Pulsed CO2 Laser Research Articles

Sensitive ablation of brittle materials with pulsed CO2 laser radiation

The interaction process between pulsed CO2 laser radiation and glass was studied systematically. The concept of the structuring process is related to an absorption-controlled ablation of small elementary material volumes with reduced melt formation, the so-called elementary volume ablation (EVA). For this purpose, suitable pulse parameters were predicted on the basis of the optical and thermal materials properties. These pulses with durations as low as 10 μs and a peak power of up to 600 W were generated using a specific arrangement consisting of a commercially available continuous CO2 laser of high beam quality and a cascade of two interference laser beam modulators. Optical microscopy, scanning electron microscopy, white light interferometry, and tactile profilometry were used to investigate the influence of the CO2 laser pulse parameters on the processing quality. The results obtained from the ablation of borosilicate glass (Borofloat33) and 100 μm thick sheets of cerium doped borosilicate glass demonstrate that the EVA method is a suitable approach to select an appropriate range of processing parameters for a high precision thermal ablation of glass without microcrack formation.

Temperature-insensitive compact phase-shifted long-period gratings induced by surface deformation in single-mode fiber

We present a temperature-insensitive compact phase-shifted long-period grating (PS-LPG) induced by using focused pulse CO2 laser via point-by-point technique. By introducing a phase shift with 1800° (π shift) in the center of the long-period grating (~420 µm per period, 20 periodicity in total), the original coupling resonance at 1318.55 nm splits into two symmetrical spectral peaks at 1283 and 1348 nm. FWHM between those two peaks is 36.55 nm, and the power intensities of two peaks are the same as −10.2 dB. The thermal characteristic of the PS-LPGs is around 8.8 pm/°C that is less than that of fiber Bragg grating (12 pm/°C). As a result, such fiber grating devices can be applied in a laser cavity as an all-fiber filter. Variation of phase shifts in LPGs give rise to different spectral peaks of coupled resonance, which makes the proposed PS-LPGs as a good candidate for the applications in sensing networks and optical telecommunications.

Performance of 100-W HVM LPP-EUV source

Abstract At Gigaphoton Inc., we have developed unique and original technologies for a carbon dioxide laser-produced tin plasma extreme ultraviolet (CO2-Sn-LPP EUV) light source, which is the most promising solution for high-power high-volume manufacturing (HVM) EUV lithography at 13.5 nm. Our unique technologies include the combination of a pulsed CO2 laser with Sn droplets, the application of dual-wavelength laser pulses for Sn droplet conditioning, and subsequent EUV generation and magnetic field mitigation. Theoretical and experimental data have clearly shown the advantage of our proposed strategy. Currently, we are developing the first HVM light source, ‘GL200E’. This HVM light source will provide 250-W EUV power based on a 20-kW level pulsed CO2 laser. The preparation of a high average-power CO2 laser (more than 20 kW output power) has been completed in cooperation with Mitsubishi Electric Corporation. Recently, we achieved 140 W at 50 kHz and 50% duty cycle operation as well as 2 h of operation at 100 W of power level. Further improvements are ongoing. We will report the latest status and the challenge to reach stable system operation of more than 100 W at about 4% conversion efficiency with 20-μm droplets and magnetic mitigation.

Time- and space-resolved spectroscopic characterization of laser-induced swine muscle tissue plasma

The spatial-temporal evolution of muscle tissue sample plasma induced by a high-power transversely excited atmospheric (TEA) CO2 pulsed laser at vacuum conditions (0.1–0.01Pa) has been investigated using high-resolution optical emission spectroscopy (OES) and imaging methods. The induced plasma shows mainly electronically excited neutral Na, K, C, Mg, H, Ca, N and O atoms, ionized C+, C2+, C3+, Mg+, Mg2+, N+, N2+, Ca+, O+ and O2+ species and molecular band systems of CN(B2Σ+–X2Σ+), C2(d3Πg–a3Πu), CH(B2Σ−–X2Π; A2Δ–X2Π), NH(A3Π–X3Σ−), OH(A2Σ+–X2 Σ+), and CaOH(B2Σ+–X2Σ+; A2Π–X2Σ+). Time-resolved two-dimensional emission spectroscopy is used to study the expanded distribution of different species ejected during ablation. Spatial and temporal variations of different atoms and ionic excited species are reported. Plasma parameters such as electron density and temperature were measured from the spatio-temporal analysis of different species. Average velocities of some plasma species were estimated.

