A full-range Fourier domain Doppler optical coherence tomography (DOCT) system based on sinusoidal phase-modulating method is developed. The system combines Doppler detection with complex Fourier domain OCT. Full-range OCT and Doppler images are achieved using the complex spectral interferogram, which is retrieved based on the sinusoidal phase modulation B-M scanning and the combination of Fourier transform analysis and bandpass filter method. With the system, the depth imaging range is doubled and high velocity sensitivity is available in the whole B-scan image. Full-range OCT and full-range Doppler images of a flow phantom are achieved with the proposed system. The minimum detectable velocity of the system is investigated, which is 5.35 μm/s.

A windowed Fourier transform (WFT) based method is proposed for extracting and compensating depth-resolved phase error in spectral domain optical coherence tomography (SDOCT) system. Firstly, by using a WFT to the interference spectrum of the light from the sample and the reference mirror, the depth-frequency distribution of A-scan of the sample is obtained. Due to the time-frequency characteristics of the WFT, the interference spectra corresponding to different interfaces at different depths are separated. The polynomial fitting for the phase variation of each complex interference spectrum is then performed and the phase errors distribution with the change of depth is obtained. Based on these phase errors, a precise numerical compensation for the phase is carried out. This method can not only be applied for extracting and compensating of depth-resolved dispersion phase error, but also can be used for depth-varied phase error compensation resulted from uneven spectrum sampling in wave-number space. A simulation for dispersion phase error extraction is conducted. Finally, the SDOCT images of the 4-layer cover glasses and fingernail of a volunteer are obtained and then used for phase error extraction with the WFT method. The results demonstrate that the proposed method has the capability of extracting the phase errors with high precision, leading to the improvement of the depth resolution and the image quality after phase error compensation.

Spinal cord injury (SCI) model is created by Allen′s method, and this study is designed to explore the effect of 810 nm low-level laser irradiation on expressions of TNF-α, IL-6 and IL-10 in acute spinal cord injury. 68 SD rats are randomly divided into normal group, SCI group and irradiation group. Light (810 nm, 150 mW) is applied transcutaneously at the lesion site of rats in irradiation group. Functional recovery is assessed by open-field test (BBB test) on 1 d, 3 d, 7 d after injury. The expressions of TNF-α, IL-6 and IL-10 in the injured spinal cords are examined by enzyme linked immuno sorbent assay (ELISA) method at the time of 1 h, 3 h, 6 h, 12 h, 1 d, 3 d, 5 d and 7 d after injury. We find that there is a statistically significant functional recovery (P<0.05) in the irradiation group compared to SCI group at 7 d. The expressions of TNF-α and IL-6 of irradiation group is significantly lower than the comparable SCI group at the time of 6 h, 12 h, 1 d (TNF-α) and 6 h, 12 h, 5 d (IL-6) (P<0.05). The expression of IL-10 of Laser group is significantly higher than the comparable SCI group at the time of 1 d, 3 d, 5 d and 7 d (P<0.05). There is no statistical difference at other time points. The results of our study show that laser irradiation can effectively inhibit the expression of pro-inflammatory cytokine TNF-α and IL-6 and significantly promote the expression of IL-10 in rats of acute spinal cord injuries, and laser irradiation can promote functional recovery of acute spinal cord injury rats.

Diffraction characteristics of reflection volume holographic gratings at nonuniform swelling or shrinking by introducing a function between swelling factor and the thickness of the grating layer are investigated. By means of Kamiya′s rigorous delamination-calculation method and Lorentz-Lorenz formula, the analytical expressions of the average refractive index and the modulation are derived. Accordingly, the diffraction efficiency curves of the 1st-order reflection are given when the swelling factors are constant, linear function and nonlinear function. The influences of the average refractive index and the modulation for an ideal grating or decay distribution for the nonideal grating on the angular and wavelength selectivity are analyzed. The diffraction characteristics of the grating are given when the swelling factors are unequal at the exposure area and the unexposed area, and the response degree of diffraction efficiency of the grating to the change of swelling factor is discussed. The results show that nonuniform distribution of the swelling factor causes a diffraction efficiency curve in the asymmetric profile; compared with the modulation of refractive index, the Bragg angle of grating is highly sensitive to the change of average refractive index; the swelling factors at the exposure area and the unexposed area affect the peak efficiency, the angular band range and the spectral bandwidth. The results have theoretical guiding sense for the swelling and shrinking process of the reflection volume holographic gratings.

