Pulsed CO2 Laser Radiation Research Articles

Effect of combination of pulsed CO2 laser irradiation and diammine silver fluoride treatment on ultrastructure of dentine

To explore the effect of combination of pulsed CO2 laser irradiation and diammine silver fluoride treatment on the ultrastructure of dentine. Each extracted molars was made into four identical dentinal specimens, which were randomly divided into 4 groups according to the treatment methods: A, control group; B, pulsed CO2 laser irradiation; C, coated with 38%Ag(NH3)2F; and D, laser irradiation plus fluoride. Scanning electron microscope (SEM) analysis was performed. As shown by SEM, group A showed clear dentinal tubuli, group B showed melted surface without dentinal tubule openings, group C showed thicker melted layer without dentinal tubule openings, and group D showed the thickest melted and recrystallized layer on dentine surface. Both pulsed CO2 laser irradiation and 38%Ag(NH3)2F treatment can seal dentinal tubule. The combination of these two techniques can form a synergistic effect.

Tunable middle infrared radiation generation in a GaSe crystal

Tunable second harmonic generation of pulsed CO2 laser radiation in a GaSe crystal was demonstrated. The nonlinear optical properties of GaSe and phase-matching conditions were investigated, and the best fitted dispersion relationships for this crystal were also determined. External conversion efficiency of 0.1% with unfocused pumped radiation had been achieved and maximum single pulse energy of 0.19 mJ was generated at 5.3 μm.

Registration of picosecond CO2 laser pulses by means of two-stage parametric transformation in nonlinear crystals

A technique for registering the temporal structure of picosecond pulses of CO2 laser radiation with an energy of 1.5–4.5 μJ at a wavelength of 10.27 μm using two-stage parametric transformation of IR radiation frequency into visible light under pumping of nonlinear crystals by Nd:YAG-laser radiation in a Q-switched mode is described. A GaSe nonlinear crystal was used at the first stage of transformation (10.27 μm + 1.064 μm → 0.964 μm). Radiation was further transformed (1.064 μm + 0.960 μm → 0.506 μm) by using the same pumping in an α-HIO3 nonlinear crystal. For the first time, no additional optical elements were present between the stages of the frequency transformer in the proposed optical scheme. The transformed radiation was registered with a Hamamatsu Temporal Disperser C1587 streak camera in a region of the photocathode maximum spectral sensitivity of ∼0.5 μm with a temporal resolution of up to 2 ps. The minimum recorded pulse duration of the CO2 laser was ∼45 ps.

Multiphoton dissociation of CF3I clusters by IR laser radiation

The results of investigation of dissociation of (CF3I) n clusters upon resonant excitation of vibrations of CF3I molecules by pulsed CO2 laser radiation are reported. The kinetics of dissociation of such clusters is studied and the dissociation yield is measured. It is shown that its value is completely controlled by fluence ΦIR of transmitted IR radiation energy and its time dependence is exponential. The results of measurements show that the dissociation lifetime of clusters is shorter than 10−8 s. The velocity and translational temperature of free CF3I molecules formed during dissociation of clusters are measured, as well as the dependence of these parameters on ΦIR. It is concluded that, under these conditions of IR excitations, the dissociation of (CF3I) n clusters can be treated as consecutive evaporation of molecules.

Exciton photoluminescence from ZnO layers produced by laser-induced gas breakdown processing

The plasma of optically-excited gas breakdown has been used to treat a Zn target in atmospheric pressure gases (air, O2, N2, Ar). The breakdown is produced near the target by a pulsed CO2 laser radiation, yielding to a local erosion of the target under the irradiation spot and the formation of a porous nanostructured layer, consisting of ZnO nanoscale spheres. We show that the produced nanostructured layers exhibit an intense exciton emission band in the ultraviolet range (380–385 nm), while defect-related photoluminescent bands were weak and could be completely removed by varying the fabrication parameters. Properties of the produced layers were found to be very promising for the development of optoelectronic devices.

Low-fluence CO2 laser irradiation decreases enamel solubility

This study investigated whether subablative-pulsed CO2 laser (10.6 μm) irradiation, using fluences lower than 1 J/cm2, was capable of reducing enamel acid solubility. Fifty-one samples of bovine dental enamel were divided into three groups: control group, which was not irradiated (CG); group laser A (LA) irradiated with 0.3 J/cm2; and group laser B (LB) irradiated with 0.7 J/cm2. After irradiation, the samples were subjected to demineralization in an acetate buffer solution and were then analyzed by SEM. A finite-element model was used to calculate the temperature increase. The calcium and phosphorous content in the demineralization solution were measured with an ICP-OES. ANOVA and the t-test pairwise comparison (p < 0.016) revealed that LB showed significantly lower mean Ca and P content values in the demineralization solution than other groups. A reduction in the enamel solubility can be obtained with pulsed CO2 laser irradiation (0.7 J/cm2, 135 mJ/pulse, 74 Hz, 100 μs) without any surface photomodification and a less than 2°C temperature increase at a 3-mm depth from the surface.

