Pulsed CO2 Laser Research Articles

Generation of polarized proton beams with gaseous targets from CO2-laser-driven collisionless shock acceleration

We propose obtaining polarized proton beams based on CO2-laser-driven collisionless shock acceleration (CSA) of the pre-polarized HCl gas. By tailoring the density profile of the pre-polarized HCl gas, the intense CO2 laser pulse heats the plasma target and forms a strong shock that reflects the polarized protons to high energy. According to particle-in-cell simulations implemented with the spin dynamics, directional proton beams of several MeV were generated at a total beam polarization of over 80%. Simulations showed that proton spin precession occurred in the azimuthal magnetic fields generated by the Biermann effect and plasma currents. The latter was the main depolarization mechanism in the early stage of shock wave formation. For CSA at CO2 laser intensities around 1017–1018 W/cm2, the proton depolarization was insignificant and the beam polarization purity was preserved. As pre-polarized hydrogen targets were available at gaseous densities in-state-of-art facilities, CSA driven by relatively long wavelength lasers provided a feasible solution for obtaining ultra-fast polarized proton sources.

Simulation and experimental investigation of the surface morphology formation mechanism of a D-shaped fiber processed using a pulsed CO2 laser

Traditional D-shaped optical fibers are manufactured using mechanical polishing or chemical corrosion techniques, which inevitably introduce sub-surface defects or impurities. In this study, a new D-shaped optical fiber manufacturing method using CO2 laser ablation technology is proposed. Laser ablation technology is a complex multi-physical coupling process involving phase changes. To fully understand the surface morphology formation mechanism during CO2 pulsed laser processing, a three-dimensional numerical model and experimental analyses were used to elucidate the relationship between the fiber surface temperature distribution, surface morphology evolution, processing quality, processing efficiency, and laser parameters. The simulation results showed that the residual temperature between laser pulses was lower than the structural transition temperature of the material, and the simulated morphology was consistent with the experimental results. Moreover, the overlapping spot energy resulted in the processed surface exhibiting a periodic ripple structure. The ablation depth was proportional to the pulse width and inversely proportional to the scanning speed. In addition, different laser pulse widths had almost no effect on the roughness and flatness of the processed surface, but the laser scanning speed had a significant impact on both indexes. These results can guide the optimization of CO2 laser processing methods.

Laser ion source for semiconductor applications

Carbon implantation can be effectively used for axial minority charge carriers’ lifetime control in various silicon bulk and epitaxial planar structures. When carbon is implanted, more stable recombination centres are formed and silicon is not doped with additional impurities, as for example, when irradiated with protons or helium ions. Economically, such a process competes with alternative methods, and is more efficient for obtaining small lifetimes (several nanoseconds). I-3 ion injector with laser-plasma ion source at Institute for theoretical and experimental physics (ITEP) is used as ion implanter in semiconductors. The ion source uses pulsed CO2 laser setup with radiation-flux density of 1011 W/cm2 at target surface. The ion source produces beams of various ions from solid targets. The generated ion beam is accelerated in the two gap RF resonator at voltage of up to 2 MV per gap. Resulting beam energy is up to 4 MV per charge. Parameters of carbon ion beam generated and used for semiconductor samples irradiation during experiments for axial minority charge carriers lifetime control in various silicon bulk and epitaxial planar structures are presented.

Efficient two-stage laser enrichment up to 99% of carbon-13 isotope by IR multiphoton dissociation of Freon molecules

A new method for two-stage laser enrichment of carbon-13 (13C) by isotope-selective IR multiphoton dissociation of Freon molecules is considered, which makes it possible to achieve a concentration of 13C up to 99 % or higher with high productivity. At the first stage, as a result of the selective dissociation of CF2HCl (Freon-22) molecules, it is expected to obtain a C2F4 dissociation product enriched in 13C up to 30 % – 50 %. At the second stage, CF2Br2 (Freon-12B2) is proposed to be used as a working substance, which is synthesised from enriched C2F4, and the enrichment process is carried out by selective deep ‘burning-out’ of the 12C-containing component. Experiments on multiphoton dissociation of Freon-12B2 with an initial 13CF2Br2 concentration of 30 % in a mixture with oxygen by pulsed CO2 laser radiation are performed. It is shown that reaching a 13CF2Br2 concentration of no lower than 99 % is possible at high values of the elementary separation act parameters: 15 % – 18 % dissociation yield and 40 – 75 selectivity for 12CF2Br2 molecules.

