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Deflectometry has been widely used in topography measurement of specular surface. In deflectometry with a curved screen, the range of the gradient and height field of the measured specular surface can be effectively expanded compared to deflectometry with a plane screen. As stereo deflectometry measures gradient with high accuracy, the specular surface is reconstructed by integrating the gradient. In this paper, a stereo deflectometry with a curved screen is proposed in the aspect of system calibration and measuring principle. A pair of cameras and deflectometric system are calibrated simultaneously to obtain the camera parameters and relationship between two cameras and the curved screen. Then, pairs of rectified fringe patterns are demodulated to obtain two pairs of rectified absolute phase maps and homologous points are searched along epipolar line with the principle of the same normal direction on specular surface. Finally, simulated and actual experiments are carried out and the results show high accuracy and stability.

Point spread function (PSF), which is the intensity distribution of optical system impulse response and usually acquired by imaging a single pinhole in experiment, can characterize the quality of optical imaging system. Faithful recording of the two-dimensional intensity distribution of PSF is key for accurate measurement of optical transfer function (OTF), however distortions in recorded PSF can be easily caused by a large sampling interval and the electronic noise of the detector. Under a given sampling interval, the position-phase difference between pixels and intensity signals can change the intensity distribution of acquired PSF remarkably, making the computed OTF or MTF (modulation transfer function) error prone. Aiming at problems existing in pinhole based MTF measurement methods, this paper developed a new method with underline physics similar to that of slanted edge method to realize sub-pixel sampling of PSF intensity by using accurate non-integer up-sampling matrix of separate binary pixels and applying random patterns shown on digital micro-mirror device (DMD) as target. Numerical simulations show that improvement on the discrete sampling of point spread function with this method is very helpful to improve anti-noise robustness and the accuracy of optical transfer function measurement.

It is a challenge to retrieve atmospheric sulphur hexafluoride (SF

Coherence and steerability are two essential characteristics of quantum systems. For a two-qubit state, the first-order coherence and the maximal violation of linear steering inequality are used to operationally measure the degree of coherence and steerability, respectively. Recently, a complementary relation between first-order coherence and linear steerability has been proposed. In this paper, we report an experimental verification of the complementary relation by preparing biphoton polarization entangled states in an all-optical setup. We propose an operable method for experimental measurement of the first-order coherence and linear steerability and calculate the purity of the initial states by reconstructing the density matrices of them. The experimental results coincide with the theoretical predictions very well, which provides a valuable reference for the application of optical quantum technology.

Terahertz (THz) polarization converters often working as modulators and switches have many applications in THz sensing, imaging and communication, but many of them still suffer from low polarization conversion efficiency, fixed and narrow polarization conversion band, and low output polarization purity, which are mainly due to the lack of theoretical model for THz polarization converter design and optimization. In order to solve the problem, we adopt multiple interference theory to successfully design and optimize a graphene metamaterial-based tunable broadband THz linear polarization converter: it achieves polarization conversion ratio (PCR) over 0.97, polarization azimuth angle of almost ±90° and rather low ellipticity within a broad polarization conversion band of 1.25 THz; and additionally, its polarization conversion band can be actively tuned by adjusting the graphene chemical potential and almost insensitive to the incident THz radiation angle below 50°. Considering the high performance of the optimal graphene metamaterial-based tunable broadband THz linear polarization converter, this work provides an optimal design offering a way in high-quality manipulation of THz radiation polarization; but more importantly, delivers a theoretical model for tunable THz polarization converter design and optimization.

Inertial confinement fusion (ICF) places an urgent demand for precise measurement of 351 nm (3ω) laser beam parameters when performing physical experiments on high-power laser facilities. The near-field and focal spot distributions are the utmost important parameters to characterize the quality of the laser beam. Coherent modulation imaging (CMI) is a promising technique for online laser beam measurement, however, it fails to reconstruct the near-field and focal spot profiles when it is used to measure the beam quality of a 351 nm laser beam for SGII-upgrade facility. To solve this problem, a novel CMI reconstruction algorithm is proposed in this work, and the performance of the algorithm in 3ω laser beam measurement can be obviously improved. By adopting multiple-virtual-focal-plane constraint in the proposed algorithm, the near-field and focal spot profiles of the 3ω laser beam can be successfully reconstructed. Experiments have been conducted on SGII-upgrade facility to verify the feasibility of the proposed method.

