Showing papers in "Journal of Laser Applications in 2008"
TL;DR: In this article, the state-of-the-art laser-based nanomachining methods are examined from the perspective of the requirements of nanomachines. And preliminary results obtained in our laboratory of the most recent, novel approach involving surface plasmon polaritons for the potential of massively parallel nanomachine are presented.
Abstract: Lasers are widely used for macro- and micromachining applications in numerous industries such as automotive, electronics, and medical manufacturing. However, there are many challenges encountered in the utilization of lasers for nanomachining. The most critical requirement is that the diffraction limit of laser light must be overcome. With recent developments in laser technology in terms of short-wavelength and ultrashort pulse width, there is a wealth of opportunities to beat the diffraction limit for nanomachining of structures, devices, and materials. In this review paper, first the state-of-the-art lasers are examined from the perspective of the requirements of nanomachining. Second, a set of both serial and parallel types of laser-based, “top-down” nanomachining methods is described. Third, preliminary results obtained in our laboratory of the most recent, novel approach involving surface plasmon polaritons for the potential of massively parallel nanomachining are presented. Finally, the potential of...
45 citations
TL;DR: In this paper, a unique laser/water-jet (LWJ) cutting head has been designed, built, and interfaced with a CO2 laser for cutting and scribing of hard and brittle ceramic materials.
Abstract: A unique laser/water-jet (LWJ) cutting head has been designed, built, and interfaced with a CO2 laser for cutting and scribing of hard and brittle ceramic materials. Alumina samples were used to validate the effectiveness of the LWJ cutting head in thermal fracture mode. The results were compared with vaporization mode (focused beam) as well as thermal fracture mode (defocused beam) of air-assisted laser cutting. The thermal fracture mode in both LWJ and air-assisted laser cutting required three to five times less energy input for material separation than the vaporization mode. However, the quality of the cut surfaces of the LWJ was superior to both vaporization and thermal fracture modes of air-assisted laser cutting in terms of kerf, recast zone, density of microcracks, undercutting, and spatter. The synergistic effects of laser and water-jet facilitated precise material separation and better cut quality through: thermal shock-induced fracture mode of material separation rather than energy-intensive ero...
34 citations
TL;DR: In this paper, a Q-switched Nd:YAG laser with fundamental wavelength was used for the fabrication of micro-channel networks for tissue engineering, where multidepth, multi-width microstructures on silicon were machined without photolithography-based methods.
Abstract: Application of laser direct writing to the fabrication of microchannel networks for tissue engineering was presented. A Q-switched Nd:YAG laser with fundamental wavelength was used. Multidepth, multiwidth microstructures on silicon were machined without photolithography-based methods. The molten material inside the microchannel was ejected with a modified assist gas, and thus the volume of laser ablation was increased. The debris build-up due to the strong thermal reaction of silicon to the nanosecond IR laser pulse was cleaned up with chemical wet etching in a mixture of hydrofluoric acid (HF) and nitric acid (HNO3). The chemical etching of the laser ablated silicon surface was studied to measure the etching rate and to observe the evolution of the surface morphology. Using the laser machined silicon structures as a mold, a poly(dimethylsiloxane) (PDMS) replica was created. Flow visualization was carried out with the patterned PDMS.
31 citations
TL;DR: In this paper, the authors used a CO2 laser cutting head assisted by a gas jet working in the supersonic regime to cut 2024-T3 plates by a CO 2 laser.
Abstract: Since the beginning of the aeronautic industry, aluminum alloys have played a crucial role in its development. Nowadays, different aluminum alloy families are the base material of many pieces of aerospace vehicles. In this work, a novel approach to process aluminum alloys is explored. The authors efforts are aimed to cut 2024-T3 plates by a CO2 laser. They used a novel laser cutting head assisted by a gas jet working in supersonic regime in order to accomplish this objective. This supersonic nozzle and the intrinsic geometry of the cutting head allow carrying out the processing of these alloys more efficiently than conventional cutting heads. The microstructural characterization, grain morphology, kerf dimensions, and surface finish of the cuts have been analyzed. The cut edges are free of dross and cracks and the heat affected zone is negligible. These successful results confirm laser cutting processing assisted by a supersonic assisting gas jet as a promising technique in the aerospace field.
