Fringe array is proposed as the cooperated target in the precise torsion angle detection. The target fringe array image is generated according to the structure of the optical system, and the torsion angle detection algorithm is analyzed in response to the gray distribution of the image. The factors affecting the detection precision of the fringe torsion angle are analyzed theoretically and numerically. It indicates that the detection precision of the torsion angle is 1 angular second or even less, carefully selecting the detector array. Significantly, experiments are performed to demonstrate the precision and the results match well with the simulations.

Scanning Dammann lithography (SDL) is proposed and implemented, which uses a Dammann grating to generate multiple beams with sharp step boundary for writing large-sized gratings efficiently. One of the most attractive advantages is that this technique can accelerate the writing speed, e.g. 1 \times 32 Dammann grating can be 32 times faster than the single laser scanning system. More importantly, the uniformity of the multi-beams-written lines is much better than the single laser beam scanning system in consideration of the environmental effects such as air turbulence, thermal instability, etc. Using the SDL system, a three-port high-efficiency beam splitter at visible wavelengths is fabricated quickly, and the theoretical and experimental diffraction efficiencies are both higher than 90%. Therefore, SDL should be a useful tool for fabrication of large-sized gratings.

We propose and experimentally demonstrate a scheme of high-Q microwave photonic filter (MPF) using the techniques of self-phase modulation (SPM) spectrum broadening and third-order dispersion (TOD) com-pensation. The optical pulses from a mode-locking laser are spectrally broadened by the SPM in the highly nonlinear fiber. A wideband optical frequency comb with 365 spectral lines within 10-dB power variation from the highest spectral power is obtained. By applying a cubic phase modulation via a waveshaper, the effect of TOD which broadens the MPF passband is eliminated. The final implemented MPF has a Q-value as high as 296 and a tuning range of 700 MHz.

We measure the transmission characteristics of hollow-core photonic crystal fiber (HC-PCF) gas cells with ferrule- and fusion-spliced configurations, and near- and far-field images of the HC-PCF are observed. Results show that the center of mass (COM) of the far-field image varies with the laser frequency and temperature, and the moving COM relates to the oscillatory transmission. Using a model of the spatial interference, we first demonstrate that mainly the modes with asymmetric phase distributions affect the COM position. The frequency stabilization performances of the lasers are compared. The fusion-spliced gas cell shows better performance than the ferrule-spliced one.

In this letter, we report a Ho:YVO4 laser pumped by a 1.94-μm laser in both continuous-wave (CW) and Q-switched modes. The output performance of the Ho:YVO4 laser is compared with different output coupler transmissions. By use of the output coupler transmissions of T=30%, we obtain the maximum CW output power of 3.9 W at 2052 nm, with beam quality factor of M2=1.09 for the absorbed pump power of 12.5 W. For the Q-switched mode, we achieve maximum output energy per pulse of 0.38 mJ and the minimum pulse width of 25 ns, corresponding to the peak power of 15.2 kW.

An all-optical clock recovery scheme based on monolithic amplified feedback DFB laser (AFL) diode is proposed for nonreturn-to-zero (NRZ) quadrature phase shift keying (QPSK) format signals. By using a preprocessing stage, clock recovery (CR) is successfully demonstrated for 40-Gbaud NRZ-QPSK signals based on this scheme. The dependence of the timing jitter of the recovered clock on the optical power of the injected signal is investigated. A minimum timing jitter of 362.8 fs (integrated within a frequency range from 10 Hz to 10 MHz) is obtained.

We experimentally study the chaotic behaviors in a compact all-fiber erbium-doped fiber ring laser (ED-FRL) with an added Mach-Zehnder interferometer (MZI) by using a phase-modulation method. A piezo-electric ceramic transducer (PZT) is incorporated in the MZI to introduce single-frequency phase modulation. The coexistence of intermittency and period-doubling bifurcation routes to chaos in the EDFRL system is observed by adjusting the modulation frequency or the phase modulation depth in the experiment. In addition, the EDFRL presents irregular multi-longitudinal-mode oscillation with a definite linear polarization when operating at intensity chaos state.

In this letter, a new analytical method is presented to calculate of the semiconductor optical gain coefficient. This method is particularly suitable for theoretical analyses to determine the dependence of semiconductor gain on the total carrier density and temperature in the semiconductor lasers. Also, the optical gain functions for semiconductor optical gain coefficient are presented analytically. The analytical evaluation is verified with numerical methods, which illustrates the accuracy of these obtained analytical expressions.