In the field of optical three-dimension (3-D) measurement, reconstruction usually is completed by the integration of a two-dimensional (2-D) gradient data set. Position and posture of camera and shape of the surface under test determine the location of gradient data which usually is on quadrilateral grids. This paper proposes a B-spline surface-based 3D reconstruction method for deflectometry, which reconstructs the surface under test with its 2-D gradient data set. The 2-D gradient data set consists of gradient data and the 2-D location of the gradient data in the camera coordinate system. The 2-D gradient data set is first transferred to the cameras’ virtual image plane, so it locates on rectangular grids. Then, based on the properties of the B-spline basis function and characteristics of the camera, linear equations are derived to solve control points along the virtual image plane. The solved control points reconstruct the surface under test in the camera coordinate system. The property of the B-spline basis function determines the relationship between the depth of the surface and its derivative. The characteristic of the camera determines the relationship between the depth of the surface and the 2-D location of the gradient data. Meanwhile, the accuracy of the 2-D location can also be improved by the linear equations. Finally, simulated and actual experiments show that the proposed method is accurate and efficient at reconstructing surfaces in deflectometry.

In order to break through the limitation of off-axis holography in the field of measuring rough or strong scattering objects, a new iterative algorithm based on the concept of wavefront-coding was proposed. The reference wave is regarded as a wave modulator and it starts with random guess freed from the result of traditional off-axis holography. The full frequency spectrum could be retrieved iteratively after taking full advantage of the space-bandwidth production of the detector. As one form of coherent diffractive imaging, the theoretical resolution is diffraction limitation. According to the simulations and experiments with random phase plate, when the object fails to be reconstructed by traditional off-axis holography and other iterative off-axis holography algorithm due to the frequency spectrum of object is too wide, the proposed algorithm works well. It could be a general algorithm to prominently improve the capability of off-axis holography to measure rough or strong scattering objects.

High-resolution solar absorption spectra, observed by ground-based Fourier Transform Infrared spectroscopy (FTIR), are used to retrieve vertical profiles and partial or total column concentrations of many trace gases. In this study, we present the tropospheric CO

A three-dimensional (3-D) residual stress detection technique is proposed to detect and evaluate the residual stress occurring in optical components due to repairs carried out at laser induced damage sites. It is possible with a cross-orthogonal reflective photo-elastic setup to obtain complete 3-D information of the residual shearing stress around the damage site. The damaged volume of the optical component is numerically sliced into multilayers for this purpose and reflected light intensity is recorded from each layer. The shearing stress from the reflected light intensity is then calculated based on photo-elasticity theory. The validity of the approach is also verified in experiments where it could measure 3-D residual stress with an axial resolution of 10 µm along the light path.

Self-interference digital holography (SIDH) and Fresnel incoherent correlation holography (FINCH) are recently introduced holographic imaging schemes to record and reconstruct three-dimensional (3-D) information of objects by using incoherent light. Unlike conventional holography, a reference wave in incoherent holography is not predetermined by an experimental setup, but changes with target objects in incoherent holography. This makes the relation between the 3-D position information of an object and those stored in a measured hologram quite complicated. In this paper, we provide simple analytic equations for an effective 3D mapping between object space and the image space in incoherent holography. We have validated our proposed method with numerical simulations and off-axis SIDH experiments.