28 citations
TL;DR: In this article, a 2.2kW fiber laser was used in a series of inert cutting trials on stainless steels of section thicknesses in the range of 6-10mm.
Abstract: A 2.2 kW fiber laser was used in a series of inert cutting trials on stainless steels of section thicknesses in the range of 6–10 mm. Variations in the cutting performance with changing gas pressure, focal position, and nozzle diameter were investigated. Results showed the difficulties associated in cutting with high brightness lasers, specifically in obtaining full melt eject through narrow kerfs; two distinct melt eject failure mechanisms were observed: (I) Failure of melt removal in the upper region resulted in melt ejecting out of the top surface and (II) poor base ejection giving recast and dross problems on the base of the cut. Detailed scanning electron microscope images of these phenomena are presented. A computational fluid dynamic model is used to show distinct differences in the theoretical gas performance at the center of the cut, displayed by most models, and at the edges where the melt eject is taking place. Melt eject is also shown both experimentally and theoretically to be improved for th...
25 citations
TL;DR: In this paper, scribable conditions were acquired in laser irradiation experiments using a soda-lime glass substrate having a thickness of 0.7mm, and the crack depth and crack edge profile were observed for various values of the distance between the heating area and the cooling area.
Abstract: In the laser scribing of glass a thermal stress is introduced into a glass substrate by means of a CO2 laser irradiation. The glass substrate is then rapidly cooled down by water jet immediately after the irradiation. For the purpose of theoretical clarification of the factors ruling the scribable condition and the crack depth, scribable conditions were acquired in laser irradiation experiments using a soda-lime glass substrate having a thickness of 0.7 mm. Furthermore, the crack depth and the crack edge profile were observed for various values of the distance between the heating area and the cooling area. On the basis of the scribable conditions obtained from the experiments results, a thermal elasticity analysis was conducted by a finite element method. The following results were obtained. The scribable condition can be estimated from the maximum tensile stress in the cooling area and the maximum temperature in the heating area. The crack depth in laser scribing depends on the tensile stress in the cool...
23 citations
TL;DR: In this article, a p−n junction was fabricated with these dopants and an electroluminescent broad spectrum corresponding to white light was observed This white light is a result of the combination of red, green, and blue lights formed due to DAP recombination between Al−N (blue, 460, 460-498 nm), Cr-N (green, 521-575nm), and additional other impurity state transitions (red, 698-738)
Abstract: Laser doping has been utilized for fabricating white light emitting diodes with 6H-SiC wafers The emission of different colors to ultimately generate white light is tailored on the basis of donor acceptor pair (DAP) recombination mechanism for luminescence Chromium (Cr), which is an unconventional dopant that produces multiple acceptor sites per atom, was incorporated into SiC and conventional dopants such as aluminum (Al) and nitrogen (N) were also laser-doped to produce acceptor and donors states, respectively A p−n junction was fabricated with these dopants and an electroluminescent broad spectrum (400–850 nm) corresponding to white light was observed This white light is a result of the combination of red, green, and blue lights formed due to DAP recombination between Al–N (blue, 460–498 nm), Cr–N (green, 521–575 nm) and additional other impurity state transitions (red, 698–738 nm)
20 citations
TL;DR: Additional data and analyses reinforce the earlier conclusions regarding the threshold vs. spot-size dependence of the retinal threshold and compare both the absolute values and the spot- size trend of retinal thresholds determined via ophthalmoscopic observation at 1 h postexposure to the analogous threshold data collected with observations at 24’h post exposure.
