共查询到18条相似文献，搜索用时 250 毫秒
1.
赵超樱 《上海大学学报(英文版)》2007,11(2):195-196
Parametric down-conversion is a useful method to obtain non-classical state in quantum optics.
（1） An analytical solution to the Fokker-Planck equation of non-degenerate optical parametric amplification （NOPA） for generation of squeezed light is presented. The maximum intra-cavity compression of squeezed light derived from the analytical solution is 1/16 （vacuum fluctuations 1/4）. To compare it with the previous 1/8 of degenerate optical parametric amplification （DOPA）, it seems that squeezing for NOPA is superior to DOPA. 相似文献
2.
A deep understanding of the spectral gain characteristics of optical parametric oscillators （OPOs） and optical parametric amplifiers （OPAs） is important for a highly efficient optical parametric conversion. We numerically calculated the spectral gain characteristics of a quasi-phase-matching （QPM） parametric conversion process using the periodically poled 6% （mol/mol） MgO doped LiNbO3 （PPMgLN） as the nonlinear crystal. In the simulation we utilized the approach of a transformative matrix of the periodically poled nonlinear medium, which results from the small-signal approximation of three-wave mixed nonlinear equations. Numerical simulation results show that： （1） The full width at half maximum （FWHM） of the spectral gain of the parametric process becomes wider with the increase of parametric wavelength and reaches the maximum at degeneration; （2） The gain coefficient decreases gradually with the increase of parametric wavelength; （3） The spectral gain bandwidth decreases correspondingly with the increase of the nonlinear material length; （4） There exists an optimal parametric wavelength band, which is most suitable for the high gain parametric conversion when pumped by a laser source with a wide wavelength band, such as the high power fiber laser. 相似文献
3.
The foremost acousto-optic tunable filter(AOTF) was proposed in 1967[1], but the appliedAOTF based on TeO2crystal was not put into practiceuntil 1974, when the non-linear optical design meth-od[2]was proposed. In recent years, AOTF has beenapplied widely as optical splitting component. And ithas attracted more and more attention for its meritssuch as rapid scanning speed, wide tuning range ofspectrum and large aperture of angle of incidence.AOTF is often used for spectrum measurement te… 相似文献
4.
INTRODUCTION Liquid crystal light valves (LCLV) are devices whose function is to convert an input image pos-sessing specific wavelength, intensity and coher-ence to an output image in which some or all of these parameters are varied (Efron et al., 1985). Therefore, they can be used as image amplifiers for large screen projection display, image wavelength converters and incoherent-to-coherent image converters for optical data processing and correlation. The appli-cation potentialities ar… 相似文献
5.
Zhang YZ Zhou YC Liu L Lu Y Hirofumi Y 《Journal of Zhejiang University. Science. B》2007,8(6):416-421
Objective： There are no detailed reports of three-dimensional measurement of abutment teeth in mastication, because it is knotty to observe the rotation in chewing directly, and inexact to estimate indirectly. This work studies the three-dimensional stability of rigidly fixed bridge under the stresses of distributed loads and concentrated loads by optical method that gives the tip angle and rotation angle calculated directly based on measurement data. Methods： The specimen, taken from a 25-year-old male, was a left mandible without the second premolars and the first molars. As abutments, first premolar and second molar have complete periodontium. The specimen was soaked in formaldehyde solution. The bridge was fixed between two abutment teeth （first premolars and second molars）, and the mandible was cemented in a steel box. The load was increased from 0 kg to 23 kg. Laser holographic technique was used to measure the three-dimensional bit shift of the dens, both buccolingual bit shift and mesiodistal bit shift, and determine tip angle and rotation angle. Results： The effects of stress distribution on the rigidly fixed bridge were evaluated, and stabilization of the bridge under the stresses of distributed loads and concentrated loads, respectively, were analyzed. The results showed that the tips of two abutments were very similar, and no distinct difference was observed between the distributed load and the concentrated load. However, the maximum rotation angle for the distributed load was two to four times as large as that for the concentrated load. In the experiment, the tip angle of the abutment teeth was no more than 0.65 degree, and the rotation angle was no more than 0.60 degree. All maximum angles occurred in the second molar. Conclusion： The fixed bridge is considered to be safe. In addition, a method for measuring the rotation angle was provided effectively. 相似文献
6.
