Design and experimental characterisation of a DC-excited CW/repetitively pulsed sealed off CO2 laser

This paper reports the design procedure and experimental study of a sealed off CO₂ laser. Simple algorithms for threshold and steady state excitation voltage calculation, resonator design and its temperature dependent operation are presented. The sealed off CO₂ laser was operated both in CW and pulsed modes and found stable both thermodynamically and optically. Frequency limits for pulsed operation regarding maximum and minimum output energy ranges are determined. Different aspects of CO₂ laser studied include threshold excitation voltages, temperature dependent efficiency, optical power saturation limitations, pulsed and steady state discharge currents for optimum gases mixture combinations. The laser has successfully been constructed, operated and tested for different applications within the limits of its maximum output power of 14 W.     

Dynamical analysis of acousto-optically Q-switched CO2 laser

A compacted size high power CO₂ laser has been developed using an acousto-optically (AO) Q-switch. Performance characteristics have been investigated as a function of output mirror transmittance. The theory of six-temperature model for CO₂ lasers has firstly been utilized to analyze the dynamical process in the AO Q-switched CO₂ laser. This theory perfectly explains the behavior of energy transfer between different molecules in laser gain medium, and describes the shape of pulse laser. The calculated pulse waveforms are in good agreement with the experimental result. Both the experimental and theoretical results present that the optimal value of output mirror transmittance is 39%. Under this condition, the measured peak power is 4750 W and pulsed width is 160 ns, which is consistent with the calculations. Six-temperature model is a perfect theory for CO₂ laser kinetics, which will lay a theoretical foundation for the laser optimum design.     

脉冲CO2激光器的多频动力学模型

建立了适用于各种气压下(20×133—20×10⁵ Pa)的脉冲CO₂激光器的六温度多频动力学模型，该模型考虑了增益谱线重叠效应，序列带、热带的影响，以及非洛伦兹线型效应.对模型进行数值求解可以预言和解释不同气压下的脉冲CO₂激光器的输出特性，有助于评价不同的抽运设计和研究可调谐特性，为设计脉冲CO₂激光系统提供理论支持. 关键词： 2激光器')" href="#">CO₂激光器 激光动力学 六温度模型 增益谱线重叠     

Absorption of pulsed CO2 laser radiation by air and carbon dioxide

An optoacoustical method is used in experimental study of nonlinearity in absorption of pulsed CO₂ laser radiation by air with CO₂ and H₂O added and pure CO₂. The laser pulse consists of frequencies related to several rotational transitions, generated simultaneously. Nonlinearity in absorption was detected for laser radiation levels above 0.2 MW/cm².Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 49–51, October, 1982.     

Optically pumped high-pressure DF-CO2 transfer laser

Pulsed sealed off CO₂ laser operation at 19 atm gas pressure has been demonstrated by pumping DF/CO₂/He mixtures with radiation from a pulsed DF laser. DF acts as an absorber for the pumping radiation, and the CO₂ upper laser level is populated via subsequent energy transfer. CO₂ pulse energy at 19 atm was 0.5 mJ corresponding to a photon conversion efficiency of 4% measured relative to the number of absorbed pumping photons.     

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.     

Dual excimer and CO2 laser etching studies of polyethylene terephthalate

Polyethylene terephthalate (PET) films preheated with a pulsed CO₂ laser have been ablatively etched with an XeCl laser. The observed reduction in ablation threshold, from 170 to 140 mJ cm^–2, is consistent with a thermal mechanism for XeCl laser ablation of PET. Transient changes in the UV absorption coefficient of PET caused by heating with pulsed CO₂ laser radiation have also been studied and a significant increase in absorption observed at 308 nm. Permanent changes in the ultraviolet absorption of PET following exposure to low fluence XeCl laser radiation are also reported.     

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 drives extreme ultraviolet nano-lithography — second life of mature laser technology

It was shown both theoretically and experimentally that nanosecond order laser pulses at 10.6 micron wavelength were superior for driving the Sn plasma extreme ultraviolet (EUV) source for nano-lithography for the reasons of higher conversion efficiency, lower production of debris and higher average power levels obtainable in CO₂ media without serious problems of beam distortions and nonlinear effects occurring in competing solid-state lasers at high intensities. The renewed interest in such pulse format, wavelength, repetition rates in excess of 50 kHz and average power levels in excess of 18 kiloWatt has sparked new opportunities for a matured multi-kiloWatt CO₂ laser technology. The power demand of EUV source could be only satisfied by a Master-Oscillator-Power-Amplifier system configuration, leading to a development of a new type of hybrid pulsed CO₂ laser employing a whole spectrum of CO₂ technology, such as fast flow systems and diffusion-cooled planar waveguide lasers, and relatively recent quantum cascade lasers. In this paper we review briefly the history of relevant pulsed CO₂ laser technology and the requirements for multi-kiloWatt CO₂ laser, intended for the laser-produced plasma EUV source, and present our recent advances, such as novel solid-state seeded master oscillator and efficient multi-pass amplifiers built on planar waveguide CO₂ lasers.     

Investigation of cutting of engineering ceramics with Q-switched pulse CO2 laser

In this paper, the cutting of Si₃N₄ engineering ceramics with Q-switched pulse CO₂ laser is studied. Considering the influence of the cut front shape on the absorption of the laser beam, a simplified 2D mathematic model is developed based on a pulsed laser vaporization cut process. This model is based on the conservation of energy. The experimental results show that it would realize crack-free cutting by using high-speed and multi-pass feed cutting process.     

