstrated in microelectronics, await application-specific developments. 22 refs., 1 fig.
Date: August 1, 1996
Creator: Jervis, T.R.; Nastasi, M. & Hirvonen, J.-P.
Partner: UNT Libraries Government Documents Department

FABRICATION AND ATTACHMENT OF POLYIMIDE FILL TUBES TO PLASTIC NIF CAPSULES

Description: We have developed a technique for drawing commercially available polyimide tubing to the required fill tube dimensions. The tubes are then precisely cut with an Excimer laser to produce a clean, flat tip. We have also demonstrated that one can use the Excimer laser to drill less than a 5 {micro}m diameter through hole in the {approx}150 wall of a NIF dimension GDP shell, and can then create a 10-15 {micro}m diameter, 20-40 {micro}m deep counterbore centered on the through hole with the same laser. Using a home built assembly station the tube is carefully inserted into the counterbore and glued in place with UV-cure epoxy, using a LED UV source to avoid heating the joint. We expect that the same joining technique can be used for Be shells.
Date: December 8, 2006
Creator: Takagi, M; Saito, K; Frederick, C; Nikroo, A & Cook, R
Partner: UNT Libraries Government Documents Department

Survey of Laser Markets Relevant to Inertial Fusion Energy Drivers, information for National Research Council

Description: Development of a new technology for commercial application can be significantly accelerated by leveraging related technologies used in other markets. Synergies across multiple application domains attract research and development (R and D) talent - widening the innovation pipeline - and increases the market demand in common components and subsystems to provide performance improvements and cost reductions. For these reasons, driver development plans for inertial fusion energy (IFE) should consider the non-fusion technology base that can be lveraged for application to IFE. At this time, two laser driver technologies are being proposed for IFE: solid-state lasers (SSLs) and KrF gas (excimer) lasers. This document provides a brief survey of organizations actively engaged in these technologies. This is intended to facilitate comparison of the opportunities for leveraging the larger technical community for IFE laser driver development. They have included tables that summarize the commercial organizations selling solid-state and KrF lasers, and a brief summary of organizations actively engaged in R and D on these technologies.
Date: February 24, 2011
Creator: Bayramian, A. J.; Deri, R. J. & Erlandson, A. C.
Partner: UNT Libraries Government Documents Department

Laser Machining For Fabrication Of Hohlraums And Capsules

Description: Laser machining technology has been used to demonstrate the ability to rapidly perform jobs on all aspects of ICF targets. Lasers are able to rapidly perform modifications and repairs to the gold metal parts on hohlraums, make cuts in the delicate polymer parts of the hohlraum, and drill holes in the capsules to enable them to be filled with fuel. Lasers investigated in this work include 193 nm ArF and 248 nm KrF excimers and 810 nm chirped-pulse amplification Ti:Sapphire lasers. The excimer lasers showed a definite advantage in drilling and machining of polymeric materials and the ultrashort infrared pulses of the Ti:Sapphire laser were far better for the gold structures.
Date: June 24, 2005
Creator: Shirk, M D; Kelly, B T; Haynes, S M; Stuart, B C; Sanchez, J J; Moody, J D et al.
Partner: UNT Libraries Government Documents Department

Photopolymers designed for high resolution laser ablation at a specific irradiation wavelength

Description: We have developed novel photopolymers based on the triazeno chromophore group. The absorption properties can be tailored for a specific irradiation wavelength (e.g. 308 nm XeCl laser). With the introduction of a photolabile group into the main chain of the polymer we expected a mechanism which is mainly photochemical. This should result in high resolution etching with no thermal damage or chemical / physical modification to the material. The gaseous products of the photochemical decomposition were thought to assist the material removal, and to prevent the re-deposition of solid products which would contaminate the surface. We confirmed (SEM/AFM) that the irradiation of the polymer at 308 mn resulted in high resolution etching. No debris has been found around the etched comers. Maximum ablation rates of about 3 {mu}m / pulse were achieved due to the dynamic absorption behavior (bleaching during the pulse). No physical or chemical modifications of the polymer surface could be detected after irradiation at the tailored absorption wavelength, whereas irradiation at different wavelengths resulted in modified (physical and chemical) surfaces. The etching mechanism can be described as a laser induced microexplosion, revealed by ns-imaging. The etching of the polymer starts and ends with the laser pulse, shown by ns-interferometry, confirming that the acting mechanism is mainly photochemical at high fluences for our polymers. Our results demonstrate that the mechanism of ablation can be controlled by designing special polymers, which can be used as high resolution laser dry etching resists.
Date: April 1, 1997
Creator: Lippert, T.; Bennett, L. S.; Kunz, T. & Hahn, C.
Partner: UNT Libraries Government Documents Department