We develope a simple method to stabilize the beam during propagation. Combination of the self-developed control module and the large diameter mirrors reconstruct the beam stabilization system, and some important procedures are presented, such as calibration and average filter. The results show that the horizontal pointing and vertical pointing are stabilized to within 8.43 and 7.59 μrad, and the beam horizontal position and vertical position are stabilized to within 2.16 and 2.11 μm respectively. The regulating time is within 84 ms. Thus the method presented is effective for the current stabilization system applied in lithography tools.

The influence of silver nanoparticles on Er3+ up-conversion in CaF2 precipitated oxyfluoride glass-ceramics is investigated. After heat-treatments, transmission electron microscopy images show that CaF2 nanocrystals precipitate in the glass matrix uniformity, and sliver nanoparticles are spread around the CaF2 nano-crystals simultaneously. Comparing with the samples without Ag doped, high efficiency up-conversion luminescences of Er3+ at 540 and 658 nm are distinctly observed in the silver nanoparticles containing glass-ceramics by the 980-nm excitation. Moreover, since the intensity ratio of green and red emissions changes after silver nanoparticles precipitation, the up-conversion mechanism of Er3+ is discussed.

Hyperlenses based on metamaterials can be applied to subwavelength imaging in the lightwave band. In this letter, we demonstrate both through simulations and experimentally verified results that our proposed half-cylindrical shaped hyperlens can be used for super-resolution microwave focusing in a TE mode. Based on split ring resonators, the hyperlens satisfies a hyperbolic dispersion relationship. Simulations demonstrate that the focused spot size and position are insensitive to the rotation angle of the hyperlens around its geometric center. Experimental results show that a focused spot size 1/3 of the vacuum wavelength is achieved in the microwave band.

Modulation properties of terahertz waves going through a light excited high resistivity silicon wafer are analyzed and measured. Free carrier lifetime of the silicon wafer affects the modulation depth and speed of the terahertz wave. The lifetime is reduced to less than 1 μs by thermal processing for high speed modulation. Experimental results show that the response time and modulation depth of the proposed modulating structure are close to 1 μs and 51%, respectively.

Conventional HfO2/SiO2 and Al2O3/HfO2/SiO2 double stack high reflective (HR) coatings at 532 nm are deposited by electron beam evaporation onto BK7 substrates. The laser-induced damage threshold (LIDT) of two kinds of HR coatings is tested, showing that the laser damage resistance of the double stack HR coatings (16 J/cm2) is better than that of the conventional HR coatings (12.8 J/cm2). Besides, the optical properties, surface conditions, and damage morphologies of each group samples are characterized. The results show that laser damage resistance of conventional HR coatings is determined by absorptive defect, while nodular defect is responsible for the LIDT of double stack HR coatings.

We propose a speckle-reduction method based on wavelength characteristics of speckle effect in synthetic aperture imaging ladar (SAIL). The return signal, which is the back scattering field with speckle effect from the rough surface of target, can be integrated over N chirp periods and heterodyne detected with a local-oscillator signal. After performing image processing respectively, the final image can be regarded as the incoherent superposition of the N sub-images. Numerical simulations indicate the effectiveness of this method. Our research may facilitate practical applications of SAIL.

Reconstruction the computer generated Fresnel hologram of complex 3D object based on compressive sensing (CS) is presented. The hologram is synthesized from a color image and the depth map of the 3D object. With the depth map, the intensity of the color image can be divided into multiple slices, which satisfy the condition of the sparsity of CS. Thus, the hologram can be reconstructed at different distances with corresponding scene focused using the CS method. The quality of the recovered images can be greatly improved compared with that from the back-propagation method. What’s more, with the sub-sampled hologram, the image can be ideally reconstructed by the CS method, which can reduce the data-rate for transmission or storage.

Spray behavior is regarded as one of the main factors influencing engine performances, fuel consumption and emissions for diesel engines. Under high injection pressure, diesel spray behaviors are extremely sensitive to the nozzle internal geometries, especially the geometric structures of orifice entrance. Based on the synchrotron radiation X-ray tomography technique, the 3D digital models of nozzle tips can be constructed. A new automatic method is presented to reveal the inlet structures according to these nozzle orifice models. The planes passing through the orifice axis are determined and used to cut the models, and then the corresponding cutting images are applied to measure the inlet chamfer radii around the orifice axis automatically. The orifices of a single-hole nozzle and an eight-hole nozzle are measured according to this method. The results show that this method can automatically measure the orifice inlet chamfer radii around the orifice axis with high precision. The obtained inlet chamfer radius shows the whole profile of the orifice entrance, which is a precise feedback for nozzle designing and manufacturing, and it also provides precise geometrical boundary conditions for the study of spray behaviors.

