248 nm imaging photolithography assisted by surface plasmon polariton interference

A new photolithography technique for 248 nm based on the interference of surface plasmon waves is proposed and demonstrated by using computer simulations.The basic structure consists of surface plasmon polariton（SPP）interference mask and multi-layer film superlens.Using the amplification effect of superlens on evanescent wave,the near field SPP interference pattern is imaged to the far field,and then is exposed on photo resist（PR）.The simulation results based on finite difference time domain（FDTD）method show that the full width at half maximum（FWHM）of the interference pattern is about 19 nm when the p-polarization light from 248 nm source is vertically incident to the structure.Meanwhile,the focal depth is 150 nm for negative PR and 60 nm for positive PR,which is much greater than that in usual SPP photolithography.     

Omnidirectional iridescence via cylindricallypolarized femtosecond laser processing

We report the femtosecond(fs)laser fabrication of biomimetic omnidirectional iridescent metallic surfaces exhibiting efficient diffraction for practically any angle of light incidence.Such diffractive behavior is realized by means of multi-directional low-spatial-frequency,laser-induced periodic surface structures(LSFL)formed upon exploiting the cylindrical symmetry of a cylindrical vector(CV)fs field.We particularly demonstrate that the multi-directional gratings formed on stainless steel surface by a radially polarized fs beam,could mimic the omnidirectional structural coloration properties found in some natural species.Accordingly,the fabricated grating structures can spatially disperse the incident light into individual wavelength with high efficiency,exhibiting structural iridescence at all viewing angles.Analytical calculations using the grating equation reproduced the characteristic variation of the vivid colors observed as a function of incident angle.We envisage that our results will significantly contribute to the development of new photonic and light sensing devices.     

Effect on the Propagation Characteristics of the Electromagnetic Waves by the Second-order Radiation of the Moving High-speed Train＊

The effect on the propagation characteris- tics of the electromagnetic waves by the second-order ra- diation of the moving high-speed train is analyzed in this paper. Two Lorentz transformations, one from the sta- tionary reference coordinate system to the moving system and the other vice versa, are employed to derive the the- oretical model for analysis of the propagation characteris- tics of the vertical polarized plane time-harmonic waves, which is oblique incidence to the train. The calculation re- suits show that for the transmitting wave reflected by the moving high-speed train, two main signals can be received. One is at the transmitting frequency and the other is at the second-order radiated frequency. The frequency spectrum between these two frequencies are much larger than which is introduced by the Doppler shift. The frequency and the reflection angle of the reflected wave are no longer equal to the frequency and the incident angle of the incident wave. The changed reflection frequency and angle are related to the train＇s velocity, the incident angle and the azimuth an- gle of the incident wave. The frequency shift is mainly decided by the y-component of the train＇s velocity. It has nothing to do with y-component of the train＇s velocity. The reflection angles will be smaller than the related incident angles when the train goes along --y direction. The reflec- tion angles will be larger than the related incident angles when the train goes along ＋y direction. The reflection an- gle will become larger and larger with the increase of the incident angle and the y-component of the train＇s velocity. The induced current density and the charge density on the surface of the train are increased with the train＇s velocity, and the induced charge is much smaller than the induced current.     

Optical Nonlinearity of Surface Plasmon Resonance Emission from Au Colloidal Nanoparticles

Suspended gold nanoparticles have been synthesized via electrochemical method.Fluorescence excitation and emission spectra were obtained using a spectrofluorophotometer.With varying the excitation wavelength,an emission peak fixed at 485 nm has always been observed.We believe that this peak is attributed to the surface plasmon resonance.When the detection wavelength was fixed at 485 nm (0.619×10 15 Hz),a double frequency exciting peak at 242 nm(2×0.619×10 15 Hz), a 3/2 fraction frequency exciting peak at 330 nm (about 3/2×0.619×10 15 Hz)and a 3/4 fraction frequency exciting peak at 640 nm(3/4×0.619×10 15 Hz)display.The nonlinear exciting peak at 640 nm corresponds to the two-photon absorption.Therefore,as the excitation wavelength is at 320 and 640 nm respectively,single-photon and two-photon absorption induced surface plasmon resonance emission peaks were observed. These nonlinear surface plasmon resonance emission characters of Au colloidal nanoparticles make it possible to enhance the sensitivity of conventional surface plasmon resonance device.     

