As a comprehensive description of polarization characteristics of scattering underwater images, Mueller matrix plays a crucial role in underwater polarization imaging. In this paper, we propose an underwater image restoration method by employing polarization entropy and depolarization index, both derived by sum decomposition of the Mueller matrix. The polarization entropy is applied to realize the automatic selection of the background region, based on the polarization differences between the target region and the background region. And the depolarization index is employed to determine the transmission map. By incorporating the first element of the Muller matrix and depolarization index into the traditional underwater polarization imaging model, the restored images are achieved by only optimizing the parameter alpha of the transmission map. Several imaging experiments have been conducted in turbid water. Compared with other underwater imaging methods, the results show that the contrast and clarity of the images recovered by our method are significantly improved at various turbidity levels. And the improvement holds true for targets of single polarization properties and complex polarization properties.

AZ(Aziridinium)PbI3 is considered a promising perovskite absorber material because of its appropriate bandgap, defect tolerance, and excellent stability. In this study, density functional theory (DFT) was conducted on AZPbI3 and MAPbI3 to compare their band structures, density of states, and optical properties. And, numerical simulations of AZPbI3-based perovskite solar cells (PSCs) are presented and discussed. A total of 81 different configurations of AZPbI3-based PSCs, including 9 different electron transport layers (ETLs) and 9 different hole transport layers (HTLs), were evaluated using SCAPS-1D in terms of photovoltaic (PV) performance. The simulations indicate that HTLs play a more important role in achieving high PV efficiency. Additionally, the two most promising structures, Au/Cu2O/AZPbI3/ZnO/FTO (Structure 1) and Au/PTAA/AZPbI3/ZnO/FTO (Structure 2), were selected for detailed analysis. The presence of spike-like structures at the Cu2O/AZPbI3 interface enhances hole transport, thereby reducing the likelihood of hole capture by interface defects and rendering Structure 1 less sensitive to interface defects compared to that of Structure 2. Through optimization of absorber thickness, doping concentration, defect density, and interface defect densities, the highest power conversion efficiency (PCE) of the two structures is 27 % and 28.89 %, respectively. These simulation results may provide valuable guidance for the design optimization of AZ-based perovskite solar cells.

In this Letter, we present a novel, to the best of our knowledge, approach for recovering objects directly from the Fraunhofer diffraction integral, where the diffraction field of an object is approximated by the Fourier transform of this object augmented by an additional phase factor. This phase factor at the observation plane is universal for the diffraction fields generated by objects located at the same plane and illuminated by the same monochromatic plane wave. It can be first extracted from dividing the Fraunhofer diffraction field by the Fourier transform of an object reference. Rapid recovery for unknown objects is then enabled after applying a two-dimensional inverse Fourier transform to the ratio of the Fraunhofer diffraction fields to the phase factor. This approach is verified experimentally by constructing a modified Mach-Zehnder interferometer, with a digital micromirror device (DMD) generating the objects of desired structures. To record the Fraunhofer diffraction and interference patterns on a finite-size CCD camera, a convex lens is introduced with the CCD sensing surface positioned at the focal plane of the lens. The strategy described in [Nat. Commun.7, 10820 (2016)10.1038/ncomms10820] is applied to extract the phase of the diffraction field from the interference pattern. The results demonstrate the efficiency of our approach in swiftly and accurately recovering small objects with elimination of zero-order and conjugate images.