Coherent modulation imaging (CMI) can effectively improve the convergence performance of coherent diffraction imaging by introducing a pre-characterized wave modulator. However, traditional CMI algorithms suffer from a low signal-to-noise ratio (SNR), with insufficient information redundancy inheriting from a single diffraction pattern. Additionally, the strong modulation capability of the modulator with a small basic pitch is preferred; however, it leads to the difficulty of fabrication and measurement with a limited aperture size of the detector. To overcome those obstacles, this study proposes a revised CMI algorithm based on beam splitting encoding and averaging. A diffraction pattern array was recorded after the incident wave was split by grating and modulated by a weak scattering modulator simultaneously. This approach differed from the previous grating-based single-shot phase retrieval algorithm because the diffraction array was not segmented and used integrally during the iteration process, which guarantees the capability of diffraction-limited resolution in theory. Additionally, an average process was employed in the image plane of the object to improve SNR significantly. The performance of the revised algorithm was demonstrated by simulations and experiments and can be applied as a universal single-shot phase retrieval algorithm to various fields practically with fast convergence speed and high SNR.

Deflectometry has been widely used in topography measurement of the specular surface due to the merits of full-field data acquisition, automatic data processing, high accuracy, and large dynamic range. Existing deflectometry-based methods, such as model phase measuring deflectometry, direct phase measuring deflectometry, and stereo deflectometry, employ a plane screen, so they have a small field view. The characteristics of curved screens can effectively expand the range of the gradient and height field of the measured specular surface. This paper presents a novel deflectometric technique by using a curved screen to measure large-curvature specular surface. In order to obtain a model of the curved screen, a stereo vision method has been proposed to capture fringes displayed on the curved screen. After phase correction along epipolar lines and homologous points matching, the point cloud containing location and phase is obtained. A virtual plane fixed on the screen is assumed to gain posture and position of the screen. The model of the curved screen is transferred to the deflectometric system through the virtual plane. After calibrating the deflectometric system, height of specular objects can be obtained. Simulated and actual experiments on measuring specular objects have been carried out and the results show high accuracy and large field view for large-curvature specular surface of the proposed technique.

It is a challenge to retrieve atmospheric sulphur hexafluoride (SF6) with high resolution solar spectra because it has only one single retrieval micro window and has interfered with many factors in the retrieval. Optical misalignment is one of the key factors that affect the accuracy of SF6 retrieval. In this study, we first present a long term time series of the SF6 total column over Hefei, China, between January 2017 and December 2020, retrieved by mid-infrared (MIR) solar spectra recorded by ground-based high-resolution Fourier transform infrared spectroscopy (FTIR). The sensitivities of the total column, root mean square of fitting residual (RMS), total error budgets, degrees of freedom for signal (DOFs), and vertical mixing ratio (VMR) profile with respect to different levels of optical misalignment for SF6 retrieval were assessed. The SF6 total column is sensitive to optical misalignment. In order to avoid inconsistencies in the total column due to optical misalignment, we use the true instrumental line shape (ILS) derived from regular low-pressure HBr cell measurements to retrieve the time series of SF6. The total column of SF6 over Hefei presents strong seasonal dependent features. The maximum monthly average value of (3.57 ± 0.21) × 1014 molecules*cm-2 in summer is (7.60 ± 3.50) × 1013 molecules*cm-2 (21.29 ± 9.80) % higher than the minimum monthly average value of (2.81 ± 0.14) × 1014 molecules*cm-2 in winter. The annual average SF6 total columns in 2017-2020 are (3.02 ± 0.17), (3.50 ± 0.18), (3.25 ± 0.18), and (3.08 ± 0.16) × 1014 molecules*cm-2, respectively, which are close to each other. It indicates that SF6 total column over Hefei is stable in the past four years. Our study can improve the current understanding for ground-based high-resolution remote sensing of SF6 and also contribute to generate new reliable remote sensing data in this sparsely monitored region for investigations of climate change, global warming, and air pollution.

A method based on highly tilted illumination and non-paraxial iterative computation is proposed to improve the image quality of single-shot 3D ptychography. A thick sample is illuminated with a cluster of laser beams that are separated by large enough angles to record each diffraction pattern distinctly in a single exposure. 3D structure of the thick sample is accurately reconstructed from recorded diffraction patterns using a modified multi-slice algorithm to process non-paraxial illumination. Sufficient number of recorded diffraction patterns with noticeably low crosstalk enhances the fidelity of reconstruction significantly over single-shot 3D ptychography methods that are based on paraxial illumination. Experimental observations guided by the results of numerical simulations show the feasibility of the proposed method.