The intensity distribution of depolarized field in the focal region of a high numerical-aperture optical system was investigated and found that the depolarization effect is tunable by the plate. The depolarization effect gains with the increase of the inner convergence angle of the phase plate, goes through a dramatic descent when the angle is larger than 30° and begins to come back when the angle reaches a threshold of respectively 60°and 65° for the orthogonal diffractive field and the longitudinal diffractive fields. This reveals two convergence points where the depolarization effect is the strongest and weakest, respectively, suggesting that the pure phase plate can be a promising method for altering depolarization diffractive fields and constructing optical instruments. 相似文献
7.
To improve the sensitivity of protein microarray, a prism surface replaces the surface of the common microscope slide. The protein targets arrayed on the surface are hybridized and labelled by fluorescent probes. Evanescent excitation occurs when the convergent laser reaches the surface, and a photomultiplier tube detects the emitted fluorescent signal. A two-dimensional actuator scans the whole surface to achieve planar laser excitation and fluorescence collection. The penetration depth of the evanescent field into the protein targets is only some hundred nanometers and can be controlled by different incident angle of the laser beam, so the undesired background signals are reduced dramatically and the detection sensitivity is improved by a factor of 50 to 100 comparing to confocal excitation. This approach can detect low abundance analytes without signal amplification. 相似文献
8.
To sharpen the imaging of structures, it is vital to develop a convenient and efficient quantitative algorithm of the optical coherence tomography (OCT) sampling. In this paper a new Monte Carlo model is set up and how light propagates in bio-tissue is analyzed in virtue of mathematics and physics equations. The relations,in which light intensity of Class I and Class 2 light with different wavelengths changes with their permeation depth ,and in which Class I light intensity (signal light intensity) changes with the probing depth, and in which angularly resolved diffuse reflectance and diffuse transmittance change with the exiting angle, are studied. The results show that Monte Carlo simulation results are consistent with the theory data. 相似文献
9.
We developed a novel absolute multi-pole encoder structure to improve the resolution of the multi-pole encoder, realize absolute output and reduce the manufacturing cost of the encoder. The structure includes two ring alnicos defined as index track and sub-division track, respectively. The index track is magnetized based on the improved gray code, with linear halls placed around the track evenly. The outputs of linear halls show the region the rotor belongs to. The sub-division track is magnetized to N-S-N-S （north-south-north-south）, and the number of N-S pole pairs is determined by the index track. Three linear hall sensors with an air-gap of 2 mm are used to translate the magnetic filed to voltage signals. The relative offset in a single N-S is obtained through look-up. The magnetic encoder is calibrated using a higher-resolution incremental optical encoder. The pulse output from the optical encoder and hall signals from the magnetic encoder are sampled at the same time and transmitted to a computer, and the relation between them is calculated, and stored in the FLASH of MCU （micro controller unit） for look-up. In the working state, the absolute angle is derived by looking-up with hall signals. The structure is simple and the manufacturing cost is very low and suitable for mass production. 相似文献
10.
The evaluation of the seismic stability of an expanded municipal solid waste （MSW） landfill is very important in seismic prone zones. In this paper, the pseudo-dynamic method was used to calculate the average safety factor for the expanded landfill with a trapezoidal berm based on under-berm failure conditions. Furthermore, the effects of the variation of parameters such as the amplification factor, seismic coefficient, height of berm, angle of back slope of berm, and depth of waste mass at the back slope on the seismic stability of the landfill were studied. The results indicated that the influences of the vertical seismic coefficient, height of berm, and angle of the back slope of the berm on the seismic stability of the landfill are weakened as the amplification factor increases, but the influence of the horizontal seismic coefficient on the seismic stability of the landfill is strengthened. On the other hand, a certain ratio of the height of the waste mass above the back slope to the depth of waste mass at the back slope, or the reasonable consideration of the magnitude of the amplification factor will be conducive to the seismic design of the landfill. In addition, the results obtained by the pseudo-static and pseudo-dynamic methods were compared. 相似文献
11.
