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1.
A pulsed cold-cathode glow-discharge electron beam gun emitting an electron-beam of 150 keV energy and 45 cm 2 cross-sectional area has been used to pump a short pulse CO 2 laser. A fast discharge capacitor bank was used to help make the design simpler than that employed in liquid coaxial lines. The system developed is capable of producing a CO 2 laser pulse of 1 J for about 200 ns duration. 相似文献
2.
Optical bistability has been investigated experimentally in a CO 2 laser containing CF 3Br as a saturable absorber. The frequency dependence of the hysteresis cycle of this laser containing a saturable absorber (LSA) has been studied. It has also been shown that the LSA may undergo simultaneously hysteresis cycles and Q-switching. The phase diagram of the LSA has been extended towards regions where this behavior has been observed. 相似文献
3.
A Teller–Landau six-temperature model describing the dynamic emission of single-mode TEA CO 2 laser has been adapted. This model has been also used to describe the mechanism of obtaining relatively high-power output pulses from hybrid TE-TEA or CW-TEA CO 2 laser consisting of high- and low-pressure sections. The suggested mathematical model allows to investigate the mechanism which limits the TEA oscillation to single longitudinal mode (SLM) due to the narrow gain bandwidth of low-pressure section, and also to study the effect of the laser input parameters on the smooth output laser pulse parameters. In addition, numerical solutions of non-linear rate equation system of the suggested model are quantitatively discussed. The solutions describe the radiation field intensity, the population inversion, and the energy transfer processes. The calculated values of maximum peak power, total energy in pulse, pulse width, etc. are in a very good agreement with the observed experimental values. 相似文献
4.
A study of a pulsed transversely excited (TE) CO 2 laser using an unstable resonator configuration is reported. It is shown that a large aperture (4.75 cm) wire-triggered device can successfully operate at pressures of up to 650 torr with undoped gas mixtures whose molecular gas concentration exceeds 35%. These results are utilised for a comparative study of the influence of an organic additive on the performance of the system. It is observed that the addition of traces of tri-n-propylamine leads to significant improvements of the laser output characteristics even under conditions where a glow discharge could be obtained without the additive. With the doped TE CO 2 laser employed using a relatively low magnification unstable resonator ( M = 1.45) near diffraction-limited performance has been achieved and a peak radiance of 4.5 × 10 13 W cm −2 sr −1 has been obtained with a peak power of 65 MW. 相似文献
5.
A reliable procedure for remote high-accuracy laser detection of N 2O as one of the principal destroyers of the protective ozone layer of the Earth has been developed. The procedure is based on using a CO 2-laser system emitting efficiently in the 4.5 μm range. In this case lasing from isotopic modification 12C 18O 2 of carbon dioxide with its subsequent frequency doubling by a nonlinear crystal is used. With the object of reducing the price the composition of the active medium (both for TEA laser and low-pressure longitudinal-discharge-excitation laser) has been optimized. New high-efficiency intracavity frequency doubling schemes based on nonlinear AgGaSe 2 crystals have been developed for CO 2-lasers of both types. Low concentrations of N 2O and concentrations of the principal background gases CO and H 2O have been measured under real atmosphere conditions with the aid of the lidar complex built around these lasers. 相似文献
6.
A genetic algorithm is used to optimize a CO 2 laser resonator. Three optimal parameters of a CO 2 laser resonator (the diameter of the laser discharge tube, the curvature radius of the concave reflector and the transmissivity of the output-mirror) are obtained with the maximum output of the laser power as the objective function in the genetic algorithm. After the optimization, the calculated laser power with the fundamental mode increases by 62% and the measured value increases by 35% in an experiment as compared to a non-optimized case. 相似文献
7.
The O 3 absorption coefficients for the rotational lines P(12)–P(28) of the 9.4 μm emission band of the CO 2 laser are presented. Measurements were made in O 3–air dilute mixtures (20–600 ppm) at 25°C and a total pressure of 1013.25 h Pa using a frequency stabilized cw CO 2 laser and values have been determined with greater precision than in previously reported studies. 相似文献
8.
An in situ mass-spectrometric sampling technique has been developed for lifetime studies of TEA CO 2 lasers. Using the new technique, an analysis of the gas components of a TEA CO 2 laser during its lifetime has been performed. The results show that the laser output pulse energy was strongly influenced by the oxygen concentration inside the device. 相似文献
9.
Of all the types of lasers now available, the CO 2 laser is particularly suitable for materials working. It has a very high efficiency (15–20%) and a high out-put power (up to several kW). When the laser light is focused by means of a lens or a mirror, a c.w. power density of more than 10 9 W cm -2 can be attained. The laser need not be used in vacuum. The CO2 laser is a suitable cutting tool for numerous materials. These include metals such as titanium or steel; combustible materials such as paper, textiles and wood; and plastics. The CO2 laser can also cut hard and brittle materials such as aluminum oxide and silicon carbide. If metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width, however, is determined by the size of the laser spot. Another important field of application is the growth of single crystals. Experiments are reported in which the CO2 laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. A comparative study of laser and electron beam techniques is included. 相似文献
10.
