LD侧面泵浦Nd∶GdVO4 532 nm绿光激光器

为了获得高功率窄脉宽532 nm绿光激光输出,通过高重复频率声光驱动调Q技术和LD侧面泵浦Nd∶GdVO4技术,获得高功率线偏振1 064 nm激光输出。采用内腔倍频方式,对非线性晶体KTP进行频率变换,实现高功率窄脉宽绿光激光输出。在电源输入电流30 A,调Q驱动频率10 kHz的条件下,获得最高功率30 W线偏振1 064 nm激光输出,脉宽30 ns,倍频KTP晶体获得23.4 W的532 nm绿光输出,1 064 nm到532 nm转化效率为78%。实验结果表明:通过声光调Q技术和LD侧面泵浦Nd∶GdVO4技术,可以实现高功率线偏振窄脉宽1 064 nm激光输出,倍频非线性晶体KTP可获得高功率窄脉宽532 nm激光。     

LD侧面泵浦Nd:GdVO4 532 nm绿光激光器

为了获得高功率窄脉宽532 nm绿光激光输出,通过高重复频率声光驱动调Q技术和LD侧面泵浦Nd∶GdVO4技术,获得高功率线偏振1 064 nm激光输出.采用内腔倍频方式,对非线性晶体KTP进行频率变换,实现高功率窄脉宽绿光激光输出.在电源输入电流30 A,调Q驱动频率10 kHz的条件下,获得最高功率30 W线偏振1 064 nm激光输出,脉宽30 ns,倍频KTP晶体获得23.4 W的532 nm绿光输出,1 064 nm到532 nm转化效率为78％.实验结果表明:通过声光调Q技术和LD侧面泵浦Nd∶GdVO4技术,可以实现高功率线偏振窄脉宽1 064 nm激光输出,倍频非线性晶体KTP可获得高功率窄脉宽532 nm激光.     

皮秒激光泵浦的亚10fs钛宝石激光器

研制了高稳定Nd∶YVO_4皮秒激光振荡器,并在15 W、808nm激光泵浦下得到6 W的连续锁模皮秒激光输出,光-光效率为40%.对该皮秒激光进行单通放大后得到14 W的基频光输出,倍频后可以得到7 W的532nm皮秒激光,用作钛宝石振荡器的泵浦源.在4.5 W的皮秒532nm激光泵浦下,结合腔外压缩,得到了脉宽为9.4fs、平均功率为150mW的脉冲序列输出.调节钛宝石振荡器的腔长使其与皮秒振荡器的腔长一致时,可实现自触发克尔透镜锁模.实验结果表明皮秒激光泵浦可以有效地触发钛宝石激光器的自动锁模,输出飞秒脉冲序列.     

脉冲单频Nd:YVO4激光器及其倍频输出特性研究

为了研制激光干涉成像所需的主振荡功率放大(MOPA)结构脉冲单频激光器,本文完成MOPA激光器的种子源即声光调Q脉冲单频1 064 nm激光器的特性研究,同时完成种子源腔外倍频绿光特性研究。脉冲单频激光器采用声光调Q模块实现脉宽约20 ns的1 064 nm脉冲激光输出,采用环形腔设计并采用一组不同厚度的标准具实现单纵模运转。实验研究基频1 064nm和倍频532 nm激光脉冲的线宽,得出在全脉宽范围内都具有较高时间相干性的结论。实验分别获得脉宽约28 ns峰值功率约6.5 kW的1 064 nm脉冲单频激光和脉宽约20 ns、峰值功率约0.5 kW的532 nm脉冲单频激光,腔外倍频效率为5.6%。实验同时也验证了腔外倍频的激光脉宽压缩效应。     

鲜红斑痣光动力治疗的荧光光谱监测

应用荧光光谱技术监测了鲜红斑痣(PWS)光动力治疗(PDT)中的光敏剂血药浓度与光产物生成。以532 nm倍频Nd∶YAG激光器作为PDT照射光源与荧光激发光源,以光谱仪与ICCD采集荧光光谱。在系统验证实验中,构建含有血卟啉单甲醚(HMME)的小鼠正常皮肤的荧光基本光谱,通过最小二乘光谱拟合区分HMME荧光(624 nm)与光产物荧光(652 nm)。含有PSD-007的病人患区荧光光谱拟合采用相同基本光谱,获得不同病人个体具有显著差异的光敏剂血药浓度曲线与光产物生成漂白曲线。所建立的荧光光谱监测系统与光谱拟合方法可为PDT精确量化剂量学方法的建立提供技术手段,所得结果有利于制定个性化的PDT治疗方案。     

