Fractional scanned carbon dioxide laser induces collagen remodelling in murine dermis

Resurfacing using a fractional CO₂ laser shows an important promise in the therapy on photoaged skin. The present study investigated that fractional CO₂ laser with a special sequential scanned manner induced the collagen remodelling in murine dermis. The results showed that laser resulted in the improvement of elasticity and histology in the murine dermis, meaning laser efficacy depends on both of the collagen formation and organization. We further investigated the relations between skin elasticity and type I, and type III collagen. These data demonstrated that laser could significantly lead to the collagen remodelling in murine dermis and induce neocollagenisis as a mode of resurfacing.     

量子相干控制化学反应的进展和机遇

1995年 ,人们曾预言“量子控制多体动力学将成为化学物理的主流”(引自第 2 0届Ｓｏｌｖａｙ化学会议上ＳｔｕａｒｔＡ .Ｒｉｃｅ的主旨演说 .Ｓｏｌｖａｙ会议是研讨未来科学的高级会议 .这一届会议的主题是“光化学 :化学反应及其飞秒尺度上的控制”) .现在 ,我们看到了这股潮流正源源而来 ,每年都不断地在Ｎａｔｕｒｅ、Ｓｃｉｅｎｃｅ等杂志上刻下了里程碑 .人们一直希望控制化学反应的方向和历程 .早期的控制是被动的控制 ,即通过把握反应的宏观条件 (如温度、压力等 )或者选择适当的催化剂去实现 .自从分子反应动力学发展之后 ,人们在…     

Photon kinetics for laser-plasma interactions

A photon kinetic formalism is employed to describe the propagation of short laser pulses in tenuous plasmas. The photon kinetic theory contains all of the ingredients necessary to describe the relativistic nonlinear optics of short laser pulses in plasmas, and the shortest time scale is determined by the local evolution of the index of refraction. We use this feature to implement a photon in cell code, in which the typical time step is much bigger than is the laser field time scale. Additional information provided by the photon kinetic framework is illustrated by one-dimensional (1-D) and two-dimensional (2-D) simulations     

用行波速率方程组确定半导体激光器的输出场

为了解决在平均场近似速率方程中自洽地由激光器腔内平均场来确定输出场的问题,以半导体激光器为例,采用集总形式的端面反射率,通过求解行波速率方程组,得出了半导体激光器腔内平均光子数密度与输出光子数密度的解析关系式.结果表明,半导体激光器输出场与腔内平均场之比是一个与泵浦电流有关的量,把它当成常数是有偏见的.     

Pump wavelength dependence of hot electron temperature in GaAs

We have measured the variation of the temperature of the photoexcited hot electrons in GaAs as the pump photon energy is varies from 1.54 to 2.83 eV using various dyes in N₂ laser pumped dye laser. We find that the photon flux required to obtain a given temperature (45°K) increases by a factor of 15 as the photon energy decreases from 2.83 to 1.54 eV. The results are in agreement with a simple theory, and allow us to draw interesting conclusions about energy relaxation processes in semiconductors.     

单光子波长调制吸收光谱用于1.5 μm激光器的波长锁定

提出了一种kHz调制频率量级的单光子调制技术,实现对激光器的实时锁定. 通过探测乙炔气体的单光子吸收光谱,对离散的单光子响应脉冲进行锁定放大, 获得激光器频率锁定的鉴频曲线.将1.5 μm分布反馈半导体激光器的输出频率稳定在乙炔气体 ν₁ + ν ₃带P5e支吸收峰上,在175 s内典型激光频率起伏小于25 MHz. 这种基于单光子波长高频调制吸收光谱的稳频技术消除了低频段较高背景的噪声, 可应用于单光子量级的量子保密通讯系统以及光学波分复用系统.     