Abstract: In earlier studies, we examined the dependence of the laser induced retinal damage threshold on retinal image size for extended-source ocular exposures. We reported the spot-size dependence of the retinal threshold (based on ophthalmic observations at 24 h postexposure) for two pulsewidth regimes: nanosecond-duration (Q-switched) pulses from a doubled Nd:yttrium–aluminum–garnet laser and microsecond-duration pulses from a flashlamp-pumped dye laser at 590 nm. In either case, the retinal threshold was shown to vary with the area (i.e., diameter squared) for image diameters >5 mrad. More recently, we have collected additional data for the intermediate spot-size range (1.5–10 mrad) and have compared both the absolute values and the spot-size trend of retinal thresholds determined via ophthalmoscopic observation at 1 h postexposure to the analogous threshold data collected with observations at 24 h postexposure. These additional data and analyses reinforce our earlier conclusions regarding the threshold vs. spot-size trend and are compared to and reconciled with results from previously published extended-source ocular damage studies. The experimental spot-size trends are also contrasted to the existing laser safety standard treatments of maximum permissible exposure levels for extended-source ocular exposures.
18 citations
TL;DR: The action spectrum for light-induced damage to the retina results from wavelength dependent transmission of the pre-retinal ocular media, wavelength dependent absorption in retinal chromophores, and chromatic aberration of the eye optics.
Abstract: The action spectrum for light-induced damage to the retina results from wavelength dependent transmission of the pre-retinal ocular media, wavelength dependent absorption in retinal chromophores, and chromatic aberration of the eye optics. While various light/tissue interaction mechanisms have been implicated, thermal mechanisms dominate in the visible and near-infrared spectrum for all exposure durations shorter than a few seconds and longer than 1 ns. A number of investigators have measured the transmission of the eye and the spectra of retinal absorbers, and thermal models based on these data predict the broad features of the action spectrum. This paper reports dose-response data for 100 ms duration retinal exposure in rhesus monkey to laser irradiation from a tunable Ti:Sapphire laser and from fixed-wavelength lasers over the wavelength range from 413 to 1319 nm. The wavelength dependence of these data is well predicted by the thermal action spectrum.
14 citations
TL;DR: The PROTAL® process as discussed by the authors combines an in situ pulsed laser cleaning with thermal spraying techniques, which avoids some drawbacks of the traditional degreasing and sand-blasting stages prior to thermal spraying, which is especially meaningful for ductile and notch-sensitive materials.
Abstract: Pulsed laser cleaning has emerged as a promising technology to challenge traditional surface preparation methods. This paper introduces the PROTAL® process, which combines an in situ pulsed laser cleaning with thermal spraying techniques. This laser surface preparation avoids some drawbacks of the traditional degreasing and sand-blasting stages prior to thermal spraying, which is especially meaningful for ductile and notch-sensitive materials. The laser induced phenomenon and the significant role of such laser irradiation in the coating deposition are presented.
14 citations
TL;DR: In this article, a laser solid phase diffusion technique has been utilized to fabricate endolayers in n-type 6H-SiC substrates by carbon incorporation, and the endolayer and parent silicon carbide epilayer were doped with aluminum using a laser doping technique to create p-regions on the top surfaces of the substrates.