长脉宽激光诱导击穿土壤等离子体的光谱特性研究

采用长脉宽激光(500 μs)作为激发光源,研究了长脉宽激光在低能量密度条件下诱导击穿土壤等离子体的光谱特性。实验发现,在长脉宽激光的激发下等离子体光谱特性与纳秒及超短脉宽激光相比存在较大的差异,在402~409 nm波段和420~436 nm波段,土壤等离子体光谱均没有出现强烈的连续背景辐射阶段,所激发产生的等离子体发光寿命可持续220~270 μs。特征谱线PbⅠ405.78 nm和CrⅠ425.43 nm分别在210和190 μs时出现,且谱线强度均随时间延长而逐渐增加,分别在延时320和350 μs时达到最大值。研究结果表明,采用长脉宽激光作为激发光源,增加了激光与物质相互作用的时间,有助于激发形成发光时间较长的“准稳态等离子体”;应用内标法建立了Pb和Cr元素校准曲线,8次重复实验得到分析线与内标线净信号强度比值的相对标准偏差为2.21~6.35%,长脉宽激光激发产生的等离子体发光稳定;计算得到土壤中Pb和Cr元素的检测限分别为34.7和40.0 mg·kg-1,达到国家土壤环境质量标准规定的一级含量要求;长脉宽激光激发产生等离子体的电子温度为6 612 K,电子密度为3.7×1017 cm-3,达到了局部热平衡状态。     

基于富勒烯纳米结构材料光限幅特性研究

应用倍频Nd:YAG脉冲激光,在波长为532nm,脉宽8ns,重复频率10Hz的条件下,研究了新型基于富勒烯纳米结构材料(C₆₀-bpy-Au)的光限幅特性.实验结果表明,其限幅特性较C₆₀有所提高,初步分析了光限幅和溶剂效应.     

基于级联倍频机制无啁啾激光脉宽随晶体位相失配量的非线性变化

在无啁啾激光脉冲的非线性压缩过程中,基于级联倍频机制,对影响脉冲压缩的敏感因素——晶体位相失配量进行了理论分析和实验验证。当入射基频激光(即1ω光,波长为800nm,脉宽为278fs)进入I类二倍频β-BaB2O4(BBO)晶体后,随着晶体位相失配量的增加,基频光的输出脉宽先降后升,这种趋势可总结为"U"字形非线性变化;当位相失配量为40mm-1时,脉宽缩至最小,此时脉宽压缩比最大。     

多脉冲激光对碳纳米管悬浮液光限幅特性影响

利用实验的方法研究了碳纳米管悬浮液对脉宽8 ns,波长532 nm多脉冲激光的光限幅效应.分析了直径分布为10~20 nm的多壁碳纳米管悬浮液对重复频率分别为1 Hz、 3 Hz、 5 Hz、 10 Hz情况下532 nm激光的光限幅效应,分析计算了不同重复频率下碳纳米管悬浮液的限幅阈值,比较了不同焦距的透镜会聚入射光束情况下对碳纳米管悬浮液光限幅效果的影响.实验结果表明：碳纳米管悬浮液对不同重复频率的532 nm 激光都具有较强的光限幅特性;碳纳米管悬浮液对激光在不同重复频率入射情况下的光限幅阈值变化很大,当入射激光的重复频率为5 Hz时,碳纳米管悬浮液的光限幅阈值比单脉冲激光入射时的限幅阈值低了2倍,重复频率为10 Hz时的限幅阈值比单脉冲时的限幅阈值低了近3倍;碳纳米管在紧焦系统中的光限幅效果更好.     