Parametric Study of Pulsed CO2 Laser Surface Treatment of Alumina Ceramics

AbstractThis paper focuses on investigating the influence of laser power, pulse frequency and scanning speed on material removal rate and surface roughness during CO2 laser surface treatment of alumina ceramics. Pulse frequency and laser power were the significant factors influencing the material removal rate and surface roughness, respectively. Adequate response surface models were established to correlate the laser parameters and the measured responses. Grey relational analysis predicted the optimal responses at 90 W laser power, 5 kHz pulse frequency and 400 mm/s scanning speed. Desirability function based Multi objective optimization results indicated that minimum material removal rate (0.5117 mm3/s) and surface roughness (0.5968 µm) are achieved at 90 W laser power, 5 kHz pulse frequency and 337.37 mm/s scanning speed which were in close agreement with Grey Relational results. Increase in homogeneity and smoothness of the laser treated alumina surface along with formation of micro recast particles away from the laser traverse path were evidenced by the SEM micrographs.

Time and space-resolved spectroscopic and imaging study of a laser-produced swine muscle tissue plasma

SynopsisWe investigated the optical emission and imaging features of plasmas produced by a high-power transversely excited atmospheric CO2 laser pulses on a swine muscle tissue sample in different vacuum conditions. The analyzed plasma shows electronically excited neutral Na, K, C, Mg, H, Ca, N, and O atoms, ionized C+, C2+, C3+, Mg+, Mg2+, N+, N2+, Ca+, O+, and O2+ species and molecular band systems of CN, C2, CH, NH, OH and CaOH. Time-resolved 2D emission spectroscopy is employed to study the expanded distribution of several species ejected during ablation. The expansion of the plume front was analyzed using Shock wave and Drag models.

Optimization of laser cutting parameters for Al6061/SiCp/Al2O3 composite using grey based response surface methodology (GRSM)

The second generation metal matrix composites (MMCs) find wide applications in aerospace and automotive industries. The challenge lies in cutting these advanced materials and obtaining a good surface texture. The present study reports the application of non-contact type (thermal energy based) pulsed CO2 laser cutting process on Al6061/SiCp/Al2O3 composite. The process parameters in laser cutting influence the kerf width, surface finish and cut edge slope. These quality characteristics were observed for the various combinations of cutting parameters like laser power, pulsing frequency, cutting speed and assist gas pressure. The cutting trials were designed according to Taguchi’s L18 orthogonal array and a hybrid approach of grey based response surface methodology (GRSM) was disclosed for predicting the optimal combination of laser cutting parameters. A substantial improvement in the surface finish was observed in the responses obtained with the optimal setting of parameters. The atomic force microscopy (AFM) images and P-profile graphs of the cut surface were also observed to study the surface finish and texture.

Simulation of the thermo-optic coupling effect in mid-infrared second harmonic generation of ZnGeP2 crystal

Abstract The thermo-optic coupling process of second harmonic generation was numerically simulated in ZnGeP2 crystals pumped by a pulsed CO2 laser at the wavelength of 9.6 μm, under the strong and weak cooling conditions. The conversion efficiencies, temperature distributions were calculated during the evolution of the thermo-optic coupling. The results showed that the thermooptic coupling was weak in the strong cooling condition, which nearly did not disturb the conversion processes and temperature distribution, while in the weak cooling case, the temperature distribution showed a great influence on the conversion efficiency and light intensity. Finally, it was found that compensation of the phase mismatch induced by the thermal effect can well recover the conversion efficiency.

CO2 laser emission modes to control enamel erosion

Considering the importance and prevalence of dental erosion, the aim of this in vitro study was to evaluate the influence of different modes of pulse emission of CO2 laser associated or not to acidulated phosphate fluoride (APF) 1.23% gel, in controlling enamel erosion by profilometry. Ninety-six fragments of bovine enamel were flattened and polished, and the specimens were subjected to initial erosive challenge with hydrochloric acid (pH = 2). Specimens were randomly assigned according to surface treatment: APF 1.23% gel and gel without fluoride (control), and subdivided according to the modes of pulse CO2 laser irradiation: no irradiation (control), continuous, ultrapulse, and repeated pulse (n = 12). After surface treatment, further erosive challenges were performed for 5 days, 4 × 2 min/day. Enamel structure loss was quantitatively determined by a profilometer, after surface treatment and after 5 days of erosive challenges. Two-away ANOVA revealed a significant difference between the pulse emission mode of the CO2 laser and the presence of fluoride (P ≤ 0.05). The Duncan's test showed that CO2 laser irradiation in continuous mode and the specimens only received fluoride, promoted lower enamel loss than that other treatments. A lower dissolution of the enamel prisms was observed when it was irradiated with CO2 laser in continuous mode compared other groups. It can be concluded that CO2 laser irradiation in continuous mode was the most effective to control the enamel structure loss submitted to erosive challenges with hydrochloric acid.

Safety and efficacy evaluation of pulsed dye laser treatment and CO2 laser treatment for surgical scars clearance

Safety and efficacy evaluation of pulsed dye laser treatment and CO2 laser treatment for surgical scars clearance

The effect of CO2 laser treatment on skin tissue.