Two-dimensional (2D) Ruddlesden-Popper (RP) metal halide perovskites have been widely utilized to enhance the stability of perovskite solar cells (PSCs), owing to their superior stability over their 3D counterparts. However, to date, there remain limited studies focused on the thermal stability of 2D perovskite thin films. In this study, the thermal degradation of (PEA)2PbI4 and (BA)2PbI4 thin films is systematically characterized using X-ray diffraction, scanning electron microscopy, photoluminescence, and spectroscopic ellipsometry. The optical band gaps of (PEA)2PbI4 and (BA)2PbI4, obtained from their respective dielectric functions, are 2.42 ± 0.002 eV and 2.43 ± 0.002 eV, respectively. Through an investigation of the dynamic evolution of the dielectric function, we found that (PEA)2PbI4 exhibits superior stability compared to (BA)2PbI4. The enhanced stability of (PEA)2PbI4 can be attributed to its lower density of defect states and the presence of a rigid aromatic ring spacer cation within the crystal structure. This aromatic ring spacer cation contributes to the structural stabilization via strong CH···π interactions with the alkyl chains of adjacent cations. A comprehensive understanding of the dielectric function and thermal degradation of these two 2D perovskite thin films is essential for the future design and optimization of 2D/3D PSCs.

HC(NH2)2SnI3 (FASnI3) is considered as a promising lead-free perovskite (PVK) for its wide bandgap and great temperature stability. However, Sn-based perovskites exhibit lower electron affinities than Pb-based perovskites, resulting in large band mismatch at the interfaces. The energy band alignment and defects at the interfaces play an important role in the perovskite solar cell (PSC) performance. In this simulation, we optimize the FTO/TiO2/FASnI3/PTAA/Au structure to achieve efficiently and eco-friendly FASnI3-based PSCs using SCAPS-1D, with a special focus on interface engineering. The band offsets of TiO2/FASnI3 and FASnI3/PTAA interfaces are systematically modified by changing the electron affinity values of the absorber and charge transport layers (CTLs). Additionally, the influence of defect density at the TiO2/FASnI3 and FASnI3/PTAA interface is also discussed. It is found that the efficiency of PSCs can be significantly improved by suitable energy band alignment accompanied by small spike-like band offsets and the reduction of interface defects. The initial structure is based on an experimental work with an efficiency of 2.53 %. After optimization, the device reaches the highest theoretical power conversion efficiency (PCE) of 17.92 % with fill factor (FF) of 77.79 %, open circuit voltage (Voc) of 0.93 V and short circuit current density (Jsc) of 24.81 mA/cm2.

Polarization imaging has enormous potential in underwater application scenarios. Previous polarization imaging methods mainly focused on the degree of polarization (DOP) of the backscattered light, and assumed it as a constant, resulting in no physical meaning of the optimization calculation. In this paper, particular attention is paid to the DOP of the target light, and the DOP of the backscattered light is evaluated as a function of the DOP of the target light. The global distribution of the backscattered light and its polarization degree is obtained using low-pass filtering in frequency domain. And, a novel constraint model is proposed to further confine the value range of the DOP of target light. In the proposed method, the DOP of the target light and the cutoff frequency of the low-pass filtering are chosen as the inverse parameters. To obtain the above two parameters, a two-layer multi-indicator framework is built. The proposed method can automatically realize underwater image recovery, and no background area or any prior information is required. The laboratory simulation experimental results show that the contrast and clarity of the reconstructed images have been significantly improved with different polarization characteristics under various turbidities.

Triple cation(Csx(MA0.17FA0.83)1-xPb(I0.83Br0.17)3) perovskites have attracted extensive attention owing to their excellent stability and photovoltaic performance. In this work, an efficient perovskite solar cell with a structure of TiO2/Csx(MA0.17FA0.83)1-xPb(I0.83Br0.17)3 (CsFAMA)/ CuSCN was proposed and optimized theoretically using the solar cell simulator capacitance software (SCAPS-1D). This study optimized the parameters of the absorber layer, such as the thickness, doping density, defect density and bandgap. In addition, the electron transport layer (ETL) and the hole transport layer (HTL) are optimized by varying their electron affinity, thickness and doping density. It was found that the optimization of the absorber layer thickness and doping density provided a significant improvement in the efficiency of the device, while the parameters of both ETL and HTL showed minor influence on the device performance. Moreover, the operation temperature was discussed to provide further insight concerning the device performance. It showed that an increase of the operation temperature from 300 to 700 K resulted in reduction of device performance. And the CsFAMA-based device showed the highest power conversion efficiency (PCE) of 28.66% at 300 K with fill factor (FF) of 83.18%, open circuit voltage (Voc) of 1.48 V and short circuit current density (Jsc) of 23.27 mA/cm2. The optimized values of the absorber thickness, defect density and doping density were found to be 500 nm, 2.6 x 1013 cm -3 and 1 x 1016 cm -3, respectively. The findings of this study suggest CsFAMA-based absorber materials can play an important role in high efficiency perovskite solar cells with excellent stability.

