XeF激光谱研究

XeF高分频率光谱已有很多报导,至今报导的最多激光谱线数目为40条,包括振动和转动谱。我们用31WⅡ光栅光谱仪的二级谱研究了Blumlein型横向放电XeF激光器激光谱与激射条件的关系,实验表明:     

光抽运XeF(C-A)蓝绿激光器

利用分段表面放电作为光抽运源 ,采用光解离XeF2 技术 ,研制了一台 XeF(C A) 蓝绿激光器。抽运源有效激活长度为 6 0cm ,单位长度的沉积功率为 4 5MW /cm。在 2 5 0PaXeF2 / 6 0kPaAr/ 40kPaN2 条件下 ,采用平凹腔 ,输出耦合为 4% ,获得了XeF(C A)激光输出。对XeF(C A)激光特性参数进行了测量 ,输出能量为百毫焦耳量级 ,最大能量达 16 7mJ,激光脉宽～ 6 0 0ns ,辐射光谱范围 470～ 5 0 0nm ,发散角水平方向为 1 7mrad ,垂直方向为3 7mrad。     

气体再循环的高重复率XeF激光器

巳获得脉冲重复率高达200脉冲/秒的Blumlein电路驱动XeF受激准分子激光器的持续运转。还介绍了一种简单技术，用以回收及再循环激光混合气体中的氙。     

STS与XACTIX合推新型大批量生产XeF2蚀刻设备

Surface Technology Systems公司与XACTIX公司推出新的基于二氟化氙（XeF2）气体的Chemical Vapor Etch（CVE）设备。XACTIX与STS合作开发的突破性工艺腔体设计和改进的晶圆传递机制可保证高吞吐量、均匀性、效率及运行时间,从而使XeF2蚀刻成为可行的大批量生产工艺。     

蓝绿XeF系统达到6焦耳的创记录输出

加利福尼亚门洛帕克国际空间研究所的研究者们从一个光解泵浦的氟化氙激光器中已经获得了创记录的6焦耳输出，波长在483毫微米处。与较普通的XeF激光器不同，它在B→X跃迁上产生350毫微米的紫外激光，而蓝绿的XeF系统通过C→A跃迁而运转，所产生的波长在455和525毫微米之间。这种在蓝绿区可调的高能激光发射对水下潜艇的激光通信线路是重要的，这也是国防部正在积极从事的一项应用研究。     

一种紫外,可见和红外的简易高功率TEA激光器

我们报导了一种简易、高功率的横向激励大气压激光器.它用 N_2、XeF 及 KrF 在紫外运转,用 F 及 Ar 在可见和近红外运转.用 HF、CO、CO_2及 N_2O 在红外运转。在同一种器件中,从N_2得到峰值功率0.5MW 及脉冲能量4.5mJ,从 XeF 得到1.5MW 及16mJ,从 CO_2得到18MW 及2.7J,由于在激光混合气体中加进 NF_3,N_2激光器的性能大为改善(1MW,10mJ).在接近或超过大气压时取得最大功率与能量.     

面预电离F原子激光和XeF准分子激光实验研究

本文报道了面预电离F原子激光和XeF激光输出能量以及F原子激光光斑随各气体分压的变化情况。在适当的气体混合物中放电获得了F原子和XeF准分子激光充满放电截面的完整光斑，取得了满意预电离效果。获得了F原子623．9nm、634．8nm、712．8nm和731．1nm四波长激光同时振荡以及F原子激光和XeF激光同时振荡，并作了定性分析。     

从XeF激光混合气体中除去杂质F2的反应器

用于电子束泵浦的XeF激光器混合气体的“净化”或提纯的新装置已由阿符科·埃佛雷特研究实验室的曼德耳（A. Mandll)等设计成功。在理想情况下，激光器的混合气体由NF3、Xe和缓冲气体，例如Ne组成。然而，在实际运转时，F2(也许其它氯的混合物)在混合气体中形成，而它的量随着温度接近准分子最佳运转温度(约450 °K)而增加。这些杂质在351毫微米的激光波长处有吸收，因而使性能劣化,于是在这样的温度下，必须幵环运转。这个小组设计了一种“净化”系统，它能有选择地从NF3、Xe和Ne混合气体中除去巧，使得即使在高温下也允许闭环运转。     

XeF激光器光泵技术的改进

苏联列别捷夫物理研究所采用光学泵浦方法，已在XeF中得到1%的效率和28 J的脉冲能量。V. S.朱耶夫等人用开放式大电流放电所产生的真空紫外光录浦XeF,观测到353和385 nm的激光发射。     