Low-fluence CO2 laser irradiation decreases enamel solubility

This study investigated whether subablative-pulsed CO2 laser (10.6 μm) irradiation, using fluences lower than 1 J/cm2, was capable of reducing enamel acid solubility. Fifty-one samples of bovine dental enamel were divided into three groups: control group, which was not irradiated (CG); group laser A (LA) irradiated with 0.3 J/cm2; and group laser B (LB) irradiated with 0.7 J/cm2. After irradiation, the samples were subjected to demineralization in an acetate buffer solution and were then analyzed by SEM. A finite-element model was used to calculate the temperature increase. The calcium and phosphorous content in the demineralization solution were measured with an ICP-OES. ANOVA and the t-test pairwise comparison (p < 0.016) revealed that LB showed significantly lower mean Ca and P content values in the demineralization solution than other groups. A reduction in the enamel solubility can be obtained with pulsed CO2 laser irradiation (0.7 J/cm2, 135 mJ/pulse, 74 Hz, 100 μs) without any surface photomodification and a less than 2°C temperature increase at a 3-mm depth from the surface.

脉冲CO2激光损伤K9玻璃的实验与仿真

脉冲CO₂激光损伤K9玻璃的实验与仿真

Isotope-selective multiphoton dissociation of chloromethyltrifluorosilane molecules (CH3ClSiF3) induced by pulsed CO2 laser radiation

ISSN 0012-5016, Doklady Physical Chemistry, 2007, Vol. 415, Part 2, pp. 221–224. © Pleiades Publishing, Ltd., 2007.Original Russian Text © P.V. Koshlyakov, S.R. Gorelik, E.N. Chesnokov, A.S. Rakhymzhan, A.V. Vorob’ev, A.K. Petrov, 2007, publi shed in Doklady Akademii Nauk, 2007, Vol. 415,No. 5, pp. 635–638.

A comparative study of second harmonic generation of pulsed CO2 laser radiation in some infrared crystals

A comparative study of second harmonic generation of CO2 laser radiation in different infrared transmitting crystals like HgGa2S4, AgGaxIn(1−x)Se2, sulphur and indium doped GaSe and ZnGeP2 is reported. It is also shown that sulphur doped GaSe crystal is more efficient than ZnGeP2 crystal in terms of effective figure of merit.

Attenuation of pulsed CO2 laser radiation in an argon medium containing fine aluminum particles

The attenuation of 10.6-μm radiation by aluminum aerosol particles dispersed in argon is studied experimentally. An optimal method of forming the initiating beam is found. The size and concentration of fine Al particles in the medium are estimated.

Conductivity and structure features of Ce 1− xGd xO 2− δ solid electrolytes fabricated by compaction and sintering of weakly agglomerated nanopowders

The conductivity and structure features of Ce 1− x Gd x O 2− δ ceramics prepared using weakly agglomerated nanopowders with the average particle size of about of 15 nm are discussed. The powders were synthesized by the evaporation of coarse-grained target with the use of pulsed CO 2-laser radiation. The magnetic pulsed compaction method was applied to press a dry nanopowder to densities up to 55% of theoretical one. Owing to high activity of the starting powder and uniformity of the compacts, the sintering of ceramics up to near full density was realized in non-conventionally low temperature range of 1100–1300 °C. The structure of sintered ceramics with average grain sizes from the range of 100–300 nm was investigated by X-ray analysis and microscopy methods (AFM, SEM). The structure features are discussed in interrelation with the data on conductivity of ceramics. The significant deviation in lattice parameter of elementary cubic cell for sintered fine-grained ceramics as compared with the known data for conventional coarse-grained material was revealed.

Inhibitory effects of a super pulsed carbon dioxide laser at low energy density on periodontopathic bacteria and lipopolysaccharide in vitro

Previous studies have described the effect of irradiation by a carbon dioxide (CO2) laser at high energy density on oral bacteria, and various side-effects have also been observed. However, no published studies have examined the effect of irradiation by a CO2 laser at low energy density on oral bacteria. The purpose of this study was to investigate the effects of super pulsed CO2 laser irradiation on periodontopathic bacteria and lipopolysaccharide (LPS). Bacterial suspensions of two species of periodontopathic bacteria received laser irradiation at energy densities of 0-12.5 J/cm2. The suspensions were then spread over agar plates and incubated anaerobically. The bactericidal effects were evaluated based on colony formation. Samples of LPS were laser-irradiated at energy densities of 0-12.5 J/cm2. The biological activity was measured, and LPS was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The irradiation at low energy densities of 7.5 and 12.5 J/cm2 killed more than 99.9 and 99.999% of Porphyromonas gingivalis and more than 99% of Actinobacillus actinomycetemcomitans was sterilized by the irradiation at 7.5 J/cm2. LPS biological activity was significantly decreased by laser irradiation at energy densities of more than 7.5 J/cm2 (p < 0.05), and the components of LPS analyzed by SDS-PAGE was diminished non-specifically. The results indicate that CO2 laser irradiation at low power is capable of bactericidal effect on periodontopathic bacteria and decreasing LPS activity.