激光二极管抽运Nd:YV04和频黄光激光器的理论及实验研究

为了达到最佳和频593 nm黄色激光输出,采用激光二极管(LD)端面抽运Nd:YVO4晶体,根据四能级系统的速率方程理论,建立了空间相关的两波长激光运转速率方程模型,由此导出两波光子数表达式.对LD端面抽运Nd:YVO4/KTP三镜复合腔结构的腔内和频黄光激光器,在满足参与和频的两基频光光子数密度相等的条件下,理论上得到了谐振腔的各个参数.实验比较了在满足两波光子数密度相等和两波振荡阈值相等两种情况下激光器输出的593 nm黄色激光功率.在抽运功率为12 W时,二种情况下分别得到了410 mW和340 mW的黄光输出,光一光转换效率分别为3.4%和2.8%.由此可见,在满足两波光子数密度相等的条件下可以得到更高转换效率的和频黄光输出.     

双光子技术在三维成像和三维存储技术中的应用

对双光子过程的空间分辨能力进行了理论分析。阐明了双光子技术在三维成像和三维存储中的独特优势。着重介绍了双光子技术与扫描共焦显微术、近场显微术相结合进行三维成像 ,以及一种多焦点多光子显微术和用连续光源激发的双光子三维成像技术的研究和进展情况。对建立在共焦显微镜基础之上的双光子三维光存储和微细加工方面的研究也作了回顾与展望     

Spectral density matrix of a single photon measured

We propose and demonstrate a method for measuring the spectral density matrix of a single photon pulse. The method is based on registering Hong-Ou-Mandel interference between a photon to be measured and a pair of attenuated and suitably delayed laser pulses described by a known spectral amplitude. The density matrix is retrieved from a two-dimensional interferogram of coincidence counts. The method has been implemented for a type-I down-conversion source, pumped by ultrashort laser pulses. The experimental results agree well with a theoretical model which takes into account the temporal as well as spatial effects in the source.     

MeV- and Sub-MeV-photon Sources Based on Compton Backscattering at Spring-8 and KPSI-JAEA

Recently we have constructed two facilities for generating photon beams in the MeV and sub-MeV energy regions by means of the Compton backscattering with a laser and an electron beam at SPring-8 and at Kansai Photon Science Institute of Japan Atomic Energy Agency(KPSIJAEA).The MeV-photon source at SPring-8 consists of a continuous-wave optically-pumped far infrared laser with a wavelength of 118.8 μm and an 8 GeV stored electron beam.Present MeV-photon flux is estimated to be 1.3×10~3 photons/s.On the other hand,the sub-MeV-photon source at KPSI-JAEA consists of a pulse Nd:YAG laser with a wavelength of 1 064 nm and a 150 MeV electron beam accelerated by microtron.In the first trial of the photon production in this source,backscattered photon flux is estimated to be 20 photons/pulse.Both the Compton backscattered photon sources have possibilities to be used for new tools in various fields such as nuclear physics,materials science,and astronomy.     

基于蒙特卡罗模拟的无创生化检测最佳探测距离的研究

人体内各种血液生化成分含量的变化是评价健康状况的重要信息。人体皮肤中,血糖、胆固醇等生化成分主要存在于真皮层的血液中,本文通过研究最佳的探测距离,提高真皮层的近红外光谱信号强度,排除表皮层、皮下组织产生的干扰。首先,通过对人体皮肤的组织结构进行分析,计算得到了皮肤各层的组织光学特性参数,以葡萄糖在合频波段吸收峰2 270 nm处的组织光学参数为例建立了皮肤的蒙特卡罗模型;然后,利用蒙特卡罗方法模拟了光在皮肤中的传输规律,得到了平均路径长度、平均探测深度以及各层吸收光子能量比例随入射角度、探测距离的变化情况。结果表明,光子以小于45°角入射时,可以忽略入射角度对光子传输路径的影响。探测距离为1 mm时,真皮层吸收光子能量所占比例最大,同时又能保证探测器接收到较多的能量。本文确定1 mm作为最佳的探测距离,可以有效降低皮肤中其他组织的干扰,获取真皮层中血液的光谱信息,有利于生化成分的近红外无创检测,为后续实验奠定理论基础。     