The aim of this study was to evaluate the effects of multiple pulses on the depth of injury caused by CO2 laser in an in vivo rat model. A 10600-nm CO2 laser was applied to rat skin, with one side of the rat dorsal skin being exposed, leaving the other side as a control. All of the various laser pulses tested led to gradual loss of epidermal thickness as well as a dramatic increase in thermal damage depth. Collagen coagulation was most effective with ten pulses of CO2 laser, while the strength of irradiated skin tissue increased as the influence of the laser increased. Fundamental laser-skin interaction effects were studied using a CO2 laser. The photodamaged areas obtained from laser interaction were recorded via couple charge device video camera and analyzed via ImageJ software. Photodamage induced by CO2 laser is due to photothermal effects, which involve burning and vaporizing mechanisms to ablate the epidermis layer. The burning area literally expands and penetrates deep into the dermis layer, subsequently causing collagen coagulation. This fundamental study shows in detail the effect of CO2 laser interaction with skin. The CO2 attributed severe burning, producing deep coagulation, and induced strength to treated skin.

TRANSPARENT MATERIALS FOR HIGH-POWER PULSED CO2-LASERS

In one experiment, having the aperture of the beam, comparable with dimensions of the sample, we compared the real optical damage of the main transparent materials for CO2-lasers: BaF2, NaCl, KCl, KBr, RbI, AgCl, CsI, KРС-5, KPC-6, ZnSe, ZnS, GaAs и Ge. Experimentally and theoretically we compared the nonlinear losses in 13 crystals, when the radiation in the range of 107—4 × 108 W/сm2 passed through them. The «tail» of the impulse was practically completely absorbed by plasma of optical breakdown of air in TEA CO2-laser, but the «peak» — only partially — by «hot» disbalanced charge carriers in the crystal. The losses of laser radiation exponentially depend on band gap of material. he peculiarities of damage Ge single crystals by high power pulsed CO2-laser were investigated. For the first time windows from Ge (diameter — 420 mm) were elaborated, produced and tested. We looked into, how parameters of crystal lattice, admixtures and structure of point defects, which can be changed by influence X -ray irradiation and annealing, can influence on the process of laser volume pores generation in alkali halides. We revealed dependence of pore dimensions from influence conditions, parameters of high-power laser beam, energy of crystal lattice. We studied kinetics of thermal annealing for to diminish dimensions of this pores.

Clinical curative effect observation of ultra pulse CO2 laser combined with collagen dressing in treatment of primary cutaneous amyloidosis

Objective To investigate the clinical efficacy and safety of ultra pulse CO2 laser combined with collagen dressing in treatment of cutaneous amyloidosis. Methods A total of 68 cases of primary cutaneous amyloidosis patients according to the different treatment methods was divided into two groups: the control group (n=33 cases) that was given acitretin capsules oral and topical compound flumetasone ointment packet treatment, and observation group (n=35 cases) with ultra pulse CO2 laser combined with collagen dressing external treatment. Two groups were observed in patients with curative effect and adverse reaction. Results Disease of integral observation group after treatment was significantly lower than the control group(t=3.12, P<0.05). The observation group had the efficiency of [88.6%(31/35)] that was significantly higher than that of control group[17/33(51.5%), χ2 = 11.23, P<0.01]. The observation group had significantly shorter healing time [(5.38 ± 1.81)d] compared to the control group [(10.75 ± 2.06)d, t=11.39, P<0.01]. The observation group did not have recurrence, which was significantly different from the control group (χ2=4.90, P<0.05). Conclusions Ultra pulse CO2 laser combined with collagen dressing in treatment of primary cutaneous amyloidosis is a kind of effective treatment methods with remarkable curative effect and less adverse reactions. It is worthy of clinical application. Key words: Amyloidosis/TH; Skin diseases/TH; Lasers, gas/TU; Collagen/AD

CO2 Laser irradiation of GeO2 planar waveguide fabricated by rf-sputtering

We present a fabrication protocol combining radio frequency sputtering technique and CO2 laser annealing for GeO2 based planar optical waveguides. The effects of pulsed CO2 laser irradiation on the optical and structural properties of pure GeO2 planar waveguide are evaluated by different techniques as m-line and micro-Raman spectroscopy and AFM measurements. Amorphous GeO2 planar waveguide was fabricated by Radio Frequency magnetron sputtering system on v-SiO2 substrate. An increase of the refractive index of approximately 0.04 at 1.5 μm and a decreasing of the attenuation coefficient from 0.9 to 0.5 dB/cm at 1.5 μm have been observed after pulsed CO2 laser annealing. Raman spectroscopy and AFM results showed that after an adapted pulsed CO2 laser annealing, the resulting materials showed a crystalline environment in which the phase of the crystalline GeO2 varies with varying irradiation time.