The nature of CO 2 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 CO 2 laser may therefore be used in place of the YAG laser, now widely used for marking, with some merits: CO 2 laser marking is cheaper and faster, and in addition there is no danger of injury from irradiating laser light. 相似文献
11.
Five and six-temperature models for the CO 2–N 2–He system are used to describe the process of the dynamic emission in the TEA CO 2 laser. All physical constants and relaxation rates related to these models are examined to estimate the output pulse parameters as a function of the input parameters. The two pumping processes implemented; empirical function and differential equation show a good agreement with the experimental data. 相似文献
12.
用CO 2激光烧结合成了负热膨胀材料Sc 2(WO 4) 3和Sc 2(MoO 4) 3. 实验表明, 激光合成负热膨胀材料Sc 2(WO 4) 3和Sc 2(MoO 4) 3属于快速合成技术, 合成一个样品的时间仅需几秒到十几秒, 具有快速凝固的特征; X射线衍射和拉曼光谱分析表明, 所合成的材料为正交相结构, 且具有较高的纯度; 变温拉曼光谱分析表明, 所合成的材料在室温以上没有相变, 但可能有微弱的吸水性; 在对Sc 2O 3, MoO 3, WO 3, Sc 2(MoO 4) 3和Sc 2(WO 4) 3拉曼光谱分析的基础上, 给出了激光光子能量及原料和合成产物的声子能级图, 分析了激光烧结合成的机理. 激光光子能量转化为激发声子的能量是光热转化的主要通道, 原料在熔池中反应并快速凝固形成最终产物.
关键词:
负热膨胀材料
合成
激光烧结
拉曼光谱 相似文献
13.
Infrared fluorescence from CF 2Cl 2 molecules excited with a TEA CO 2 laser below dissociation threshold, is time resolved with a HgCdTe detector without spectral resolution in the range 1100-700 cm -1. The signal fits well to a sum of three exponentials, which are interpreted as a bulk vibration-vibration (V-V) energy transfer between the fraction of highly excited and non-excited molecules in the irradiated volume, vibro-translation (V-T) deactivation and diffusional heat and mass transport to the surrounding. The measured V-V and V-T rates increase with vibrational excitation and the V-T deactivation is independent on the observed modes ( v1/ v6 or v8) if v8 or v1 are excited respectively. 相似文献
14.
Results of parametric studies on short CO 2 laser pulse generation by laser induced dielectric breakdown in a plasma shutter cell are described. From the rise time of such short pulses obtained, threshold breakdown intensity ( Ith) has been estimated for different gases. The technique is further extended to obtain 40 ns pulses on two-frequency emission from a single TEA CO 2 laser. Pressure dependent studies of Ith are utilised to model the process of such laser induced plasma. 相似文献
15.
The reaction of CO 2 and H 2O to form bicarbonate (HCO −3) was examined on the nearly perfect and vacuum annealed surfaces of TiO 2(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO 2(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO 2 only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti 4+ sites (TPD peak at 137 K) typical of the nearly perfect TiO 2(110) surface. Vibrational HREELS indicates that CO 2 is linearly bound at the latter sites with a νa(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H 2O to bridging OH groups which recombine to liberate H 2O in TPD at 490 K. No evidence for a reaction between CO 2 and H 2O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO 2 adsorption is blocked by the presence of preadsorbed H 2O, adsorbed CO 2 is displaced by postdosed H 2O, and there is little or no evidence for bicarbonate formation in either case. However, when CO 2 and H 2O are simultaneously dosed, a new CO 2 TPD state is observed at 213 K, and the 166 K state associated with CO 2 at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO 2 TPD state to a bicarbonate species. The 213 K CO 2 TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO 2+H 2O exposure. Sticking coefficient measurements suggest that CO 2 adsorption at 110 K is precursor-mediated, as is known to be the case for H 2O adsorption on TiO 2(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H 2O–CO 2 van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO 2 and H 2O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO 2, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution. 相似文献
16.