Abstract: A laser solid phase diffusion technique has been utilized to fabricate endolayers in n-type 6H-SiC substrates by carbon incorporation. X-ray energy dispersive spectroscopic analysis shows that the thickness of the endolayer is about 100 nm. High resolution transmission electron microscopic images indicate that the laser endotaxy process maintains the crystalline integrity of the substrate without any amorphization. The resistivity of the endolayer formed in a 1.55 Ω cm silicon carbide wafer segment was found to be 1.1×105 Ω cm, which is sufficient for device fabrication and isolation. Annealing at 1000 °C for 10 min to remove hydrogen resulted in a resistivity of 9.4×104 Ω cm. The endolayer and parent silicon carbide epilayer were doped with aluminum using a laser doping technique to create p-regions on the top surfaces of the substrates in order to fabricate p-type-intrinsic type-n-type (PIN) diodes. The current-voltage characteristics of these diodes were compared with other PIN diodes fabricated using epilayers and other doping techniques.A laser solid phase diffusion technique has been utilized to fabricate endolayers in n-type 6H-SiC substrates by carbon incorporation. X-ray energy dispersive spectroscopic analysis shows that the thickness of the endolayer is about 100 nm. High resolution transmission electron microscopic images indicate that the laser endotaxy process maintains the crystalline integrity of the substrate without any amorphization. The resistivity of the endolayer formed in a 1.55 Ω cm silicon carbide wafer segment was found to be 1.1×105 Ω cm, which is sufficient for device fabrication and isolation. Annealing at 1000 °C for 10 min to remove hydrogen resulted in a resistivity of 9.4×104 Ω cm. The endolayer and parent silicon carbide epilayer were doped with aluminum using a laser doping technique to create p-regions on the top surfaces of the substrates in order to fabricate p-type-intrinsic type-n-type (PIN) diodes. The current-voltage characteristics of these diodes were compared with other PIN diodes fabricated using ...
TL;DR: In this paper, the effect of Nd:yttrium-aluminum-garnet laser on the microtopography and physicochemical properties of Ti6Al4V alloy are investigated in the view of biomedical applications.
Abstract: The effect of Nd:yttrium-aluminum-garnet laser on the microtopography and physicochemical properties of Ti6Al4V alloy are investigated in the view of biomedical applications. The surface roughness and hardness for laser treated samples (LTS) at 140 J cm−2 were measured 7±0.02 and 825 vickers hardness number, respectively. This superior microhardness value is attributed to grain refinement associated with laser melting and rapid solidification. The electrochemical property, mainly pitting corrosion resistance, has been carried out in Hanks salt balanced physiological solution using standard potentiodynamic polarization testing. A higher corrosion potential of −0.21 V was achieved for LTS. At the optimium treating value of laser fluence (140 J cm−2), the energy dispersive x-ray analysis showed about a 30% decrease of vanadium. The contact angle measurements also indicated an improved surface wettability (i.e., hydrophilicity) characteristic at 35°. Finally, the cell culture studies provided a useful tool to...
TL;DR: In this paper, the authors measured the dynamic bidirectional reflectance distribution function (BRDF) of a material under high-energy laser irradiation by using a witness screen to measure the reflected laser energy.
Abstract: With high-energy lasers, not only the direct laser beam can pose significant eye and skin hazards, but also light reflecting off material illuminated by the beam. Proper hazard analysis for a material irradiated by a laser relies upon the reflecting properties of the material surface, as these properties determine the magnitude and direction of the reflected laser energy commonly characterized by the bidirectional reflectance distribution function (BRDF). However, a high-energy laser heating and possibly melting a material can change the reflecting properties of that material, so these changes must be included in the hazard analysis. Traditional methods for measuring the BRDFs of materials are not practical for measurement of materials with rapidly-changing surface properties. However, BRDF measurement by imagery of a witness screen allows for practical measurements of the dynamically-changing BRDFs of materials under high-energy laser irradiation. Using this technique, the dynamic BRDFs of stainless stee...
TL;DR: In this paper, a fuzzy logic controller was developed for laser welding of zinc coated steel sheets in an overlap configuration, which is capable of steering the process towards full penetration keyhole welding, avoiding both blowholes and lack of penetration.
