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.     

Pulse stretching with CO in a tea CO2 laser

By the addition of CO in conjunction with a high Q cavity, a TEA CO₂ laser has been operated to give pulses with durations up to 150 μs. Preliminary investigations of the dependence of delay to initiation, pulse energy and duration, on gas mixture, charging voltage and output mirror reflectivity are described.     

An injection-locked single-mode tea CO2 laser for SMM laser pumping

A D₂O laser has been developed for collective Thomson scattering measurements of ion temperature in high temperature plasmas. A pulse duration and a spectral width of a high power D₂O laser has been successfully controlled for this purpose, by using a TEA CO₂ laser injection-locked by an etalon-tuned TEA CO₂ laser as a pump source.     

Reflectivity measurements of a CO2 laser produced plasma

Reflectivity measurements on a CO₂ laser produced plasma are presented and results are compared with the conflicting results of other recent papers. The results presented here show strong anomalous absorption above an irradiance level of ～4 × 10¹⁰W cm^-2 which is a factor of two lower than is predicted from the theory of the parametric instability.     

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。     

Stimulated brillouin scattering from CO2 laser produced plasma

Preliminary observations of stimulated backscatter from CO₂ laser produced plasma are reported. The scattered radiation has been spectrally resolved and the measured shift found to be consistent with that expected from ion acoustic waves. The change in wavelength shift when helium is substituted for hydrogen is in agreement with √m_i, where m_i = ion mass.     

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.     

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.     

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.     

Reflectivity measurements from a nanosecond CO2 laser produced plasma

The back-scattered light from a laser produced plasma has been studied using a nanosecond gigawatt CO₂ laser. The spectral shift and width of the reflected light have been determined as a function of the incident laser energy.     

CO2 laser induced compton effect in underdense hydrogen plasma

Recent experimental observation of induced scattering of CO₂ laser radiation by an underdense hydrogen plasma can be explained theoretically by non-linear and Compton scattering from ions in the highly cooperative plasma conditions prevailing (kλ_D? 1).     

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.     

Model of a microwave beam coupling to CO2 laser plasma

We have designed a transmission line model of the microwave coupling mechanism for a microwave pumped CO₂ laser. The model is a total loss ridge waveguide transmission line having nonuniform impedance. The laser plasma is modeled as a frequency-dependent lossy dielectric and acts as a distributed resistance in the length of the microwave cavity. The coupling structure of the microwaves is designed not to be resonant at the microwave source frequency of 2.45 GHz at 1 kW and propagating the total microwave field energy to be absorbed without internal reflection. An exact solution to this general transmission line propagation constant for a shunt resistance along length of the guide is found. The measurements and predictions of the parameters of the plasma conductivity as a function of the attenuation constant agree closely.     

Temporal shaping of CO2 laser pulses by controlled plasma switching

Coumarin derivatives, 6, 30, and 102, were excited in a simple dye laser by the output at 427.8 nm from a nitrogen ion laser pumped by charge transfer from He⁺₂. Tuning ranges and stabilities of the dyes are reported.     

Time-resolved photography of X-ray emission from CO2 laser generated plasma

The construction and use of an X-ray pinhole camera with a nanosecond shutter is described. Photographs of X-ray emission from plasma generated by a CO₂ laser (at incident intensities of ? 10¹³ W cm^?2) were recorded with time and space resolution of 6 ns and ～ 20 μm respectively, and the structure of localised X-ray emission regions was measured. These observations are related to contemporary theories of non-linear laser-plasma interactions.     

Studies on CO2 laser marking

The nature of CO₂ laser marking was studied with a view to putting these lasers to practical use in the semiconductor industry. The marking is found to be due to surface spattering rather than burning, which is the main factor in YAG laser marking. The visibility greatly increases by the application of a surface treatment such as marker ink, varnish or poster color. The CO₂ laser may therefore be used in place of the YAG laser, now widely used for marking, with some merits: CO₂ laser marking is cheaper and faster, and in addition there is no danger of injury from irradiating laser light.     

Pulsed inductive discharge CO2 laser

A pulsed inductive discharge CO₂ laser with a wavelength of 10.6 μm has been created for the first time. The excitation system of a cylindrical pulsed inductive discharge (pulsed inductively coupled plasma) in the gas mixture of CO₂:N₂:He was developed. The temporal and energy parameters of the laser radiation were investigated. The maximum inductive discharge CO₂ laser radiation energy of 104 mJ was achieved. An average power of 3.2 W was obtained at laser generation energy of 65 mJ and pulse repetition rate of 50 Hz. In the cross-section, the laser radiation had the ring shape with an external diameter of 34 mm and thickness of 4-5 mm. The measured divergence of laser radiation was 12 mrad.     

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.