We present the trend and seasonal variability of stratospheric NO

Ptychography is a lensless phase imaging technique that obtains an image by scanning a specimen at several points with respect to a localized illumination beam. For larger specimens, it takes a longer time to complete scanning and hence higher stability is required in the setup which is often not guaranteed. An alternative technique is proposed here that reduces the sequential scanning time for such applications. A pinhole array is used to generate multiple tiny spatially separated beams to scan an object simultaneously at various points. The resulting diffraction patterns are recorded and processed in the Fresnel regime to obtain the images. Unlike other ptychographic methods using multiple beams, the proposed method does not require the use of a multimode ptychography algorithm or autocorrelation filtering of the diffraction patterns. The effectiveness of the method is studied through simulations and experiments. In contrast to conventional single-beam ptychography, the proposed method has the ability to achieve a larger field of view while leaving the number of scanned positions unchanged.

High-resolution solar absorption spectra, observed by ground-based Fourier Transform Infrared spectroscopy (FTIR), are used to retrieve vertical profiles and partial or total column concentrations of many trace gases. In this study, we present the tropospheric CO2 columns retrieved by mid-infrared solar spectra over Hefei, China. To reduce the influence of stratospheric CO2 cross-dependencies on tropospheric CO2, an a posteriori optimization method based on a simple matrix multiplication is used to correct the tropospheric CO2 profiles and columns. The corrected tropospheric CO2 time series show an obvious annual increase and seasonal variation. The tropospheric CO2 annual increase rate is 2.71 ± 0.36 ppm yr-1, with the annual peak value in January, and CO2 decreases to a minimum in August. Further, the corrected tropospheric CO2 from GEOS-Chem simulations are in good agreement with the coincident FTIR data, with a correlation coefficient between GEOS-chem model and FTS of 0.89. The annual increase rate of XCO2 observed from near-infrared solar absorption spectra is in good agreement with the tropospheric CO2 but the annual seasonal amplitude of XCO2 is only about 1/3 of dry-air averaged mole fractions (DMF) of tropospheric CO2. This is mostly attributed to the seasonal variation of CO2 being mainly dominated by sources near the surface.

A method based on highly tilted illumination and non-paraxial iterative computation is proposed to improve the image quality of single-shot 3D ptychography. A thick sample is illuminated with a cluster of laser beams that are separated by large enough angles to record each diffraction pattern distinctly in a single exposure. 3D structure of the thick sample is accurately reconstructed from recorded diffraction patterns using a modified multi-slice algorithm to process non-paraxial illumination. Sufficient number of recorded diffraction patterns with noticeably low crosstalk enhances the fidelity of reconstruction significantly over single-shot 3D ptychography methods that are based on paraxial illumination. Experimental observations guided by the results of numerical simulations show the feasibility of the proposed method.

A high-speed coherent diffraction imaging method is proposed by varying the curvature of illumination with a focus tunable lens. The imaging setup is free of conventional mechanical translation and takes only milliseconds to refocus by changing the electric signal applied on the lens. It is more compact and also an inexpensive alternative to coherent diffraction imaging with computerized translational stages. A detector that is kept at a fixed distance from the sample records diffraction patterns each time the spherical wavefront illuminations on the sample is changed with a control current. The complex wavefront of the object is then quantitatively recovered from the diffraction intensity measurements using an iterative phase retrieval algorithm. The feasibility of the proposed method is experimentally verified using various samples. Extremely short response time of the focus tunable lens makes the proposed method highly suitable for applications that requires high speed imaging.

