Theoretical investigation of the kinetics and of the energy characteristics of electron-beam-controlled discharge lasers

Mathematical simulation of the physical processes in an active medium is used to carry out detailed theoretical investigations of the kinetics and of the lasing characteristics of electron-beam-controlled (EB) discharge lasers operating on vibrational-rotational transitions of the molecules C0₂, CO, H₂, and HD. The power, energy, efficiency, and lasing spectrum are obtained as functions of the composition of the active medium and of the pumping conditions (the value of E/N, the power and duration, the spatial homogeneity). The influence of the isotopic composition of the carbon monoxide on the lasing characteristics of a CO laser is studied. The restrictions connected with the breakdown of the active medium by its own radiation are investigated for CO₂, H₂, and HD molecules.This article is a report of the results of theoretical investigations of electron-beam-controlled discharge lasers performed at the Quantum Radiophyiscs Laboratory of the Lebedev Institute in 1973–1977.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva Akademii Nauk SSSR, Vol. 116, pp. 7–53, 1980.     

Numerical investigation of a fast-axial-flow CW CO2 laser

This paper presents the results of the calculation of the parameters of the active medium of a fast-axial-flow CO₂ laser using numerical methods in the framework of a one-dimensional approximation of the set of continuity equations, Bernoulli equation, equation of gas state, energy equation and multi-temperature rate equations with regard to diffusion for the gas flow in the cylindrical discharge tube. The spatial distribution of the small-signal gain and gas temperature along the gas flow direction have been calculated for a given set of initial conditions, namely, gas flow velocity, gas pressure and the tube diameter. In addition, the dependence of small-signal gain, the asymmetric stretch vibrational temperature of CO₂ (T₃) and the gas temperature on the discharge current were studied.     

Effect of the active medium temperature on the operation of fast-flow CO2 lasers

A new formula is obtained for estimating the output power of fast-flow CO₂ lasers. It is shown that a higher specific output power of these CO₂ lasers in comparison with sealed-off CO₂ lasers is caused mainly by the higher saturation intensity of the former. It is concluded that the temperature of the laser active medium affects almost only the charge stability and that, under stable discharge conditions, the same output power can be obtained at different temperatures of the active medium.     

Saturation of the net electron excitation of the CO2(00°1) laser level as a function of discharge input energy

Measurements are made of the small signal gain in He:CO₂ and He:N₂:CO₂ gas mixtures as a function of pulsed discharge energy. In all case it is found that the gain saturates as the discharge energy is increased. Thermal effects cannot account for this gain saturation which appears to be a fundamental property of high-pressure CO₂ discharges.     

Detailed vibrational population distributions in a CO2 laser discharge as measured with a tunable diode laser

A tunable diode laser (TDL) operating in the 2150–2350 cm^–1 wavenumber region is used to probe a conventional cw CO₂ laser discharge. Absorption lines in more than 25 different vibrational bands are observed, enabling us to determine absolute vibrational populations inall levels of concern to the dynamics of the 10 m CO₂ laser. Levels in thev ₃ mode of CO₂ as high as 00°9 are monitored, and it is found that anharmonic effects play a significant role in the populations of such levels. Thev ₁ andv ₂ mode populations are also investigated in detail, and it is found that these modes are strongly coupled and maintain a common vibrational temperature under all discharge conditions. The use of a TDL is shown to be a powerful technique for investigating the dynamics of infrared molecular lasers.This work was supported in part by the National Science and Engineering Research Council, Canada     

Assignments of optically pumped CD3OH laser lines

Six FIR laser lines from CD₃OH pumped by the 10R(36) and the 10R(18) CO₂ laser lines are assigned to specific rotational energy levels in the excited C–0 stretch state. It is found that their upper laser levels are shifted by a Fermi resonance between the C–0 stretch vibration and the third and forth harmonics of the torsional mode. The Fermi resonance shifts are +0.332 cm^–1 and +2.251 cm^–1 for the upper laser levels pumped by the 10R(36) and the 10R(18) CO₂ laser lines, respectively. Calculated frequencies of the pump and the laser transitions agree with those of the pump CO₂ laser lines and the observed FIR laser lines within estimated accuracy.     