碳酸盐是碳在地球内部的重要载体之一,其在地幔高温高压条件下的晶体化学是理解地球深部碳的赋存状态和循环过程的关键,而结构稳定性和相变是晶体化学最基本的研究内容。碳酸钠(Na 2CO 3)是一种常见的碱性碳酸盐矿物,在产自地幔过渡带-下地幔的金刚石中已发现含钠的碳酸盐矿物包裹体,这成为碳酸钠能够俯冲进入地幔深部的直接矿物学证据。前人利用拉曼光谱技术研究了Na 2CO 3在常温常压下的晶格振动模式,但其在高压下的稳定性和结构变化却鲜有报道。利用金刚石压腔装置结合先进的共聚焦拉曼光谱技术,以硅油作为传压介质,在准静水压力条件下,在0.001~27.53 GPa压力区间对Na 2CO 3粉末在600~1 200 cm-1波段的振动特征进行了细致地分析。本次实验重点分析了[CO 3]2-基团振动模式在升压和卸压过程中的行为。结果表明,在0.001~11.88 GPa压力范围内,[CO 3]2-基团对称伸缩振动 γ1(1 088.06和1 070.76 cm-1)、反对称伸缩振动 γ3(865.10和797.50 cm-1)和面内弯曲振动 γ4(720.10和696.71 cm-1)都出现了振动峰的分裂。随着压力增加,所有振动峰都向高频率漂移,半高宽也逐渐增加。在13.40 GPa时,Na 2CO 3发生结构相变,具体表现为690.08 cm-1处出现1条新的拉曼峰,并且随着压力升高该峰的强度逐渐增大。同时反对称伸缩振动峰 γ3以及面内弯曲振动峰 γ4的强度持续减弱,半高宽也继续变大。这些现象表明Na 2CO 3结构相变源于[CO 3]2-内部晶格变化。当压力卸载到4.18 GPa时,[CO 3]2-的振动模式与常温常压下的完全吻合,相变出现的新峰也已经消失,表明该相变是由[CO 3]2-基团畸变引起的并且具有可逆性。继续升压至27.53 GPa,拉曼光谱继续蓝移,Na 2CO 3的拉曼谱线再没有变化,说明高压相在这一压强范围内保持稳定。在整个加压过程中,反对称伸缩振动 γ3和面内弯曲振动 γ4处的拉曼峰出现强度减弱现象。同时也计算了各个峰频率对压力的依赖系数d γ/d P,结果显示[CO 3]2-基团内各个振动模式对压力的响应是不同的,这很可能与C-O键的键长有关。最后,对比发现,对称伸缩振动 γ1峰的强度比反对称伸缩振动 γ3和面内弯曲振动 γ4峰的强度大,并且[CO 3]2-基团对称伸缩振动 γ1受压力影响相对较小,可以用来区别不同种类的碳酸盐矿物。 相似文献
17.
基于品位匹配和多能源综合梯级利用的原则,本文提出了低CO 2排放的太阳能与化石能源互补发电系统LESOLCC,并对其进行了热力经济性能分析。所提系统以甲醇为燃料,中低温太阳能首先提供甲醇重整反应的反应热,从而转化为富氢合成气的化学能,实现品位提升;其次通过燃烧前对CO 2的捕集,实现燃料的清洁燃烧,最终在高效联合循环中实现其热功转换。结果表明:基本工况下,系统当量效率达到55.1%,比投资为833$/kW,发电成本为0.124$/kWh,回收期17年;与相同化石燃料输入及CO 2捕集水平的尾气捕集CO 2的常规燃气-蒸汽联合循环(CC-Post)相比,发电成本下降了10.1%,充分显示其优越性。 相似文献
18.
A new phase of Ba 2(Cu 0.7Cd 0.3)O 3 has been discovered. The composition of the phase was examined by energy dispersive X-ray spectrometry. The phase exhibits a tetragonal structure with lattice constants a=4.077 Å and c=7.970 Å, and its space group is P4/mmm. We propose a double-center-perovskite structure model, which is similar to that of (Ba, Sr) 2CuO 2(CO 3) [1, 2]. The simulated XRD is close to the observed one. The analysis results of elemental analyzer and Fourier transform infrared spectrometer reveal that the phase does not contain CO
. The cuprate is an insulator, but its new cell structure and the large size of the CuO 2 planes seem to suggest a good reason for researching new superconductors. The roles of CdO in the solid state reaction and the formation of the new phase are discussed. 相似文献
19.
A solid-state electrochemical cell of the type O 2(air), Pt La0.9Sr0.1MnO3/ Li2CO3(+5 mol% Li3PO4 + 6 mol% Al2O3)/Au, CO2, O2 was composed to determine CO 2 concentration, where Li 2CO 3, a lithium ion conductor, was used as an electrolyte, and the perovskite-type oxide ( La0.9Sr0.1MnO3)/ O2-electrode as a reference electrode. The electromotive force (EMF) of the cell was found to be proportional to the logarithm of CO/ 2 partial pressure in CO 2/O 2/N 2 gas mixtures at temperatures between 300 and 400 °C. The EMF responded to changes of CO 2 partial pressure within 1 min at 400 °C. The sensitivity to CO 2 of this cell was not affected by coexistence of O 2, and the EMF remained constant after the first 15 days. The mechanism for sensing CO 2 is discussed. 相似文献
20.
Two new methods for phase-locking are used in the axisymmetrical-fold combination CO 2 laser. We demonstrate the feasibility of two methods by theoretical deduction, and give the light intensity distribution of far field by numerical simulation. When phase is locked, the axisymmetrical-fold combination CO 2 laser can provide a high output power with good beam quality. Furthermore, the peak light intensity of output beam with phase-locking is obviously higher than that without phase-locking. 相似文献
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