Besides traditional lens-based imaging techniques, coded aperture imaging (CAI) can also provide target images but without using any optical lenses, therefore it is another solution in imaging applications. Most CAI methods reconstruct target image only from a single-shot coded image using a fixed coding mask; however, the collected partial information inevitably deteriorates the reconstruction quality. Though multi-exposure CAI methods are designed, these existed algorithms can hardly improve reconstruction signal-to-noise ratio (SNR) and spatial resolution simultaneously; additionally, dynamic coding mask display still requires expensive devices and complicated systems. In order to reconstruct target image with both enhanced spatial resolution and SNR but using cost-effective devices and a simple system, we design a noise reduced dynamic synthetic coded aperture imaging camera (NoRDS-CAIC) in this paper. The NoRDS-CAIC only consists of a programmable liquid crystal display (LCD) and an image recorder, and both of them are integrated with a three-dimensional printed shell with the compact size of 19 cm × 15 cm × 16 cm and controlled by our designed software to automatically realize coding mask display, coded image recording and target image reconstruction. When using the NoRDS-CAIC, the optimized coding mask is first sent to the programmable LCD and displayed, then the corresponding coded image is automatically captured using the image recorder. Next, cycle the above procedures to capture enough coded images with previously known coding masks and measured point spread functions (PSFs), and the target image can be finally reconstructed using our designed NoRDS-CAIC decoding algorithm, which is shown with better noise suppression capability and higher reconstruction resolution compared to other classical CAI algorithms. According to the experimental verifications, the NoRDS-CAIC can reach the high resolution of 99.2 µm and the high SNR of 19.43 dB, proving that the designed NoRDS-CAIC can be potentially used for lensless imaging in practical applications.

A single-shot phase retrieval algorithm based on a random aperture and partially saturated diffraction pattern is proposed. The diffraction pattern in the saturated area could be retrieved during the iterative process, which circumvents the problem of limited dynamic range of the detector. Besides, the random aperture is easier to be manufactured and if the accuracy of the random aperture is high enough, the design value could be used directly for iterations. It has the potential to be adapted for different wavelengths without additional transmission measurement of the wave modulator. The validity has been demonstrated by simulations and experiment.

We present the trend and seasonal variability of stratospheric NO2 column for the first time over the polluted atmosphere at Hefei, China, retrieved using Fourier transform infrared spectroscopy (FTIR) between 2015 and 2018. The FTIR observed stratospheric NO2 columns over Hefei show a peak in June and reach a minimum in January. The mean stratospheric NO2 column concentration in June is (3.49 ± 0.25) × 1015 molecules*cm−2, and is 39.20% ± 8.95% higher than that in January with a mean value of (2.51 ± 0.21) × 1015 molecules*cm−2. We find a negative trend of (−0.34 ± 0.05) %/yr in the FTIR observations of stratospheric NO2 column. The FTIR data are compared to the satellite OMI observations to assess the new data set quality and also applied to evaluate the GEOS-Chem model simulations. We find in general the OMI observations and GEOS-Chem model results are in good agreement with the coincident FTIR data, and they all show similar seasonal cycles with strong correlation coefficients of 0.84-0.86. The annual average OMI minus FTIR difference is (1.48 ± 5.33) × 1014 molecules*cm−2 (4.82% ± 17.37%), and average GEOS-Chem minus FTIR difference is (2.36 ± 2.33) × 1014 molecules*cm −2 (7.66% ± 7.49%). Their maximum differences occur in April and May with mean differences of 12-16%. We also found negative trends in the stratospheric NO2 column over Hefei for 2015-2018 with both OMI observations (−0.91 ± 0.09%/yr) and GEOS-Chem model results (−0.31 ± 0.05%/yr), demonstrating some consistency among them.

Aperture-scanning Fourier ptychography [Opt. Express22, 13586 (2014)] is a promising non-interferometric wavefront measurement technique. It eliminates the thin-sample requirement in typical Fourier ptychography employing angle-varying illumination. However, as aperture-scanning Fourier ptychography is based on step-by-step scanning, it requires long data acquisition time and a high-stability optical system. In this paper, we propose a single-shot aperture-scanning Fourier ptychography method. In our method, multiple low-resolution images are collected in a single shot by inserting a Dammann grating at a certain distance before the aperture, and the images are subsequently converted to a high-resolution complex wavefront. Compared with scanning-based aperture-scanning Fourier ptychography, the total acquisition time of the proposed method is dramatically reduced. The feasibility of our proposed method is demonstrated by proof-of-concept experiments.

