In order to research the influence on the beam transmission properties due to the different time intervals in the high-power pulsed transversely excited atmospheric CO2 laser with unstable resonator, the finite element analysis of thermodynamics instantaneous method are adopted to analyze the mirror thermal deformation irradiated by the high-power laser beam. The mirror thermal deformation is fitted by Zernike polynomials. Then the angular spectrum propagation theory of diffraction is used to calculate the far-field transmission properties. The simulation results show that with the decrease in the time interval between each pulse, the mirror temperature and thermal deformation gradually increase, and peak power and the average energy density decrease, and beam broadens. With the 500 Hz repetition rate relative to the 10 Hz repetition, the peak intensity decreases almost 40%; the optical spot broadens about 60%. When the repetition rate is larger than 100 Hz, the surface of mirror will have obvious deformation, which will cause apparent degradation in the optical beam quality for the far-field transmission.

We present the birefringence measurements induced in K9 specimen by cracks produced by 1 064-nm Nd:YAG laser. The birefringence data are converted into units of stress, permitting the estimation of residual stress near cracks. The laser parameters and characterization of the optical material influence the value of residual stress. Residual stress in optical materials can affect fracture; thus, this factor should be considered in any formulation that involves enhanced damage resistance of optical components used in laser-induced damage experiments. The probability of the initial damage and the direction of the energy dissipation in cracks determine the residual stress distribution. Moreover, thermal-stress coupling enlarges the asymmetry of residual stress distribution. Therefore, the physical mechanism of asymmetric damage is useful for understanding the nature of optical materials under high-power laser irradiation.

We propose a continuous-wave (CW) middle infrared (MIR) and long infrared (LIR) dual-band laser for the calibration and effect research of infrared detecting and imaging systems. A total output power of 18 W is achieved by the proposed dual-band laser through one DF gain medium module and one parallel placed CO2 gain medium module using a common stable resonator and output mirror with nominal transmissivities of ~5% in the MIR band and ~10% in the LIR band. Spectra of dual-band laser are acquired. The power extracting efficiency of this dual-band laser can be significantly improved, as validated by a single-band test of optimized parameters.

A new method for laser-frequency stabilization by controlling the pulse setup time is presented. The frequency-stabilization system monitors the pulse setup time continuously, and controls it by adjusting the cavity length. Laser frequency is stabilized to the center of the gain curve when the setup time is the shortest. The system is used to stabilize a radio-frequency-excited waveguide CO2 laser tuned by grating, and the shift of laser frequency is estimated to be less than §25 MHz for an extended period. The system has the advantages of compact structure, small volume, and low cost. It can be applied for frequency stabilization of other kinds of pulsed lasers with adjustable cavity.

The lifetime of optical components in high-fluence ultraviolet (UV) laser applications is typically limited by laser-initiated damage and its subsequent growth. Using 10.6-μm CO2 laser pulses, we successfully mitigate 355-nm laser induced damage sites on fused silica surface with dimensions less than 200 \mu m. The damage threshold increases and the damage growth mitigates. However, the growth coefficients of new damage on the CO2 laser processed area are higher than those of the original sample. The damage grows with crack propagation for residual stress after CO2 laser irradiation. Furthermore, post-heating is beneficial to the release of residual stress and slows down the damage growth.

To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.

Air-breathing mode laser propulsion experiment with a long-pulse transversely excited (TE) CO₂ laser is carried out, and its ignition problem is solved with the ignition needle of lightcraft. Owing to the ignition needle, an order of magnitude reduction in the ignition threshold is demonstrated. The result is compared with previous study. The momentum coupling coefficient is also measured in the experiment and its dependence upon laser pulse energy (6-14 J) and pulse width (20, 32, and 40 \mu s) is discussed.

The influence of scanning speed on hard bone tissue ablation is studied with a 10.6-\mum laser. The groove morphology and the thermal damage created in bovine shank bone by pulsed CO2 laser are examined as a function of incident fluence by optical microscope following standard histological processing. The results show that ablation groove width, depth and ablation volume, as well as the zone of thermal injury, increase gradually with incident fluence. As compared to the result for high scanning speed, the lower scanning speed always produces larger ablation volume but thicker zone of thermal injury. It is evident that scanning speed plays an important role in the ablation process. In clinical applications, it is important to select appropriate scanning speed to obtain both high ablation rates and minimal thermal injury.

The feasibility of measuring crater geometries by use of optical coherence tomography (OCT) is examined. Bovine shank bone on a motorized translation stage with a motion velocity of 3 mm/s is ablated with a pulsed CO2 laser in vitro. The laser pulse repetition rate is 60 Hz and the spot size on the tissue surface is 0.5 mm. Crater geometries are evaluated immediately by both OCT and histology methods after laser irradiation. The results reveal that OCT is capable of measuring crater geometries rapidly and noninvasively as compared to histology. There are good correlation and agreement between crater depth estimates obtained by two techniques, whereas there exists distinct difference between crater width estimates when the carbonization at the sides of craters is not removed.