Abstract: A fuzzy logic controller (FLC) scheme has been developed for laser welding. Process light emissions are measured and combined to determine the current status of the welding process. If the process is not in a desired welding state, the FLC will adapt the laser power. The FLC has been demonstrated for the laser welding of zinc coated steel sheets in an overlap configuration. Experiments showed that the controller is capable of steering the process towards full penetration keyhole welding, avoiding both blowholes as well as lack of penetration. Under the presence of different process disturbances, like changes in focal position and material thickness, the controller proved to be able to maintain full penetration keyhole welding. The architecture of the controller is generic, thus facilitating an implementation for the laser welding process of other materials or configurations
TL;DR: In this article, the authors compared the International Commission on Non-Ionizing Radiation Protection (ICNIRP) exposure limits with relevant experimental animal injury data for cornea and lens exposure in the nanosecond to microsecond pulse duration regime.
Abstract: Laser exposure limits as promulgated by the International Commission on Non-Ionizing Radiation Protection are compared to relevant experimental animal injury data for cornea and lens exposure in the nanosecond to microsecond pulse duration regime in both the ultraviolet (UV) and infrared spectral ranges. In the UV spectral range, thermal and photochemical damage mechanisms compete and thresholds must be carefully distinguished as a function of wavelength and pulse duration. The thermal UV damage data are compared with levels inferred from CO2 radiation thresholds and it is shown that the reduction factors between experimental data for thermal injury and the corresponding exposure limits appear to be unnecessarily high. The lack of data for nanosecond exposures for wavelengths below 355 nm is identified. Available experimental data for infrared radiation (1.4–4 μm) can be fitted well with an inverse-absorption curve for saline. The exposure limits roughly follow the absorption curve with a varying degree o...
TL;DR: In this article, the Rosenthal two-dimensional thermal model for a moving-line heat source was used to predict weld width for both partial-penetration and full-Penetration welds, as well as the steady-state temperature field associated with the welding process.
Abstract: Bead-on-plate welding tests were performed using a 600 W fiber-delivered fiber laser. Uniform, high-aspect-ratio keyhole welds were observed in 1018 low-carbon steel, 1100 aluminum, and 304 stainless steel. The Rosenthal two-dimensional thermal model for a moving-line heat source was effective in predicting weld width for both partial-penetration and full-penetration welds. By setting the temperature at the perimeter of the keyhole equal to the vaporization temperature, this same model provided a first-order estimate of the weld depth for partial-penetration welds, as well. The two-dimensional model was used to calculate the steady-state temperature field associated with the welding process as well as the temporal thermal history of points in the weld pool and in the heat-affected zone next to the weld pool. A comparison of calculated weld-bead geometries with dimensions scaled from micrographs of bead cross sections showed reasonable agreement.
TL;DR: In this paper, the TGM model does not take into account the influence of the different stiffness of a plane or bended sheet on the stress and strain history in the laser treated zone.
Abstract: In order to investigate the thermomechanical phenomena during the laser bending process, a simulation is performed. The governing thermoelastic-plastic equations are integrated by the finite element method. The results are related to predictions as given by the so-called temperature gradient mechanism (TGM), which is often used in the context of laser bending. It turns out that approximative identical temperature time cycles result in a plane and a prebended sheet in completely different forming behavior, whereby the forming behavior for the bended sheet depends on which side is laser treated. This means that a quantification of the extension and homogeneity of laser generated temperature field is insufficient for the prediction of forming behavior. The TGM model does not take into account the influence of the different stiffness of a plane or bended sheet on the stress and strain history in the laser treated zone. For this reason the TGM model can’t predict the different forming behavior of the plane and the bended sheet.
TL;DR: In this paper, the behavior of lap welds with respect to the laser beam inclination was investigated in a large field RWS with a CO2 laser and a small field Nd:YAG laser.
Abstract: Remote welding provides new possibilities for highly productive and flexible joining of metal structures, especially in the automotive industry. This study presents an experimental investigation on the behavior of the lap welds’ geometrical characteristics with respect to the laser beam inclination. Two remote welding systems (RWSs) have been utilized: a large field RWS with a CO2 laser and a small field RWS with an Nd:YAG laser. The materials investigated include steels (noncoated, zinc-coated, and stainless) and an Al alloy. Conclusions are drawn related to the behavior of the process mechanism under different laser beam inclinations, useful for the industrial application of the process and for further research in the field.