Given the recent development of agile optical satellites for rapid-response land observation, side-oblique image-motion (SOIM) detection and blur correction have become increasingly essential for improving the radiometric quality of side-oblique images. The Chinese small-scale agile mapping satellite Kuaizhou-1 (KZ-1) was developed by the Harbin Institute of Technology and launched for multiple emergency applications. Like other agile satellites, KZ-1 suffers from SOIM blur, particularly in captured images with large side-oblique angles. SOIM detection and blur correction are critical for improving the image radiometric accuracy. This study proposes a SOIM restoration method based on segmental point spread function detection. The segment region width is determined by satellite parameters such as speed, height, integration time, and side-oblique angle. The corresponding algorithms and a matrix form are proposed for SOIM blur correction. Radiometric objective evaluation indices are used to assess the restoration quality. Beijing regional images from KZ-1 are used as experimental data. The radiometric quality is found to increase greatly after SOIM correction. Thus, the proposed method effectively corrects image motion for KZ-1 agile optical satellites.

Single-shot ultrashort extreme-UV(EUV) pulse waveform measurement is demonstrated by utilizing strong field ionization of H2 gas for transmission gating. A cross-propagating intense near-IR gate pulse ionizes the EUV absorbing H2 molecules into EUV-non-absorbing H2++ (two protons) and creates a time sweep of transmission encoded spatially across the EUV pulse. The temporal envelope is then retrieved from the lopsided spatial profile of the transmitted pulse. This method not only measures EUV temporal envelope for each single shot, but also determines timing jitter and envelope fluctuation statistically, thus is particularly useful for characterizing low-repetition-rate fluctuating EUV/soft x-ray sources.

Coherent modulation imaging (CMI) is a promising technique for online laser beam diagnostics; however, obvious speckle noise is always generated in the reconstruction, seriously degrading the spatial resolution and, accordingly, the accuracy. To solve this problem, both the optical setup of the common CMI and its reconstruction algorithm are slightly modified, and the performance of CMI in laser beam diagnostics can be obviously improved. By adding the second detector to record additional intensity distribution and using it to strengthen the intensity constraint of common CMI algorithm, the speckle noise in the reconstructed image can be distinctively reduced, and thus both the spatial resolution and the measurement accuracy are improved significantly. The feasibility of this proposed method is verified by proof-of-principle experiments.

Determining the complete optical behavior of anisotropic samples using ptychography is always a difficult problem. We propose a novel birefringence measurement method based on mixed-state ptychography that can simultaneously obtain the azimuth angle and retardation of anisotropic samples in a single scan. By using a reference system transformation, the two mutually orthogonal object states are unambiguously retrieved, and their errors are greatly reduced. The normalized root mean square errors of the obtained azimuth angle and retardation are 0.0011 and 0.0041, respectively. This method offers more rapid data acquisition; compared to interferometric based methods, it has the advantages of unlimited field of view and a simpler, more stable setup. Further, it opens a new possibility for investigating anisotropic samples by means of mixed-state ptychography.

The image reconstructed in ordinary digital holography was unable to bring out desired resolution in comparison to photographic materials; thus making it less preferable for many interesting applications. A method is proposed to enhance the resolution of digital holography in all directions by placing a random phase plate between the specimen and the electronic camera and then using an iterative approach to do the reconstruction. With this method, the resolution is improved remarkably in comparison to ordinary digital holography. Theoretical analysis is supported by numerical simulation. The feasibility of the method is also studied experimentally.

Wavefront control is a significant parameter in inertial confinement fusion (ICF). The complex transmittance of large optical elements which are often used in ICF is obtained by computing the phase difference of the illuminating and transmitting fields using Ptychographical Iterative Engine (PIE). This can accurately and effectively measure the transmittance of large optical elements with irregular surface profiles, which are otherwise not measurable using commonly used interferometric techniques due to a lack of standard reference plate. Experiments are done with a Continue Phase Plate (CPP) to illustrate the feasibility of this method.

