Abstract:Five samples of Ag-In alloy films with different compositions were deposited on Si substrates by magnetron sputtering. The optical properties of these films were studied by spectroscopic ellipsometry. The dielectric functions of the alloy films significantly increase as the In concentration in the Ag-In alloy films is increased. For Ag-based alloys, a typical interband transition occurs near 3.9 eV. In the tested alloy films, however, this transition energy exhibits a blue shift with increasing In concentration. The optical properties of the alloy films were found to be tunable by varying their In concentrations. The values of the Quality (Q) factors of the Ag0.93In0.07 film are higher than those of other alloy films. At a certain wavelength range, the alloys’ Q factors even exceed those of pure Au and Cu. Our results show that Ag-In alloys have significant potential for application in metamaterials and plasmonic devices.

Abstract:The effects of Ga doping on structural, electrical, and optical properties of hydrogenated ZnO-Ga (GZO) thin films deposited by sol-gel technique have been investigated. From the X-ray diffraction observations, the films doped with different gallium concentrations were found to be pure wurtzite-structured ZnO. The electrical properties of the hydrogen-annealed films were improved and a lowest resistivity of 3.410×10-3Ω·cm was obtained. The refractive index and extinction coefficient of ZnO-Ga thin films were determined in the range of 270~1600 nm by varying angle spectroscopic ellipsometry (VASE). The simulation was carried out using a double oscillator model, which includes the Psemi-MO equation and the rho-tau Drude equation.

Abstract:A periodic multilayer structure with metal and dielectric layers is proposed to obtain a broad stop-band filter. The influence of three factors (the number of the metal layer (n), the metal layer and the dielectric layer) on the stop-band and central frequency of cross ring resonator (CRR) filter has been investigated. Simulated results indicate that the stop-bandwidth can reach to 2.2THz. Moreover, The stop-band and central frequency can be modulated by selecting appropriate n or dielectric layer, but it is not sensitive to the metal layer.

Abstract:The 3×1 fused tapered fiber bundle (FTFB) signal combiner consisting of three signal fibers and a multi-mode output fiber was studied. The simulation results indicate that the transfer efficiency and output beam quality are getting better with longer taper length. Moreover, transfer efficiency for low-order mode launching is higher than that for high-order mode launching. A 3×1 signal combiner with taper length of 10 mm was fabricated in experiment. The input beam with high beam quality results in high transfer efficiency, which agrees with the simulation results. The transfer efficiency of 96.6%, total output power of 602 W and output beam quality of Mx2=10.5, My2=9.7 were achieved as two fiber lasers with 258 W and 365 W were combined by the FTFB signal combiner.

Abstract:A grating-resonator composite structure was investigated. The output characteristics of Smith-Purcell radiation in this grating-resonator composite structure were studied by optical theoretic analysis and particle-in-cell simulation method. The results show that tunable coherent Smith-Purcell radiation at Terahertz wavelengths can be generated by this novel structure. This novel grating-resonator composite structure has the following advantages: it can reflect all radiation with an emission angle and random azimuthal angles which backs onto the electron beam with same phase and cause the electrons to be modulated.

Abstract:Recent progress of HgCdTe infrared detector with subwavelength photon trapping structure has been reviewed in this paper. A combination approach of finite element method and finite difference time domain method, which can be used for jointly simulating of "light" and "electricity" characteristics in infrared detector, was systematically introduced. Numerical simulation and analysis results based on the HgCdTe infrared detectors with subwavelength microstructure were also demonstrated. The theoretical analysis and experimental data have shown that the subwavelength microstructure can trap photons in active region of infrared detectors. The subwavelength photon trapping structure has a promising prospect on improving the performance of long wavelength infrared detector.

Abstract:Blocked impurity band detectors are of interest for various astronomy applications such as the Infrared Astronomical Satellite and Cosmic Background Explorer. The fabrication details and characterization of Si:P blocked impurity band detectors have been reported. The bottom contact was epitaxially grown instead of utilizing ion-implantation to improve the quality of epitaxial stack. The photocurrent spectra and dark current of the detectors have been measured. The spectral response extends from 2.5 μm to 40 μm. Several additional sharp peaks superimposed on the broadband response are designated to associate with impurity transitions of phosphorus in the blocking layer. The origin of dark current at small bias has been studied at low temperature. It was found that the shield of cryostat is the source of the background infrared light which hits the detectors to produced the dominant dark current at this regime. The detectors attain a peak responsivity of 20.1 A/W (at 28.8) and peak detectivity of 3.7×1013 cm·Hz1/2/W (below a flux of 1013 ph/cm2·s ), which exhibits highly competitive figure of merits.

Abstract:High quality InAs0.94Sb0.06 films were grown on InAs substrates by the liquid phase epitaxy technique. The structural characteristics and cross-section morphology of InAs0.94Sb0.06 samples were investigated by high-resolution x-ray diffraction measurements and scanning electronic microscopy measurements, respectively. The refractive index and extinction coefficient spectra of InAs0.94Sb0.06 film near the energy band gap were obtained by fitting room temperature infrared spectroscopic ellipsometry with the model of dielectric function in the range of 3 000 to 6 000 nm. The energy band gap of InAs0.94Sb0.06 was 0.308 eV, which was determined by refractive enhancement.