In this work, the second harmonic (SH) of higher-order Poincaré sphere (HOPS) beam was introduced and demonstrated with two orthogonal 5%MgO:PPLN crystals. Based on the quasi-phase-matching technique, the vectorial coupled wave equations were derived to simulate the SH of HOPS beams through the two crystals, including the cylindrical vector beams (CVBs), elliptically polarized CVBs (EPCVBs), and circularly polarized vortex beams. Then, the experimental setup was established to reveal that the SH of CVBs and EPCVBs present the four-lobed structure and still exhibit vector characteristics. Meanwhile, the circularly polarized vortex beams become the linearly polarized vortex beams with double phase topology, confirming the conservation of orbital angular momentum. Moreover, the maximum SH conversion efficiency of CVBs, EPCVBs, and circularly polarized vortex beams can reach 25.3%, 23.4%, and 29.4%, respectively, which may be instructive for promoting the SH generation of vector vortex beams with high efficiency.

This paper reports the strong coupling between Al nanostructure and two-dimensional (2D) layered perovskite PEA 2 PbI 4 (PEPI) films. The high exciton binding energy of 118 meV and long carrier lifetime of 216 ps are characterized from the 2D PEA 2 PbI 4 film, which indicates that the excitons in perovskite are robust and can couple to metal plasmons. The ordinary and extraordinary optical dispersions are revealed from the anisotropic 2D perovskite. The transmission spectra of PEA 2 PbI 4 /Al nanoparticle arrays are simulated under different polarization excitations, and the typical anti-crossing behaviors originating from exciton-plasmon strong coupling are demonstrated. We found that compared with transverse magnetic (TM) polarization, transverse electric (TE) polarization excitation is more conducive to the realization of exciton-plasmon coupling with a larger Rabi splitting. Furthermore, the PEA 2 PbI 4 /Al nanoparticle arrays are proposed, which present polarization-dependent local electrical field enhancement due to the exciton-local surface plasmon polariton coupling. Additionally, it is noticed that the proposed plasmonic structure increases the photo-generation rate inside the active material with improved current density. Therefore, the 2D proposed plasmonic design increases the power conversion efficiency (PCE) with an enhancement of 3.3% and 1.3% relative to the planar structures for TE and TM polarizations, respectively. This study provides a deeper understanding of polarized exciton-plasmon coupling properties, promoting the development of the field of plasmon and providing guidance for the design and preparation of efficient optoelectronic devices.

In this work, we present a novel approach to resolve the refractive indices of transparent and translucent liquids from straight interference fringes. The optical path difference between the two arms of the Mach–Zehnder interferometer is first derived by assuming a reference plane wave interfering with a plane wave passing through a rectangular cuvette. The analytic expressions for the liquid refractive indices are then deduced, describing how the refractive index is related to the fringe spacings, spatial frequencies, and directions. The structure coefficients in the above formulas are determined from the fringe spacings and directions of the interference patterns of the empty cuvette and the cuvette filled with a liquid of a known refractive index. The NaCl solution and Coca Cola are adopted as the test examples to show experimentally the validity of the proposed method. There is good agreement between the refractive indices obtained from the fringe spacings and direction of a single interference pattern. The sensitivity and resolution of this method are dependent on the structure of the experimental systems and thus can be adjusted in a controlled manner. The proposed method is simple to implement and can be easily extended to other high precision optical interferometer systems.