Broad area quantum cascade lasers operating in pulsed mode above 100 ℃ at λ ～ 4.7μm

We demonstrate a broad area (400 μm) high power quantum cascade laser (QCL). A total peak power of 62 W operating at room temperature is achieved at λ~4.7 μm. The temperature dependence of the peak power characteristic is given in the experiment, and also the temperature of the active zone is simulated by a finite-element-method (FEM). We find that the interface roughness of the active core has a great effect on the temperature of the active zone and can be enormously improved using the solid source molecular beam epitaxy (MBE) growth system.     

A switchable dual-wavelength erbium-doped fiber laser based on Sagnac loop inserted with two FBGs

A novel switchable dual-wavelength erbium-doped fiber （EDF） laser is demonstrated. The wavelength selection ele- ment consists of two fiber Bragg gratings （FBGs）, a polarization controller （PC） and a 3 dB coupler forming a Sagnac loop inserted with two FBGs. We study the effect of coupling ratio on filtering performance in this paper. By adjusting PC, we can change the wavelength-dependent loss, and then using nonlinear polarization rotation effect to suppress the mode competition caused by the homogeneous broadening of EDF, we obtain single- and double-wavelength laser outputs. At room temperature, under 200 mW pump power, dual-wavelength laser is achieved, and the center wave- lengths are 1545.34 nm and 1548.20 nm, respectively. The peak power values are -13.36 dBm and -14.58 dBm, and side mode suppression ratios （SMSRs） are 41.10 dB and 39.88 dB, respectively. Within two hours, the maximum fluctuation of peak power is less than 0.7 dB, which shows that the demonstrated fiber laser is stable. Moreover, by adjusting PC, singel-wavelength laser output is obtained, the peak power is -6.27 dBm or -5.45 dBm, and SMSR is 40.03 dB or 39.96 dB at 1545.34 nm or 1548.20 nm, respectively.     

Optical Pulse Compression Based on High-doped Erbium Fiber Amplifier and Standard Single-mode Fiber

Proposed is a novel optical pulse compression technique based on high-doped erbium fiber amplifier and standard single-mode fiber（SMF）. We used the amplifier with the erbium ion concentration of 6.3）〈 10^-3 to amplify a hyperbolic secant pulse from a regeneratively mode-locked fiber laser. The central wavelength, pulsewidth and peak power of the pulse are 1 550 nm, 12. 5 ps and 3 mW, respectively. Then the amplified pulse with peak power level corresponding to a higher-order soliton is compressed when it propagates through a 3-km-long single-mode fiber. Studied are the compressed pulses under different pump powers and fiber lengths. The results show that it can get a narrower pulse, and solve the difficulty that pulses at low power can not be compressed directly in the fiber. And the construct is compact.     

Study on reflection characteristics of underwater target and laser echo power

For the design of the underwater laser detection system, the echo power equation of underwater target is derived, and the effects of water’s attenuation coefficient and incident angle on target’s echo power are analyzed. The bidirectional reflection distribution function(BRDF) of the single-station model is used to study the reflection characteristics of the target. The influence of the correlation coefficients of specular and diffuse reflection components on the reflected light intensity of special axisymmetric targets is studied. The signal-to-noise ratio(SNR) values of three types of target under different surface BRDF are given. The simulation results show that the larger the attenuation coefficient is, the smaller the echo power received, and the incidence angle is closer to 90°, the echo power is equal to 0. A smaller surface slope or a larger diffuse reflected coefficient will cause a smaller reflected intensity.     