虚拟仪器技术在篮绿激光器上的运用

将以PC为基础,使用PCI和USB总线的数据采集卡为硬件,labview软件编写的操作面板等组成的虚拟仪器技术运用于蓝绿激光器的状态监测中,对于保持气室中工作气体XeF2浓度的稳定性,提高激光器在重频运行过程中对光电信号的数据处理效率,减少手工操作内容,增强激光器的自动化水平,具有重要的作用。     

Controlled Layer Thinning and p‐Type Doping of WSe2 by Vapor XeF2

This report presents a simple and efficient method of layer thinning and p‐type doping of WSe₂ with vapor XeF₂. With this approach, the surface roughness of thinned WSe₂ can be controlled to below 0.7 nm at an etched depth of 100 nm. By selecting appropriate vapor XeF₂ exposure times, 23‐layer and 109‐layer WSe₂ can be thinned down to monolayer and bilayer, respectively. In addition, the etching rate of WSe₂ exhibits a significant dependence on vapor XeF₂ exposure pressure and thus can be tuned easily for thinning or patterning applications. From Raman, photoluminescence, X‐ray photoelectron spectroscopy (XPS), and electrical characterization, a p‐doping effect of WSe₂ induced by vapor XeF₂ treatment is evident. Based on the surface composition analysis with XPS, the causes of the p‐doping effect can be attributed to the presence of substoichiometric WO_x (x < 3) overlayer, trapped reaction product of WF₆, and nonstoichiometric WSe_x (x > 2). Furthermore, the p‐doping level can be controlled by varying XeF₂ exposure time. The thinning and p‐doping of WSe₂ with vapor XeF₂ have the advantages of easy scale‐up, high etching selectivity, excellent controllability, and compatibility with conventional complementary metal‐oxide‐semiconductor fabrication processes, which is promising for applications of building WSe₂ devices with versatile functionalities.     

Study and formation of 2D microstructures of sapphire by focused ion beam milling

Dry etching of C-plane sapphire wafer has been studied using Ga⁺ focused ion beam milling (FIBM). Due to a much lower milling rate of sapphire compared to GaN, it has been proven that gas-assisted FIBM (GAFIBM) is a necessity. Furthermore, it needs to be determined whether XeF₂- or I₂-GAFIBM can improve the technique. We found that XeF₂-GAFIBM gave the highest milling rate. The obtained enhancement factor of the XeF₂-GAFIBM milling rate compared to FIBM rate varied from 2.3 to 1.2 for the ion beam current in the range 20 pA-1 nA. A favorable milling rate selectivity of sapphire to nickel film of about 1.5 was obtained by XeF₂-GAFIBM at 350 pA. We have successfully fabricated a variety of 2D sapphire-based submicron pillar or hole arrays in regular crystals, quasicrystals and aperiodic symmetries. The nearest neighbor distance was down to 230 nm. The depth achieved was deeper than 400 nm. The air filling factor ranged from 12% to 60%. These sapphire-based 2D microstructures were applied on flip-chip GaN-based light emitting diodes (LEDs) and more than 40% improvement in light extraction was obtained.     

ArF excimer laser-enhanced photochemical vapor deposition of epitaxial Si from Si2H6: A simple growth kinetic model

Photolysis of Si₂H₆ using 193 nm radiation from an ArF excimer laser has been used to deposit homoepitaxial Si films in the temperature range of 250 to 350°C. Photolytic decomposition of Si₂H₆ generates growth precursors which adsorb on to a hydrogenated Si surface. A growth kinetic model is proposed based on single-photon 193 nm absorption by Si₂H₆, and chemical reaction of the photofragments as they diffuse to the sub-strate surface. With the laser beam positioned parallel to the Si substrate, the deposi-tion yield of solid Si from photo-excited Si₂H₆ is estimated to be 0.20 ± 0.04. Growth rates vary linearly with laser intensity and Si₂H₆ partial pressure over a range of 1–15 mJ/cm² · pulse and 5–40 mTorr, respectively, and epitaxial films are deposited when laser intensity and Si₂H₆ partial pressure conditions are such that the initial photofragment concentration is less than ~10¹³ cm⁻³.     

Heterodyne frequency measurements on the 12°0-00°0 band of OCS

Heterodyne frequency measurements have been made on the 12°0-00°0 band of carbonyl sulfide in the wavenumber range from 1866 to 1915 cm^?1. Frequency measurement techniques reported earlier are used to measure the OCS absorption lines by means of a tunable diode laser, a CO laser local oscillator, and two CO₂ lasers used as secondary frequency standards. A table of calculated absorption frequencies is given for OCS from 1866 to 1919 cm^?1.     