Stochastic resonance in single-mode semiconductor lasers

Owing to the considerable virtues of semiconductor lasers for applications, they have become the main optical source for fiber communication systems recently. The behavior of stochastic resonance (SR) in direct-modulated semiconductor laser systems is investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the modulated laser system were calculated using the linear approximation method. We found that the SR always appears in the dependence of the SNR upon the bias current density, and is strongly affected by the cross-correlation coefficient of the carrier and photon noises, the frequency of modulation signal and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNR of direct-modulated semiconductor laser systems and improve the quality of optical communication.     

1064 nm激光不同辐照时间对小鼠皮肤热损伤的实验与理论研究

通过实验和理论分析的方法研究1064 nm激光不同辐照时间对小鼠皮肤的热损伤规律。利用皮肤镜图像和光学相干断层图像评估小鼠皮肤组织热损伤程度,利用Arrhenius热损伤方程计算热损伤参数,建立激光诱导皮肤组织热损伤模型,并与实验结果进行对比。结果表明,在靶功率密度为30 W/mm2的1064 nm激光辐照下,0～100 ms辐照时间内,小鼠皮肤组织损伤可恢复;150～280 ms辐照时间内,小鼠皮肤组织出现水肿现象和热凝固损伤;280～550 ms辐照时间内,小鼠皮肤表皮层出现汽化现象,损伤斑周围出现焦痂,真皮层发生变性;660 ms辐照时间以上,小鼠皮肤表皮层和真皮层出现汽化现象,伤口渗出组织液,皮下组织发生变性。理论分析与实验结果一致,建立的热损伤模型能够验证小鼠皮肤热损伤程度。     

Low-pump sum frequency generation of frequency-stabilized 453 nm blue laser for photonic quantum interface

Generation of a cavity-enhanced nondegenerate narrow-band photon pair source is a potential way to realize a perfect photonic quantum interface for a hybrid quantum network. However, to ensure the high quality of the photon source, the pump laser for the narrow-band photon source should be generated in a special way. Here, we experimentally generate the blue 453 nm laser with a sum frequency generation process in a periodically poled lithium niobate waveguide. A 13 mW laser at 453 nm can be achieved with a low-power 880 nm laser and 935 nm laser input, and the internal conversion efficiency is 21.6% after calculation. The frequency of a 453 nm laser is stabilized by locking two pump lasers on one ultrastable optical cavity. The single pass process without employing cavity enhancement can ensure a good robustness of the whole system.     

Photo-induced surface charge separation of highly oriented TiO2 anatase and rutile thin films

Surface charge separation behavior of photo-generated carriers in highly oriented TiO₂ anatase and rutile films was investigated using a technique in which the transient surface charge is observed by laser pulse irradiation without metal contacts and an externally applied field. According to the measurements, the quantum efficiency of photo-generated holes transported toward the surface was determined as a function of incident laser energy. The photo-generated holes in anatase can be transported toward the surface for irradiation at the photon energy of its bandgap. The holes transported toward the rutile surface, however, were generated close to the surface for irradiation at the photon energy much higher than its bandgap.     

铀原子多色三光子共振电离谱研究

利用Ｎｄ：ＹＡＧ二倍频激光同步泵浦的脉冲染料激光系统、原子束装置、飞行时间质谱和Ｂｏｘｃａｒ技术测量了＾２３８Ｕ的多色三光子共振电离谱。研究了电场对铀原子第一激发态的影响。解决了如何确定三角三光子共振电离谱图中所含的单色,双色和三色共振电离峰的问题。     