Carbon Dioxide Laser as a Sustainable Method for Producing a Pattern on Denim Fabric: Evaluation of Colour and Durability

Laser treatment of denim fabrics was demonstrated as one of the methods of producing distressed effects and is continuing to attract textile and fashion designers to develop bespoke designs that appeal to all age groups. Two dark shaded indigo-dyed 100% cotton twill fabric with varying weights representing various garment applications were laser treated using a commercially available pulsed CO2 laser of wavelength 10.62�m. Pulses per inch, which is the degree of closeness of laser irradiation, was maintained at 300 and 400 PPI. Treated denim fabrics were evaluated for tensile strength, colour measurements, including colour hue (H), saturation (S), brightness (B), reflectance, K/S (colour yield), CIE L* a* b*, fabric thickness and colourfastness after wash. Results indicated that colour contrast of denim fabric enhanced with the increase in grayscale (tone density) for both the LW (lightweight) and HW (heavyweight) fabrics, mainly at lower laser speed (80%) and higher laser power (40%). At higher grayscale (30% GS), surface fibers charred due to laser and the oxidation of cellulose occurred, causing a distinct yellow tone compared to pristine denim. Fabric tensile strength was affected as grayscale and laser parameters increased, the variation from pristine denim for LW fabric was 40 - 45% at 30% GS, whilst for HW fabric, variation was 25-30%. Colourfastness tests revealed limited colour staining, and it removed charred fibers showing a distinct tone change. This research recommends a combination of fabric and laser parameters to produce patterns without affecting the overall quality of the fabric.

Carbon Dioxide Laser as a Sustainable Method for Producing a Pattern on Denim Fabric: Evaluation of Colour and Durability

Laser treatment of denim fabrics was demonstrated as one of the methods of producing distressed effects and is continuing to attract textile and fashion designers to develop bespoke designs that appeal to all age groups. Two dark shaded indigo-dyed 100% cotton twill fabric with varying weights representing various garment applications were laser treated using a commercially available pulsed CO2 laser of wavelength 10.62μm. Pulses per inch, which is the degree of closeness of laser irradiation, was maintained at 300 and 400 PPI. Treated denim fabrics were evaluated for tensile strength, colour measurements, including colour hue (H), saturation (S), brightness (B), reflectance, K/S (colour yield), CIE L* a* b*, fabric thickness and colourfastness after wash. Results indicated that colour contrast of denim fabric enhanced with the increase in grayscale (tone density) for both the LW (lightweight) and HW (heavyweight) fabrics, mainly at lower laser speed (80%) and higher laser power (40%). At higher grayscale (30% GS), surface fibers charred due to laser and the oxidation of cellulose occurred, causing a distinct yellow tone compared to pristine denim. Fabric tensile strength was affected as grayscale and laser parameters increased, the variation from pristine denim for LW fabric was 40 - 45% at 30% GS, whilst for HW fabric, variation was 25-30%. Colourfastness tests revealed limited colour staining, and it removed charred fibers showing a distinct tone change. This research recommends a combination of fabric and laser parameters to produce patterns without affecting the overall quality of the fabric.

Metal powder-assisted laser induced breakdown spectroscopy (LIBS) using pulse CO2 laser for liquid analysis

Analysis of impurity and trace element in liquid is urgently needed in environment and industries. In this present work, new sampling technique of laser induced breakdown spectroscopy (LIBS) has been devised using metal coarse utilizing pulse CO2 laser. Experimentally, a liquid and polluted liquid was dropped into a metal coarse powder. A pulse CO2 laser (10.6 µm, 200 ns) beam with a laser energy from 0.75 to 1.5 J was bombarded on a metal coarse to induce a plasma. The plasma contains elemental analytical lines obtained from the liquid material; the metal coarse itself is never ablated and only works to induce a plasma. By this present technique, identification of major and minor elements in liquid material target such as commercial milk liquid and multi-vitamin liquid has successfully be made. Furthermore, a quantitative analysis of impurity of Cr has been demonstrated, resulting in good precision and good sensitivity with limit of detection of approximately 2 µg/ml. This present developed technique is possible to be employed for analysis of major, impurity, and trace elements in liquid and water without any tedious sample pretreatment.

