Study of intensity-dependent nonlinear optical coefficients of GaP optical crystal at 800 nm by femtosecond pump-probe experiment

The intensity-dependent two-photon absorption and nonlinear refraction coefficients of GaP optical crystal at 800 nm were measured with time-resolved femtosecond pump-probe technique.A nonlinear refraction coefficient of 1.7 × 10-17 m2/W and a two-photon absorption coefficient of 1.5 × 10-12 m/W of GaP crystal were obtained at a pump intensity of 3.5 × 1012 W/m2.The nonlinear refraction coefficient saturates at 3.5 × 1012 W/m2,while the two-photon absorption coefficient keeps linear increase at 6 × 1012 W/m2.Furthermore,fifth-order nonlinear refraction of the GaP optical crystal was revealed to occur above pump intensity of 3.5 × 1012 W/m2.     

Study of intensity-dependent nonlinear optical coefficients of GaP optical crystal at 800 nm by femtosecond pump-probe experiment

The intensity-dependent two-photon absorption and nonlinear refraction coefficients of GaP optical crystal at 800 nm were measured with time-resolved femtosecond pump-probe technique. A nonlinear refraction coefficient of 1.7×10-17 m2/W and a two-photon absorption coefficient of 1.5×10-12 m/W of GaP crystal were obtained at a pump intensity of 3.5×1012 W/m2. The nonlinear refraction coefficient saturates at 3.5×1012 W/m2, while the two-photon absorption coefficient keeps linear increase at 6×1012 W/m2. Furthermore, fifth-order nonlinear refraction of the GaP optical crystal was revealed to occur above pump intensity of 3.5×1012 W/m2.     

一个力学问题剖析的启示

1 提出问题 许多大学物理教材或参考书在讲授角动量守恒定律之后会安排类似这样的例题或习题例如:当地球处于远日点时,到太阳的距离是1.52×1011m,轨道速度为2.93×104 m/s.地球处于近日点,到太阳的距离为1.47×1011m.求地球在近日点时的轨道速度.     

锁定放大器在光速测量中的应用

结合声光调制原理和锁定放大器的工作原理,设计了基于调制法的测量光速实验.通过测量和计算得出光速为2.993×108 m/s和3.000×108 m/s,与光在空气中的速度值2.997×108 m/s相比,误差分别为0.13%和0.10%.此方法的优点是光速经过调制后,光的频率被调制为60～100 MHz,使得光波长调制为3～5 m,便于在实验室里进行光速测量.     

Micro thermal shear stress sensor based on vacuum anodic bonding and bulk-micromachining

This paper describes a micro thermal shear stress sensor with a cavity underneath, based on vacuum anodic bonding and bulk micromachined technology. A Ti/Pt alloy strip, 2μm×100μm, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200μm×200μm×400μm, is placed between the silicon nitride diaphragm and glass （Corning 7740）. This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique.     

Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays

The maximum power conversion efficiencies of the top-emitting,oxide-confined,two-dimensional integrated 2×2 and4×4 vertical-cavity surface-emitting laser(VCSEL) arrays with the oxide-apertures of 6 μm,16 μm,19 μm,26 μm,29 μm,36 μm,39 μm,and 46 urn are fabricated and characterized,respectively.The maximum power conversion efficiencies increase rapidly with the augment of oxide-aperture at the beginning and then decrease slowly.A maximum value of27.91%at an oxide-aperture of 18.6 μm is achieved by simulation.The experimental data are well consistent with the simulation results,which are analyzed by utilizing an empirical model.     

Charge sharing effect on 600 μm pitch pixelated CZT detector for imaging applications

We are currently investigating the spatial resolution of highly pixelated Cadmium Zinc Telluride （CZT） detector for imaging application. A 20 mm × 20 mm× 5 mm CZT substrate was fabricated with 600 μm pitch pixels （500μm anode pixels with 100 μm gap） and coplanar cathode. Charge sharing between two pixels was studied using collimated a 122 keV gamma ray source. Experiments show a resolution of 125 μm FWHM for double-pixel charge sharing events when the 600 μm pixelated and 5 mm thick CZT detector biased at -1000 V. In addition, we analyzed the energy response of the 600 μm pitch pixelated CZT detector.     

Charge sharing effect on 600 μm pitch pixelated CZT detector for imaging applications

We are currently investigating the spatial resolution of highly pixelated Cadmium Zinc Telluride(CZT)detector for imaging application. A 20 mm×20 mm×5 mm CZT substrate was fabricated with 600 μm pitch pixels(500 μm anode pixels with 100 μm gap) and coplanar cathode. Charge sharing between two pixels was studied using collimated a 122 keV gamma ray source. Experiments show a resolution of 125 μm FWHM for double-pixel charge sharing events when the 600 μm pixelated and 5 mm thick CZT detector biased at-1000V. In addition, we analyzed the energy response of the 600 μm pitch pixelated CZT detector.     

