蒙特卡罗模拟多束光辐照下生物组织中的光吸收分布

用蒙特卡罗方法模拟了均匀分布光和高斯分布光在生物组织内的传播。通过比较单束以及多束均匀分布光和高斯分布光照射下组织内的光子能量分布规律,分析了不同光源和光斑大小对光吸收分布的影响。结果表明:与均匀光束比较,高斯光束辐照时,激光能量较为集中,但侧向传播范围较窄。在总功率相同的情况下,使用单束大功率宽光源与多束功率较小的小光斑光源均能明显地增大光的侧向传播距离,但使用多束功率较小的小光斑光辐照时生物组织中的最大光吸收率增大。多束组合光源光束间距对光吸收分布影响很大。

多束光在皮肤组织中传输的蒙特卡罗模拟

光在皮肤组织中的输运情况决定了激光皮肤外科手术治疗的有效深度和疗效。采用蒙特卡洛方法,模拟多束平圆光和高斯光辐照皮肤组织,分析光束间距对光分布的影响,比较平圆光束和高斯光束光能流率分布的异同。结果表明,光束间距为2R的多束光入射时,平圆光束的光能流率实现了均匀的径向展宽。光束间距为R时,高斯光束穿透深度更深,光能流率峰值更大;平圆光束和高斯光束在叠加区域光能流率均明显增大,平圆光束增幅较大,二者光能流率在非叠加区域均与单束光相近;二者辐照光束越多,叠加区域出现径向展宽越大。光束间距对光能流率影响的研究有助于激光皮肤外科手术中治疗方案的优化设计。

多束光读取头为消费者带来福音

CD-ROM驱动器是受广大消费者欢迎的电子产品,特别是由于近年来CD-ROM盘片所收藏的图形、活动 图像信息日益丰富,需求更显高涨。遗憾的是CD-ROM驱动器的连续数据传送速度很低,1倍速产品的的数据传送速度仅为150KB/s;虽然,现行最高速CD-ROM已有36倍速产品,售价偏高姑且不谈,实际运行并不可靠,也实在令人恼火。鉴于此情,一家叫作Canwood的公司和美国的ZEN Research Inc.合作,现已开发出40倍速的新型CD-ROM产品(UCR004010),可以说是消费者一大福音。这种UCR004010型CD-ROM驱动器。

空气隙厚度对格兰—泰勒棱镜透射光强扰动影响的理论分析

以格兰–泰勒棱镜为例,根据实验现象对透射光强随旋转角扰动的原因进行了理论分析。通过泰勒棱镜的单色偏振光束在空气隙处发生多束光的干涉,使得透射光强依赖于入射角的大小。实验中棱镜振动引起入射角的微小扰动,导致了透射光强的扰动。着重分析了泰勒棱镜空气隙的厚度对于扰动的影响,并在此基础上讨论了减小扰动的方法,通过选取合适的空气隙厚度以及对棱镜的结构角做相应的调整可有效地减小扰动。

掌声

妈妈说我迷糊得哪天把自己弄丢了还不知道,妹妹笑我高度近视得像“大侠(瞎)”,可为什么我的坏记性却总还记得那一刻的掌声?为什么记忆里还清晰的映着那副美妙、温馨的画面?……五十多双天真无邪的小眼睛期盼而猜疑的望着教室门口,于是五十多束光在这里织成一张密密的网——但愿别把那位新来的小女孩吓住。老师说,她是一个“自卑”的小女孩。什么是自卑呢?妈妈说,就是害羞呗。害羞?因为大家望着她吗?

Waveguide Prism Based on Porous Silicon

The fabrication of the oxidized porous silicon waveguide prism is reported by selectively electrochemical anodisation process. The direction changes of light beams in TE and TM polarization out of this waveguide prism were respectively measured,and the experimental results were analyzed.

New modulator for the optical signal in a fiber

A new modulator for the optical signal in a fiber based on multi-beam interference is designed.In the experiment,the distance of a couple of abutted fibers was modulated through a piezoelectric ceramic pipe driven by 50 Hz AC voltage,so that the amplitude of the transmitted optical signal was modulated.The modulation ratio is about 10%,S/N ratio is about 60 dB and the bandwidth is about 200 KHz.

Evidence of Dual Scale Porous Mechanisms During Fluid Migration in Hardwood Species (Ⅰ) Using the Attenuation of a Aolychromatic X-ray Beam to Determine the Evolution of Moisture Content During Imbibition of Beech

An experimental device able to determine the moisture content of wood usingX-ray attenuation is used to study the imbibition of beech samples (Fagus silvatica). The apparatusincludes an X-ray generator, a protective tube, collimating plates and a 50 mm detector. Detectedparticles can be categorised by energy (accuracy of the order of 20%) or by position (accuracy 100μm). The independent choice of both the energy spectrum (through the voltage) and the counting rate(through the current intensity) makes the installation very flexible. However, a rigorous treatmentis necessary to deal with the attenuation of a polychromatic spectrum. The appropriate calculationsare presented and validated with homogeneous samples made of wood and water. In addition, someresults are presented with samples heterogeneous in density and moisture content. Finally, theexperimental device is used to study the evolution of moisture content during saturationexperiments, for which the moisture migration is mainly due to capillary forces. The geometricalconfiguration was so arranged that the transfer can be studied in two directions simultaneously.

Terahertz polarization beam splitter based on photonic crystal and multimode interference

We design a compact terahertz(THz) polarization beam splitter. Both plane wave expansion method and finite-difference time-domain method are used to calculate and analyze the characteristics of the proposed device. The designed polarization beam splitter can split TE-polarized and TM-polarized THz waves into different propagation directions. The simulation results show that the extinction ratios are larger than 18.36 dB for TE polarization and 13.35 dB for TM polarization in the frequency range from 1.86 THz to 1.91 THz, respectively. The designed polarization beam splitter has the advantages of small size and compact structure with a total size of 4.825 mm×0.400 mm.

Enhancing the electric fields around the nanorods by using metal grooves

To enhance electric fields around nanorods,a Ag nanorod-groove system is presented and its electric field distribution is studied using the finite difference time domain method.Since the superposition of the electric fields of the split multi-beam of light works as excitation for electron oscillations in the nanorods,enhanced electric fields occur around the nanorods.In addition,the effects of topological parameters of the nanorod-groove system,such as the oblique angle of the groove,displacement of the nanorod to the bottom of the groove,and separation between the nanorods on electric field distributions are also studied.These results may be helpful for designing substrates to obtain larger electric fields around nanorods.

Beam conditions for radiation generated by an electromagnetic Hermite-Gaussian model source

Within the framework of the correlation theory of electromagnetic laser beams,the far field cross-spectral density matrix of the light radiated from an electromagnetic Hermite-Gaussian model source is derived.By utilizing the convergence property of Hermite polynomials,the conditions of the matrices for the source to generate an electromagnetic Hermite-Gaussian beam are obtained.Furthermore,in order to generate a scalar Hermite-Gaussian model beam,it is required that the source should be locally rather coherent in the spatial domain.