Impedance matching in RF excited fast axial flow CO2 laser: The role of the capacitance due to laser head

Impedance matching in an indigenously developed 2 kW RF-excited fast axial flow (RF-FAF) CO₂ laser was seen to be significantly influenced by the capacitance formed between the laser head and the electrodes. We find in the published literature that this capacitance is generally assumed to be negligible while designing the matching network in the RF-FAF CO₂ lasers. It is shown that this capacitance could have a significant value and consequently would modify the design of the matching network remarkably for a specific laser design studied in the present case. The widely used discharge load model for capacitively coupled RF (CCRF) discharge excited CO₂ laser plasma is extended to include this capacitance. The method of measurement of this capacitance using a bridge and the ANSYS software based simulation of its formation due to the laser head structure are discussed.     

Operational characteristics and power scaling of a transverse flow transversely excited CW CO<Subscript>2</Subscript> laser

Transverse flow transversely excited (TFTE) CO₂ lasers are easily scalable to multikilowatt level. The laser power can be scaled up by increasing the volumetric gas flow and discharge volume. It was observed in a TFTE CW CO₂ laser having single row of pins as an anode and tubular cathode that the laser power was not increasing when the discharge volume and the gas volumetric flow were increased by increasing the electrode separation keeping the gas flow velocity constant. The discharge voltage too remained almost constant with the change of electrode separation at the same gas flow velocity. This necessitated revision of the scaling laws for designing this type of high power CO₂ laser. Experimental results of laser performance for different electrode separations are discussed and the modifications in the scaling laws are presented.     

Design considerations and scaling laws for high power convective cooled CW CO2 lasers

Various criteria for designing high power convective cooled CO₂ lasers have been discussed. Considering the saturation intensity, optical damage threshold of the optical resonator components and the small-signal gain, the scaling laws for designing high power CW CO₂ lasers have been established. In transverse flow CO₂ lasers having discharge of square cross-section, the discharge lengthL and its widthW for a specific laser powerP (Watt) and gas flow velocityV (cm/s) can be given byL = 1.4 x 10⁴ p ^1/2 V ^-1 cms andW = 0.04P ^1/2 cms. The optimum transmitivity of the output coupler is found to be almost constant (about 60%), independent of the small signal gain and laser power. In fast axial flow CO₂ lasers the gas flow should be divided into several discharge tubes to maintain the flow velocity within sonic limit. The discharge length in this type of laser does not depend explicitly on the laser power, instead it depends on the input power density in the discharge and the gas flow velocity. Various considerations for ensuring better laser beam quality are also discussed.     

Optical fiber cleaved at an angle by CO2 laser ablation: Application to micromachining

Laser ablation can be achieved by delivering short power pulse with durations much smaller than the heat diffusion time. In this investigation, we are collimating and magnifying a beam from a CO₂ laser with a Keplerian telescopic system. Then we study the quality of the cut performed by scanning the beam at a fast speed over an optical fiber just after focusing a well collimated CO₂ beam at λ=10.6 μm. It is found that the best results for cutting optical fibers depend upon both the time required in raising matter temperature to the vaporization point and the scanning speed of the CO₂ laser beam. Some aspects of the laser beam collimation before focusing is reviewed briefly and results for optical fibers being cleaved at low and fast speed under various conditions are also shown and discussed.     

Novel considerations of functions of helium and nitrogen in a fast flow CO2 laser

In a research of fast axial flow CO₂ laser sustained by 150 kHz silent discharge, we found the optimized gas mixing ratio was CO₂:N₂:He=1:22:5 or the content of helium was only about 18%. This result upset the situation of common CO₂ lasers in which the most important laser gas is helium. An explanation of our particular results and supporting experimental evidence are given.     

Novel colliding plasma pulse clipper and optical isolator for high power infra-red lasers

The properties of a high density plasma focus produced inside a ring target with an Nd laser have been investigated. Studies of the axial propagation of a CO₂ laser beam through the plasma focus have shown that the device can be used either as a fast pulse clipper or as an optical isolator for high power infra-red lasers. Self-focussing, strong refraction and defocussing and non-classical absorption of the CO₂ laser beam have all been observed.     