In recent years, three-dimensional (3D) imaging technique based on the structured light illumination has been studied deeply and applied widely. Most commonly, in the technique proposal, a fringe pattern with a carrier frequency component is projected onto the imaged object, then the deformed fringe patterns caused by the height distribution of the tested object′s surface are recorded by a imaging device from the other direction. By demodulating the deformed fringe patterns, the 3D digitized reconstruction of the object can be retrived. Comparing with 3D holographic imaging, such 3D imaging process based on the structured light projection can also be divided into two imaging steps. The two-dimensional (2D) fringe image modulated by the imaged object is captured by a camera. Then, the 3D digitized image of the object can be reconstructed by demodulating the deformed fringe patterns. The progress in this 3D imaging techniques based on the structured light illumination made by author′s research group is reviewed. Different 3D imaging methods based on the Fourier fringe analysis, phase-shifting fringe analysis and dynamic 3D imaging are deeply discussed and some related experimental results are also demonstrated to readers. In addition, the characteristics of the 3D imaging based on structured light imaging and their developing trends in the future are pointed out as well.

The digital holography is characterized by its full field of view, non-contact, non-destructive, real-time and quantitative detection, which is especially suitable for the three-dimensional reconstruction and fast tracking of living cells without staining or labeling. The digital holography imaging has been developed rapidly in the field of the biomedical science. The basic principle of digital holography is introduced for the cell detection, and the major progress of the research and application is reviewed based on the cell morphology, biological parameters, physiological status, drug effect and dynamic analysis. The potential application and future research are discussed, and the challenge and problems of digital holography technology are pointed out.

With the maturation of terahertz (THz) technology, the THz digital holography, which is one of the most important development directions, gradually exhibits the application powers in various research and industrial fields. The work in the improvement and applications of the THz digital holography in recent years is discussed. A THz holographic imaging system with a high spatial resolution, high signal to noise ratio, and polarization information measurement ability is built. Furthermore, it is demonstrated that this imaging system can be used to check the performances of THz planar elements, measure transmission modes of the THz waveguide, and observe the Gouy phase shift of the converging THz beam. This work is valuable for promoting the practicability of the THz digital holography.

Incoherently illuminated or self-luminous objects are composed of many independent object points. Any two points from the object are spatially incoherent whereas the two beams from the same object point are spatially coherent. Incoherent digital holography is a technology of recording holograms of incoherent objects and reconstructing three-dimensional information of the original object. The hologram of a point object can be formed based on spatial self-coherence of the beams by suitable optical beam-splitting technique and the hologram of an extended object is the superimposing of all point-holograms incoherently. The investigations on incoherent digital holography have verified that this technique has great potential in non-scanning fluorescent microscopy, incoherent color holography, and incoherent adaptive optics. The basic principle of incoherent digital holography is firstly demonstrated and some typical incoherent holographic imaging systems are summarized. The key imaging characteristics and research progress are analyzed and discussed based on self-reference incoherent holography.

The volume holographic correlator (VHC) can store multiple images in the common volume of the storage medium by angular multiplexing based on the Bragg selectivity of volume gratings. During the correlation, all the correlation results between the stored images and the input search argument can be simultaneously got. Each correlation result is represented by the intensity of the corresponding correlation spot. The key technologies and constraint factors of the practical utilization of the VHC are analyzed. The research progresses in suppressing the channel crosstalk by speckle modulation, eliminating the impact of pattern dependent behavior, improving the processing accuracy by multi-sample parallel estimation, and system integration of the read-only VHC are summarized. Parallel processing ability with more than 7500 channels and processing speed up to 138 GHz are achieved in the current portable VHC system. The successful applications in remote sensing image matching and biometric recognition have proved the high speed high accuracy abilities of the system.

In-line digital holography is widely applied in many areas due to its simple optical path, low requirement of coherence and fully utilization of camera′s bandwidth. The reconstruction quality of in-line digital holography, however, suffers from the superposition of twin-image contamination, which can be solved via phase retrieval algorithm. By iteratively applying certain constraints on an estimate of an object in real and reciprocal domain, the real image is well seperated from the unwanted components. The recording and reconstruction process of in-line digital holography and fundemental phase retrieval methods including Gerchberg-Saxton (GS), error reduction (ER) and hybrid input-output (HIO) algorithms are introduced. Then, the phase retrieval algorithms for in-line digital holography is divided into four categories, i.e., constraints, multiple axially recording, wavelength divergency and initial guess. The constraints and experimental results of these phase retrieval algorithms are listed. Finally, a prospect is given for the possible improvement and potential applications of phase retrieval methods in in-line digital holography.

Human eye is the key organ of three-dimensional display, it plays unique roles in perception including depth visual, space/time resolution, color/brightness response, etc. The critical characteristics of three-dimensional display such as stereo-image quality, viewing comfort, and effect of presence are investigated. The stereo visual fatigue, surface deformation, image quality of large view angle, and color ribbon effect in auto-stereoscopic display are researched. The impulse response function of lenticular lens is analyzed, and solutions are put forward. Multi-view auto-stereoscopic display is used in the science popularization of Chengjiang Biota. Unit image processing, stereo depth and resolution of integral imaging, as well as the human visual effects in holographic display are also discussed.