Adaptive optical design in surface plasma resonance sensor

A double-prism adaptive optical design in surface plasma resonance （SPR） sensor is proposed,which consists of two identical isosceles right-triangular prisms. One prism is used as a component of Kretschmann configuration, and the other is for regulation of the optical path. When double-prism structure is angle-scanned by an immovable incident ray, the output ray will be always parallel with the incident ray and just has a small displacement with the shift of output point. The output ray can be focused on a fixed photodetector by a convex lens. Thus it can be avoided that a prism and a photodetector rotate by 8 and 28 respectively in conventional angular scanning SPR sensor. This new design reduces the number of the movable components, makes the structure simple and compact, and makes the manipulation convenient.     

Diode-pumped Doubly Q-switched Nd∶YAG Laser with Acoustic-optical Modulator and Cr~(4+)∶YAG Saturable Absorber

A diode-pumped doubly Q-switched Nd∶YAG laser operating at 1064nm both with an acoustic-optical(AO)modulator and Cr4+∶YAG saturable absorber in the cavity is demonstrated.At the incident pump power of 11.8W the laser can generate stable 8ns pulse with the peak power of 23.6kW at a 10kHz repetition rate.The pulse temporal profile is more symmetric and shorter compared with that of passively Q-switched lasers with only AO-active and Cr4+∶YAG.A reasonable analysis is developed to explain the experimental resul...     

激光入射角度对激光表面硬化效果的影响

研究不同激光入射角度对不同类型高功率ＣＯ_２激光表面硬化效果的影响。选定激光器后，在相同的输出功率，扫描速度，离焦量下，随着激光入射角度的变化，试样表面吸收的实际功率密度发生变化，因此引起激光硬化深度、硬化宽度、表面显微硬度变化。只有法线方向的能量被吸收，随着入射角度的增大。淬硬层的宽度逐渐增大，实际结果和理论计算基本相一致。     

高曝光深度的表面等离激元光刻直写头设计分析

设计了一种新的具有高曝光深度的纳米光刻直写头，它由用薄银层制得的V型孔、匹配液和有机固化层组成。V型孔被用来聚焦入射光束于200 nm的光斑中。直写头通过匹配液在光刻胶上移动，而匹配液与石英基底相结合，构成了表面等离激元（SPP）谐振腔，由传播波及反射波形成的驻波的传播深度将达到几百纳米。模拟证明了新的直写头可通过F-P效应及SPP多次激发增强方式实现在光刻胶中深度曝光，当直写头与光刻胶的间距大于90 nm时，不仅可避免光刻胶和直写头的相对磨损，也有助于降低机械移动工艺的要求，因此在纳米掩模板和纳米光子器件的制备上有较高实际应用的可能性。     

近红外波长下COMSOL软件实现新型耦合器的设计

一直以来条状表面等离子波导被认为是实现高集成光路的有效器件,首先采用经典的Drude模型对条状波导中SPP激发与传播特性完成了分析。针对可见光到近红外入射波长的条件完成了条状SPP波导的模场分布的研究,得出,当金属的厚度不变宽度越大,电磁场分布就越集中在条状波导的两侧;当金属条状的宽度不变,厚度越大时电磁场分布会越集中在金属内;入射波长越长会使得金属条状周围电场的集中越小,且还会导致信道间的干扰。利用得到的条状波导特性进而设计了一种新型的耦合器,器件设计结果表明:条状SPP波导在有限传输距离上能量完全转移只发生一次;波长较长时,场的集中度减小,耦合增强;条状SPP波导耦合器可以实现1310 nm和1550 nm的光波分复用。这一研究对光子器件的发展有一定的理论和实际意义。     

A theory of wave scattering from an inhomogeneous layer with an irregular interface

Bistatic wave scattering from a layer of Rayleigh scatterers with an irregular interface is investigated by combining the doubling method in volume scattering with the Kirchhoff method in rough surface scattering. Theoretical results are shown illustrating the effect of the rough interface. It is found that for scattered and incident angles near the vertical, the rough interface causes a substantial increase relative to the plane interface in both the like and cross-scattering coefficients over all azimuth angles. However, for large scattered and incident angles, the reverse is true except for azimuth angles around the specular direction. It is interesting to note that while one dominant peak of the like polarized scattering coefficient occurs along the specular direction, two dominant peaks of the cross-polarized scattering coefficient may appear symmetrically with respect to the specular direction. In backscattering, the surface roughness causes a peak to appear in both the like and cross-scattering coefficients at near vertical incidence and also a decrease of these coefficients at large incidence angles.     