Numerical modeling of a fast-axial-flow CW–CO2 laser

A four-temperature model has been applied on a fast axial flow, longitudinal discharge CO₂ laser. Using Runge–Kutta method, a set of differential equations of the model is numericaly solved. These equations describe the operation of the laser with certain ratio 1:3:6 of the mixture CO₂:N₂: He and average output power of 550 W.The temporal behaviour of the output power and photon density was obtained. The effects of kinetic temperature, coupled mirror reflectivity, gas flow speed, and cavity loss on the output power were studied.Calculated output power was compared with its measured value taken from experiment and a good agreement was observed.     

Accuracy in determination of the temperature and partial pressure of CO<Subscript>2</Subscript> in CO<Subscript>2</Subscript>:N<Subscript>2</Subscript>:H<Subscript>2</Subscript>O:NO<Subscript>2</Subscript> mixtures by multiple-frequency laser probing

We present the results of analysis of the errors introduced by hot-band transitions 11¹0-01¹1, 03¹0-01¹1, 12⁰0-12⁰1 of the CO₂ molecule and the absorption lines of the H₂O and NO₂ molecules in determination of the temperature and partial pressure of CO₂, included in the gas mixture CO₂: N₂:H₂O: NO₂ at atmospheric pressure, by multiple-frequency laser probing using a CO₂ laser tunable over the lines of the 00⁰1-[10⁰0,02⁰0]_I,II ground-state laser transitions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 810–815, November–December, 2007.     

The stability of the active medium of RF-exited CO2 lasers with gold as catalyst

Using mass-spectrometric investigations the gas composition of the active medium of sealed-off cw RF-excited CO₂ waveguide lasers have been studied. It has been found that a low degree of CO₂ dissociation and a laser power improvement can be achieved by means of a gold catalyst in the laser discharge volume. The conditions for long operational lifetimes of these lasers are described. Received: 21 December 1999 / Revised version: 1 May 2000 / Published online: 6 September 2000     

Determination of an optimal five-gas combination in a sealed-off CO<Subscript>2</Subscript> laser

For obtaining the maximal output power, five lasing gas mixtures (CO₂, N₂, He, Xe and H₂) in a sealed-off CO₂ laser are optimized by applying a genetic algorithm and solving CO₂ laser kinetics equations. A comparison of numerical simulations shows that the optimal pressures of CO₂ and N₂ are 1.15 Torr and 7.32 Torr, respectively. Accordingly, the maximum laser power of 124 W is obtained by utilizing the optimal gas combination and an optimized resonator with a length of 1.2 m. Received: 14 August 2002 / Published online: 22 January 2003 The project supported by Zhejiang Provincial Natural Science Foundation of China (No. 602098). RID="*" ID="*"Corresponding author. Fax: +86-571/8832-0369, E-mail: chengch@mail.hz.zj.cn     

射频激励相移阵列谐振腔波导CO2激光器输出特性研究

为保持器件结构紧凑型的同时获得稳定的高功率、高光束质量激光输出,将相移光学阵列谐振腔技术用于射频激励扩散型冷却板条波导CO₂激光器．实验发现,该设计方案虽然波导结构为矩形宽波导,但是由于采用了具有相移阵列结构的全反射镜,获得的激光束输出空间分布具有阵列输出光束的基本特征．在波导截面为1mm×20mm、增益介质长度为20cm的波导结构条件下,获得了46W的激光功率输出和11.3%的电光转换效率．激光束输出的远场空间分布呈空间压缩的极锐单峰．由于该结构具有的选模特性,远场为单峰空间分布特 关键词：     

A Chemosorption Vacuum Pump for a Chemical Oxygen Iodine Laser with CO<Subscript>2</Subscript> Buffer Gases

We present the design and investigation of a novel chemosorption vacuum pump (CSVP) for discharging the exhaust gases of a chemical oxygen-iodine laser system diluted with carbon dioxide (CO₂-COIL). The CSVP comprises two fixed-bed reactors separately filled with CO₂/H₂O and O₂/I₂/Cl₂ adsorbents, which can efficiently chemically absorb the CO₂-COIL exhaust gases at room or higher temperature. We consider the effects of the adsorbents in different specifications and fixed beds of various constructions on the adsorption performance of the CSVP. We develop and study the sealed CO₂-COIL system with the CSVP. We achieve a stable operation with a cumulative duration time of 40 s for four runs and an average output power up to 2.0 kW at a Cl₂ flow rate of ～158 mmol/s and a CO₂ flow rate of 132 mmol/s. The experimental results indicate that the COIL system with the CSVP performs similarly to a conventional COIL with a vacuum tank. Taking into account that the CSVP is free of vibration and noise, avoids air pollution, is easily operated, and has a short preparation time, we believe that the chemosorption vacuum pump is an excellent alternative pump system for a transportable COIL system.     