室内声学时域有限差分模拟中的边界条件

给出了时域有限差分法用于室内声学问题模拟中的边界条件,结合声波方程的基本差分格式,模拟并分析了高斯脉冲在4m×4m房间中的波动过程和脉冲响应;模拟了一9m×6m×4m房间的简正频率,并与经典理论计算值进行了对比;模拟了一12m×5m×4m水平地面房间中的坐席吸声低谷效应,并与Joe LoVtri的模拟结果进行了对比;模拟并实际测量了一10.6m×5.8m×3.4m房间在几个受声点的脉冲响应和早期衰变时间EDT,将模拟结果与实际测量结果进行了对比分析,计算程序是用Metlab语言编写的。模拟与经典理论、相关研究、实际测量几方面的对比分析,验证了本边界条件的可靠性。     

GC-FTIR和GC-MS联用在环状硫代碳酸酯混合物中的应用

采用GC-FTIR和GC-MS建立环状硫代碳酸酯和环状碳酸酯的分析方法.选用HP-5毛细管色谱柱(30m×320μm×0.25μm),分流比50∶1,进样量1μL,进样口起始温度120C,保持5min,升温速率15℃/min,进样口终止温度270℃.质谱采用EI源,选取Scan模式,扫描范围为50到550m/Z.结果表明GC-FTIR可鉴定出3种环状硫代碳酸酯,而GC-MS可同时鉴定出4种环状硫代碳酸酯.     

Chirality-asymmetry force between ɑ-quartz and copper block

The chirality-asymmetry macroscopic force mediated by light pseudoscalar particles between α -quartz and some achiral matter is studied. If this force between achiral source mass and α -quartz with some chirality is attractive, it will become repulsive when the chirality of the α -quartz crystal is changed. According to the tested limits of the coupling constant g_s g_p /\hbar c< 1.5× 10^-24 at the Compton wavelength λ = 10^-3 m, the force (F) between a 0.08× 0.08× 0.002 m³ block of α -quartz and a 0.08× 0.08× 0.01 m³ copper block with a separation being 0.5× 10^-3 \mbox{m} in between, is estimated from the published data at less than 4.64× 10^-24 N, i.e. F < 4.64× 10^-24 N.     

13.5 nm Schwarzschild microscope with high magnification and high resolution

A Schwarzschild microscope with a numerical aperture of 0.2 and a magnification of 130 in a 100μm field of view(FOV)is designed and is working at 13.5 nm.Meanwhile,a CCD is used as a detector with a pixel size of 13μm×13μm and imaging area of 13 mm×13 mm.The imaging quality with tolerances of system and errors of mirrors are considered.We obtain that the best on-axes object resolution can be up to about 200 nm,the average value is 230 nm,and the resolution is about 360 nm at 80μm FOV.     

Snapshot imaging spectrometer based on a microlens array

This Letter proposes a snapshot imaging spectrometer, which obtains the spectral information and spatial information in one "shot". The device proposed can achieve the data cube size of 21 × 29 × 40 in the waveband of400–800 nm. The core element of this system is the microlens array, which contains 60 × 60 microlenses in a square arrangement, each microlens has an aperture of 125 μm× 125 μm, and the F number is 15. The microlens array is mounted in a rotation mount, which provides 360° of rotation around the optical axis to maximize the spectral resolution. The final resolution of the system is about 10 nm.     

Mid-infrared laser with 1.2 W output power based on PPLT

The optical parametric oscillator (OPO) based on the periodically poled lithium tantalate (PPLT) crystal (40 mm×5 mm×1 mm) is fabricated. The OPO is pumped by a Q-switched Nd:YAG laser working at 1.064 μm. An average idler output power (around 3.8 μm) of 1.2 W and signal output power (around 1.48 μm) of 3 W are obtained when the pump power is 20 W.     

A restraining multipath effect method for the measurement of insertion loss of underwater acoustic materials

A method suppressing multipath effect when measuring the underwater acoustic materials in a reverberant field is proposed, which is called "virtual end-fire array method".To weaken the coherence of the same-frequency reflection interference of each path, signal of different phases at different positions was transmitted by a single transducer in the simulation design, and a sharp directionality in the direction of the array length was formed. All signals at the above positions were superimposed to eliminate the clutters. The insertion loss(IL) of the material was finally calculated by extracting the desired waveforms. In the measured frequency range of 3–20 k Hz, the aluminum plate with size of 1.1 m × 1.0 m × 8 mm and the round aluminum plate with 0.5 m in diameter and 8 mm in thickness were measured in a reverberant tank with size of 5.5 m × 3.5 m × 3.5 m. Results showed the measured lowest effective frequency limit can be reduced by the virtual end-fire array technique compared with the conventional method.In the measurement of round aluminum plate and rectangular aluminum plate, errors in the effective measurement band was less than 0.5 d B and the interference of the acoustic multipath propagation effects was reduced effectively. The ability of the transducer in reverberant tank to measure acoustic materials has been improved after implementing this method.     

