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Graphite is applied to structural material of the high temperature reactor and nozzle of high energy rocket engine. The excessive vibration and stress field can be occurred for this material due to the severe thermal condition. In this study, the thermal stress and vibration characteristics of ATJ graphite under high temperature condition are investigated by finite element analysis (FEA). The specimen is designed as a disk shape in order to simulate the rocket nozzle combustion condition. The experiment of thermal heat is also conducted using by CO₂ laser.

A novel photothermoelectric resistance effect of the Ti/SiO₂/Si films induced by 10.6 $\mu$m CO₂ laser is discovered and investigated. The transient response of the resistance is observed and analyzed in this work. Under the continuous irradiation of the laser, the thermal resistance value changes with the irradiating time and gradually reaches a stable saturation. The results indicate that the rise time of thermal resistance is shortened and its change rate increased as laser power gets higher. The inner battery of the ohmmeter exerts the positive or negative bias voltage, causing the diffusion motion direction of the hot electrons to be opposite or the same direction with the drift motion, which can increase or decrease the thermal resistance value. Those experimental phenomena are explained by the drift and diffusion motion of the electrons. Based on the results, the Ti/SiO₂/Si structure is an attractive candidate for thermal effect devices.

The conditions for the existence of heteroclinic connections between the transverse modes of a CO₂ laser whose setup has a perfect cylindrical symmetry are discussed by symmetry arguments for the cases of three, four and five interacting modes. Explicit conditions for the parameters are derived, which can guide observation of such phenomena.

Silicon has been widely used to fabricate microfluidic devices due to the dominance of silicon microfabrication technologies available. In this paper, theoretical analyses are carried out to suggest suitable laser machining parameters to achieve required channel geometries. Based on the analyses, a low-power CO₂ laser was employed to create microchannels in Acrylic substrate for the use of manufacturing an optical bubble switch. The developed equations are found useful for selecting appropriate machining parameters. The ability to use a low-cost CO₂ laser to fabricate microchannels provides an alternative and cost-effective method for prototyping fluid flow channels, chambers and cavities in microfluidic lab chips.

In this work, the influence of laser pulse trains on thin mild steel sheet blades is investigated. The method is based on varying the duty cycle (DC) of a pulsed RF slab CO₂ laser during the process of laser percussion drilling. Here, an experimental methodology to correlate laser parameters and their effects on the characteristics of the melting material ejected was carried out. In the experiments, the interaction time such that of 5%, 10%, and 15% DC were considered for the pulse trains. Results showed a significant effect on the characteristics of melt material ejection during laser percussion. We demonstrate that it was not evident the influence and molten material for pulse width of less than 500 μs and larger than 4500 μs, respectively, when having 5% DC; spatter formation (droplets) for 10% and 15% DC with pulse periods > 2000 μs; debris formation (re-solidified material) at pulse periods from 200 to 1250 μs at 15% DC.

A novel method named soak sacrificial layer ultrasonic method (SSLUM) has been presented for optimizing the surface roughness of the microchannels of polymethyl methacrylate (PMMA)-based microfluidic chips. CO₂ laser was used for ablative microchannels on the PMMA sheet, and the effects of key parameters including laser power, laser ablation speed and solution concentration on the surface roughness of microchannels were estimated and optimized by SSLUM. The experimental observation demonstrates that the surface roughness results mainly from the residues on the channel wall, which are produced by the bubbles movement and bursting. The research results show that the surface roughness can be improved effectively by using SSLUM. In our experiment, the best value was Ra $=$ 110nm with laser power 12W, laser ablation speed 10mm/s, the solution concentration 75%, and the time of ultrasonic vibration 25min. SSLUM is proven to be an effective, simple and rapid method for optimizing the surface roughness of microchannels of microfluidic chips.

The paper demonstrates four different polymer substrate microchannels are fabricated by CO₂ laser machine. The four different polymer substrates are Polymethyl-methacrylate (PMMA), Polycarbonate (PC), Polystyrene (PS) and Polyethylene Terephthalate (PET), respectively. A number of microchannels are obtained and all roughness is measured. The four different polymer substrate microchannels are processed with different processing parameters. Laser power is set from 4W to 32W and laser cutting speed is set from 5mm/s to 30mm/s. The results show the roughness of PS substrate microchannel is lower than that of other three polymer substrate microchannels at the same parameters. When laser power is below 4W, the roughness of four polymer substrates are similar. The roughness of different polymer substrate microchannels decreases with the increase of laser power. The roughness of different polymer substrate microchannels also happens to change with increase of laser cutting speed.