Properties of powders produced by evaporating CeO<Subscript>2</Subscript>/Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> targets exposed to pulsed-periodic radiation of a CO<Subscript>2</Subscript> laser

The characteristics (phase composition, grain shape, grain size distribution, and specific surface area) of Ce_0.78Gd_0.22O_2-δ nanopowders produced by exposing the target to pulsed CO₂ laser radiation are reported. Reasons for a threefold increase in the output of the experimental powder-preparation unit (up to 60 g/h) with the characteristic grain size (≈10 nm) remaining unchanged are discussed.     

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.     

On the repetitive operation of a self-switched transversely excited atmosphere CO<Subscript>2</Subscript> laser

The repetition rate capability of self-switched transversely excited atmosphere (TEA) CO₂ laser was studied for different gas flow configurations. For an optimized gas flow configuration, repetitive operation was achieved at a much smaller gas replenishment factor between two successive pulses when compared with repetitive systems energized by conventional pulsers.     

Diode-pumped Nd<Superscript>3+</Superscript>:YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> laser at 1338 nm

A high-power diode -pumped Nd³⁺:YAl₃(BO₃)₄ (Nd:YAB) laser emitting at 1338 nm is described. At the incident pump power of 9.8 W, as high as 734 mW of continuous-wave (CW) output power at 1338 nm is achieved. The slope efficiency with respect to the incident pump power was 9.0%. To the best of our knowledge, this is the first demonstration of such a laser system. The output power stability over 60 min is better than 2.6%. The laser beam quality M ² factor is 1.21.     

Wide-aperture superatmospheric-pressure CO<Subscript>2</Subscript> laser amplifier pumped by a self-sustained volume discharge

Initiation of a self-sustained volume discharge in CO₂-containing gaseous mixtures kept under a pressure of up to 10 atm with the aim of amplifying picosecond IR pulses is considered. Experimental electricdischarge and optical characteristics of a wide-aperture high-pressure CO₂ amplifier are presented. The feasibility of designing terawatt laser equipment with a master oscillator and preamplifier is discussed.     

Sub-wavelength micromachining of silica glass by irradiation of CO<Subscript>2</Subscript> laser with Fresnel diffraction

We investigated a simple and productive micromachining method of silica glass by ablation using a TEA CO₂ laser (10.6 μm) with a spatial resolution down to sub-wavelength scale. The silica glass was irradiated by the TEA CO₂ laser light through a copper grid mask with square apertures of 20×20 μm² attached to the silica glass surface. After the irradiation, circular holes with a diameter of several μm were formed on the silica glass surface at the centers of the apertures due to the Fresnel diffraction effect. The minimum diameter of the holes was 3.4 μm. The characteristics of the micromachining are discussed based on the electric field distributions of the CO₂ laser light under the mask using a three-dimensional full-wave electromagnetic field simulation.     

CH<Subscript>3</Subscript>OH optically pumped by a <Superscript>13</Superscript>CO<Subscript>2</Subscript> laser: new laser lines and assignments

We report 12 new THz (far-infrared) laser lines from methanol (CH₃OH), ranging from 58.1 μm (5.2 THz) to 624.6 μm (0.5 THz). A ¹³CO₂ laser of wide tunability (110 MHz) has been used for optical pumping, allowing access to previously unexplored spectral regions. Optoacoustic absorption spectra were used as a guide to search for new THz laser lines, which have been characterized in wavelength, polarization, offset, relative intensity, and optimum operation pressure. For 20 laser lines previously observed, we have measured the absorption offset with respect to the ¹³CO₂ laser line center. PACS 33.20.Ea; 33.20.Vq; 33.80.-b     

Efficient continuouswave laser at 560 nm by intracavity frequency summation of fundamental and first-stokes wavelengths in a Nd:YVO<Subscript>4</Subscript>-BaWO<Subscript>4</Subscript> Raman laser

We report for the first time an efficient CW laser emission at 560 nm by sum-frequency mixing of the fundamental and first-Stokes fields generated within an Nd:YVO₄-BaWO₄ Raman laser. Intracavity sumfrequency mixing with LiB₃O₅ (LBO) nonlinear crystal yielded 1.12 W of visible yellow-green emission; the output power stability over 4 h is better than 3.3%. The laser beam quality M ² factors are 1.84 and 2.43 in both horizontal and vertical dimensions respectively.