全固态多波长飞秒脉冲激光系统

利用棱镜对引进频谱空间啁啾来补偿飞秒脉冲激光二次谐波产生中的相位失配,提高了倍频效率建立了一套全固态、多波长(1065nm, 532nm,823.1nm, 402nm)飞秒脉冲激光系统自制的Nd:YVO4激光器输出532nm绿光激光,最高平均功率可达5.6W当用2.5W绿光激光泵浦时,从自制的钛宝石激光器及经BBO倍频可分别输出中心波长为823.1nm和402nm,平均功率300mW和73mW,谱宽32.3nm和5.1nm,脉宽22fs和33.3fs、重复率108MHz的近红外和蓝光激光整个系统具有结构紧凑、倍频效率高、运行稳定的特点.     

飞秒激光诱导玻璃内析出BaTiO3晶体

使用800nm、120fs、200kHz的高重复频率超短脉冲激光照射BaO-TiO2-SiO2系玻璃，玻璃经飞秒激光照射数秒钟后，激光会聚点的发光由800nm波长的红色突然转变为非常强的400nm的蓝色，对激光辐照点的发光光谱和X射线衍射分析表明，具有倍频效应的BaTiO3晶体已经产生。     

Laser induced crystallization of as-deposited amorphous Ge2Sb2Te5 films

Crystallization is induced by pulsed laser irradiation of s-deposited amorphous Ge2Sb2Te5 films. Changes of the irradiated areas have been analyzed with the reflectivity contrast. As laser fluences increasing,the reflectivity contrast increases from 0% - 2% to 14% - 16%, which indicates the structure of as deposited films transforms from amorphous to crystalline phases. The process of crystallization driven by the movement and rearrangement of atoms is described. And also the influence of the pulse duration on the threshold of crystallization is discussed, the results show that a lower threshold of crystallization can be produced for as-deposited films irradiated by the laser with short pulse duration. However, by the laser with long pulse duration, crystallization can only be formed with a higher threshold. The crystallization of films by irradiation of laser pulses is studied by Raman spectra.     

Laser irradiation effects on gold

Investigations on the laser irradiation effects on gold are explored in terms of plasma-plume dynamics and morphological and crystallographic changes. Annealed 4N gold samples were irradiated with a Q-switched Nd:YAG laser (53 mJ, 21 MW, 532 nm, and pulse width 6–8 ns) for plume dynamics using 10-ns gated fast photography. A Q-switched pulsed Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns) was used to irradiate the surface of the samples for morphological and crystallographic studies of laser-irradiated gold in a vacuum ～10^?3 Torr. The annealed samples were exposed to 50 shots of a Nd:YAG laser (10 mJ, 1.1 MW, 1064 nm, and pulse width 9 ns). The investigation on the plume was done by using an intensified charged-couple device ICCD-5760/IR-UV camera. The morphological investigation of the irradiated surface was carried out by analyzing micrographs obtained using an Hitachi S 3000 H scanning-electron microscope (SEM). The crystallographic studies of the irradiated samples were performed by analyzing the XRD patterns obtained using an X’ Pert Pro Pan Analytical X-ray diffractometer. The investigation on gated ICCD images of the plume reveal that, at very earlier times, the plasma-plume expansion has a linear trend, whereas, at later times, the plasma-plume expansion is nonuniform. SEM micrographs exhibit the primary mechanisms of pulsed-laser ablation (PLA), such as hydrodynamic sputtering, thermal sputtering, exfoliation sputtering, and splashing. The surface morphology was explained in terms of crater formation, swelling, burning, nucleation, grain growth, and nonsymmetric heat conduction. The nonuniform thermal expansion of gold due to thermal-energy transfer is also studied by SEM micrographs, which was supported by XRD analysis. The structural analysis on the basis of XRD shows that the composition of the irradiated samples is not disturbed even after laser irradiation. The grain sizes also changed due to laser irradiation.     

Nd:YAG纳秒激光诱导硅表面微结构的演化

利用Nd:YAG纳秒激光(波长为532和355 nm)对单晶硅在真空中进行了累积脉冲辐照,研究了表面微结构的演化情况.在激光辐照的初始阶段,532和355 nm激光脉冲均在硅表面诱导出了波纹结构,后者辐照硅表面后形成了近似同心但稍显混乱的环形波纹结构.随着脉冲数的增加,波纹结构逐渐演化为一种类似珠形的凹凸结构,最后形成准规则排列的微米量级锥形结构,该微结构的生长依赖于表面张力波和结构自组织.分析发现,形成的交叉环形结构主要是在355 nm激光辐照硅的过程中,表面张力波导致波纹结构部分叠加的结果.     