基于舰船尾流激光雷达的Monte Carlo模型及方差消减方法研究

对舰船尾流激光散射机理及探测过程的数值模拟是研究舰船尾流激光探测与制导的重要基础.首先分析了Monte Carlo方法引入到尾流激光雷达数值模拟领域研究的可行性.结合自行研制的尾流激光雷达实际参数,建立了尾流激光探测的Monte Carlo数值仿真模型.通过对仿真结果进行统计,深入剖析了仿真结果方差大及光子利用率低等问题的成因.为解决该问题,基于有偏采样理论和分裂-轮盘赌基本原理提出了接收光学视场内光子强行碰撞方法和以光子自由程总长度为准则的光子分裂方法,并进行了两方法的融合.仿真与实验结果的对比分析表明,提出的模型仿真结果与实验数据符合较好,验证了模型的正确性;提出的接收光学视场内光子强行碰撞方法和光子分裂方法能有效减小方差并提高光子利用率;解决了Monte Carlo方法引入到尾流激光雷达模拟过程中的适用性问题.     

光的受激放大

求解在激发作用下通过活性介质的光的输运方程与活性介质中的粒子反转数方程,我们得到在具有任意形式输入下的光子数与粒子反转数的时空分布函数的解析表达式;并以一个方形脉冲或一系列方形脉冲为例进行讨论。此外,我们还研究了强光注入laser对laser的稳定工作点的影响,以及在一定条件下通过微扰方法给出这时laser内的光子数与粒子反转数的形式解,对以红宝石laser为例所作的计算表明通过注入强光有可能成为加强巨脉冲的手段之     

基于激光共焦扫描术的亚心形扁藻显微图像与光谱

采用激光共聚焦扫描显微技术,针对亚心形扁藻开展了研究.从获得的488 nm Ar+激光单光子激发的亚心形扁藻自体荧光光谱与图像,可知细胞内有一杯状叶绿体物质,其荧光峰值为682 nm,对应叶绿体发出的红色荧光.在单通道模式下,获得800 nm fs激光双光子激发的扁藻自体荧光光谱与图像,可知每个杯状叶绿体的内部有一个自体荧光更强的圆形物质.在双通道模式下,可分别获得小圆形物质的自体荧光图像,杯状叶绿体自体荧光图像,以及两个通道图像的叠加.进一步获得了双光子藻细胞荧光图的6个主要的荧光峰.采用单光子激光激发可获得亚心形扁藻叶绿体自体荧光图像及其荧光光谱,而双光子激光激发荧光光谱的多通道以及Lambda模式下采集光谱信号与图像,不仅可观察到亚心形扁藻的内部形态结构,还可能从双光子激发荧光图中研究分析亚心形扁藻生化物质的存在,灵敏度较单光子激发高.激光扫描共聚焦显微技术,特别是双光子荧光与图像技术可为海藻的检测与研究提供一种快速、实时、有效、简便的方法.     

混沌光场光子统计分布及二阶相干度的分析与测量

利用通信波段双通道单光子探测器,采用Hanbury Brown-Twiss关联测量方案,理论分析并实验测量了光反馈半导体激光器产生的混沌光场的光子统计分布及不同混沌状态光场的二阶相干度.通过对混沌光场二阶相干度g~((2))(τ)的理论分析,得出随着延迟时间和相干时间的变化,其与相干光、热光及单光子态的二阶相干度可明显区分并呈现出不同分布.同时实验上产生了频谱宽度6.7 GHz的混沌光场,测量了不同光子数分布的结果,并用高斯随机分布、泊松分布、玻色-爱因斯坦分布对光子数分布进行理论拟合,发现随着入射平均光子数的增加,光子数分布从玻色-爱因斯坦分布过渡到泊松分布,但整个过程都与高斯随机分布符合较好,且光场的二阶相干度g~((2))(0)由2降至1.通过改变偏置电流(I=1.0Ith-2.0Ith)和反馈强度(0—10%),实验上研究了混沌光场由低频起伏到相干塌陷的过程中不同状态宏观动力学特性与二阶相干度的对应关系.结果表明:混沌光场在此过程中始终呈现出明显的聚束效应,并在频谱宽度最大时达到最强;同时给出了光子计数测量中聚束效应减弱的物理原因.实验表明该系统及方法能很好地揭示不同状态混沌光场的光子统计特性.