This paper reports the strong coupling between Al nanostructure and two-dimensional (2D) layered perovskite PEA2PbI4 (PEPI) films. The high exciton binding energy of 118 meV and long carrier lifetime of 216 ps are characterized from the 2D PEA2PbI4 film, which indicates that the excitons in perovskite are robust and can couple to metal plasmons. The ordinary and extraordinary optical dispersions are revealed from the anisotropic 2D perovskite. The transmission spectra of PEA2PbI4/Al nanoparticle arrays are simulated under different polarization excitations, and the typical anti-crossing behaviors originating from exciton-plasmon strong coupling are demonstrated. We found that compared with transverse magnetic (TM) polarization, transverse electric (TE) polarization excitation is more conducive to the realization of excitonplasmon coupling with a larger Rabi splitting. Furthermore, the PEA2PbI4/Al nanoparticle arrays are proposed, which present polarization-dependent local electrical field enhancement due to the exciton-local surface plasmon polariton coupling. Additionally, it is noticed that the proposed plasmonic structure increases the photo-generation rate inside the active material with improved current density. Therefore, the 2D proposed plasmonic design increases the power conversion efficiency (PCE) with an enhancement of 3.3% and 1.3% relative to the planar structures for TE exciton-plasmon coupling properties, promoting the development of the field of plasmon and providing guidance for the design and preparation of efficient optoelectronic devices.

YBa2Cu3O7-x (YBCO) is a crucial aspect of research in the field of superconducting applications, where its high anisotropy is generally undesirable in strong power transmission. However, from a dialectical perspective, a thorough investigation of material anisotropy can offer an additional degree of freedom to tune potential properties and design innovative devices. This work employed pulsed laser deposition to fabricate a high-quality YBCO thin film (Tc = 89 K) and used the Mueller matrix spectroscopic ellipsometer (MMSE) to determine the complete dielectric tensor of the YBCO film across the ultraviolet to near-infrared spectrum (245-1000 nm), enabling a comprehensive, quantitative study of the optical anisotropy of YBCO. It provided optical constants and dielectric function spectra for different axes. We found that YBCO exhibits birefringence and dichroism both in-plane and out-of-plane. By combining standard critical point (SCP) analysis and first-principles calculations, we identified specific interband transitions related to SCP in the YBCO dielectric spectra, revealing the physical essence of anisotropic optical transitions from a quantum mechanical standpoint. Temperature-dependent studies of the transitions and optical constants were conducted. The work fills a partial void in the optical parameters of the anisotropy of YBCO and holds relevance for understanding the origins of copper-based hightemperature superconductivity.

The organic-inorganic hybrid perovskite materials have attracted a lot of attention in the photovoltaics field due to their excellent photovoltaic properties and simple preparation process in recent years. The well-known hole transport layer PTAA in the inverted perovskite solar cells (PSCs) is prone to trigging the nonradiative recombination and limiting the device performance. Here, we added benzylamine thiocyanate (BnASCN) bottom interface passivation layer between PTAA/perovskite layers to regulate the crystal growth of perovskite film, thus increase the grain size of perovskite film. The amino-passivation of BnA+ and the interaction of the strongly electronegative S and N in pseudo-halogens with the undercoordinated Pb2+, the defect density of the perovskite films is reduced, which effectively reduced the nonradiative recombination and inhibited ion migration, and the device power conversion efficiency improved from 17.12 % to 19.48 %. Moreover, the stability of the device is improved.

In this study, we numerically investigate the strong coupling between organic-inorganic hybrid perovskite MAPbBr3 films and plasmonic aluminum nanoparticle lattices. The open cavity structure of the plasmonic nanoparticle lattice provides a simple strategy for modulating exciton-plasmon coupling strength, which can be controlled by changing the thickness of the perovskite MAPbBr3 film or the refractive index of the top dielectric layer. The finite-difference time-domain simulations of the transmission and optical dispersion spectra demonstrate the typical avoided crossings of the upper and lower polariton branches originating from the strong exciton-plasmon coupling. We also study the exciton-plasmon coupling based on oscillator strength adjustment in the Lorentz model. The relationship between the polariton coupling strength and the exciton/plasmon mixing ratio is revealed by a two-state model. Our results theoretically reveal the continuous modulation of the exciton-plasmon coupling, which has theoretical significance and can be helpful for realizing large-scale tunable polariton devices in the future.