In the study of off-axis digital holography, digital hologram may be considered as a light wave field which is illuminated by the unit amplitude plane wave. The Fresnel diffraction integral can be calculated by only one fast Fourier transform (FFT). It is the most popular method of wavefront reconstruction (called 1-FFT). However, applying the spherical wave as the reconstruction wave, there is another method of wavefront reconstruction using the angular spectral diffraction theory and image plane filtering. This method requires four fast Fourier transforms (called FIMG4FFT). Two methods are researched based on the fast Fourier transform theory. The result demonstrates that the FIMG4FFT method needs four FFTs, but it can use less computation resource to reconstruct the equivalent quality object wave field. Finally, the application examples of the FIMG4FFT method are shown in detail in the reconstruction of color digital holograms and micro deformation detection.

A consecutive spatial frequency modulation technique using 4f imaging system and diffractive grating is proposed. Based on this technique, a three-dimensional (3D) image printing system is designed and fabricated, by which a large formate (15 cm×20 cm) and true color 3D image with wide view angle (more than 90°) is made. Characteristics of frequency modulation structure in 3D image are analysed. Mathematical expressions with parameters of frequency modulation structure are given. Principles of consecutive spatial frequency modulation are analysed and frequency modulation rules are deduced. Validity of the rules and system of spatial frequency modulation are varified by experiments. Color 3D images are outputed by laser printing system.

An improved off-axis dual-wavelength digital holography method is presented for three-dimensional surface topography measurement of objects with significant variations. The object beams informations of the two different laser wavelengths are recorded on one hologram based on polarization splitting principle, thus the measurement range can be expanded to micron or millimeter scales by means of the equivalent wavelength induced by difference frequency effect between the two wavelengths and the equivalent wavelength is longer than any single one. So the problems of inevitable phase unwrapping when the object morphology with significant variations are measured by a single wavelength is overcame effectively. The morphology of a staircase sample with micron height variations is measured. The experimental results are consistent with the nominal values and the values measured by profile-system, which shows the effectiveness of the proposed method.

To simulate the natural three-dimensional (3D) display, both binocular parallax and smooth motion parallax are required. Normally, it requires a huge amount of spatial information to increase the number of views and to provide smooth motion parallax for natural 3D display similar to real life. Holographic stereogram can be used to display a description of 3D discrete images or a set of 3D data points. Here, three methods are used to realize natural 3D displays with smooth motion parallax, which are functionally equivalent to the holographic stereogram. With digitally generated active partially pixelated masks in the liquid crystal panel combining with a precision lenticular lens array, the 3D display with 1200 views from a computer numerical model is demonstrated in 56° viewing angle. The displayed depth is more than 40 cm and the screen size is 50.7 cm×28.5 cm. With a holographic functional screen with a size of 1.3 m×1.8 m, a demonstrated system including optimally designed camera-projector arrays and a video server can display the fully continuous 3D scene with more than 1 m image depth. Based on the digitally generated tompographic images, a 3D display with smooth motion parallax is demonstrated in a 50 inch (1 inch=2.54 cm) LCD panel with the resolution of 3840 pixel×2160 pixel.

The quantitative relation of hologram information capacity with parallax and field angle is computed. The result points out that there is a mass of information in order to provide adequate parallax and field angle for three-dimensional display. With enough parallax and field angle, the limit of information reduction is given, and the characteristics of reconstruction image of grating sampled hologram (GSH) is analyzed. A design for using the GSH to three-dimensional displaying is proposed. This work can be guidance for fast computing hologram and holographic video.

Real-time dynamic holographic video display is presented in a super fast liquid crystal thin film with holographic response in the order of a millisecond and without any applied electric field. Both the formation time and self-erasure time of holographic images are 1 ms. Real-time dynamic holographic videos are achieved at red, green and blue laser without cross talk between the holograms. Furthermore, color holographic display in RGB model is realized by holographic multiplexing. Because the sample is easy to be made into a large size screen and needs no external electric field, any spatial light modulators or other holographic display devices resulting from this material will not be pixilated, and it can conquer the defect of existing spatial light modulator. It is believed that the film can be developed into a high resolution, large-size, real-time dynamic, and color holographic three-dimensional display in the future.

An iterative method to extract actual phase shift in two-step phase-shifting digital holography is proposed, in which peak signal-to-noise ratio (PSNR) of the reconstructed reference wave is taken as a judging condition. The relationship between PSNR of the reconstructed reference wave and phase shift error is investigated. According to the 1st and 2nd order derivative of PSNR, the iterative direction and whether PSNR undergoes a maximum can be determined. Optical experiment is performed to demonstrate its validity.