Surface Engineering of Silicon and Carbon by Pulsed-Laser Ablation

Description: Experiments are described in which a focused pulsed-excimer laser beam is used either to ablate a graphite target and deposit hydrogen-free amorphous carbon films, or to directly texture a silicon surface and produce arrays of high-aspect-ratio silicon microcolumns. In the first case, diamond-like carbon (or tetrahedral amorphous carbon, ta-C) films were deposited with the experimental conditions selected so that the masses and kinetic energies of incident carbon species were reasonably well controlled. Striking systematic changes in ta-C film properties were found. The sp{sup 3}-bonded carbon fraction, the valence electron density, and the optical (Tauc) energy gap ail reach their maximum values in films deposited at a carbon ion kinetic energy of {approximately}90 eV. Tapping-mode atomic force microscope measurements also reveal that films deposited at 90 eV are extremely smooth (rms roughness {approximately}1 {angstrom} over several hundred nm) and relatively free of particulate, while the surface roughness increases in films deposited at significantly lower energies. In the second set of experiments, dense arrays of high-aspect-ratio silicon microcolumns {approximately}20-40 {micro}m tall and {approximately}2 {micro}m in diameter were formed by cumulative nanosecond pulsed excimer laser irradiation of silicon wafers in air and other oxygen-containing atmospheres. It is proposed that microcolumn growth occurs through a combination of pulsed-laser melting of the tips of the columns and preferential redeposition of silicon on the molten tips from the ablated flux of silicon-rich vapor. The common theme in this research is that a focused pulsed-laser beam can be used quite generally to create an energetic flux, either the energetic carbon ions needed to form sp{sup 3} (diamond-like) bonds or the overpressure of silicon-rich species needed for microcolumn growth. Thus, new materials synthesis opportunities result from the access to nonequilibrium growth conditions provided by pulsed-laser ablation.
Date: February 28, 1999
Creator: Fowlkes, J.D.; Geohegan, D.B.; Jellison, G.E., Jr.; Lowndes, D.H.; Merkulov, V.I.; Pedraza, A.J. et al.
Partner: UNT Libraries Government Documents Department

Laser induced diffusion of ion-implanted bismuth in fused silica

Description: The near surface regions of optical grade fused silica discs (Spectrosil A) were modified by implantation with bismuth ions at 160 and 320 keV and at room temperature. The glasses implanted with a nominal dose of 6 {times} l0{sup 16} Bi{sup 2+} ions/cm{sup 2} were subsequently annealed with a 5 eV KrF pulsed excimer laser and by a furnace in oxygen atmosphere. Rutherford backscattering and optical absorption were measured before and after the anneals. Backscattering profiles after laser anneal showed shifts of the profiles toward the surface with decrease in retained dose. We attribute the diffusion of bismuth to Soret effect. Profiles of furnace annealed samples showed that the diffusion was both toward and away from the surface.
Date: December 31, 1994
Creator: Park, S.Y.; Weeks, R.A. & Zuhr, R.A.
Partner: UNT Libraries Government Documents Department

The Effect of Excimer Laser Treatment on the Surface Roughness and Fracture Strength of Alumina Substrates

Description: The microelectronics industry requires alumina substrates with exceptionally smooth surfaces and few surface defects to allow successful deposition of metallic films for reliable electronic performance. Irradiation by a 248-nm wavelength excimer laser beam (KrF) at a fluence of 125 mJ/mm{sup 2} and at various angles of incidence is shown to significantly reduce the surface roughness of alumina substrates. However, irradiation also creates a fine particulate deposit of alumina that only partially adheres to the substrate and impedes deposition of metal films. Annealing in air between 1350 C and 1450 C was found to remove the particles by sintering. As-received material showed surface roughness average (R{sub a}) mean values of 457 nm, which was reduced to 60 nm (mean) following irradiation and 71 nm (mean) following irradiation and annealing at 1350 C. Irradiation also produced a decrease in the number and severity of surface defects. The flexural strength and Weibull modulus were both increased by laser irradiation and thermal treatment. Flexural strength went from an as-received value of 450 MPa to 560 MPa following irradiation/sintering, measured at 10% probability of failure. The Weibull modulus was increased from the as-received value of about 9, to about 13 following irradiation/sintering. It was concluded that irradiation at an angle of incidence of 60{degree} from perpendicular was most effective in producing a low surface roughness.
Date: May 13, 1998
Creator: Smoot, J. E.
Partner: UNT Libraries Government Documents Department