Mn2+ doping effectively realizes white light emission in three-dimensional lead halide perovskite nanocrystals. Meanwhile, research on Mn-doped two-dimensional layered perovskite single crystal is limited. We report centimeter-scale Mn-doped PEA2PbBr4 (C6H5CH2CH2NH3+ and PEA+) single crystals prepared by a slow evaporation method. Mn2+ dopants mainly act as substitutional doping and exhibit paramagnetic properties in the crystal at low doping density, while interstitial doping of Mn2+ prevails and induces antiferromagnetic characteristics at high doping density. Mn:PEA2PbBr4 single crystals exhibit dual-band chromacity-tunable blue-orange photoluminescence originating from excitons and Mn2+ emission. The negative temperature quenching effect is achieved by Mn-doping defects for the temperature-dependent exciton photoluminescence. Upon testing in the low-pressure vacuum chamber, the Mn2+ peak of the single crystal shows a dramatic shift from 610 to 690 nm. These results indicate that Mn:PEA2PbBr4 single crystal can serve as a potential and promising luminescent device material that achieves color tunable properties by regulating the systematic changes in the intensity ratio of exciton emission and Mn2+ emission, which will be very helpful for exploring the application of perovskite in magneto-optical devices in the future.

Underwater imaging is of great significance in exploring seabed resource , monitoring marine environment, implementing underwater rescue and military reconnaissance, etc. by providing clear vison. Among various underwater imaging techniques, the polarization imaging is considered to be an effective way to improve the quality of underwater imaging. It can realize underwater image restoration by using the difference in polarization characteristic between the target light and backscattered light. A classical underwater active polarization imaging method was presented by Treibitz [Treibitz T, Schechner Y Y 2009 IEEE Trans. Pattern Anal. Mach. Intell. 31 385], in which the degrees of linear polarization (DoLPs) of target light and backscattered light are used to recover clear image. A variety of improved methods have been derived from this, but most of them require background areas and human-computer interaction. Then, a new underwater active polarization imaging method without prior knowledge was presented by Zhao [Zhao Y, He W, Ren H, Li Y, Fu Y 2022 Opt. Lasers Eng. 148 106777], in which the DoLPs of target light and backscattered light can be automatically obtained without background region. However, sometimes the above two parameters are very close and thus introduce a lot of noise into the restored images, for this method takes only the contrast into account.In this work, an underwater active polarization imaging method based on two-layer multi-index optimization is proposed. First, the mutual information and contrast are taken as the upper objective functions, and the Pareto optimal solution set is obtained by the multi-objective genetic optimization algorithm. Second, the information entropy is taken as the lower objective function to obtain the optimal parameters from this optimal solution set. Based on the optimal parameters, the restored images are obtained. According to the difference between the DoLPs of target light and backscattered light, these restored images are further improved by the digital image processing method.The experimental results indicate that our method can not only enhance image details effectively but also balance various evaluation indexes of the imaging quality to obtain high-quality restored images. The proposed algorithm is suitable for underwater targets with low and high DoLPs, with or without background regions.