High computational complexity is the bottleneck of the holographic display. Aiming at the problem, a new hologram coding and reconstruction algorithm based on compressed sensing theory and lensless Fourier transform is proposed. Lensless off-axis Fourier hologram is generated by computer, and then the hologram is sampled and reconstructed by the theory of compressed sensing. At last, the original image is reconstructed by the hologram. The advantage of this method is that only some useful sampling coefficients of the hologram is used to reconstruct the original image well, which solves the problem of large volume of sampling data of the sensor and achieves the goal of reduction of the computational complexity. Simulation results show that the correlation coefficient of reconstructed image with 20% compressive sampling rate is 0.85; when compressive sampling rate of hologram with 50%, the coefficient reaches 0.9999. In addition, a holographic reconstruction system is built to verify the hologram compression sampling theory. The experimental results indicate that the original image can be clearly reconstructed by the system, which proves the feasibility of the method.

In order to recover wrapped phase map with the noisy and under-sampled area rapidly and accurately, the algorithms of fast Fourier transform (FFT)-based method of least squares (FFT-LS), discrete cosine transform (DCT)-based method of least squares (DCT-LS), lateral shearing based method of least squares (LS-LS) and the algorithm of preconditioned conjugate gradient (PCG) method are compared through theoretical analysis, computer simulation and experimental verification. The results show that the algorithm of DCT-LS is the fastest, the algorithm of LS-LS is second to DCT-LS, and the algorithm of PCG is the slowest. For strong noise, the algorithm of PCG has the best effect, and the algorithm of LS-LS has the best effect for dealing with under-sampling.

A method of imaging on multiple focal planes based on fractional Fourier transformation is presented. It is used to compute the holograms, so that different images are projected at different depths in the same system. By using synchronization information sent by the spatial light modulator, the circuits control the switch of the polymer doped liquid crystal screens. That means only the one with the right depth is switched off corresponding to the projected image, others let light pass through. With the sequential loaded holograms on the spatial light modulator, different holographic images are presented on multiple focal planes. Three-dimensional (3D) display by holographic display imaging on multiple focal planes is realized as a result of visual staying phenomenon. The imaging depth can be adjusted according to parameters of the optical system and sampling conditions. Besides, the system is simple and easy to carry out.

To obtain the real phase in digital holographic microscopy (DHM), it needs to compensate the additional phase induced by the microscope. Based on the theoretical analysis, both two-step compensation algorithm and Zernike polynomials fitting algorithm are employed to perform the phase reconstruction for biological cell. The obtain results show that both two-step compensation algorithm and Zernike polynomials fitting algorithm are useful for system phase compensation of DHM. In two-step compensation algorithm, since the subtraction operation is performed between the reconstructed phases with the object and without the object, the DHM system phase error can be compensated effectively while it is still time-consuming and needs high experimental stability for recording holograms. In Zernike polynomials fitting algorithm, only one group of digital holograms with the object is required for compensating the additional phase induced by the microscope, therefore it is suitable for the dynamic phase measurement while the constructed phase error increases with both the increase of object height and transverse area. To decrease the reconstruction phase error of Zernike polynomials fitting phase compensation algorithm, it is required to ensure that one of the variations of object optical height or transverse area to be a small value. The result supplies a useful tool for the study and application of biological cell phase compensation by DHM.

Terahertz Gabor in-line digital holographic system has the characteristics of high resolution and compact structure, and it has potential application prospects. The lateral resolution of the system is related to the recording distance, so the research on the effect of recording distance on imaging results in actual imaging system has important application values. By using self-made targets with resolutions of 0.4 mm and 0.6 mm, 2.52 THz Gabor in-line holography imaging experiments with different recording distances are carried out and digital reconstructions are realized by angular-spectrum representation. The reconstructed images are compared and analyzed, and experimental results are close to the theoretical calculation results of the lateral resolution changing with the recording distance.

A new three-dimensional (3D) imaging method that combines both fringe projection and pseudorandom pattern projection technique is presented. In proposed approach, we only need to project four equal-step phase-shift images and a pseudorandom pattern image. Combined with the epipolar constraint and image correlation, the congruent relationship of the wrapped phase between left and right cameras is obtained. In each corresponding folding phase, the phase values as coding can implement the binocular matching, so 3D reconstruction can be realized without phase unwrapping. The experimental results show that the proposed method can reduce the time of image sequence acquisition, comparing with conventional fringe projection technique. In addition, the compactness, robustness and accuracy of 3D image have not been affected.