像素分割对LED电流密度及光照度分布的影响

将300μm×300μm LED芯片阵列化为间隔为20μm的3×3个80μm×80μm的子单元,阵列化后,总饱和光输出功率是未阵列化前的5.19倍,最大注入电流提高近7倍,表明阵列可以注入更大的电流和输出更高的饱和光功率。此外,采用多颗阵列化后的LED芯片形成的芯片组照明,得知芯片组间距为最大平坦条件dmax时,接收面上照度均匀性最佳;芯片组数越多,接收面上均匀照度的面积越大。同时,9颗300μm×300μm的芯片阵列化为9个80μm×80μm LED芯片后,以dmax排列照明相对于9颗未阵列化的300μm×300μm芯片以dmax排列照明时,接收面上的光照度均匀性不变,照度值提高了3倍。     

Mid-infrared optical parametric oscillator based on ZnGeP2 pumped by 2-μm laser

We present a 3 5 μ m optical parametric oscillator (OPO) based on ZGP pumped by KTP OPO 2.1-μ m laser. The tuning curves of ZGP OPO are calculated. The 8 ×6 ×18 (mm) ZGP crystal, whose end faces are antireflection coated at 2.1 and 3.7 4.6 μ m, is cut as θ =53.5°, φ =0°. When the pump power of 2.1-μ m polarized laser is 15 W at 8 kHz, 5.7-W output power and 46.6% slope efficiency are obtained with a ZGP type I phase match. Central wavelengths of the signal and idler lasers are 4.10 and 4.32 μ m, respectively. Pulse duration is about 27 ns. Beam quality factor M 2 is better than 1.8. The tunability of 3 5 μ m can be achieved by changing the angle of the ZGP crystal.     

太阳能光催化-导光管北京夏季晴天降解甲醛的实验研究

太阳能光催化-导光管将太阳光导人的同时兼具光催化空气净化功能.导光管的长度为0.55 m,直径为0.28 m,导光管内表面的平均反射比为0.82.散光板的直径为0.28 m,为雪花型散光板,将光催化剂DegussaP25溶液均匀地喷涂在散光板凹凸不平的一侧,附着在散光板上的DegussaP25质量为1.75 g.实验表明,涂层背对太阳时散光板下的照度比无涂层的散光板下的照度有一定程度的减弱,但是减弱的幅度并不大,平均降幅只有3.03%,因此不会对室内采光产生明显影响.实验表明,夏季晴天上午太阳直射下,太阳能光催化-导光管能够使0.1 m3小室内甲醛体积分数从1.0×10-6下降到0.19×10-6 .中午太阳直射下1 h之内甲醛体积分数从1.0×10-6下降到0.17×10-6;比上午的降解速度加快,降解甲醛更为完全;下午太阳直射下甲醛降解,1 h之内,甲醛体积分数从1.0×10-6下降到0.2×10-6,降解速度比上午、中午都慢,但也达到了良好的降解效果.     

在“汽车以恒定功率行驶”教学中应注意的一个问题

题目:(2009年高考上海题)质量为m=5×103kg的汽车在t=0时刻速度v0=10 m/s,随后以P=6×104W的额定功率沿平直公路继续前进,经t＝72s达到最大速度.设汽车受恒定的阻力,其大小为f=2.5×103N.求: (1)汽车的最大速度vm; (2)汽车在72s内经过的路程s.解析:(1)当达到最大速度时     

水声无源材料插入损失虚拟聚焦测量方法

提出了一种适合在有限尺寸水池中测量水声材料插入损失的方法,称为"虚拟聚焦法"。该方法利用一弧形发射阵以一定规则对样品进行扫描,通过对接收数据进行叠加处理,使得同频声干扰贡献随机化和无规则化,从而提取出反映材料声参数的透射波信号。在尺寸为5.5 m×3.5 m×3.5 m的非消声水池,测量频率为2~15 kHz,对1.1 m×1 m×8 mm标准铝板样品和1 m×1 m×35 mm聚氨酯材料样品进行了测量,结果表明测量值与理论值有较好的吻合,测量不确定度为2.0 dB(k=2)。