Hot carrier effects on Brillouin amplification in AIIIBV and AIIBVI semiconductors

A theoretical formulation followed by numerical analysis is carried out to study the hot carrier effects (HCEs) on Brillouin amplification in AIIIBV and AIIBVI semiconductors. The threshold condition for the onset of Brillouin amplification and the parameters characterizing Brillouin amplification of the Brillouin cell are estimated. Numerical analysis is made for three different Brillouin cells at illuminated by a pulsed CO2 laser. HCEs of intense pump beam modifies the momentum transfer collision frequency of carriers and consequently the nonlinearity of the Brillouin medium, which in turn (i) lowers the threshold intensity, (ii) enhances the parameters characterizing Brillouin amplification, (iii) shifts the enhanced Brillouin gain spectrum towards smaller values of magnetic field, and (iv) widens the range of magnetic field at which peak of Brillouin gain spectrum (around resonance) occurs. The incorporation of HCEs in the analysis validate the selection of appropriate Brillouin medium for the fabrication of efficient Brillouin amplifiers.

Influence of Laser Treatment on End Notched Flexure Bonded Joints in Carbon Fiber Reinforced Polymer: Experimental and Numerical Results.

Surface pretreatment for bonding is one of the most important steps for the manufacturing of a reliable bonded joint. In this paper, the effectiveness of an innovative pretreatment by CO2 pulsed laser for bonding Carbon Fiber Reinforced Polymer (CFRP) was investigated. End Notched Flexure (ENF) specimens were made with different densities of laser treatment, and the respective fracture toughness was obtained through the Compliance-Based Beam Method (CBBM). Furthermore, a cohesive model for simulating debonding processes was illustrated, and the cohesive parameters were obtained by an inverse method. The achieved results represent a fundamental step for the development of a numerical model useful for the determination of laser texturing as a function of the applied local stress into the bonded joint.

Evaluation of Meibomian Gland Function after Therapy of Eyelid Tumors at Palpebral Margin with Super Pulse CO2 Laser.

Purpose To investigate the effect on meibomian gland function of super pulse carbon dioxide (CO2) laser excision in the treatment of eyelid tumors at palpebral margin. Methods 36 patients with 36 eyelid tumor size ≤ 1 cm and within 1 mm to palpebral margin were recruited in this study. Of which, 16 cases with tumors in the upper eyelid and 20 cases in the lower eyelid were involved. The eyelid tumors of all the patients were treated by super pulse CO2 laser with its power density varied between 0.6 and 21.1 W/mm2 and in repeat mode. The laser spot size ranged from 120 to 200 μm. Ocular surface parameters including tear film break-up time (BUT) and meibograde, meibum expressibility, and meibum quality were evaluated at pretherapy, 1 week, 1 month, and 3 months posttherapy in all 36 patients. Result All the patients were satisfied with the therapy. No infective complications and recurrence occurred in any of the 36 patients at the following period. The eyelid wound recovered well with nearly normal appearing after 2 to 3 weeks. The morphology of limbi palpebralis, BUT, meibograde, meibum expressibility, and meibum quality of all the 36 patients showed no significant difference before and after the therapy. Conclusions Super pulse CO2 laser had no effect on meibomian gland function and morphology in the excision of tumors at palpebral margins, which was an efficacy and well-tolerated therapy with lower complications and recurrence.

CO2 laser assisted deactivation of bacteria and bacteriophage samples

It is well-known that the exposure of bacteria and germs to electromagnetic radiation can lead to their annihilation. In this work, we have attempted to characterize the effect of laser radiation on test samples comprising bacteria and bacteriophages. A pulsed transverse excitation atmosphere CO2 laser that operates in the mid-infrared region of the electromagnetic spectrum has been employed for the studies. Aeromonas bacterium and its specific virus, P2 bacteriophage, cultured on a typical matrix of tryptic soya agar, served as the test samples. Agar overlay technique was used to examine the test results. A detailed analysis of the laser-exposed samples showed a complete neutralization of Aeromonas bacteria and its bacteriophage for appropriate laser parameters. Since bacteriophages are extensively used as a surrogate organism to study virucidal effects, it is anticipated that exposure to CO2 laser radiation will have a similar effect on SARS CoV2 and viruses of similar nature.

Experimental comparative study of the effect of fractional CO2 laser combined with pulsed dye laser versus each laser alone on the treatment of hypertrophic scar of rabbit ears.