B316 赤外線パルスレーザー加熱による材料表面微細加工状況の実時間観察

In this paper, surface forming process on glass plate was studied by using pulsed CO2 laser irradiation. The process was visualized by a high speed camera. Surface forming process of humped lens-like surface that had 470 μm in diameter and 18.3 μm in height and ablated surface that had 522 μm in diameter and 3.2 μm in depth were visualized. In comparatively high laser intensity the center of lens-like surface ablate and the surface get dented.

Optical confinement of 10-μm radiation by silver chloride nanoparticles

The results of experiments on the nonlinear optical confinement of microsecond pulses of CO2 laser radiation in a composite material comprising a potassium iodide matrix containing dispersed silver chloride nanoparticles coated by an island film of metallic silver are presented. The energy threshold for the laser radiation confinement is 15 mJ/cm2 and the dynamic range of confinement amounts to 103.

Properties of powders produced by evaporating CeO2/Gd2O3 targets exposed to pulsed-periodic radiation of a CO2 laser

The characteristics (phase composition, grain shape, grain size distribution, and specific surface area) of Ce0.78Gd0.22O2-δ nanopowders produced by exposing the target to pulsed CO2 laser radiation are reported. Reasons for a threefold increase in the output of the experimental powder-preparation unit (up to 60 g/h) with the characteristic grain size (≈10 nm) remaining unchanged are discussed.

The early stages of silicon surface damage induced by pulsed CO2 laser radiation: an AFM study

The early stages of the surface microstructural modification of silicon, induced by single pulses of CO2 laser irradiation (λ=10.6μm), have been studied, in both vacuum and air, by contact mode AFM. The laser pulse was found to be absorbed at the front surface of the sample, facing the laser; this was shown to be due to the presence of native oxide, which absorbs at this wavelength. We found that this absorption of energy caused the stress-induced formation of vertically oriented, square-shaped fragments, 400–700nm in length, often with short branches, that form a wall around the impact site; they oriented toward the plane of the sample with distance from the impact site, aligning more in the electric field direction of the pulse. In addition, electrically charged, branched fragments were redeposited at the outer extremities of the pulse site.

IR multiphoton dissociation of trichlorosilane induced by pulsed CO2 and NH3 laser radiation

The IR multiphoton dissociation of trichlorosilane (SiHCl3) molecules irradiated by pulses from CO2 and NH3 lasers is studied. The dependences of dissociation yield on the frequency and energy density of laser radiation, as well as on the parent pressure of SiHCl3, are determined. It is found that HCl and a solid precipitate, probably with a common chemical formula (SiCl2)n, are the main products of dissociation of trichlorosilane.

Effect of vaporization and melt ejection on laser machining of silica glass micro-optical components.

A new regime for silica glass machining for micro-optical fabrication applications, which uses pulsed CO2 laser radiation in the 2.5-100-micros pulse width region that has been generated by an acousto-optic modulator, is investigated. A filamentary melt ejection process that generates fibers and significant melt displacement limits machining quality below 30-micros pulse width. Ablation and melt ejection thresholds are quantified relative to pulse width, and the region from 30 to 50 micros is identified for low-threshold, smooth machining without melt displacement and ejection effects.

Evidence for the physical basis and universality of the elimination of particulates using dual-laser ablation. II. Dynamic time-resolved target reflectivity of metals and film growth of Zn

We have presented, in Part I of this series of two articles, the applicability of dynamic melt studies of the surface of a target under pulsed CO2 laser radiation to determine the onset of melt in these targets. Determination of this time and the accurate synchronization of an excimer (KrF) laser to coincide with the onset of melt on the target surface was shown to lead to particulate-free film deposition for Y2O3 and ZnO films. A key feature of the pump–probe reflectivity studies was the dynamic enhancement of the reflected probe signal, indicating the onset of melt. Some metallic targets, depending on the diameter of the precursor powder globules, such as the zinc target used in this study, do not yield such observable enhancements. In this article (Part II) we present the determination of the time for ablation of a variety of metallic targets under pulsed CO2 laser radiation, by monitoring the dynamic target reflectivity. The melt time is either directly determined or, in the absence of observable melt, estimated based on a simple thermal model for the absorption of the laser radiation by the target. Correlation of the calculated melt times with the morphological quality of particulate-free film growth of Zn is demonstrated. The effect of variable CO2 laser fluence on the deposited films is also demonstrated. The universality of applicability of the target reflectivity studies to a wide range of dissimilar materials, as well as the physical basis for the removal of particulates in dual-laser ablation is established.