Detection of lead in soil with excimer laser fragmentation fluorescence spectroscopy (ELFFS)

Description: Excimer laser fragmentation fluorescence spectroscopy (ELFFS) is used to monitor lead in soil sample and investigate laser-solid interactions. Pure lead nitrate salt and soil doped with lead nitrate are photolyzed with 193 nm light from an ArF excimer at fluences from 0.4 to 4 J/cm{sup 2}. Lead emission is observed at 357.2, 364.0, 368.3, 373.9 and 405.8 nm. Time-resolved data show the decay time of the lead emission at 405.8 nm grows with increasing fluence, and a plasma is formed above fluences of 2 J/cm{sup 2}, where a strong continuum emission interferes with the analyte signal. Fluences below this threshold allow us to achieve a detection limit of approximately 200 ppm in soil.
Date: March 1, 2004
Creator: Choi, J.H.; Damm, C.J.; O'Donovan, N.J.; Sawyer, R.F.; Koshland, C.P. & Lucas, D.
Partner: UNT Libraries Government Documents Department

Fabrication of x-ray spiral masks by laser ablation.

Description: The manipulation of x-rays by phase structures is becoming more common through devices such as compound refractive lenses, blazed zone-plates and other structures. A spiral phase modulation structure can be used to condition an x-ray beam to produce an x-ray vortex. An x-ray beam in this form can be used as the first step towards a self-collimating beam. Also it can be used as a controllable pathological feature in studies of x-ray phase retrieval. The authors describe the microfabrication of a spiral phase modulation structure by excimer laser ablation. A multi-step fabrication using 15 separate chrome-on-quartz mask patterns is used to create a 16 step spiral staircase structure approximating the desired spiral ramp. The results of simulations and initial experimental results are presented.
Date: July 2, 2002
Creator: Peele, A. G.; Nugent, K. A.; McMahon, P. J.; Paterson, D.; Tran, C. Q.; Mancuso, A. et al.
Partner: UNT Libraries Government Documents Department

Review of long-pulse laser development

Description: A brief review of some present techniques to obtain long-pulse laser action in excimer discharge devices will be presented. An attempt will be made to point out the strengths and weaknesses of these techniques. 18 refs., 15 figs.
Date: January 1, 1989
Creator: Sze, R.C.
Partner: UNT Libraries Government Documents Department

Layered target burnthrough experiments using 50 nsec KrF laser pulses

Description: Experiments have been performed on two types of planar layered targets using the Sprite KrF laser. The targets lused were: (1) 0.25 to 3.0 microns of Al deposited on an SiO/sub 2/ substrate and (2) 0.25 to 3.0 microns of CH (parylene-N) deposited on 0.20 microns of Al on an SiO/sub 2/ substrate. The laser was characterized by a pulse length of 50 nsec FWHM, an intensity of 2 x 10/sup 10/ watts/cm/sup 2/ and a wavelength of 248.5 nm. A filtered photoiodide and a streak camera, each operating in the visible, viewed the rear of the target. We measured the time from the beginning of the laser pulse to the onset of the visible light signal as seen by the photoiodide at the rear of the initially opaque target. This time is referred to as the burnthrough time. We obtain an estimate of the mass ablation by plotting the mass ablation depth (mass density times target thickness in ..mu..gm/cm/sup 2/) versus the burnthrough time. These results are consistent with earlier mass loss measurements and with analytic and hydro-code calculations (LASNEX). The streak camera data shows emission at target positions larger than the laser focal spot, and thus are consistent with 1-D and 2-D calculations which show target surface ablation to be primarily driven by reradiated photons from the hot laser produced plasma.
Date: January 1, 1986
Creator: Kephart, J.F.; Dingus, R.S.; Gitomer, S.J.; Kopp, R.A. & Shaw, M.J.
Partner: UNT Libraries Government Documents Department

Kinetics modeling and interpretation of experimental results for XeF. Annual report, December 1985--November 1986