TL;DR: In this paper, the authors investigated if near infrared ultrashort laser pulses produced DNA damage by exciting short wavelength-absorbing chromophores via multiphoton absorption, and the experiments were carried out in nonpigmented and artificially pigmented hTERT-RPE cells, a line of human derived retinal pigment epithelial (RPE) cells.
Abstract: Although laser-induced breakdown has the lowest energy threshold in the femtosecond domain, and appears to be responsible for production of threshold retinal lesions by ultrashort pulse lasers, previous findings suggested a role for multiphoton absorption in retinal damage. In this study, we investigated if near infrared ultrashort laser pulses produced DNA damage by exciting short wavelength-absorbing chromophores via multiphoton absorption. The experiments were carried out in nonpigmented and artificially pigmented hTERT-RPE cells, a line of human-derived retinal pigment epithelial (RPE) cells. Cells were exposed to 0.25 s pulses of CW and mode-locked 810 nm laser emissions, at irradiances equivalent to 0.5 and 1.0 times the ED50 for threshold damage in the primate eye, and DNA strand breaks were measured using the comet assay (single cell gel electrophoresis). At 0.5 X ED50, increased DNA strand breakage occurred after the ultrashort (mode-locked) exposures, but not the CW exposures, compared to contro...
TL;DR: In this paper, the Tauc energy gap was calculated from in situ UV/VIS optical spectra immediately after exposure to air together with a 1'eV redshift of the C'1s core-level energy in x-ray photoelectron spectra of these samples.
Abstract: Diamondlike amorphous carbon films have been deposited on silicon and quartz substrates by laser ablation of graphite using 120 fs pulses from an amplified Ti:sapphire laser operating at 800 nm. Ultraviolet/visible (UV/VIS) and micro-Raman spectra of these materials have shown that the sp3-bonded carbon fraction in these films is ≈27%, 55%, and 20% when deposition occurs at substrate temperatures of 77, 300, and 573 K, respectively. The presence of sp1 chains in these films is indicated by the appearance of an excitation band at 2000–2100 cm−1 in UV-Raman spectra. We also find a remarkable increase in the Tauc energy gap calculated from in situ UV/VIS optical spectra immediately after exposure to air together with a 1 eV redshift of the C 1s core-level energy in x-ray photoelectron spectra of these samples. The properties of sp1-, sp2- and sp3-bonded components of these materials have also been studied using UV/VIS Raman spectroscopy. The enhanced stability of sp1 chains in tetrahedral carbon matrix is di...
TL;DR: In this article, a direct-write metallization technique was used for patterning a silver seed layer with a subsequent step of electroless plating to increase thickness and electrical conductivity.
Abstract: Copper (Cu) has been patterned using a laser direct-write metallization technique for fabrication of printed wiring boards. The approach consists of writing a silver (Ag) seed layer with a subsequent step of electroless Cu plating to increase thickness and electrical conductivity. Ag seed layers were patterned with a frequency tripled Nd:YVO4 (λ=355 nm) laser with a spot size of approximately 50 μm. Final Cu linewidths after electroless plating were found to be 150 μm with a thickness of 2 μm and electrical resistivity of 5 μΩ cm. An optimal laser power of 0.81 W was found by a factorial-type design experiment. A modern prototype circuit was also patterned with this technique, demonstrating its compatibility with current resolution requirements.
TL;DR: In this paper, a brazing process has been developed in which aluminium and steel can be joined, with an enhanced deformation behavior, and tailored hybrid blanks with deep drawing ratios of 1.9 are possible.