In this work, second harmonic generation has been investigated for radiation in IR-range of spectrum at the constant-intensity approximation. The detailed analysis of nonlinear interaction of optical waves have been studied in CGA, ZAP and AgGa_0.6In_0.4Se₂ crystals and the comparison of the obtained results have been made on conversion efficiency with experimentally calculated values. The conditions for realization have been determined for the regime close to the uncritical angular phase matching. The recommendations are suggested on elaboration of the reliability of highly efficient generators for second harmonic in the IR-range, specially the generators of second harmonic of the CO₂ lasers.

To compare the efficacy and safety of CO₂ laser plus 5-aminolevulinic acid (ALA) photodynamic therapy (PDT) with CO₂ laser for the treatment of multiple condyloma acuminatum (CA), 120 patients with multiple CA were allocated into two groups — combined group (CO₂ laser plus ALA-PDT, n = 60) and CO₂ laser group (CO₂ laser plus placebo-PDT, n = 60). After CO₂ laser, a 20% ALA or a placebo solution was applied to the CA area 3 h before illumination with red light (635 nm, 100 mW/cm², 80 J/cm²). The treatment was repeated seven days after the first treatment if the lesions were not completely resolved. The complete response rate, recurrence rate and adverse effects in the two groups were analyzed. After two treatments, the complete response rates in the CO₂ laser group and combined group were 100% (509/509) and 100% (507/507) in the CA (p > 0.05), respectively. The recurrence rates in the CO₂ laser group and combined group were 44.9% (229/509) and 10.6% (54/507) in the CA (p < 0.05), respectively. The adverse effects in CO₂ laser group was more than that in combined group. The combined group is a more effective treatment for multiple CA compared with CO₂ laser group. T/S. Style the highlighted text as abstract.

Molecules such as water, proteins and lipids that are contained in biological tissue absorb mid-infrared (MIR) light, which allows such light to be used in laser surgical treatment. Esters, amides and water exhibit strong absorption bands in the 5–7 μm wavelength range, but at present there are no lasers in clinical use that can emit in this range. Therefore, the present study focused on the quantum cascade laser (QCL), which is a new type of semiconductor laser that can emit at MIR wavelengths and has recently achieved high output power. A high-power QCL with a peak wavelength of 5.7 μm was evaluated for use as a laser scalpel for ablating biological soft tissue. The interaction of the laser beam with chicken breast tissue was compared to a conventional CO₂ laser, based on surface and cross-sectional images. The QCL was found to have sufficient power to ablate soft tissue, and its coagulation, carbonization and ablation effects were similar to those for the CO₂ laser. The QCL also induced comparable photothermal effects because it acted as a pseudo-continuous wave laser due to its low peak power. A QCL can therefore be used as an effective laser scalpel, and also offers the possibility of less invasive treatment by targeting specific absorption bands in the MIR region.

A quantitative analysis method of CO₂ laser treatments promotes laser treatment performance and rapid clinical application of novel treatment devices. The in silico clinical trial approach, which is based on computational simulation of light-tissue interactions using the mathematical model, can provide quantitative data. Although several simulation methods of laser tissue vaporization with CO₂ laser treatments have been proposed, validations of the CO₂ laser wavelength have been insufficient. In this study, we demonstrated a tissue vaporization simulation using a CO₂ laser and performed the experimental validation using a hydrogel phantom with constant physical parameters to evaluate the simulation accuracy of the vaporization process. The laser tissue vaporization simulation consists of the calculation of light transport, photothermal conversion, thermal diffusion, and phase change in the tissue. The vaporization width, depth, and area with CO₂ laser irradiation to a tissue model were simulated. The simulated results differed from the actual vaporization width and depth by approximately 20% and 30%, respectively, because of the solubilization of the hydrogel phantom. Alternatively, the simulation vaporization area for all light irradiation parameters, which is related to the vaporization amount, agreed well with the actual vaporization values. These results suggest that the computational simulation can be used to evaluate the amount of tissue vaporization in the safety and effectiveness analysis of CO₂ laser treatments.