A method of computer-generated hologram for the three-dimensional (3D) object based on integral imaging is proposed. The method uses the micro-lens array to form an array of the elemental images and gains an array of the orthographic projection images through pixel extraction. According to the principle of the 3D central slice theorem, a series of the two-dimensional (2D) Fourier spectra of orthographic view images are put in the corresponding 3D Fourier space, and the intersections are extracted and superimposed to obtain the distribution of the 3D object′s spectra in the later focal plane of the lens. The distribution of Fresnel diffraction on the specific propagation distance is calculated, and the Fresnel computer-generated hologram is obtained by using holographic encoding method. The numerical reconstruction images of the Fresnel holograms at different distances show that the method is feasible. The method can obtain the hologram of real-existing 3D objects using the 3D Fourier spectrum with regular incoherent illumination. It reduces the complexity of the system, and the algorithm is simpler.

A novel method is presented to optimize recording wavefront aberration of holographic lens (HL) based on spatial light modulator (SLM). According to the theory of wavefront aberration, aberration characteristics and expressions are obtained, and one-dimensional aberration curves are drawn, and optimizing approach of holographic lens based on SLM is proposed. We theoretically analyze the approach of reducing aberrations by recording the holographic lens via single exposure with a hologram loaded on the SLM. The effect which zero-order crosstalk of the SLM does to the holograms as well as the stop surface of the field of view does to the aberrations is discussed. Using the optimized hologram containing the aspheric information, we design the experiment of recording the holographic lens based on the SLM, and the result is consistent with the theoretical analysis.

Reconstructed image of digital holography has problems such as serious interference of speckle noise, low contrast and so on. Thus a method based on speckle reducing anisotropic diffusion (SRAD) model and nonsubsampled contourlet transform (NSCT) is proposed for improving reconstructed image quality of digital hologram. SRAD model is adopted to eliminate speckle noise of reconstructed image. After NSCT decomposition, a low-frequency sub-band and several high-frequency sub-bands are produced. Low-frequency sub-band coefficients are adjusted based on a nonlinear gain function and an image segmentation method. In high-frequency sub-bands, edges are enhanced using a NSCT modulus maximum edge detection method. A large number of experimental results show that, compared with nonlinear diffusion denoising methods and NSCT enhancement methods proposed recently, the proposed method can more effectively eliminate speckle noise and improve the contrast of reconstructed image. Furthermore, the edges are smooth and clear. As a result, the accuracy of recognition and measurement in digital holography can be improved.

A fast reliability-guided phase unwrapping algorithm for digital holography is proposed. The value of reliability is nonlinearly quantized to form a quality map. The phase is unwrapped reliably and fast by combining the nonlinear quality map with look-up table operation. The residues are searched in the wrapped phase map, and the maximum intensity of residues is set as threshold. The measured region is segmented to the reliable region and the doubtful region by the threshold. A nonlinear quality map is derived by setting the reliability of reliable region to maximum and setting those of the doubtful region to quantized value of intensity. Flood-fill algorithm using look-up table is implemented with the nonlinear quality map to unwrap the phase map. In experiments, the speed of proposed algorithm is about 68 times faster than that of conventional flood-fill algorithm and about 3 times faster than that of branch cut algorithm. The experimental results demonstrate that the speed of proposed algorithm is significantly increased and the quality of unwrapped phase is good as well.

A model is given out for computing energy coupling coefficient in the process of laser ablating glass fiber/expoxy composites. By the simulation of laser irradiating glass fiber/expoxy composites, laser transmission and the front surface temperature are abtained in the ablation process, which agree well with the experimental results. The result indicates that energy coupling coefficient in the process of laser irradiating glass fiber/expoxy composites can be computed by the proposed model. Besides, the change law of energy coupling coefficient with different laser intensities is computed with the proposed model. The computed result indicates that laser energy absorption mechanism changes from bulk absorption to surface absorption. More intensive laser beam causes that energy coupling coefficient increases more quickly and the conversion process from bulk absorption to surface absorption is faster.

It is important to accelerate the development of the laser welding technology of marine high strength steel E36. Laser butt welding of 3.2-mm thick E36 is performed by using a YbYAG laser. The microstructure and hardness of weld joints are analysed and the effects of the welding speed on properties of the weld joints are studied. The result shows that the microstructure of weld zone (WZ) is mainly martensite, and the microhardness of WZ is higher than that of base metal (BM). The hardness distribution of weld joint is non-uniform. The weld edge has an highest hardness. Heat affected zone (HAZ) is very narrow and the hardness in this zone drops quickly. With the increase of the welding speed, the properties and microhardness also change: When the welding speed is 70 mm/s, the highest hardness of the WZ is 448.9 HV, which is the highest of all the samples, and the hardness in its HAZ drops most quickly. The tensile samples which are welded at speed from 20 mm/s to 60 mm/s are all broken in base metal. When the welding speed is 70mm/s, the samples are all broken in fusion line and its ductility is obviously worse than that broken in base metal.