Abstract: A consistent lightweight concept necessitates the combination of different lightweight materials. Because of the significant weight reduction, multimaterial design is becoming more and more interesting for the transportation industry. Mixed material concepts are partially limited because of the insufficient deformation behavior of the joining seams. To overcome this limitation, a brazing process has been developed in which aluminium and steel can be joined, with an enhanced deformation behaviour. Tailored hybrid blanks with deep drawing ratios of 1.9 are possible. Process studies, metallographic analyses, and tensile tests were carried out for AA6016 sheets in combination with DX56D. The AA6016 surface has to be activated using a noncorrosive flux. Although it is possible to avoid melting of the aluminium base metal, intermetallic FeAl compounds occur and were characterized using energy dispersive x-ray analysis. It was proven that the intermetallic compounds affect the mechanical characteristics of the seam. During tensile tests, butt seams show approximately 70% of the strength of the weaker base metal. The results of cupping tests show the ultimate possibility of using tailored hybrid blanks in a various number of applications.
TL;DR: In this article, the powders of chromium carbide, tungsten carbide and molybdenum (Mo) were laser cladded on AISI 304L steel and the laser processing parameters were optimized to fabricate sound metallurgical clad surfaces with minimum dilution for all three powders.
Abstract: Wear resistance of austenitic steels is low and needs to be improved for applications in abrasive and erosive environments. In the present work, the powders of chromium carbide (Cr3C2), tungsten carbide (WC) and molybdenum (Mo) were laser cladded on AISI 304L steel. The laser processing parameters have been optimized to fabricate sound metallurgical clad surfaces with minimum dilution for all three powders. The fabricated laser clad samples have been subjected to abrasion and erosion wear tests. It is observed that the abrasion resistance is improved in the range of 2–8 times as compared to that of the substrate for the cladding with these three powders. Erosion resistance has also shown an improvement of the order of 1.5–2 times for cladding with Cr3C2 and WC powders, whereas it deteriorated for Mo powder cladding. Surface topography of worn surfaces has been studied to understand the wear mechanisms of the clad surfaces.
TL;DR: In this paper, a method for profiling high aspect ratio and undercut laser drilled holes using sacrificial layers is presented, which is used to compare and contrast laser ablation of polyethylene films under exposure to ultraviolet (266 nm) and near-infrared (800 nm) radiation from an ultrafast, femtosecond laser.
Abstract: We present a novel method for profiling high aspect ratio and undercut laser drilled holes using sacrificial layers. This profiling method is used to compare and contrast laser ablation of polyethylene films under exposure to ultraviolet (266 nm) and near-infrared (800 nm) radiation from an ultrafast, femtosecond laser. We find that ultraviolet femtosecond pulsed laser processing of this polymer exhibits similar characteristics to that reported for nanosecond pulsed excimer lasers; namely, that thermal ablation contributes to material removal at high fluences. In addition, the total volume of material removed via IR femtosecond laser ablation is shown to be up to 4 times that for UV femtosecond laser ablation at a similar fluence and low pulse repetition frequency.
TL;DR: Evaluating the influence of low-power helium-neon laser on cartilage damage using an experimental short-term assay in rabbits found an organized fibrous tissue inside the lesion, whereas knees exposed to laser therapy pointed out a cartilage tissue filling the lesions in the majority of treated knees.
Abstract: Objectives. The purpose of this study was to evaluate the influence of low-power helium-neon laser on cartilage damage using an experimental short-term assay in rabbits. Material and Methods. A total of 21 adult male New Zealand rabbits underwent bilateral knee cartilage damage using a spherical bur. Helium-neon laser light with power of 6 J/cm2 and wavelength of 632.8 nm was applied on the left knees submitted to surgical procedures only. The right knees lesions served as negative control (nonexposed to laser therapy). All animals were randomized and seven animals were killed at postoperative days 7, 21, and 40 days. Results. At seven days, similar histopathological patterns were noted for laser exposed and nonexposed knees. At 21 days, the control group showed an organized fibrous tissue inside the lesion, whereas knees exposed to laser therapy pointed out a cartilage tissue filling the lesion in the majority of treated knees. At 40 days, a well-organized fibrous tissue filled fully the lesion in the co...