Objective Perovskite solar cells (PSCs) have attracted considerable research interest due to their large absorption coefficients, long diffusion lengths, tunable bandgap, and high charge mobility. The power conversion efficiency (PCE) of PSCs has increased from 3. 8% in 2009 to 26. 08% in 2023. However, their mass-scale production is limited by the inherent instability of the perovskites, which decompose easily during reaction with moisture, oxygen, light and heat. Formamidinium-cesium (FAC) mixed cations perovskites have demonstrated excellent thermal stability and suitable bandgap for solar spectrum absorption. On the other hand, the carrier mobility of Br-is higher than that of I-. Therefore, we choose Cs-doped FA(1-x)Cs(x)PbBr(3) (FACsPbBr3) thin films to study optical properties and construct high-efficient and stable PSCs. However, experimental PCE verification of PSCs is costly and time-consuming. Numerical simulation provides a simple and effective way to evaluate the PSCs performance and explore new possible device architectures. The complex dielectric function is an important optical parameter. Fundamentally, the complex dielectric functions are critical for simulating the external quantum efficiency (EQE) of the PSCs. Furthermore, determining the bandgap from the complex dielectric functions provides information on the band structure and enables the detection of temperature-dependent phase changes. We prepare Cs-doped FA(1-x)Cs(x)PbBr(3) (x= 0, 0. 05, 0. 10, 0. 15) perovskite thin films and study the corresponding complex dielectric functions by spectroscopic ellipsometry (SE). The resultant complex dielectric functions are then employed to simulate EQE. Meanwhile, the temperature-dependent EQE simulation of FA(0. 95)Cs(0. 05)PbBr(3) PSC is also performed. We hope that the basic findings can help design highly efficient and stable PSCs and understand the relationship between the complex dielectric functions and EQE of PSCs. Methods FACsPbBr(3) thin films with different Cs doping concentrations are prepared by one-step anti-solvent method, and the surface morphology of samples is characterized by atomic force microscopy (AFM). Additionally, the crystal structure of the samples is studied using a D8 Advance X-ray diffractometer, and the effects of Cs-doped concentrations on the surface morphology and crystal structure of the prepared samples are investigated. The optical properties of the samples are analyzed by SE. The resultant complex dielectric functions are adopted to simulate the short-circuit current density (J(sc)), open-circuit voltage (V-oc), fill factor (FF), and PCE of the devices. The doping effects on the PSCs performance are discussed in detail. Next, the temperature-dependent ellipsometric measurements (303-423 K) and room temperature absorption measurement of the sample with the highest simulated EQE are performed. Based on the temperature-dependent complex dielectric functions, the influence of temperature and absorber thickness on both the simulated EQE and the short-circuit current density of the device is studied. Results and Discussions The prepared FACsPbBr(3) thin films exhibit smooth and compact surface morphology with pebble stone-like structures, indicating the high quality of the samples (Fig. 1). When the doping concentration increases to 0. 1, the appearance of the d-phase non-perovskite structure is observed in the XRD pattern (Fig. 1). The ellipsometric measurements show that the amplitude of the complex dielectric functions decreases with the increasing doping concentrations (Fig. 2). The EQE simulation shows that Cs doping improves the PCE, but excessive Cs doping degrades PCE of the devices, which might be attributed to the appearance of the delta-phase. The maximum PCE can reach up to 23. 47% under the doping concentration of x= 0. 05 (Table 1). Furthermore, an increase in bandgap with the rising temperature is observed based on the temperature-dependent dielectric functions of FA(0. 95)Cs(0. 05)PbBr(3). Additionally, an orthogonal-tetragonal phase transition is observed around 393 K (Fig. 5). The temperature-dependent EQE simulation of FA(0. 95)Cs(0. 05)PbBr(3) perovskite solar cell shows that the maximum PCE of the device can stabilize at about 23. 47% and exhibits little dependence with temperature. However, there is a rapid EQE decrease in the near-infrared region with the increasing temperature, which reduces the device bandwidth (Fig. 6). Conclusions We prepare Cs-doped FA(1-x)Cs(x)PbBr(3) (x= 0, 0. 05, 0. 10, 0. 15) perovskite thin films by a one-step antisolvent method. The complex dielectric functions of FACsPbBr(3) thin films are studied by SE, and the temperaturedependent complex dielectric functions and absorption spectra of FA(0. 95)Cs(0. 05)PbBr(3) are researched by spectroscopic ellipsometry and UV-visible spectrophotometer respectively. The optical bandgaps obtained by SE are consistent with that obtained by absorption spectra. The EQE simulation results show that Cs doping can improve the device performance. When the doping concentration is 0. 05, the PCE can reach up to 23. 47%, but excessive Cs doping concentration will introduce non-perovskite delta-phase, decreasing the device performance. According to temperature-dependent ellipsometric measurements, we find that the bandgap increases with the rising temperature, and there is an obviously orthorhombictetragonal phase transition at about 393 K. With the increasing temperature, the device PCE slightly decreases, while the short-circuit current slightly increases. However, the light absorption capability of the device in the NIR region obviously reduces with the increasing temperature. The response bandwidth reduction could be attributed to the increased bandgap. Thus, by considering the performance and stability of the devices, FACsPbBr(3) PSCs with a Cs-doped concentration of 0. 05 have the best overall photovoltaic performance.