The use of fractional CO2 laser and pulsed dye laser (PDL) therapy to treat and/or prevent scarring following burn injury is becoming more widespread with a number of studies reporting reduction in scar erythema and pruritus following treatment with lasers. The objective of this study was to directly compare the efficacy of PDL, fractional CO2 , and PDL and fractional CO2 laser therapy in immature red hypertrophic scars in a standardized animal model. Ten New Zealand big-eared rabbits were used to make rabbit ear hypertrophic scar models. A total of 80hypertrophic scar models were obtained and randomly divided into groups: control (Group A), Fractional CO2 laser (Group B), pulse dye laser (Group C), combined (Group D), 20 in each group. Wound sites were treated with PDL, Fractional CO2 laser, or both at 28days post-grafting. Grafts receiving no laser therapy served as controls. Hypertrophic scar appearance, morphology, size, and erythema were assessed, and punch biopsies were collected. At days 7 and 28, additional tissue was collected for biomechanical analyses and markers for HE staining, Masson staining, immunohistochemical method to determine the CD31 content in the scar; Western blot to detect the expression of VEGF protein in scars. After the day 7 and 28, the scars were collected. Histomorphological change in scars was observed by hematoxylin-eosin staining, Masson staining. The expression of CD31, VEGF protein, and the cell apoptosis rate was detected by immunohistochemical method. (i) In morphological observation, HE staining and Masson staining, both the number of fibroblasts and amount of collagen fibrils in the experimental group were significantly reduced compared with those in control group. (ii) Micro-vessel Density (MVD) value can be found much smaller in the experimental groups than the control (p<0.05). Among the four experimental groups, there was a significant difference among 14d, 21d, and 28d groups (p<0.05). (iii) On days 7 and 28 after treatment, expression of VEGF could be regulated in experimental group (p<0.05). Among the three experimental groups, the decrease of VEGF in the combined group was significantly stronger than that of the other two. The effect of Fractional CO2 laser combined with pulsed dye laser treatment was shown to be better than that of Fractional CO2 laser or pulsed dye laser alone and inhibits the early hypertrophic scar in rabbit ears.

Generation of tail-free short pulses using high-pressure CO2 laser

The spectral linewidth of a transversely excited pulsed CO2 laser is broadened at high working pressures. This phenomenon causes a decrease in the upper-level lifetime such that the pulse width is significantly compressed. Although the tail part of CO2 laser pulses owns a non-negligible proportion of total energy, it has minor effects during the interaction process between photons and materials due to its low amplitude. Thus, it is of great significance to yield the tail part and generate a narrow pulse in most applications. In this study, a continuously tunable pulsed CO2 laser with a low nitrogen proportion in the mixture is developed to generate tail-free short pulses; a minimum pulse width of 30.60 ns with a maximum pulse energy of 481 mJ is synchronously achieved at a pressure of 7 atm, and the estimated peak power is above 15 MW. A numerical simulation is also conducted for comparison with the experimental results. The contribution of the spectral gain toward the compression of the pulse width is discussed in the last section of this paper.

Pulsed RF excitation inductive discharge CO-=SUB=-2-=/SUB=- laser with the radiation energy of 1 J and high efficiency

An efficient pulsed gas-discharge inductive CO2-laser with a radiation energy of 1.05 J has been developed for the first time. In this case, the pulse duration of the laser radiation was about 10 msec. The maximum efficiency of 21.1% was obtained at a radiation energy of 340 mJ. HF current pulses propagated along the inductor conductor and, thus, an inductive discharge was formed to create a population inversion at the infrared (IR) transitions of CO2* molecules. The temporal and energy characteristics of the radiation of the inductive CO2-laser depending on the duration of the pump pulse are investigated. The spatial characteristics and spectrum of the radiation of the developed laser are estimated. The divergence of the laser radiation was 0.52 mrad. The cross-sectional dimension of the laser output beam was about 35 mm in diameter. Keywords: inductive discharge in a mixture of gases, high-frequency modulation of the pump voltage, population inversion, output characteristics of laser radiation.

Импульсный индукционный CO-=SUB=-2-=/SUB=--лазер с энергией излучения 1 J и высоким КПД с ВЧ возбуждением

An efficient pulsed gas-discharge inductive CO2-laser with a radiation energy of 1.05 J has been developed for the first time. In this case, the pulse duration of the laser radiation was about 10 msec. The maximum efficiency of 21.1% was obtained at a radiation energy of 340 mJ. RF current pulses propagated along the inductor conductor and, thus, an inductive discharge was formed to create an inverse population at the infrared (IR) transitions of CO2* molecules. The temporal and energy characteristics of the radiation of the inductive CO2-laser depending on the duration of the pump pulse are investigated. The spatial characteristics and spectrum of the radiation of the developed laser are estimated. The divergence of the laser radiation was 0.52 mrad. The cross-sectional dimension of the laser output beam was about 35 mm in diameter.