TL;DR: In this article, a ring beam optics was developed for a circular seam welding of the automotive parts using a 2 1/kW fiber laser, and the characteristics of the ring beam were investigated by a prime beam monitor.
Abstract: A ring beam optics was developed for a circular seam welding of the automotive parts using a 2 kW fiber laser. The characteristics of the ring beam optics were investigated by a Primes Beam Monitor. As a result, with increase of focal length of collimating lens, the outer diameter of the ring beam was hardly changed, however the inner diameter of the ring beam decreased. Therefore, the width of the ring beam was increased in the experiment. A distance (L12) between first axi-cone lens and second axi-cone lens increases, the outer diameter and inner diameter of the ring beam increases simultaneously. And the width of the ring beam was almost fixed. Moreover, it was confirmed that the intensity distribution of the ring beam becomes uniform by adjusting the coaxial performance of collimating lens, first axi-cone lens, and second axi-cone lens. After the ring beam optics connects to the fiber laser facility, a transparent thermoplastic resin and opaque thermoplastic resin with a circular seam was welded by a ...
TL;DR: In this article, a dual-line DPSSL emitting at 491 and 532 nm for high resolution CLSM fluorescence imaging is shown for the first time, and the equally high fluorescence image quality together with the many advantageous characteristics inherent to solid state lasers suggests that excitation using a DPSSL is favored.
Abstract: Diode-pumped solid-state lasers (DPSSLs) have been integrated as light sources in confocal laser scanning microscopy (CLSM). The standard argon ion laser at 488 nm is compared with a DPSSL operating at 473 nm in terms of noise and CLSM image characteristics. The equally high fluorescence image quality together with the many advantageous characteristics inherent to solid-state lasers suggests that excitation using a DPSSL is favored. The application of a dual-line DPSSL emitting at 491 and 532 nm for high resolution CLSM fluorescence imaging is shown for the first time.
TL;DR: In this paper, double-walled carbon nanotubes (DWNT) were connected by current-assisted laser irradiation after bandaging their overlapped ends with DWNT films.
Abstract: Macro-sized (centimeters long) double-walled carbon nanotube (DWNT) strands were connected by current-assisted laser irradiation after bandaging their overlapped ends with DWNT films. During the laser processing, structural transformation of DWNT bundles happened at the joints, which provided molecular bonding between the strands. Tensile tests indicate that the joints made in this way have relatively high tensile strength with a maximum value of 335.6 MPa corresponding to that of the original strands. And the electronic properties of the connected strands were not greatly weakened in our investigation on their temperature dependence of resistivity. This work may offer a promising potential for future extensive use of macro-sized carbon nanotube structures in many fields.
TL;DR: In this paper, the authors defined the definition of optimal laser hardening conditions with production rate as the main goal and applied an optimization algorithm to identify the optimal solution as a function of the imposed constraints.
Abstract: The present paper is a contribution to the definition of optimal laser hardening conditions with production rate as the main goal. When the part to be treated is given, the optimization problem can be expressed in terms of minimal execution time subjected to two constraints: the depth of treatment and hardness of transformed layer. When the analytical expression of the objective function and the constraints was determined, the feasibility area was described and analyzed. Finally, an optimization algorithm was applied to identify the optimal solution as a function of the imposed constraints.
TL;DR: In this article, the spectral transmittance of an ultrafast laser through an interference filter typifying those currently used in laser eye protection is reported and the impact of spectral and angular leakage on the level of protection provided.
Abstract: The inherently broad spectral bandwidth of ultrafast (mode locked) lasers can potentially exceed the protection bandwidth of laser eye protection. This is a particular concern for reflective laser eye protection technologies which by design possess sharp often narrow spectral protection notches. The purpose of this paper is to report spectral transmittance of an ultrafast laser through an interference filter typifying those currently used in laser eye protection and to examine the impact of spectral and angular leakage on the level of protection provided.