A simple current pulsed low-pressure CO2 laser with passive Q-switching

We report on a simple and stable pulse tunable CO₂ laser suitable for many investigations in the region around 10m. The pulsed discharge when combined with the passiveQ-switching technique provides pulses of 100 ns duration with a peak power of few kilowatts.Due to the interest in pulsed low-pressure CO₂ lasers as useful irradiation sources, extensive investigations have been carried out. In particular, various Q-switching techniques have been developed to generate short CO₂ laser pulses [1–4].     

Rate equations for an optically-pumped,far infrared laser

Rate equations for an optically-pumped, far infrared laser are developed and solved for the case of a high intensity, pulsed pump beam. Conditions for saturated absorption and for saturated stimulated emission are established. A comparison is made to experimental data for absorption of 9.55 μm, CO₂ laser radiation in CH₃F. Generalized requirements for efficient, high power, FIR laser oscillator-amplifier systems are discussed.     

Laser cleaving on glass sheets with multiple laser beams

A multiple laser system consisting of CO₂ line-shaped and Nd-YAG pulsed lasers was applied to cleave a soda-lime glass substrate in this study. Due to an increase of absorption coefficient of the wavelength of 1.06 μm for Nd-YAG laser on the soda-lime glass at high temperatures, the glass sheets were preheated by the CO₂ line-shaped laser and followed with the pulsed Nd-YAG laser to generate a mixture fracture mode on the substrate. The stress distribution on the glass substrate cleaved by the multiple laser beams has been analyzed. An uncoupled thermal–elastic analysis based on the finite-element method (FEM) was made. The numerical results show that the stress field of the fracture region is caused by a complex stress state and the cleavages are significantly affected by the pulsed laser. A clean cut of the soda-lime glass substrate could be obtained due to a large shear stress state on the cutting direction with the pulsed laser radiated on the glass substrate.     

Interaction of CO2 laser radiation with glasses

An illustration of an interaction of pulsed multimode TEA CO₂ laser radiation, through or without a mask, as well as of a laser scanning process of a frequency Q-modulated cw CO₂ laser beam on glass surfaces has been shown. As an object of investigation glass articles with composition as a standard industrial potassium-boron silicate glass, we have used. A complex of investigations shows that the laser treatment leads to qualitative constant changes (well defined peeling structure) depending on the time surface treatment, defocusing and the pulse length of the laser output.     

Theoretical prediction on the wavelength-temperature shift in pulsed TE CO2 lasers

The wavelength-temperature shift observed in pulsed TE CO₂ lasers is discussed theoretically by means of Six-temperature model rate equations for tunable TE CO₂ lasers. Numerical calculations of the temperature-wavelength shift in a pulsed TE CO₂ laser with a simple plano-concave stable resonator, whether excited by conventional low-inductance fast-discharge scheme or by a long-pulse Pulser/sustainer discharge scheme, show that the laser output wavelengths are within the 10P branch as the ambient temperature varies from 228 to 338 K, but will change as the ambient temperature varies. The laser output wavelengths will move to the transition lines with longer wavelengths in the 10P branch as the ambient temperature increases and vice versa. The calculated results also illustrate that near the ambient temperature of 310 K, the laser is more likely to operate on multi-transition lines. Considering this wavelength-temperature shift, the chilling device adopted in high-power high repetition rate TE CO₂ lasers is important in maintaining a stable laser output spectra as well as a stable laser output power. The numerical results also suggest that a frequency agile resonator is highly recommended if stable laser output spectra are required in TE CO₂ lasers.     

Effect of He and N2 on pulsed operation of CO2 lasers

Addition of He to a CO₂ laser quenched much the saturation effect of the pulsed output to increase its pulse width and its peak power. It was also newly found that the discharge current of a CO₂:N₂ mixture was suppressed to give rise to laser emission only during its suppressed period.     

Study of the compounds formed on damaged ZnSe windows by multi-pulse microsecond pulsed TEA-CO2 laser irradiation in air

We report on experimental data of chemical compounds formed in the damaged area at the surface of certain optical ZnSe windows subjected to multi-pulse microsecond pulsed TEA-CO₂ laser irradiation in air. The results are analysed from the viewpoint of implication of the oxidation process activated under the action of CO₂-laser power in plasma initiation and evolution of surface damage process.     

Rotational relaxation studies in CO2 molecules by means of a multiline tea CO2 laser system

If a CO₂ laser amplifier is injected by a single-frequency oscillator, the efficiency is limited. A multiline pulsed oscillator has been developed to overcome this limitation.     

Laser action in CdS by optical pumping with radiation from a CO2 laser-produced plasma

Radiation from a CO₂ laser-produced plasma has been used to produce laser action in CdS at 5260 Å. This technique compares favorably with optical pumping of CdS by 3371 Å radiation from a pulsed N₂ laser and its potential as a new source for the optical pumping of solids at short wavelengths is strongly indicated.     

New Strong MM FIR Emissions in CH2=CF2 Pumped by a Pulsed CO2 Laser

By pumping with a suitable pulsed CO₂ laser we have produced several strong MM laser lines in 1,1 difluoroethene. All the emissions are easily identified because the emission spectroscopy is simplified in pulsed optical pumping.