METAL-SUPPORTED LASER-INDUCED BREAKDOWN SPECTROSCOPY FOR THE TRACE ELEMENTAL IDENTIFICATION OF MATERIAL

Trace elemental identification of Cr deposited on a material target was made using metal-supported laser-induced breakdown spectroscopy. Experimentally, an almite material containing a trace element of Cr on its surface was perpendicularly placed on a Cu metal plate. A pulse CO2 laser beam was irradiated on the Cu plate to produce a plasma. The plasma then interacts with the trace elements deposited on the material surface, and finally, the elements are effectively excited in the gas plasma region. The role of laser irradiation in the analyte intensity was examined. The results certified that the intensity of impurity decreased with the number of laser bombardments on the material target. Furthermore, rapid identification and analysis of Cr as a trace element can be made successfully. The limit detection of Cr as a trace element was 1 mg/kg. This method has a great deal of promise for use in the surface examination of material businesses to systematically check the material's quality.

Multifunctional compact dual band repetitively pulsed slab RF discharge CO laser with average output power up to 40 W

A new repetitively pulsed cryogenically cooled slab RF discharge CO laser running in both fundamental and first-overtone bands without its active medium forced replacement with average output power three times as much as that of previous models was developed. Compared to our previous installations, the output power was increased due to using gold-coated copper electrodes of ∼ 1.5 times larger surface area. The fundamental band free-running lasing was obtained within the spectral range of 5.06–5.92 μm with average output up to ∼ 40 W. Under Q-switching the laser operated in the spectral range of 4.95–7.0 μm with pulsed peak power up to 4.5 kW. The first-overtone band lasing was observed in the spectral range of 2.6–3.05 μm with maximum average power of ∼ 6 W.

Terahertz NH3 Laser with Optical Pumping by “Long” (~100 μs) Pulses of CO2 Laser for Plasma Diagnostics

Terahertz NH3 Laser with Optical Pumping by “Long” (~100 μs) Pulses of CO2 Laser for Plasma Diagnostics

Shaping Optical Microresonators on the Surface of Optical Fibers With Negative Effective Radius Variations

We examine moderate CO2 laser heating as a method of forming negative effective radius variations in conventional optical fiber. Fiber samples were subjected to focused CO2 laser radiation in the form of 100 ms pulses with power 0.36 to 1.3 W and thermalization time up to 2.2 s. Fiber temperatures reached 200 to 300 degrees Celsius in each pulse. The temper atures are significantly smaller than the glass transformation temperature, which is nearly 1500 °C. We show that short CO2 laser pulses may introduce negative variations up to 5 nm. The magnitude of the introduced variation increases roughly linearly for up to 6 pulses, and then fiber saturation is achieved. We reveal that it is possible to produce optical whispering gallery modes resonators in low-temperature heating mode and create a triangular-shape microresonator solely with the negative variations. The negative variations may also occur in peripheral areas of high-temperature heated fiber while introducing positive effective radius variations. To eliminate it, we propose low-temperature fiber annealing before high-temperature variations introducing. The negative variations may also be implemented to develop a new independent approach of shaping optical whispering gallery modes microresonators.

Enhanced Raman gain coefficients of semiconductor magneto-plasmas

Considering the origin of stimulated Raman scattering in Raman susceptibility, we obtain expressions for Raman gain coefficients (under steady-state and transient regimes) of semiconductors magneto-plasmas under various geometrical configurations. The threshold value of excitation intensity and most favourable value of pulse duration (above which transient Raman gain vanishes) are estimated. For numerical calculations, we consider n-InSb crystal at 77 K temperature as a Raman active medium exposed to a frequency doubled pulsed CO2 laser. The variation of Raman gain coefficients on doping concentration, magnetic field and its inclination, scattering angle and pump pulse duration have been explored in detail with aim to determine suitable values of these controllable parameters to enhance Raman gain coefficients at lower threshold intensities and to establish the suitability of semiconductor magneto-plasmas as hosts for compression of scattered pulses and fabrication of efficient Raman amplifiers and widely tunable Raman oscillators.