Abstract:InGaAs 8×1 linear arrays photodetectors with n-on-p structure and deep mesa, which can response at extended wavelength of 2.4 μm, were fabricated by ICP etching (inductively coupled plasma etching) process in the paper. The device surface was cleaned by N2 plasma activated by ICP, then SiNx passivation layer was deposited by ICPCVD (inductively coupled plasma chemical vapor deposition)) on the device surface. The current-voltage analysis of different area devices indicated that the lateral surface current was suppressed effectively at both room and lower temperature. Activation energy analysis illustrated the excellent dark current characteristics. At -10 mV bias, the dark current density is 94.2 nA/cm2 and 5.5×10-4 A/cm2 at temperatures of 200 K and 300 K, respectively.

Abstract:Femtosecond laser drilling induces PN junction in p-HgCdTe. In this work, femtosecond laser with repetition rate of 1 kHz was used to generate different micrometer-sized holes. It was found that the pulse number is an important parameter which influences the effect of junction formation. Laser beam induced current (LBIC) characterization shows that the inversion layer thickness reduces from 13.5 μm to 10.5 μm when the pulses increase from one to ten. The LBIC profile of a hole created with one hundred pulses deviates severely from the line shape of ideal PN junction, resulting in large leakage current. In addition, the fitting of LBIC curves shows that the diffusion length of the hole created by a single pulse is 17 μm whereas the one created by ten pulses reduces to 12 μm.

Abstract:Four-quadrant detectors which consist of four well balanced detectors have been used for beam collimation and target tracking. In this article, we report a Stokes polarimeter based on a four-quadrant detector. By placing polarizers and wave plates in front of the individual detectors, the four detection channels were turned into four polarization analyzing channels of a Stokes polarimeter. An optimization algorithm was proposed to determine the axis directions of the individual polarizers, as well as the axis direction and the retardance of the wave plates for minimizing the errors and increasing the robustness of the measurements. The polarimeter is capable of simultaneous measurements of fast varying polarization states. Using properly selected polarization optics and following the same optimization algorithm, the polarimeter can be extended to other wavelength range, such as the infrared.

Abstract:To compare the actual luminescence intensity of different samples acquired in a wide wave number range using FTIR emission spectroscopy, a feasible and convenient correction scheme of calculated emission spectroscopy instrument function was proposed. The feasibility, limitations and matters need attention were discussed in detail. Based on those schemes, the luminescence intensities of a group of photoluminescence samples cover a wide wave number range have been corrected and compared with original data. Consistent results were gained. The validity of the schemes was confirmed.

Abstract:Liquid crystal phase retarder (LCVR) is a new polarization state control device. Correct calibration of its photoelectric characteristics significantly effects the precise optical polarization measurements based on this device. A new testing method including only one polarizer was proposed by modeling light intensity, phase retardation and eigen-axis azimuth. Without rotating any component, multi-wavelength retardations can be rapidly acquired using this simply structured method. In addition, this new setup can be integrated into other polarization measuring instruments for on-line calibration of LCVR. Experimental results show that the repeatability of measured retardations is better than 5‰, while the resolution of eigen-axis azimuth is better than 0.1°.

Abstract:Analysis model of the fiber gratings with random spaced index modulations was established. The random spaced index modulated fiber grating can be treated as the random combinations of long period uniform gratings and short period uniform gratings. The reflective and transmissive characteristics of a random fiber grating with the averaged random modulation space 20 μm were calculated with transmission matrix method and beam propagation method. The results confirmed the coexistence of the coupling between the forward and backward propagated fundamental core modes and the coupling between the fundamental core modes and cladding mode. A random fiber grating with 500 modulation points was fabricated by femto-second laser, the spaces between the adjacent random modulation points were about 10~20 μm. The reflective and transmissive spectra of the grating were measured experimentally. The experimental results further validated the numerical analysis.

Abstract:In order to study the scattering properties of non-spherical ice particles which are detected by millimeter-wave radar, the backscattering cross sections of six kinds of non-spherical ice crystals of cirrus were studied. The double-exponential function relationships between particles’ maximum sizes and backscattering cross sections is fitted. Three assumed models: I. B-H mixing model, II. Equivalent ellipsoid model, III. Equivalent sphere model, respectively, were used to simulate the data provided by the NASA’s synchronous satellite and airplanes experiment for cloud observation on July 31, 2007. The results showed that the data retrieved by B-H mixing model agree very well with the measured results at four positions compared with the results retrieved by other two models. However the retrieved results by B-H mixing model at 1#, 2#, 3# positions are lower than values detected by CRS millimeter wave radar. This is because cloud size distribution detector ignores the droxtals which are beyond the detection range. Considering these droxtals and fitting all size distributions at 1#, 2#, 3# and 4#, the common size distribution which meets B-H model can be acquired and the relationship between Ice Water Content (IWC) and Z can be fitted. Putting IWC measured by CVI instrument into above formula (IWC-Z), the retrieved radar reflectivity factors can be acquired, and then compared with the results detected by CRS millimeter wave radar. The results show that the influence of air content on radar reflectivity factor is larger than particle’s orientation when IWC is below 0.134 2 g/m3. The influence of air content can be ignored while the particle’s orientation should be considered when the value of IWC is between 0.134 2 g/m3 and 0.199 4 g/m3. B-H model is not applicable when IWC is larger than 0.199 4 g/m3. Based on above analysis, the orientation and air content must be considered under the premise of IWC in order to accurately retrieve ice particles using millimeter-wave radar.