Characterization of Si homoepitaxial films grown with and without surface photoactivation by ArF excimer laser-induced photodissociation of Si2H6

Silicon homoepitaxial films have been grown by photodissociation of Si₂H₆ by the 193 nm line of an ArF excimer laser in an ultra-high vacuum system. Silicon epitaxy has been achieved in two ways: one, in which the laser shines into the chamber parallel to the substrate and another, in which the laser is directly incident on the substrate at grazing angles (87° with respect to the substrate normal). Controllable growth rates of 0.5–4Å/min have been achieved for crystalline films by the first method using substrate temperatures as low as 250° C, Si₂H₆ partial pressures of 20 mTorr and photon flux densities of 10¹⁶ photons/pulse.cm². In the second method, where the laser beam is directly incident on the wafer at grazing angles, very high growth rates of up to 80Å/min have been achieved at 300° C, 20 mTorr Si₂H₆ partial pressure and a photon flux density of 2 × 10¹⁵ photons/pulse.cm². A comparison of the microstructure of the films grown by the two methods is presented on the basis ofin situ reflection high energy electron diffraction (RHEED) analysis and selected area transmission electron microscopy (TEM) studies. In both cases, the growth rates are found to be linearly dependent on the photon flux density for the process parameter ranges studied.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 μm–1200 μm range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^?4–10^?3 accuracy is achieved in the measurement of the FIR wavelengths. The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^?1 of this main isotope.     

Multi-Mode Optical Manometry Based on Li4SrCa(SiO4)2:Eu2+ Phosphors

Optical manometry is a highly promising method for measuring pressure. However, its wider application is limited by the lower sensitivity and influenced by environmental factors. Herein, multi-mode optical pressure sensors based on Eu²⁺-doped Li₄SrCa(SiO₄)₂ phosphors suitable for a variety of complex pressure-measuring environments are designed. The phosphors contain two separate luminescence centers at 443 nm (Eu_Sr) and 584 nm (Eu_Ca), respectively. In the lower pressure range, the emission peak undergoes a massive redshift of 5.19 nm GPa⁻¹ of Eu_Ca, which is 14× better than commercially available ruby sensors. In order to improve the pressure response range and the accuracy of pressure measurement, for the first time, a new approach in the pressure readout method in which single Eu²⁺ ions doping based on fluorescence intensity ratio (FIR) pressure measurement is realized in designed materials. Meanwhile, the measured full width at half maximum (FWHM) as an indicator of pressure sensor performance also reveals that the sensing performance is d FWHM/d P ≈ 1.23 nm GPa⁻¹ and d FWHM/d P ≈ 0.84 nm GPa⁻¹ for Eu_Sr and Eu_Ca positions, respectively. Additionally, the structural stability of the phosphor is confirmed by in situ Raman spectrum. The above results indicate that the Li₄SrCa(SiO₄)₂:0.04Eu²⁺ phosphor is a good candidate for multi-mode optical pressure sensors.     

一种自稳频大功率单频He-Ne激光器的功率估算

介绍了一种大功率单频、自稳频、高输出功率He-Ne激光器功率估算方法的改进。用这种方法的估算值与实际输出功率值符合得较好。     

Laser ablation of SiO2 for locally contacted Si solar cells with ultra‐short pulses

We apply ultra‐short pulse laser ablation to create local contact openings in thermally grown passivating SiO₂ layers. This technique can be used for locally contacting oxide passivated Si solar cells. We use an industrially feasible laser with a pulse duration of τ_pulse ∼ 10 ps. The specific contact resistance that we reach with evaporated aluminium on a 100 Ω/sq and P‐diffused emitter is in the range of 0·3–1 mΩ cm². Ultra‐short pulse laser ablation is sufficiently damage free to abandon wet chemical etching after ablation. We measure an emitter saturation current density of J_0e = (6·2 ± 1·6) × 10⁻¹³ A/cm² on the laser‐treated areas after a selective emitter diffusion with R_sheet ∼ 20 Ω/sq into the ablated area; a value that is as low as that of reference samples that have the SiO₂ layer removed by HF‐etching. Thus, laser ablation of dielectrics with pulse durations of about 10 ps is well suited to fabricate high‐efficiency Si solar cells. Copyright © 2007 John Wiley & Sons, Ltd.     

A Tunable Difference Frequency Spectrometer for Quantitative Analysis of Heavy Molecules

A continuous-wave (cw) mid-infrared spectrometer based on laser difference frequency generation (DFG) in gallium selenide (GaSe) crystal was developed for quantitative analysis of heavy molecules. The spectrometer and its spectroscopic applications to study of molecular line parameters (such as line strength, pressure broadening coefficients) are presented. The first measurement, to our knowledge, of the self and air broadening coefficients for the ν₇ 8 _2,7 ← 8 _1,7 ethylene (C₂H₄) transition line at 958.1531 cm^?1 is reported.