High quality electron bunch generation with CO2-laser-plasma interaction

CO2 laser-driven electron acceleration in low-density plasma is demonstrated using particle-in-cell simulation. An intense CO2 laser pulse of long wavelength excites a wake bubble that has a large elongated volume for accelerating a large number of electrons before reaching the charge saturation limit. A transversely injected laser pulse is used to induce and control the electron injection. It is found that an electron bunch with total charge up to 10 nC and absolute energy spread less than 16 MeV can be obtained. As a result, the charge per energy interval of the bunch reaches up to 0.6 nC/MeV. Intense CO2-laser based electron acceleration can provide a new direction for generating highly charged electron bunches with low energy spread, which is of much current interest, especially for table-top X-ray generation.

Laser acceleration of protons using multi-ion plasma gaseous targets

We present a theoretical and numerical study of a novel acceleration scheme by applying a combination of laser radiation pressure and shielded Coulomb repulsion in laser acceleration of protons in multi-species gaseous targets. By using a circularly polarized CO2 laser pulse with a wavelength of 10 μm—much greater than that of a Ti: Sapphire laser—the critical density is significantly reduced, and a high-pressure gaseous target can be used to achieve an overdense plasma. This gives us a larger degree of freedom in selecting the target compounds or mixtures, as well as their density and thickness profiles. By impinging such a laser beam on a carbon–hydrogen target, the gaseous target is first compressed and accelerated by radiation pressure until the electron layer disrupts, after which the protons are further accelerated by the electron-shielded carbon ion layer. An 80 MeV quasi-monoenergetic proton beam can be generated using a half-sine shaped laser beam with a peak power of 70 TW and a pulse duration of 150 wave periods.

0808 膨張波管を用いた印加磁場による再突入機の抗力増大効果の実験的検証

The aerodynamic force enhancement effect occurs by applying magnetic field around a reentry vehicle in a weekly-ionized flow behind the strong detached shock wave. Recently, this force enhancement effect was experimentally investigated using an expansion tube which can produce high speed and high enthalpy flow. Because aerodynamic force measurement is difficult due to short test flow period in expansion tube, drag measurement system which employed a piezofilm with fast responsiveness was developed in this study. This drag measurement system was calibrated using CO2 pulse laser and applied to experimental investigation on the aerodynamic force enhancement effect in expansion tube. The aerodynamic force acting on simple models in the flow produced by the expansion tube can be measured in this system. Additionally, the increase of the drag force due to magnetization in a weekly-ionized flow was observed.

Influence of molecular absorption of a ground atmospheric path on characteristics of filamentation region of high-power CO2 laser radiation

Theoretical aspects of self-focusing and filamentation in air of high-power pulsed CO2 laser radiation with a carrier wavelength of 10.6 μm are considered. The frequency-differential molecular absorption of atmospheric air is included in a theoretical model. The super-broad pulse spectrum is shown to be strongly affected by atmospheric absorption that destabilizes the filamentation process and considerably reduces the length of a plasma channel formed in a beam channel under the conditions of pulse self-phase modulation.

The Spectroscopical and Microstructural Investigations of Nanoclusters and Micron-Sized Periodic Structures Created at the Surface of the Crystal and Amorphous Silica by Resonant CO2Laser Irradiation

The action of pulsed CO2 laser radiation (pulse energy of 1 J, pulse time of 70 ns) at the surface of silica (crystal quartz and fused quartz ) have been investigated. By means of spectroscopical and microstructural investigations it has been established the appearrance of two kind of structures – periodical micron-sized structures with the period length close to wave length of CO2 laser irradiation and nanoclusters with size close to 50-100 nanometers.

Analytical capability of the plasma induced by IR TEA CO2 laser pulses on copper based alloys

The applicability of nanosecond infrared (IR) transversely excited atmospheric (TEA) CO2 laser, operating at 10.6 ?m and 100 ns pulse length (initial spike), induced plasma under reduced air pressure for spectrochemical analysis of bronze and brass samples was investigated. The plasma consisted of two clearly distinguished and spatially separated regions and expanded to a distance of about 10 mm from the surface. Elemental composition of the samples was determined using a time-integrated space-resolved laser-induced plasma spectroscopy (TISR-LIPS) technique. Sharp and well resolved spectral lines mostly atomic, and negligibly low background emission, were obtained from a plasma region 7 mm from the target surface. Good signal to background and signal to noise ratios were obtained. Estimated detection limits for trace elements Mg, Fe, Al and Ca were in the order of 10 ppm in bronze and around 50 ppm in brass. Damage on the investigated samples induced by TEA CO2 laser radiation was negligible.