二维粗糙面两束波束散射特性研究

基于Kirchhoff近似,推导两束波束散射强度相关系数的表达式,数值计算漫射强度及散射强度相关系数随角度差、相关长度及粗糙度变化情况。结果表明:散射角对粗糙表面相干散射强度与光滑表面相干散射强度的比值有影响,当两束波束的入射角、方位角均相等,意味着两束波束相互重合且散射强度比值为单波束比值的四倍;当两束波束的入射角、方位角中有一个角度不相等,由散射场干扰效应的影响,相干散射强度比值都会减小。相关长度的变化与漫射强度和散射强度相关系数均成正比;随着入射角度差增大,漫射强度的后向散射效应增强,且散射强度相关系数变小,说明两束波束的干扰越严重;随着散射角的增大,总散射强度受干扰项散射强度影响较大,则后向散射效应增强。     

基于SPP的1550纳米光波导的超长传输特性

采用严格电磁理论研究了介质-金属-介质型光波导激发表面等离子激元(SPPs)的电磁特性,对比分析了SPP波在SiO2/Ag/SiO2和Si/Ag/Si光波导的传输距离。研究表明,对于1550nm光通信波长入射光及10nm厚的金属银膜层,SiO2/Ag/SiO2光波导中非对称SPP的传输距离可达40cm,明显高于对称SPP波的传输距离,也显著高于非对称SPP波在Si/Ag/Si波导中的传输距离,具有超长传输距离;随着金属层厚度的增加SPP波的传输距离明显减小,当银层厚度超过50nm后,非对称的SPP在SiO2/Ag/SiO2及Si/Ag/Si波导中的传输距离趋于一致,约为200nm;此时银层厚度变化对SPP波传输距离的影响明显减弱。     

Light Emission Characteristics of Metal/Insulator/Metal and Metal / Insulator/ Si Tunnel Junctions Mediated by Surface Plasmon-polaritons

The Au/Al2O3/Al metal/insulator/metal junction（MIMJ） and Au/SiO2/Si metal/insulator/Si junction（MISJ） have been constructed successfully. The light emission of these junctions was mediated by surface plasmon-polaritons（SPPs） under surface roughness. The light emission from MISJ was more uniform and stable than that from MIMJ. The light power of MISJ was about 2-3 orders higher than that of MIMJ. The light emission spectrum of MISJ was analyzed especially. In the spectrum, there was one main peak located at the wavelength of 610 nm-640 nm, which was mainly due to the couple of SPP with the surface roughness at the Au/air and Au/SiO2 interfaces. A weak peak located at the shorter wavelength region in the spectrum was also found, which was caused by the direct radiation of doped-Si plasma oscillation.     

Coherent Control of Wave Beams Via Unidirectional Evanescent Modes Excitation

Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. This study proposes a more general metasurface paradigm for coherent perfect absorption with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. It shows theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e., switching from coherent perfect absorption to full reflection. It hopes that this study will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, optical computing, one-side sensing, photovoltaics, and radar cross-section control.     

MDM光波导激发高阶SPP模的传输特性

研究了金属-介质-金属(MDM)型表面等离子体激元(SPP)光波导的电磁特性。理论计算结果表明,对于633nm的TM偏振入射光,当介质膜层厚度小于85nm时,波导中只能激发产生一阶SPP模(基模),其余高阶模全部截止。随着介质膜厚度增加,高阶SPP模逐渐被激发产生。当介质膜层厚度较小时,SPP模的有效折射率的实部随阶数的增加而减小,而虚部则随阶数的增加而增加,SPP基模具有最大传输距离。然而,当MDM波导中的介质层厚度超过0.555μm时,由于三阶SPP模的电磁场主要集中在离金属层相对较远的介质层中,其有效折射率的虚部具有最小值,具有最大的传输距离,而非基模。当入射光波长为633nm介质层厚度为0.9μm时,Ag/SiO2/Ag光波导中三阶SPP模的传输距离达到约150μm。