AZ91D wrought magnesium alloy plates, with thickness of 6.3 mm, are welded by a CO2 laser beam with a laser power of 3500 W, welding speed of 2.5 m/min, defocusing of +2 mm and a constant argon gas flow of 10 L/min. The microstructure, tensile properties and fracture morphology of the joint are investigated. The results show that a favorable weld can be obtained. The fusion zone consists of finer α-Mg equiaxed matrix and β-Mg17Al12 precipitates distributed along the grain boundaries with pores and microcracks frequently found. The width of the partly melted zone is very narrow, about 50～80 μm, and the grains near the fusion zone are locally melted while those near the base metal are not. Tensile results indicate that the ultimate tensile strength (UTS) and elongation of the joint are respectively 232 MPa and 6%, about 90% and 25% of that of the base metal. The final fracture of the joint occurs at the center of the fusion zone and the fracture morphology shows a combination of brittle and ductile features.

To improve the clearance surface roughness of non-assembly mechanisms fabricated by selective laser melting (SLM) and to manufacture non-assembly mechanisms with good surface quality and high density, the inclined surface roughness of the clearance is studied theoretically firstly. Then the clearance junction structure is designed. The effects of laser surface remelting and process parameters on surface roughness are analyzed, respectively. Results show that the inclined surface roughness (Ra) of the clearance is affected by inclined angle and the slice thickness theoretically. Ra decreases as the inclination angle increases and the slice thickness decreases. The clearance is designed as drum shaped hole to improve fabrication quality. Laser surface remelting process can not only improve the density, but also improve the surface quality. During the process, volume energy density should be controlled in success prototyping zone. When fabrication reaches the top of the clearance, the scanning speed should be increased to reduce the dross to improve surface quality. At last, the universal joint is fabricated successfully. The outside surface Ra is 8.25 μm, the clearance surface Ra is 12.47 μm, and the relative density is 99.1%.

A single-stage femtosecond laser direct amplification system with all polarization-maintaining, double-cladding, Yb-doped large-mode-area photonic crystal fiber (LMA-PCF) is constructed. The photonic crystal fiber (PCF) oscillator operates in soliton mode-locking regime, and the PCF amplifier is employed in nonlinear amplification. The all-PCF single-stage amplifier directly generates a high-average power of 34 W and a pulse width of 50 fs at the repetition rate of 42 MHz, corresponding to pulse energy of 0.8 μJ and peak power of 16.2 MW.

A novel multiwavelength Brillouin-erbium fiber laser (MW-BEFL) based on the feedback fiber loop (FFL) is proposed. The main single pass ring is constructed by an optical circulator and a 50 m single mode fiber (SMF). In order to guarantee the single longitudinal mode operation of each Stokes waves and anti-Stokes waves, the FFL is configured with a 10 m SMF of traditional Brillouin-fiber laser. The system is enclosed in temperature control system so that environment disturbance is reduced. 45 dB sidemode suppression and 3.23 kHz linewidth of the first-order Stokes wave are measured by delay interference method. Through the cascaded stimulated Brillouin scattering (SBS) and degenerate four-wave mixing (FWM) process, the laser can be freely and steadily tuned in 50 nm range from 1525 nm to 1575 nm with 0.084 nm wavelength spacing.

Due to the high measurement accuracy and no speed accumulated error, Doppler lidar becomes an important equipment of modern navigation system. In order to improve the performance of three-beam Doppler vehicle lidar, Oren-Nayar model is used to analyze the relationship between the beam pointing angle and the echo power. The dependences of the signal-to-noise ratio and speed sensitivity on beam pointing angle are studied too. The ranges of horizontal deflection angle and the complement of zenith angle are provided. The comparative experiments are conducted with the complement of zenith angle equal to 53° and 24°, separately. Experimental results show that the chosen angles are appropriate.

With the method of high-tempreture thermal decomposition, Li:YF4:Er,Yb nanocrystals with an average diameter of about 10 nm are synthetized, which are doped into SU-8 and used as the active layer of the waveguide amplifier. The waveguide amplifier based on SU-8 doped with Li:YF4:Er,Yb nanocrystals is fabricated by using SiO2 as an upper cladding and P(MMA-GMA) as a lower cladding. For an input signal power of about 0.05 mW and a 980 nm pump power of about 180 mW, a relative optical gain of about 2.3 dB/cm at 1535 nm is achieved in polymer waveguide doped with Li:YF4:Er,Yb nanocrystals.

NaGdF4:Nd3+ nanoparticles and nanorods are synthesized by hydrothermal method. X-ray diffraction(XRD) and scanning electron microscope(SEM) are used to characterize the crystal strcucture and morphologies of these nanocrystals, respectively. Their luminescent properties at room temperature are studied and compared with those of the bulk powders. In particular, thermal queching characteristics for the luminescence of Nd3+ are studied, and the temperature dependence of luminescence of NaGdF4:Nd3+ nanocrystals and bulk powders are fitted. It is observed that the thermal quenching rate in NaGdF4:Nd3+ nanocrystals is lower than that in the bulk powders, and the thermal quenching rate in nanoparticles is close to that in nanorods.

