Nonlinear interaction of CO2 laser radiation with aluminum and polyethylene targets

The characteristics of A1 and (CH₂)_n plasmas produced by a high-power CO₂ laser are investigated over the flux range 10¹⁰-5 × 10¹¹W/cm² where absorption processes other than simple inverse Bremsstrahlung are active. The threshold dependent behavior of the measured plasma parameters indicates the presence of the parmetric decay instability.     

Gas breakdown with nanosecond CO2 laser radiation

The thresholds for CO₂ laser induced breakdown and their variation with pulse width have been measured at various pressures for Ar, N₂ and an 8/1/1 laser mixture of He/CO₂/N₂ using 3–40 ns duration pulses. These measurements indicate that excited state production plays a dominant role in determining the threshold for nanosecond duration pulses. This has been confirmed by the good agreement obtained between the measured and theoretical thresholds.     

脉冲CO2激光烧蚀锡靶等离子体的数值研究

使用一维辐射流体力学程序MULTI模拟了脉冲CO2激光烧蚀平面锡靶的过程,研究了脉冲宽度、峰值功率密度、靶材初始密度对锡等离子体电子密度、电子温度的时空分布的影响,并结合统计分析得到最有利于产生13.5 nm 极紫外光的激光脉冲宽度。模拟结果表明,脉冲宽度为100~200 ns的长脉冲激光产生的等离子体有利于实现极紫外输出的最佳条件,通过分析等离子体的电子密度、电子温度的分布对这一结论进行了解释。临界电子密度区域有效吸收了脉冲能量,而低密度的羽辉对激光与极紫外辐射的吸收很少。采用长脉冲激光,使得辐射极紫外等离子体持续时间更长,是提高极紫外辐射效率的有效手段。同时模拟还发现,靶材初始密度对等离子体参数的影响不大。     

Frequency stabilization of pulsed CO2 laser using setup-time method

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 CO 2 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.     

N2F4 as saturable absorber of CO2 laser radiation

Tetrafluorohydrazine induces passive Q switching in a continuous-wave CO₂ laser in both the P and R branches of the 10.4 μ system, showing comparable effectiveness on all the accessible lines. At higher pressures, this gas forces the laser to oscillate in the 9.3 μ system in non frequency-selective cavities.     

Inert gas cutting of titanium sheet with pulsed mode CO2 laser

The present work aimed at studying the dynamic behavior of melt ejection in laser cutting of 1 mm thick titanium sheet and to obtain dross-free cuts with minimum heat affected zone (HAZ). CO₂ laser cutting of titanium sheet was carried out with continuous wave (CW) and pulsed mode laser operation with different shear gases namely argon, helium and nitrogen. Laser cutting with high frequency and low-duty cycle pulse mode operation produced dross-free cuts with no noticeable HAZ. Helium, because of its high heat convection and ability to generate high shear stress, produced laser-cuts with narrow HAZ and low dross, as compared to those produced with argon as the shear gas. Microscopic features of laser cut surfaces were analyzed and correlated with dynamic mechanism involved in laser cutting process. Process parameters for laser piercing, required for the initiation of fusion cut within the sheet, were also studied. Laser piercing requires either CW or high-duty cycle (>80%) pulse mode operation.     

Self focussing of CO2 laser radiation in NH3 gas

Self focussing of CO₂ laser radiation in ammonia gas is reported for a number of laser emissions in near coincidence with NH₃ absorption lines. Detailed results for the aR(11) NH₃ transition are in excellent accord with theory accounting for intensity dependent saturation of both absorption and the associated anomalous dispersion responsible for nonlinear refraction n₂, giving a value for n₂ of 2.375 x 10^-11 esu torr^-1.     

Short single-mode CO2 laser pulse generation by pulsed Q-switching

A simple method for the generation of short, single-mode CO₂ laser pulses produced by applying two voltage gates (of amplitude 3U_λ/4 and U_λ/4) to an electro-optic Q-switch placed in a three-mirror cavity is proposed. Single, single-mode, well-synchronizable pulses of 3 ns duration and of 3 mJ energy have been experimentally achieved from a TEA CO₂ laser with an intracavity Pockels cell with 3 ns switching time. Using a numerical simulation it is shown that with shorter switching time (≈1 ns) the method enables one to obtain, from such a laser, a single, megawatt pulse of 1 ns duration.     