A physical model of laser-assisted blocking of blood flow: I. Rectangular radiation pulses

A method for the calculation of blocking blood flow upon treatment of vessel pathologies by laser irradiation at a wavelength of 530 nm are considered. The model is based on the assumption that blood-vessel occlusion is a consequence of preceding photothermal coagulation of internal layers of the vessel wall. The irradiation regimes are determined that provide homogeneous coagulation of the vessel wall at a minimal energy consumption and high selectivity of action upon irradiation by rectangular laser pulses.     

二极管激光侧面泵浦腔内倍频Nd：YAG板条激光器研究

用准连续６０Ｗ的二极管激光列阵侧面泵浦“之”字形Ｎｄ：ＹＡＧ板条激光器，当泵浦功率为４５Ｗ，脉宽为４００μｓ时，得到３．５ｍＪ的激光输出。用ＫＤ＊Ｐ电光开关调Ｑ，得到１８ｎｓ（ＦＷＨＭ）、２ｍＪ的脉冲激光输出，用ＫＴＰ晶体作腔内倍频，得到１５ｎｓ、０．８５ｍＪ的二次谐波激光输出。在腔内无调Ｑ元件且腔长小于５ｃｍ时，于近阈值处得到单频绿光输出，而当泵浦功率稍大，腔内有数个纵模振荡时，观察到激光的反相态，并用数值模拟的结果对此作了解释。     

Structural and optical properties of laser irradiated nano structured cadmium oxide thin film synthesized by sol-gel spin coating method

Cadmium oxide CdO nanostructured thin films are synthesized using sol-gel spin coating method. The prepared samples of CdO thin films are irradiated with 10 mJ laser from pulsed Q-Switched Nd:YAG laser at 1064 and 532 nm wavelength. The samples were exposed to 45 pulses of 7 ns pulse duration. Morphology and structural analysis were carried out with scanning electron microscope (SEM) micrographs and X-ray diffraction (XRD) patterns. Optical investigations were obtained with spectrometer and fluorospectrometer from Shimadzu. SEM micrographs confirm the nanostructure of the CdO film and indicate agglomeration of nanoparticles with laser irradiation. XRD patterns show decrease in the intensity of orientation peaks after laser irradiation. Variation in band gap energy, absorption peaks, and photoluminescence spectra with laser irradiation are observed.     

Visualization of nanosecond laser-induced dewetting,ablation and crystallization processes in thin silicon films

In the present work, nanosecond pulsed laser crystallization, dewetting and ablation of thin amorphous silicon films are investigated by time-resolved imaging. Laser pulses of 532 nm wavelength and 7 ns temporal width are irradiated on silicon film. Below the dewetting threshold, crystallization process happens after 400 ns laser irradiation in the spot central region. With the increasing of laser fluence, it is observed that the dewetting process does not conclude until 300 ns after the laser irradiation, forming droplet-like particles in the spot central region. At higher laser intensities, ablative material removal occurs in the spot center. Cylindrical rims are formed in the peripheral dewetting zone due to solidification of transported matter at about 500 ns following the laser pulse exposure.     

双光束组合激光辐照光导型CdS光电探测器的实验研究

为研究波段内和波段外组合激光对光导型光电探测器的辐照效应,实验采用532nm(波段内)和1319nm(波段外)双光束组合连续激光辐照光导型CdS光电探测器,分别改变两束激光的辐照功率,得到探测器的电压响应曲线。实验结果表明,光电探测器对波段内和波段外激光都有响应,但在激光开始和停止辐照瞬间探测器对两束激光的响应电压刚好相反。探测器对波段外激光的电压响应随线性工作区间内的波段内激光功率升高而增大;随着波段内激光趋于饱和,对波段外激光的响应电压近似指数级下降。分析认为,光电探测器对波段外激光的响应为光激发热载流子效应,是由自由载流子吸收激光能量产生带内跃迁引起的;波段内激光辐照影响探测器对波段外激光的吸收系数。