In this paper we explored the propagation characteristics of rotationally-symmetric power-exponent-phase vortex beam (RSPEPVB) through the oceanic turbulence. Based on the extended Huygens-Fresnel diffraction integral and the oceanic turbulence theory the theoretical model of RSPEPVBs propagating in oceanic turbulence was established. Then the propagation properties of RSPEPVBs were explored by numerical simulation and the influences of the propagation distance z the rate of dissipation of turbulence kinetic energy per unit mass of fluid ε the temperature-salinity contribution ratio ω and the dissipation rate of the mean-squared temperature χT were discussed. The results illustrated that the intensity of RSPEPVBs propagating through oceanic turbulence weakened and the size of RSPEPVBs diffused with the increasing distance and strong oceanic turbulence of larger values of parameters χT and ω and the smaller value of the parameter ε. Meanwhile the coherence of RSPEPVBs would decrease in stronger oceanic turbulence. Further an experimental setup was demonstrated to confirm that the RSPEPVBs will diffuse in strong oceanic turbulence which was strengthened with the rise of salinity and the increase of propagation distance. Contrarily with the increase of temperature the loss of RSPEPVBs mitigated and the intensity increased gradually. The obtained results may provide a potential application for optical underwater communication and imaging.

Previous polarization imaging methods tend to assume that the degree of polarization of the target reflected light is a constant, while the targets with nonuniform polarization characteristics are less considered. The required background area or prior knowledge hinders the practical application of underwater polarization imaging technology. In this paper, we analyzed the basic physical model of underwater imaging, and proposed a new underwater polarization de-scattering method by considering orthogonal polarization decomposition of both the target reflected and backscattered light. The polarized-difference intensity of the backscattered light can be directly calculated from the polarization orientation angle of the two horizontal decomposition components. Meanwhile, a low-pass filter was used to suppress noise and globally evaluate the degree of polarization of the backscattered light. The proposed method can automatically distinguish the underwater targets polarization characteristics, and no background area or any prior information is required. The laboratory simulation experimental results demonstrate that this method can effectively improve the quality of underwater images under different conditions.

This article is devoted to studying the optical properties of a novel single-crystal LiTi2O4 thin film. A high-quality (011)-oriented LiTi2O4 single-crystal thin film was prepared on a MgAl2O4 (011) substrate by pulsed laser deposition. The weak in-plane optical anisotropy is discovered by Mueller-matrix spectroscopic ellipsometry, which can be attributed to the cooperative Jahn-Teller distortion in the Ti-O octahedrons. The pseudo-dielectric functions were determined in the photon energy of 1.24-5.06 eV using the ellipsometric spectra. The optical conductivity, plasma frequency, effective mass, scattering time and other dielectric-related factors are also discussed. The critical points obtained in the pseudo-dielectric functions are originated from the charge-transfer transitions of the Ti related pairs. The results demonstrate that the enhanced effective mass is responsible for the high optical transparency of LiTi2O4 rather than the large high frequency dielectric constant & epsilon;& INFIN;.