Interaction of intense CO2 laser radiation with a dense laser produced carbon plasma

A high density laser produced carbon plasma is heated with the beam from a pulsed CO₂ laser. The evolution of the electron density profiles is studied by interferometry.     

Current CO2 laser surgery

With the development of suitable instrumentation, human-engineered to fulfil the requirements of the clinical surgeon and designed to fit in with the physical conditions prevailing in the operating theatre, laser surgery has advanced rapidly in the past few years. It shows signs of even more rapid progress and general acceptance as its application and advantages in more and more fields of surgery are demonstrated.     

Advanced CO2 laser rangefinders

Factors affecting the design of compact heterodyne- and direct-detection systems are contrasted. Recent UK achievements are placed in context: a TEA laser direct-detection rangefinder and a chirp-pulse-comparison rangefinder-velocimeter are described.     

Absolute frequencies of CO2 laser transitions by multiplication of CO2 laser difference frequencies

Frequencies of CO₂ laser transitions have been compared to the Cs standard by a four-step frequency chain using difference-frequencies from five CO₂ isotope lasers. A tungsten-nickel diode generates the differences and their harmonics. Measurement of the 10.71 μm R(6) transition of ¹³C¹⁸O₂ is described. The absolute frequency was found to be 27 979 469.512(65) MHz. Simultaneously, the four other CO₂ frequencies in the chain were also determined.     

Reflection measurements in CO2 laser solid deuterium target interaction

Using a 60 nsec, 300 MW CO₂ TEA laser reflection measurements from solid deuterium targets have been investigated. Energy, reflected and scattered pulse shape are recorded at various angles: 0°, 45°, 90°, 135°. Reflection, X-ray measurements and ion mean kinetic energy are correlated at the focussing lens position with respect to the target position. The maximum plasma temperature varies from 20 to 35 eV for incident laser fluxes ranging from 5 × 10¹⁰ up to 5 × 10¹¹ W/cm². The cut-off density inside the deuterium ice has been observed and located. In each case reflection has been found to be weak less than 5% for each direction. For the maximum fluxes X-ray energies greater than 0.5 keV have been observed.     

Sulfur isotope enrichment in SF6 by high intensity CO2 laser radiation

Enrichment of ³⁴SF₆ following irradiation of SF₆?H₂ mixtures by the focused output of a pulsed TEA CO₂ laser has been studied as a function of the number of laser pulses, excitation wavelength, total pressure, and laser energy.     

CO2 laser cutting of slate

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate.Following the previous work focused on the drilling and cutting of slate tiles using a Nd : YAG laser, we present in this paper the results of the work carried out to explore the possibilities to cut slate plates by using a CO₂ laser. A 1.5 kW CO₂ laser was used to perform different experiments in which, the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO₂ laser is a feasible tool for a successful cutting of slate.     

Coupling coefficient for cw CO2 laser radiation on stainless steel

Coupling coefficients for 10.6μm laser radiation on stainless steel have been measured experimentally under oxidizing and vacuum conditions. A theoretical model has been developed that relates the growth of an oxide layer to changes in coupling coefficients.     

Dissociation of NH3 to electronic ground-state fragments by high-intensity CO2 laser radiation

The dissociation of NH₃ into electronic ground-state fragments NH₂(²B₁) + H by high-intensity CO₂ laser radiation has been observed under essentially collision free conditions and as a function of NH₃ pressure, using laser fluorescence excitation for the NH₂ detection. Luminescence from excited NH₂ (²A₁) produced directly by the CO₂ laser has also been observed. The relative yield of NH₂ (²A₁) is estimated to be smaller than that of NH₂ (²B₁) by several orders of magnitude.     

Collisionless dissociation and isotopic enrichment of SF6 using high-powered CO2 laser radiation

Dissociation of ³²SF₆ and the resultant isotopic enrichment of ³⁴SF₆ using high-powered CO₂ laser radiation has been studied with higher experimental sensitivity than previously reported. Enrichment factors have been measured as a function of laser pulse number, wavelength, energy and time duration. A geometry-independent dissociation cross section is introduced and measured values are presented. Threshold energy densities, below which no dissociation was observed, were also determined.     

Temperature distribution along oversized hollow-core waveguides for CO2 laser radiation

Temperature distributions along various hollow waveguides are fully analysed experimentally when the waveguides are excited by CO₂ laser light. It is shown that the temperature decreases in an oscillatory manner along the waveguides due to the interference effect of guided modes. The distributors are well explained by a theory developed previously.