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.     

A Compact Pulsed HF Laser Based on an Auto-Wave Photon-Branched Chain Reaction

Huge energy gain is detected theoretically in a pulsed chemical laser-amplifier based on a photon-branched chain reaction initiating in a gaseous disperse medium composed of H₂–F₂–O₂–He and Al particles by focused external infrared radiation. It is shown that this effect is observed due to the other optical effect of diffractive multifocal focusing of the input radiation on a certain type of bicomponent optical system coupled structurally with the input mirror of an unstable telescopic laser cavity. Such a relatively simple bicomponent diffraction system, consisting of two plane screens with circular apertures on a given optical axis, enables one to focus the input beam without using classical refraction elements such as lenses and prisms. The focusing of the input signal ensures the minimization of the initially excited volume of the laser active medium and the appropriate sharp lowering of the necessary energy of the input pulse up to 10^-6 J. This enables the laser system to reach a high value of the energy gain of 10⁹. The huge laser energy gain allows us to use a master oscillator in the form of a small microjoule laser powered by an accumulator, and consequently makes it possible to construct a completely self-contained compact pulsed chemical HF-laser.     

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.     

Plasma-chemical processes in the active medium of a CO laser

The concentrations of plasma-chemical products (C, O, CO₂, C₂, and C₃O₂) were measured under conditions typical of the active medium of an electrical discharge CO laser. The dependence of the concentration of C₃O₂ molecules on the experimental conditions was studied. A reaction scheme responsible for the concentration of C₃O₂ molecules formed in the discharge was proposed.     

Tunable CW CO2 lasers with waveguide cavity

A laser that is tunable up to 1.6 GHz is described. A cavity with two selectors is described, capable of tuning the emission frequency in a band wider than the intermode distance. The gain in the laser active medium, including in CO₂ isotopes, is measured. Lasers with such parameters can be used in spectroscopy, photochemistry, and optical communication and ranging.Translated from Lazernye Sistemy, pp. 92–101, 1982.     

Multiline laser probing of CO:He, CO:N2, and CO:O2 active media in a wide-aperture pulsed amplifier

Multiline laser probing was applied for the diagnostics of the active medium of a wide-aperture carbon monoxide laser amplifier. The temporal behavior of the small-signal gain in the active medium of a pulsed electron-beam sustained discharge CO laser amplifier was studied with a specially designed probe CO laser in a wide range of ro-vibrational spectral lines (from V = 5 up to V = 31). The results were analyzed in order to reconstruct the temporal behavior of gas temperature and vibrational populations in CO-containing gas mixtures, CO:He and CO:N₂, and oxygen-rich CO: O₂ mixtures. __________ Translated from Preprint No. 13 of the P. N. Lebedev Physical Institute, Moscow (2005).     

Temperature field modeling during multi-modes CO2 laser irradiation of human enamel

We examine the temperature fields of human enamel [Yu D, Fox JL, Hsu J, Lynn Powell G, Higuchi WI. Computer simulation of surface temperature profiles during CO₂ laser irradiation of human enamel. Opt Eng 1993; 32(2)] during multi-modes CO₂ laser irradiation. For this we use the integral transform method as well as direct and inverse Laplace transform [Oane M, Sporea D. Temperature profiles modeling in IR optical components during high power laser irradiation. Infrared Phys Technol 2001; 42(1): 31–40; Oane M, Sporea D. Study of heat transfer in IR optical components during CO₂ laser irradiation. Proc SPIE 2001; 4430: 898–904; Oane M. Mathematical modeling of the thermal field distributions in solids under multiple laser irradiations. Proc SPIE 2003; 5227: 329–34; Oane M, Apostol I, Timcu A. Temperature field modeling in laser heated metals for laser cleaning of surfaces. Proc SPIE 2003; 5227: 323–8]. The enamel block is modeled as homogeneous cylinder in three dimensions. Results indicate that (i) the thermal field depends on multi-modes structure; (ii) heat transfer coefficient plays an important role in temperature distribution.     