The effect of 248 nm excimer laser irradiation on the photoluminescence and electrical properties of ZnO thin films under different atmospheres (air, oxygen and nitrogen) is investigated. Based on Gaussian curve, the photoluminescence spectra of ZnO thin films irradiated by laser under different atmospheres are fitted, and the photoluminescence peaks around 3.31, 3.28, 3.247, 3.1 eV are assigned and analyzed in mechanism. After laser irradiation, ultraviolet (UV) emission is obviously lower and shows a little red-shift, while D0X-1LO and D0X-2LO transitions merges into one peak. After laser irradiation under oxygen rich atmosphere, the acceptor density of ZnO thin films increases, and the donor density decreases. After laser irradiation under oxygen deficiency atmosphere, the acceptor density of ZnO thin films decreases, and the donor density increases. After laser irradiation, the resistivity of ZnO thin films is decreased by three orders of magnitude, carrier concentration is increased by two orders of magnitude, and carrier mobility is increased by one orders of magnitude.

A novel camera calibrating method based on orthogonal vanishing points is proposed after analyzing camera model, calibration of single and stereo vision systems and geometrical characteristics of the vanishing point. Only one camera photographing at least three checkerboard patterns in different orientations is required. The pinhole and the first two terms of radial distortion model is introduced. The presented method mainly contains the computation and optimization of vanishing points, a linear calibration of intrinsic parameters, the improved Tsai′s two-steps for extrinsic parameters and a nonlinear global refinement. Experimental result demonstrates that the proposed algorithm is fast and accurate. After global optimization, the re-projective mean pixel error is 0.0043 pixel and the time consumption is 1.7911260 s. This novel method can be widely applied in fields including the computer vision research, the industry three-dimensional measurement and reconstruction and road mapping.

The contrast between the effective refractive indices (RIs) of the core mode in a uniaxial-crystal fiber yielded respectively by two fiber analysis models, namely the two-layered medium model and three-layered medium model, is simulated and analyzed. Based on this, the surrounding RI, temperature and axial strain sensitivities of a long-period fiber grating (LPFG) are calculated. The result shows that the core-mode effective RI difference produced by the two fiber analysis models is significant, especially in the case of thin cladding layer. Moreover, the surrounding RI, temperature and axial strain sensitivities calculated from the two layer model and/or the materials′ sensing-parameter-induced optical coefficients have significant error, and it is necessary to employ the three layer model and the correspondent model effective RI coefficients to obtain accurate results. The relationship between the sensitivities and the cladding mode order for different clad radii is calculated. This paper provides guidance to the analysis and design of LPFG based sensors.

Optical voltage sensor is an important voltage sensing instrument which has been widely applied because of its unique advantages. We have proposed and accomplished a new type of quasi-reciprocal reflection type integrated optical voltage sensor, using Y-cut LiNbO3 waveguide based on Ti-diffused technique as the electric field sensor. All digital closed-loop negative feedback detection technology and digital filtering technology have been used to improve the dynamic range and linearity, the alternating current (AC) and direct current (DC) voltage which is benefit to temperature compensation and AC signal measurement are separated. The reciprocity of light path is good. Under the power-frequency voltage of 1.4~4600 V, the nonlinear error of measurement is less than 0.35% and transformation ratio error is less than 1% as AC voltage changing from 80~4600 V.

A multi-parameter photochemical sensing technology of long-period fiber gratings (LPFGs) based on wavelength division multiplexing (WDM) is put forward. Utilizing the wide wavelength space between two resonance peaks corresponding to two neighboring cladding modes of a uniform LPFG, the characteristic peaks of respective sensing units in the multi-parameter sensing system are tuned to distribute in the wavelength space discretely by designing grating periods of different sensor units of LPFG, eroding cladding or depositing films on cladding. There is no cladding modes interference between LPFGs and the peak shifts induced by the variations of corresponding parameters are independent, and finally the respective parameters are obtained by directly interrogating the corresponding characteristic peaks. In the experiment, a multi-parameter photochemical sensing system consisting of LPFG coated with polypropylene amine hydrochloride/polyacrylic acid (PAH/PAA) film, thin cladding LPFG and LPFG coated with TiO2/SnO2 composite film is set up, which can perform the measurements of pH value, concentration of NaCl solution and relative humidity (RH), respectively. The sensing mechanism and system structure of this WDM-based LPFG multi-parameter photochemical sensing technology are simple and the design of respective sensing units can be carried out independently, which enables this technology to be applied in the distributed sensing of multiple environmental parameters.