Description: In this report the author presents a detailed discussion of a computer model of the electron beam pumped XeF laser which was developed for Los Alamos National Laboratory during FY86. In its present form, it should provide useful modeling and scaling of XeF laser experiments currently of interest. Additional modifications will be required for long pulse (t{sub P}>5{mu}sec) simulations. The model includes all of the important energy transport processes which contribute to the formation and quenching of XeF in the B-state (upper laser level), X-state (lower laser level), C-state (which mixes with the B-state as a loss mechanism), and the unbound (repulsive) A-state to which the C-state decays. The gain of the B to X transition is resolved for the three most important laser (vibrational) lines: (0-3) at 353 nm, (0-2) and (1-4) at 351 nm. This report describes the kinetics model and computer code for electron beam pumped XeF lasers which use gas mixtures composed of argon (the buffer), xenon, and fluorine. The temperatures, energy flow, and chemistry (plasma and neutral) are calculated in a self-consistent manner; balances of energy, matter, and charge are tracked by the code and output with each print cycle. The model includes the time history of all of the important absorbers: Ar{sub 2}{sup +}, Xe{sub 2}{sup +}, Ar{sup *} and Xe{sup *} (s and p states), F{sub 2}, F{sup {minus}}, and Xe{sub 2}F{sup *}. Energy extraction in the form of lasing is computed using a modified Rigrod analysis which treats multiline lasing. This extraction model assumes a spatially uniform laser flux and is therefore a one dimensional (in time) treatment. The more general extraction model which treats non-uniform spatial effects (laser flux and pumping by a non-uniform electron beam) is being developed, and will be integrated with excimer model in the FY87 reporting period. ...
Date: December 31, 1986
Creator: Salesky, E. T.
Partner: UNT Libraries Government Documents Department

Simultaneous determination of gain parameters in steady state lasers

Description: The optical gain parameters of pulsed steady-state lasers, such as dye and excimer lasers, are determined from a single set of experiments from either a laser oscillator or an amplifier. The gain parameters determined by this technique are the small-signal gain coefficient, the saturation intensity for stimulated emission, the saturation fluence for stimulated emission, and the non-saturable absorption coefficient. The measured saturation properties of laser amplifiers and oscillators are used in a data fitting routine that finds all of the gain parameters simultaneously. The values of the gain parameters are determined with greater accuracy than by the conventional methods of measuring each of the parameters individually. The knowledge of the values of all the gain parameters allows for the determination of fluorescence lifetime of a gain medium.
Date: February 1, 1993
Creator: Jensen, C. C.; Branning, D. A. & Marchbanks, R. D.
Partner: UNT Libraries Government Documents Department

Excimer laser processing of tool steel: Tribological effects of multiple pulse processing and titanium alloying

Description: Excimer lasers were used to modify the surface of AISI type A-7 tool steel, a high C, high V, high Cr material used in many cutting applications. Multiple pulses of laser radiation at 248 nm were used to alter the composition of the surface alloy. Hardness and modulus were not significantly affected by the treatment, but friction in dry sliding against an alumina pin was reduced. The reduction was small but persistent for multiply melted and resolidified surfaces. These surfaces showed a marked increase in the surface Cr concentration. Greater reductions in friction were obtained from a Ti rich surface layer formed by laser mixing an evaporated Ti layer into the material. The friction coefficient of the Ti alloyed surface deteriorated after approximately 1000 cycles, indicating wear=through of the modified surface. The observed properties will be discussed in terms of the excimer laser modification process and the microstructure and composition of the resulting surfaces.
Date: December 1, 1995
Creator: Jervis, T.R.; Nastasi, M.; Griffin, A.J. Jr.; Zocco, T.G.; Taylor, T.N. & Foltyn, S.R.
Partner: UNT Libraries Government Documents Department

Laser cutting of energetic materials

Description: The authors have demonstrated the feasibility of safely and efficiently cutting and drilling metal cases containing a variety of high explosives (HE) using a Nd:YAG laser. Spectral analysis of the optical emission, occurring during the laser-induced ablation process, is used to identify the removed material. By monitoring changes in the optical emission during the cutting process, the metal-He interface can be observed in real time and the cutting parameters adjusted accordingly. For cutting the HE material itself, the authors have demonstrated that this can be safely and efficiently accomplished by means of a ultraviolet (UV) laser beam obtained from the same Nd:YAG laser using the third or fourth harmonics. They are currently applying this technology to UXO identification and ordnance demilitarization.
Date: December 1, 1998
Creator: Rivera, T.; Muenchausen, R. & Sanchez, J.
Partner: UNT Libraries Government Documents Department

Measurements of barium photocathode quantum yields at four excimer laser wavelengths