Line-dependent saturation in CO2 lasers

Line dependent saturation has been studied in a CO₂ waveguide laser, operating cw in 100 lines of the 9 m and 10 m bands. In both bands, for constant discharge conditions, the saturation intensity is found to be strictly inversely proportional to the small signal gain for lines in the range J=2 to J=48 in both the P and the R branches. For lasers operating well above threshold this implies an output power which is essentially independent of the line number. The effect is verified experimentally, and discussed theoretically.Supported by the Danish Science Research Council under grant no. 11-7777     

The high resolution infrared spectrum and laser Stark spectroscopy of thev8 band of propyne

The perpendicularv ₈ band lying in the 1000–1100 cm^–1 region has been studied from infrared and laser Stark, spectra. We were interested in the part of spectrum corresponding to the spectral range of the 9 m CO₂ laser lines. Assignments of rovibrational lines with J'<40 and K'<6 have been made. About 100 Stark resonances have been assigned to 12 rovibrational transitions. Effective molecular constants and dipole moment have been determined with high accuracy. A list of close resonances with CO₂ laser lines is given and may be used for optical pumping experiments.     

X-ray preionized CO2 laser

A short pulse (100 ns) high-energy x-ray source has been used to preionize a transversely excited carbon dioxide gas discharge laser of 600 cm³ active volume. The maximum output power of 60 MW in a 50 ns FWHM pulse was achieved from a CO₂–N₂–He–CO–Xe static gas mixture at 600 Torr pressure. The energy conversion efficiency was 6%.     

中远红外双波段激光器增益介质匹配

对中远红外双波段激光器中DF和CO2两种增益介质的匹配进行了研究。根据对DF和CO2两种增益介质分布的理论分析,发现DF相比于CO2介质增益峰值位置更靠前,激活区长度更短,据此设计加工了一台双波段激光器,使CO2气体注入孔位置可调,通过D2和CO2注入孔位置的差别来实现两种介质增益峰值位置的匹配。实验证明了这种设计是有效的,并确定了激光器共同光轴的最佳位置位于D2气注入孔下游3 mm,CO2注入孔下游33 mm处,此处双波段激光的输出功率均接近最大值。     

Gain and saturation measurements in a discharge excited F2 laser using an oscillator amplifier configuration

The small-signal gain coefficient and the saturation intensity of a F₂ pulsed discharge molecular laser at 157 nm have been measured using two discharge devices in an oscillator-amplifier configuration. The small signal gain coefficient was measured to be 5.2±0.4% cm^–1 at 3 atm total pressure and 1.5 cm electrode spacing and 4.1±0.4% cm^–1 at 2 atm total pressure and 2 cm electrode spacing while the values of the saturation intensity were 5 MW/cm² and 4.6 MW/cm², respectively.     

基于光放大的长脉冲抽运太赫兹激光

为了获得较窄增益带宽、较大光强的太赫兹辐射,尝试了利用TEA CO₂激光器对6 W可调谐连续波CO₂种子激光实行双程光放大实验,以期望获得长脉冲、高峰值功率的抽运光.通过实验,获得了大约30倍的放大系数,放大光输出功率随种子光注入功率的增加而增加,其中10 P （20）支线表现更加突出,并且被放大的激光支线半峰全宽在14 μs左右.基于这种长脉冲抽运源,建立了一种产生脉冲太赫兹的动力学模型,给出了产生太赫兹辐射的饱和抽运光强表达式,确定了抽运光的光强范围.另外, 关键词： 激光物理 长脉冲 动力学模型 太赫兹激光     

Coherent tunable far infrared radiation

Tunable, cw, far infrared (FIR) radiation has been generated by nonlinear mixing of radiation from two CO₂ lasers in a metal-insulator-metal, (MIM) diode. The FIR difference-frequency power was radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO₂ lasers. Using the combination of lines from a waveguide CO₂ laser, with its larger tuning range, with lines from CO₂, N₂O, and CO₂ isotope lasers promises complete coverage of the entire far infrared band from 100 to 5000 GHz (3–200 cm^–1) with stepwise-tunable cw radiation.Contribution of the National Bureau of Standards, not subject to copyright