吴丽双 《泉州师范学院学报》1999,(4)
用５ｍ ｍ 的 Ｋ Ｔ Ｐ（ Ｋ Ｔｉ Ｏ Ｐ Ｏ４）和 Ｂ Ｂ Ｏ（β Ｂａ Ｂ２ Ｏ４）非线性晶体,对皮秒的 Ｃ Ｐ Ｍ , Ｎｄ： Ｙ Ａ Ｇ 脉冲激光的腔外倍频效应进行研究,获得倍频能量转换效率分别为４２％ 和３２％ ,证明 Ｋ Ｔ Ｐ倍频效率高于 Ｂ Ｂ Ｏ,结果与理论分析相符 相似文献
12.
在应用高分辨电子显微技术测定蛋白质晶体结构中,由于蛋白质晶体对辐射损伤的敏感性和真空损伤等原因,使蛋白质晶体高分辨成象困难且有别于通常的高分辨成象.本文应用光学衍射方法,对蛋白质晶体高分辨成象条件进行了测定和分析. 相似文献
13.
利用传输矩阵法理论,对双正、双负和单负介质构成的对称结构光子晶体能带谱进行了对比研究,结果得到：由不同介质材料构成的对称结构光子晶体,其能带谱存在很大的差异,其中以单负介质光子晶体禁带宽度最宽,双负介质光子晶体次之,双正介质光子晶体的禁带宽度为最窄;当周期数变大时,光子晶体禁带中的透射峰带宽均逐渐变小并趋于尖锐,且以单负介质的光子晶体透射峰带宽减小的速度为最快;介质厚度dB对单负介质光子晶体的调制效果要优于对双正和双负光子晶体的调制效果;入射角对单负介质光子晶体能带谱的影响要大于对双正和双负介质光子晶体.不同介质材料构成的对称结构光子晶体的这些光传输特性,可为镜像对称结构光子晶体的设计以及窄带或是宽带光子晶体光学滤波器件等提供理论指导. 相似文献
14.
徐海斌 《湖州师范学院学报》2005,27(2):36-39
从非线性耦合的基本方程出发,描述了光学二次谐波（SHG）产生,分析了影响二次谐波转换效率的各个因素,阐述了相位匹配的概念,解释了准相位匹配（QPM）技术对提高非线性光频转换效率的作用,最后与传统的双折射相位匹配（BPM）相比较,总结得出利用准相位匹配技术在实现非线性光频转换过程中所具有的优点. 相似文献
15.
高潮 《深圳信息职业技术学院学报》2007,5(2):14-18
本文结合有源矩阵液晶显示器件及其驱动技术的发展,分析了TFT-LCD驱动电路的工作原理与电源设计,介绍了一种用于六位数字屏的全新TFT-LCD驱动电路,并对头盔显示器液晶显示及驱动电路设计方法加以详细讨论,软件编程调试与电路实验,取得了好的显示效果。 相似文献
16.
李卓 《周口师范学院学报》1999,(5)
研究设计了一种高效异型BaTiO3晶体自泵浦相位共轭镜,获得了共轭反射率大于60％的高效输出,测出了共轭反射率随光束入射位置和晶体内光束与十C夹角的不同而变化的实验曲线,文中还给出了其它实验结果和结论． 相似文献
17.
采用传输矩阵的计算方法,研究了一维光子晶体掺杂结构对光传输特性的影响,利用MATLAB绘制不同结构参数的一维光子晶体第一带隙透射率图谱.通过绘图发现：对称一维光子晶体的周期结构（（BA）m（AB）m）,在带隙内部出现光子局域,在中心波长处产生共振隧穿效应;增加对称周期层数,能够降低隧穿效应的透射率,降低光子局域带宽;提高掺杂层折射率,降低光子局域带宽,局域中心向短波方向移动;增大入射角,光子局域中心向短波方向移动;选择适当的结构参数能够实现在1 550 nm光波附近的窄带滤波器的设计. 相似文献
18.
由两矢量间的角引入由一矢量到另一矢量的有向角,讨论了它的性质,给出了用有向角表示矢量的几个公式并由此得出求图形参数方程的方法. 相似文献