We propose and experimentally demonstrate a cost-effective radio-over-fiber (RoF) system to simultaneously generate and transmit multiband and multi-gigabit 60-GHz millimeter wave (MMW) signals using frequency quintupling technique. Multiband signals at 56-GHz and 60-GHz are realized with two cascaded single-drive Mach-Zehnder modulators (MZMs), where phase control is not required. Furthermore, only low-frequency (≤12GHz) optical and electrical devices are used in the central station (CS), which enable a cost-effective system. At the user-terminal, two-stage down-conversions are employed by envelope detection (ED) and intermediate frequency (IF) mixing, eliminating expensive high-speed synthesizer and critical phase control components. Error-free performances are achieved for the multiband MMW signals after 50-km single-mode fiber (SMF) and 10-ft wireless link transmissions.

A special optical alignment is adopted and corresponding reconstruction algorithm is developed to reduce the reconstruction error induced by the hysteresis or backlash error of the translation stage in Ptychographical Iterative Engine (PIE) imaging with weak scattering specimen. In this suggested method, the positions of the scanning probe are determined directly from the recorded diffraction patterns rather than from the readout of the stage meter. This method not only remarkably improves the reconstruction quality, but also completely lowers the dependency of PIE on the device accuracy and accordingly enhances its feasibility for many applications with weak scattering specimen.

In this study, we fabricate ZnO thin films with nano-crystalline Si (nc-Si) quantum dots (QDs) using a ZnO/Si multilayer deposition structure and a post-annealing process, and the formation of high crystallinity of Si QDs embedded in the crystalline ZnO matrix is demonstrated. For optical properties, the essential features of ZnO material, high transmission in long-wavelength and high absorption in short-wavelength ranges, are preserved. We observe significantly enhanced light absorption and an unusual photoluminescence emission peak contributed from the nc-Si QDs in the middle-wavelength range. In addition, we confirm the formation of optical sub-bandgap and the obtained value is quite close to the unusual PL emission peak. We show that meaningful sub-bandgap can form in ZnO thin film by embedding nc-Si QDs while maintaining the advantageous properties of ZnO matrix. This newly developed composite material, nc-Si QD embedded ZnO thin films, can be useful for various electro-optical applications.

We observed that increasing the clusters size and laser pulse contrast can enhance the X-ray flux emitted by femtosecond-laser-driven-cluster plasma. By focusing a high contrast laser (10(-10)) on large argon clusters, high flux Kα-like X-rays (around 2.96 keV) is generated with a total flux of 2.5 × 10(11) photons/J in 4π and a conversion efficiency of 1.2 × 10-4. In the case of large Kr clusters, the best total flux for L-shell X-rays is 5.3 × 1011 photons/J with a conversion efficiency of 1.3 × 10-4 and, for the Kα X-ray (12.7 keV), it is 8 × 10(8) photons/J with a conversion efficiency of 1.6 × 10-6. Using this X-ray source, a single-shot high-performance X-ray imaging is demonstrated.

Given the recent development in high-resolution (HR) optical satellites, the study of both attitude jitter (AJ) detection and compensation has become increasingly essential to improving the radiometric and geometric quality of HR images. A group of HR optical stereo mapping satellites in China, mapping satellite-1 (MS-1) has launched two satellites and will launch one satellite to build a satellite network. The geometric accuracy of the launched MS-1 satellites is greater than 80 m because of the AJ caused by the instability of the platform. AJ detection and compensation are critical issues that must be addressed to improve the accuracy of geo-positioning and mapping before launching a new satellite. The present study employs a method of jitter detection based on short-time asynchronous images to detect MS-1 jitter. The adjacent overlapping areas of an original panchromatic image are used as detection images instead of the traditional multispectral images, and a differential recursion optimal estimation filter is proposed for the optimal estimation and elimination of the gross errors of the registration data procedure, thereby increasing the detection accuracy. The space variant blurring model and viewing angles correction method are employed for the radiometric and geometric jitter compensation of images, respectively. The methods of radiometric objective evaluation indices and geometric checkpoint are then utilised to evaluate the quality of jitter compensation. Finally, the DeZhou regional image (ShanDong province, China) from MS-1 is used as the experimental data. Results for the AJ of MS-1 are analysed and reported for the first time. The assessment results obtained show that both radiometric and geometric qualities greatly increase after the jitter compensation procedure. Thus, the work of this study for jitter detection and compensation effectively addresses the jitter of MS-1 HR optical satellites.