Abstract:Scanning probe microscope (SPM) based super-resolution near-field fingerprint microscopy is a promising technique for detecting molecular structures and identifying the composition of materials on the nanometer scale. In recent years, tip-enhanced Raman scattering, Fourier-transform infrared nanospectroscopy and scattering-type scanning near-field terahertz spectroscopy have been developed based on the combination of Raman scattering spectroscopy, infrared absorption spectroscopy and terahertz spectroscopy with a SPM, respectively. These scattering-type scanning near-field optical microscopy techniques are realized by using different experimental setups and can provide different but complementary information on the structure or components of materials. In this review, the characteristics of the above three techniques are examined and compared in depth, and the applications and recent progresses of them are also summarized concisely.

Abstract:The traditional atmospheric radiative transfer calculation method has been unable to meet the needs of space-borne hyper-spectral infrared atmospheric remote sensing data processing because of the limitation of the computing resources and efficiency. Based on the optimal spectral sampling method, this paper developed a fast and accurate high spectral resolution infrared atmospheric radiative transfer model FFRTM_IR. This model was used to simulate the measurement of hyper-spectral infrared radiance atmosphere sounder (HIRAS) aboard on FY-3D satellite. Independent profiles validation results show that the bias of FFRTM_IR were less than 0.06 K and the standard deviation were no more than 0.1 K for all HIRAS channels. Under the same calculation environment, the speed of FFRTM_IR was slightly faster than the general radiative transfer model, such as CRTM. Along with the FFRTM_IR model, an analytical method was used to drive the temperature, water vapor, carbon dioxide and ozone profiles jacobian matrix, which agree well with results obtained from accurate perturbation method. All these validation and analysis results showed that the developed initial efficient infrared atmospheric radiative transfer model can be used in space-borne hyper-spectral infrared atmospheric sounding instrument simulation and data processing.

Abstract:Based on the measured optical constants of titanium alloy TC4 in temperature range 298~773K, the bidirectional reflectance distribution function (BRDF) of rough titanium alloy TC4 surface was studied by numerical simulation with the Monte Carlo raytracing approach. The effect of different polarized light incidence, different surface roughness and different temperature on BRDF distribution of rough titanium alloy surface was analyzed. The results show that, the change of BRDF distribution with the incident angle and the roughness of titanium alloy under polarized light is the same as that for unpolarized light. The BRDF of rough titanium alloy surface in incident plane changes with light polarization has the same trend with that of smooth plate. The BRDF peak under TE light incidence is greater than that of TM light. The BRDF peak in specular reflective direction of rough titanium alloy surface decreases with temperature increasing. In the temperature range studied in this paper (298~773 K), the peak changes within 10.2%. The effect of temperature on the BRDF distribution of titanium alloy under TM polarized light is greater than that of TE light, which increases with the increase of incident angle.

Abstract:In optical scatterometry, the sensitivity has a significant impact on the precision of the extracted structral parameters in addition to the quality of the measured signatures. As the sensitivity of structral parameters can be improved with the proper selection of measurement configuration (a combination of wavelengths, incidence, and azimuthal angles), we proposed a method to determine an optimal one for optical scatterometry based on sensitivity analysis. Experiments performed on a one-dimensional periodic grating show agreement between the theoretically predicted and experimentally obtained optimal measurement configurations, which demonstrates the validity of the proposed optimization method.

Abstract:In order to improve tracking performance of the single-observer infrared search and tracking (IRST) system, an algorithm called the robust improved Gaussian-sum cubature Kalman filter (RIGSCKF) was proposed. For the initial value fuzzy problem, the cubature Kalman filter framework was firstly divided into a set of weighted sub-filters, each with a different initial value, where the weights were determined by the likelihood function. In the measurement update, the predictive density was split in the direction of the maximum eigenvector and was merged according to sub-filters when nonlinear degree exceeded a threshold. It is certified that the method makes the tracking more accurate. Furthermore, to deal with the contaminated Gaussian noise in the measurements, the weights of outliers were reduced according to equivalent weight function which could improve the innovation covariance efficiently. Simulations show shat the RIGSCKF performs superior accuracy when there are no outliers. On the contrary, when outliers appear, the performance of conventional algorithms degrades rapidly, but that of the RIGSCKF is still accurate and robust.