A new spectroscopic methodology is proposed to measure optical rotatory dispersion (ORD) of optically active media. ORD is obtained from a three-step phase shifting algorithm using transmission spectra taken at three independent probing angles. Optical rotation angles of four sugar solutions are investigated. The results obtained by using the new method show excellent agreement with the reference data, indicating the new method can be used as a reliable way for studying ORD of optically active media.

Improved all-optical OR gates are proposed, using a novel fiber nonlinearity-based technique, based on the principles of combined Brillouin gain and loss in a polarization-maintaining fiber (PMF). Switching contrasts are simulated to be between 82.4%-83.6%, for two respective configurations, and switching time is comparable to the phonon relaxation time in stimulated Brillouin scattering (SBS).

We present an experimental study on a unidirectional surface plasmon polariton (SPP) launcher based on a compact binary area-coded nanohole array, where the symmetry breaking is realized via effective-index modulation in the binary pattern of the gold film, thus avoiding the challenge of modulating nanostructure in its depth. It is shown that SPPs can be unidirectionally and effectively excited at normal incidence. The SPP intensity and asymmetric excitation ratio, which are two key figure-of-merits of SPP launchers, can be improved by increasing the number of array rows. The proposed device is compatible with most mature top-town nanofabrication techniques and thus is perspective for low-cost mass production.

A laser ranging system using all fiber high speed pseudorandom (PN) coded laser at 1550 nm and photon counting is proposed to realize high spatial resolution. Different lengths of PN code are employed in the optical fiber delay ranging test, the results show the improvement in both ranging accuracy and signal-to-noise ratio (SNR) as PN code trains increase. A ranging accuracy of 3 cm is acquired when transmitting pulses propagate to a target of 1.77 km away and received by an InGaAs/InP avalanche photodiode (APD). Simulation is also carried out under space borne condition based on current system. The system is demonstrated to have a potential for remote ranging and imaging.

Laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) based on single Nd:YAG laser is used to analyze copper impurity in silver jewellery with enhanced sensitivity and minimal sample ablation. 6-30 folds signal enhancement can be achieved under the re-excitation of the breakdown laser and the spatial resolution is only determined by the ablation laser. 50 ppm limit of detection of copper is achieved when the crater diameter is 17.2 \mu m under current experimental condition. This technique gives higher analysis sensitivity under the same sample ablation in comparison with single pulse (SP) LIBS. It is useful for high sensitive element microanalysis of precious samples.

Core mineral spectrometer is one of the advanced and important tools for core digitalization, altered mineral mapping, ore deposits exploring, and ore-searching in surrounding mine and beneficiation process. In this letter, a new core mineral spectrometer (CMS 350) is designed and developed. The basic principle, structural design, function module, key components, data acquisition, and processing methods of CMS 350 are introduced. In addition, some applications and results of CMS 350 in Zijin Mining are presented to validate the performance of CMS 350.

Terahertz (THz) emission from laser-induced air-plasma is presented. The frequency spectra of THz wave are investigated using an air-biased-coherent-detection method. The frequency spectra are measured under different pump-pulse and probe-pulse energies. The frequency spectra become narrow with the increasing pump power and we speculate it caused by collision behavior. Meanwhile, the bandwidth of the frequency spectra is broadened by the increasing probe power, which can be explained by pulse compression. Based on this finding, the optimal frequency spectrum of THz can be achieved by regulating the probe and pump beam.

A time-resolved multispectral X-ray imaging approach with new version of multi-channel Kirkpatrick-Baez (KB) microscope is developed for laser plasma diagnostics at the kilojoule-class Shenguang-II laser facility (SG-II). The microscope uses a total external reflection mirror in the sagittal direction and an array of multilayer mirrors in the tangential direction to obtain multiple individual high-resolution, highthroughput, and quasi-monochromatic X-ray images. The time evolution of the imploded target in multiple X-ray energy bands can be acquired when coupled with an X-ray streak camera. The experimental result of the time-resolved 2.5 and 3.0 keV dual-spectral self-emission imaging of the undoped CH shell target on SG-II is given.

We establish a system to measure the functional absorption cross section of photosystem II (PSII) (\sigma PSII) and maximum quantum yield of photochemistry in PSII (Fv/Fm). The system utilizes a sequence of high-frequency excitation flashes at microsecond intervals to induce a microsecond-level fluorescence yield curve. Parameters \sigma PSII and Fv/Fm are calculated by fitting the curve using nonlinear regression. Experimental results show that the relative standard deviation (RSD) of the system is less than 3%, and the correlation coefficient of Fv/Fm values measured by this system and those measured by pulse amplitude modulation method is 0.950.