Description: The electron quantum yields from barium cathodes excited by excimer laser radiation at 193, 248, 308, and 351 nm have been determined. Experiments with different cathode surface preparation techniques reveal that deposition of barium film a few microns thick on a clean copper surface under moderate vacuum conditions achieves relatively high quantum efficiencies. Quantum yields measured from surfaces prepared in this manner are 2.3 x 10{sup -3} at 193 nm, 7.6 x 10{sup - 4} at 248 nm, 6.1 x 10{sup -4} at 308 nm, and 4.0 x 10{sup -4} at 351 nm. Other preparation techniques, such as laser cleaning of a solid barium surface, produced quantum yields that were at least an order of magnitude lower than these values.
Date: June 1992
Creator: Van Loy, M. D.; Young, A. T. & Leung, K. N.
Partner: UNT Libraries Government Documents Department

Meso-Machining Capabilities

Description: Meso-scale manufacturing processes are bridging the gap between silicon-based MEMS processes and conventional miniature machining. These processes can fabricate two and three-dimensional parts having micron size features in traditional materials such as stainless steels, rare earth magnets, ceramics, and glass. Meso-scale processes that are currently available include, focused ion beam sputtering, micro-milling, micro-turning, excimer laser ablation, femtosecond laser ablation, and micro electro discharge machining. These meso-scale processes employ subtractive machining technologies (i.e., material removal), unlike LIGA, which is an additive meso-scale process. Meso-scale processes have different material capabilities and machining performance specifications. Machining performance specifications of interest include minimum feature size, feature tolerance, feature location accuracy, surface finish, and material removal rate. Sandia National Laboratories is developing meso-scale mechanical components and actuators which require meso-scale parts fabricated in a variety of materials. Subtractive meso-scale manufacturing processes expand the functionality of meso-scale components and complement silicon based MEMS and LIGA technologies.
Date: June 1, 2001
Creator: BENAVIDES,GILBERT L.; ADAMS,DAVID P. & YANG,PIN
Partner: UNT Libraries Government Documents Department

Report on the Study of Radiation Damage in Calcium Fluoride and Magnesium Fluoride Crystals for use in Excimer Laser Applications

Description: A study was performed to investigate the effects of radiation damage in calcium fluoride and magnesium fluoride crystals caused by gamma rays and UV photons from excimer lasers. The purpose was to study and correlate the damage caused by these two different mechanisms in various types of material used for fabricating optical elements in high power excimer lasers and lens systems of lithography tools. These optical systems are easily damaged by the laser itself, and it is necessary to use only the most radiation resistant materials for certain key elements. It was found that a clear correlation exists between the, radiation induced damage caused by high energy gamma rays and that produced by UV photons from the excimer laser. This correlation allows a simple procedure to be developed to select the most radiation resistant material at the ingot level, which would be later used to fabricate various components of the optical system. This avoids incurring the additional cost of fabricating actual optical elements with material that would later be damaged under prolonged use. The result of this screening procedure can result in a considerable savings in the overall cost of the lens and laser system.
Date: October 4, 1999
Partner: UNT Libraries Government Documents Department

High resolution transmission electron microscopy of metallic film/laser-irradiated alumina couples

Description: A near-surface thin layer is melted when single crystal alumina (sapphire) is pulsed laser-irradiated in an Ar-4%H{sub 2} atmosphere. {gamma}-alumina grows epitaxially from the (0001) face of {alpha}-alumina (sapphire ) during the rapid solidification of this layer that occurs once the laser pulse is over. Cross sectional high resolution transmission electron microscopy (HRTEM) reveals that the interface between unmelted sapphire and {gamma}-alumina is atomistically flat with steps of one to a few close-packed oxygen layers; however, pronounced lattice distortions exist in the resolidified {gamma}-alumina. HRTEM also is used to study the metal-ceramic interface of a copper film deposited on a laser-irradiated alumina substrate. The observed changes of the interfacial stricture relative to that of unexposed substrates are correlated with the strong enhancement of film-substrate bonding promoted by laser irradiation. HRTEM shows that a thin amorphous film is produced after irradiation of 99.6% polycrystalline alumina. Formation of a diffuse interface and atomic rearrangements that can take place in metastable phases contribute to enhance the bonding strength of copper to laser-irradiated alumina.
Date: December 31, 1995
Creator: Pedraza, A.J.; Cao, S.; Allard, L.F. & Lowndes, D.H.
Partner: UNT Libraries Government Documents Department