We demonstrate wavefront correction of terawatt-peak-power laser beams at two distinct and well-separated wavelengths. Simultaneous near diffraction-limited focusability is achieved for both the fundamental (800 nm) and second harmonic (400 nm) of Ti:sapphire-amplified laser light. By comparing the relative effectiveness of various correction loops, the optimal ones are found. Simultaneous correction of both beams of different color relies on the linear proportionality between their wavefront aberrations. This method can enable two-color experiments at relativistic intensities.

It is demonstrated that photoluminescence of DCJTB can be enhanced by surface plasmons occurred in silver nanoparticle arrays on glass substrates fabricated by using nanosphere lithography (NSL) combined with reactive ion etching (RIE). By changing the size of the seed polystyrene nanosphere with fixed thickness of SiO(2) film as a buffer layer between silver nanoparticles and fluorescent dye, we systematically studied the interaction between surface plasmons in Ag nanostructures and fluorescent dye by measuring the photoluminescence and time-resolved photoluminescence (TRPL) of the samples. As compared with pure DCJTB, it is observed that PL enhancement as high as 9.4 times and life time shortening from 0.966 ns shortened to 0.63 ns can be achieved with polystyrene nanosphere 430 nm in diameter. The physical origin due to plasmonic excitation has been clarified from 3D finite element simulations, as well as the assistance of UV-visible reflectance spectrum.

Ultra-high-speed optical communication systems which can support ≥ 1Tb/s per channel transmission will soon be required to meet the increasing capacity demand. However, 1Tb/s over a single carrier requires either or both a high-level modulation format (i.e. 1024QAM) and a high baud rate. Alternatively, grouping a number of tightly spaced "sub-carriers" to form a terabit superchannel increases channel capacity while minimizing the need for high-level modulation formats and high baud rate, which may allow existing formats, baud rate and components to be exploited. In ideal Nyquist-WDM superchannel systems, optical subcarriers with rectangular spectra are tightly packed at a channel spacing equal to the baud rate, thus achieving the Nyquist bandwidth limit. However, in practical Nyquist-WDM systems, precise electrical or optical control of channel spectra is required to avoid strong inter-channel interference (ICI). Here, we propose and demonstrate a new "super receiver" architecture for practical Nyquist-WDM systems, which jointly detects and demodulates multiple channels simultaneously and mitigates the penalties associated with the limitations of generating ideal Nyquist-WDM spectra. Our receiver-side solution relaxes the filter requirements imposed on the transmitter. Two joint DSP algorithms are developed for linear ICI cancellation and joint carrier-phase recovery. Improved system performance is observed with both experimental and simulation data. Performance analysis under different system configurations is conducted to demonstrate the feasibility and robustness of the proposed joint DSP algorithms.

We report a novel technique for highly stable transfer of a frequency comb over long optical fiber link. The technique implements an electronic compensation loop to cancel out the phase fluctuations that is introduced by the fiber. We utilized this technique to transfer a stable microwave frequency through a 20 km urban fiber link and an 80 km open air fiber link respectively. For the 20 km urban fiber link, the active compensation system reduced the phase fluctuation from 75 mrad (118 ps) to 4 mrad (6.3 ps) in 48 hours, and the frequency stability was improved by three orders of magnitude. For the 80 km open air fiber link, the active compensation system reduced the rms phase fluctuation from 580 mrad (914 ps) to 10 mrad (16 ps) in 24 hours, and the frequency stability was improved by two orders of magnitude.

Polarized images generated by the scattering near-field scanning optical microscopic interferometer were numerically studied by modeling the interferometer as a coupled point-dipole system. It was shown that, for a given specimen, the resolution of the near-field intensity and phase images were strongly dependent on both the polarization-direction of the reference light and the position of the far-field detector, revealing the strong polarization dependence of the near-field images. In the case of evanescent illumination, highly accurate images could be realized only when the detector was placed at a large enough view angle with the specimen and the reference light was polarized in the detecting-plane, which is vertical to the sample plane and contains both the detection point and the probe-tip.