A microwave photonic band-pass filter based on multi-wavelength laser and cascaded dispersion devices is proposed. To achieve the reconfigurable of the filter, a birefringence fiber loop mirror is used to shape the output signal of multi-wavelength laser shaping. The shaped signal is selected as the filter tap. The frequency selectivity of the filter is achieved by a delay unit which is the concatenation of standard single-mode fiber (SSMF) and fiber delay loop mirror. The tunability of the filter can be realized by changing the wavelength interval of the source or the length of the standard SSMF. The results show that the quality factor of the proposed microwave photonic filter increases by 182.26 and 3 dB bandwidth decreases by 670 MHz, compared to the filter only with SSMF as delay units.

Through controlling wavefront, liquid crystal optical phase array can realize precise and arbitrary angle beam steering within a certain field of view. Beam steering methods based on mutiaperture interference and stochastic parallel gradient descent algorithm are studied. By numerical simulating these two methods, beam can point to the target in far field. Pointing accuracy and steering efficiency have been compared and analyzed. A novel beam steering method is presented, which can improve beam pointing accuracy and beam steering efficiency in total range of beam steering.

The noise characteristics existing in the laser beam width measurement based on CCD camera are analyzed, and the methods of effectively restraining noise are presented. The importance of the limitation of integration area for the 4σ beam width measurement, and the method to correctly select integration area are discussed. Factors affecting the accuracy of the laser beam width measurement with CCD camera are summarized. The analyses of experimental data prove that random noise and baseline offset have great effects on the small beam width with 4σ method, and the limitation of integration area for the 4σ beam width measurement is necessary. Furthermore, the experimental results show that the optimum integration area size is 2 times of the beam width; the CCD spatial resolution has little impact on the 4σ beam width measurement in the absence of noises, that is, a few pixel data can get the correct results. Besides, the effect of high frequency random noise on the 4σ beam width measurement repeatability and the methods to improve the meaurement accuracy are discussed; the effect of baseline error on the 4σ laser beam width measurement is analyzed, and the proper method of the background map subtraction is proposed to reduce the influence of noise.

25 solutions of chlorobenzene in CCl4 with different concentrations are studied by using laser Raman spectroscopy technique. The results show the linear relationship between the Raman spectral intensity ratio of chlorobenzene and CCl4 and the concentration of chlorobenzene in 253~0.44 g/L range. The linear correlation coefficient obtained by the least square method is 0.995. Laser Raman spectroscopy technique has the advantages of rapid, nondestructive detection and no need of sample pretreatment. It is proved that this spectral measurement method is feasible for low-concentration detection and quantitative analysis of organic molecules.

A method is established based on micro-Raman spectroscopy in situ quantitative detection technology for the screening of carotenoid high-producing mutants from rhodotorula glutinis colonies growing on solid culture medium. In order to eliminate the interference of medium background signal with the quantitative results, vector correction algorithm is used to preprocess spectral data to obtain pure bacterial signal without medium interference. The effect of two different spectral collection modes on spectral repeatability is investigated. The results show that spectral signal collected with area-scan excitation mode can possess better repeatability than with fixed-point detection. Confocal micro-Raman spectroscopy is applied to estimate carotenoid content of rhodotorula glutinis colonies on solid culture medium, which is verified by laser tweezers Raman spectroscopy. A good correlation between carotenoid Raman peak intensities at 1512 cm-1 by above two approaches is observed. The data indicate that confocal micro-Raman spectroscopy is a reliable approach for the quantitative analysis of carotenoids in rhodotorula glutinis colonies on solid culture medium. Two carotenoid high-producing variants are obtained with the screening procedure established above. This evidence confirms that the proposed strains screening method is more objective and efficient than conventional methods.

A dual galvanometer based multi-points parallel scanning lidar is designed, which provides 30°×30° field of view (FOV) and maximum 10 Hz imaging frame rate. We analyze the lidar′s emitting and receiving optic different demands for galvanometers, and figure out geometric minimum shapes of galvanometers without reducing the system performance, which provides theoretical basis to design smaller galvanometers. Moreover, we analyze the system errors through the footprint coordinate formula of the lidar, and carry out a systematic error calibration experiment according to the analysis results. The co-planarity errors of images acquired in the experiment are 3.6 cm after post-processing, which correspond to theoretical calculations.

In order to achieve the potential accuracy of the system, a rigorous calibration process is needed as a whole. The proposed approach which is based on the analysis of system parameter error and influence establishes the discrepancy analysis model between parallel overlapping flight strips. And then through the registration process by using optimization iterative closest point (ICP) algorithm, we can get the rigid body transformation matrix between adjacent overlap strips. By using transformation matrix composed of elements of exterior orientation angle and translation vector, detecting differences between parallel overlap strips again are realized. The differences expressed by the transformation parameters can be applied to the error analysis model of overlapping strip. At this point, we can finish the calibration using the derived set parameters. Experimental results confirm the effectiveness of this approach.