Nanoparticle production by UV irradiation of combustion generated soot particles

Description: Laser ablation of surfaces normally produce high temperature plasmas that are difficult to control. By irradiating small particles in the gas phase, we can better control the size and concentration of the resulting particles when different materials are photofragmented. Here, we irradiate soot with 193 nm light from an ArF excimer laser. Irradiating the original agglomerated particles at fluences ranging from 0.07 to 0.26 J/cm{sup 2} with repetition rates of 20 and 100 Hz produces a large number of small, unagglomerated particles, and a smaller number of spherical agglomerated particles. Mean particle diameters from 20 to 50 nm are produced from soot originally having a mean electric mobility diameter of 265nm. We use a non-dimensional parameter, called the photon/atom ratio (PAR), to aid in understanding the photofragmentation process. This parameter is the ratio of the number of photons striking the soot particles to the number of the carbon atoms contained in the soot particles, and is a better metric than the laser fluence for analyzing laser-particle interactions. These results suggest that UV photofragmentation can be effective in controlling particle size and morphology, and can be a useful diagnostic for studying elements of the laser ablation process.
Date: July 1, 2004
Creator: Stipe, Christopher B.; Choi, Jong Hyun; Lucas, Donald; Koshland, Catherine P. & Sawyer, Robert F.
Partner: UNT Libraries Government Documents Department

Amorphous diamond-like carbon film growth by KrF- and ArF- excimer laser PLD: Correlation with plume properties

Description: A comparative study of ArF- and KrF-laser deposition of amorphous diamond-like carbon (DLC) films and relevant carbon plasmas has been performed. Spectroscopic ellipsometry and EELS analysis of the DLC films deposited on Si <100> and NaCl substrates were utilized to characterize the high quality ArF- and KrF-laser deposited films (up to 84% of sp{sup 3} bonded carbon in 7 J/cm{sup 2} -ArF-laser DLC film). Gated ICCD imaging, luminescence and ion current probe diagnostics of the carbon plume have revealed quite different properties of carbon plasmas generated by ArF- and KrF- lasers. KrF-laser (6.7 J/cm{sup 2}) irradiation produces a less energetic carbon plasma containing larger amounts of C{sub 2} and probably larger clusters compared with ArF-laser irradiation at the same energy fluence. We conclude that the more energetic and highly-atomized ArF-laser carbon plasma results in the better diamond-like properties.
Date: April 1, 1995
Creator: Puretzky, A.A.; Geohegan, D.B. & Jellison, G.E. Jr.
Partner: UNT Libraries Government Documents Department

Laser Micromachining and Information Discovery Using a Dual Beam Interferometry

Description: Lasers have proven to be among the most promising tools for micromachining because they can process features down to the size of the laser wavelength (smaller than 1 micrometer) and they provide a non-contact technology for machining. The demand for incorporating in-situ diagnostics technology into the micromachining environment is driven by the increasing need for producing micro-parts of high quality and accuracy. Laser interferometry can be used as an on-line monitoring tool and it is the aim of this work to enhance the understanding and application of Michelson interferometry principle for the in-situ diagnostics of the machining depth on the sub-micron and micron scales. micromachining is done on two different materials and a comprehensive investigation is done to control the width and depth of the machined feature. To control the width of the feature, laser micromachining is done on copper and a detailed analysis is performed. The objective of this experiment is to make a precision mask for sputtering with an array of holes on it using an Nd:YAG laser of 532 nm wavelength. The diameter of the hole is 50 {micro}m and the spacing between holes (the distance between the centers) is 100 {micro}m. Michelson interferometer is integrated with a laser machining system to control the depth of machining. An excimer laser of 308 nm wavelength is used for micromachining. A He-Ne laser of 632.8 nm wavelength is used as the light source for the interferometer. Interference patterns are created due to the change in the path length between the two interferometer arms. The machined depth information is obtained from the interference patterns on an oscilloscope detected by a photodiode. To compare the predicted depth by the interferometer with the true machining depth, a surface profilometer is used to measure the actual machining depth on the silicon. It is ...
Date: December 31, 2001
Creator: Theppakuttaikomaraswamy, Senthil P.
Partner: UNT Libraries Government Documents Department

Narrow band tuning with small long pulse excimer lasers

Description: We discuss frequency narrowing and tuning with simple dispersion elements with small long-pulse excimer lasers. The improved performance over short-pulse lasers is discussed and attributed to the increased number of round trips. A physical model of the dynamics of line narrowing is presented.
Date: December 1, 1985
Creator: Sze, R.C.; Kurnit, N.; Watkins, D. & Bigio, I.
Partner: UNT Libraries Government Documents Department