The operation principle, characteristics and also practical applications of holographic sights are introduced. The influence of tiny angular deflections of the reconstructing beam in vertical and horizontal directions on the deflection angle of virtual cross image is studied. With analytical and experimental results obtained, both of them agree with each other well. The wavelength drift influence on the deflection angle of the virtual cross image is also analyzed. This provides a basis for the design of compensating optical arrangement.

NiAlBSi high-temperature alloy coatings are prepared by laser cladding on the 45# medium steel. The microstructures and properties of the NiAlBSi alloy coatings obtained at different scanning velocities are investigated by means of X-ray diffraction, scanning electron microscopy, electron probe microanalyzer, Vickers hardness tester, friction wear testing machine, and thermal analyzer. The results show that all coatings consist of Ni-Al dendrites. With the increase of scanning velocity, the hardness values of the coatings increase gradually due to the refinement of dendrites, while the wear resistance and the high temperature oxidation resistance present the trend of first increasing then decreasing, and the highest values are obtained at the scanning velocity of 4 mm/s.

A three-dimensional model is developed for numerical analysis of the temperature and stress fields in wire filling laser multilayer welding on high strength steel of 16 mm in thickness by the MARC software. During the calculation, with the technique of element birth and death, the Gaussian cylindrical heat source of heat flux linear attenuation and the double ellipsoid heat source are used to simulate the keyhole effect and the filler wire heating process, respectively. Predicted results are in good accordance with the experimental data. The results show that interlayer heat insulation can effectively reduce the cooling rate of the welded joint and decrease the residual stress, which improves the properties of welded joint. The stress concentration is mainly located in the lower part of the weld; the groove tends to shrink in welding and the work piece exhibits a certain angular distortion after welding.

Laser solid forming (LSF) is a promising manufacturing technology. During LSF process, powder flow plays an important role in the formation of deposition layer. A turbulent flow model is build, and based on the analysis of the movement of particles in the turbulent flow, a powder flow model is developed by the numerical method and solved by using the Fluent software, so the powder mass concentration of the powder flow can be obtained. Comparisons between the simulations and the experimental results are carried out. It is found that the simulations of the powder flow agree well with the experimental measurements. The powder mass concentrations have a few obvious differences with the change of particle diameter range, as proved by the simulation results of particle diameters of 50~240 μm and 65~75 μm.

Experiments of laser percussion drilling are carried out on nickel-based superalloy using a modified pulsed Nd:YAG laser. Peak power, pulse energy and assist gas pressure are optimized experimentally. Experimental results demonstrate that a pulse combination with increasing pulse energy is an effective method to produce non-tapered holes. Even negative taper holes can be produced through increasing the number of pulses in the pulse combination. Focal position is an important factor that affects the taper of holes, and 1.1~1.7 mm above the surface of the sample helps reducing the taper of holes. Non-tapered holes with diameter of 480 and 510 μm are drilled on nickel-based superalloy with thickness of 1.5 and 3.0 mm. Variation of hole diameter is about 30 μm, and hole taper is less than 1%. A feasible method of producing parallel holes and an applied Nd:YAG laser have been presented for laser percussion drilling, may also be used on other materials.

A low alloy high strength steel (11CrNi3MnMoV) of 16 mm in thickness is well joined by laser-metal active gas (MAG) hybrid welding and the hardness, tensile and impact properties of weld seam and base metal are analyzed, respectively. Furthermore, the fracture mechanism is investigated through fractography. The results of the tensile test indicate that the strength of weld seam is about 817 MPa, which is 13% higher than that of base metal. The dimples in the fracture of weld seam are fine and uniform, whereas that of base metal are large, which shows that the tensile strength of weld seam is much higher, while the tenacity of base metal is much better. The results of the impact test indicate that the impact energy of base metal changed slightly, while that of weld seam decreases gradually as the testing temperature reduced. In addition, the tenacity-fragility transformation occurres in weld seam as the testing temperature decreases to -40 ℃. The fracture of weld seam exists both ductile and brittle rupture zone, while that of base metal only exists ductile rupture zone.

A finite element model (FEM) based on numerical model is established to study the process of laser-assisted pre-stress forming and further verified with experimental data. Based on the verified FEM model, the effects of pre-stress and laser parameters on forming efficiency are investigated via a set of dimensionless quantities. A higher pre-stress level results in a higher forming efficiency in the elastic range. A larger beam radius at constant scanning velocity and power density, or a higher power at constant scanning velocity and beam radius, or a faster scanning velocity at constant beam radius and injected energy, results in a higher forming efficiency.

The matching of Z-increment and single cladding layer height is a key factor for improving cladding quality of thin-walled parts, so arc-section inclined thin-walled parts are formed by laser cladding forming with variable Z-increments. Under three-axis and open-loop control, the relationship curve between offset and Z-increment is obtained by laser cladding vertical and inclined thin parts. The result shows that Z-increment decreases gradually with offset increasing and when the offset ΔX is between 0.06 and 0.08 mm, the Z-increment ΔZ reaches its maximum decreasing rate. The biggest slope angle of deposited inclined thin parts is 36.6°. The offsets and Z-increments at the quinquesection points calculated by the relationship curve compose two-dimensional arrays. The optimized cross-section path is simulated by filtering and combining the arrays in accordance with the arc shape through Matlab program. Using the arrays of offsets and Z-increments obtained, arc-section inclined thin-walled parts with 136 layers are formed, and the dimension error of cladding height is under 0.78 mm, which is in agreement with the simulation and demonstrates the feasibility of forming arc-section inclined thin-walled parts with the method of variable Z-increments.

The processing techniques including output current, scanning speed, defocusing distance, auxiliary gas species and pressure, which influence the quality of the flow curve, have been studied with the NdYAG lasers. The cutting quality is measured by the kerf width, surface roughness of the incision and slag quantity. The best processing parameters have been gained with the analyses and experiments. The high quality flow curve has been cut with the output current of 175 A, pulse width of 0.3 ms, pulse frequency of 70 Hz, scanning speed of 40 mm/s, defocusing distance of 0 and oxygen gas pressure of 1.0 MPa.

Laser derusting is a novel method removing metal corrosion by laser. It is key technology to develop a new real-time monitoring system for evaluating the derust effect. We use a low-cost photodiode to monitor the light intensity of laser induced plasma, which transform the light signal into the voltage signal by oscilloscope. We can obtain the derusting threshold according to tendency chart of the peak voltage at different laser pulse energy. Furthermore, we can evaluate whether the metal surface has been cleaned by checking the peak voltage of repeated laser radiation at the same impact point. This rapid and effective method provides the basis for analysis and control of laser derusting technology, which has the merits of low cost and high efficiency.

In order to keep the proper temperature gradient of molten pool in the process of solidification and then make the columnar crystals grow from substrate during laser metal direct forming, the liquid argon is sprayed to the two sides to refrigerate entity-wall; and the influence of liquid argon cooling on microstructure and microhardness of 316 L stainless steel parts are investigated. It can be concluded from the experiments that heat accumulation can be reduced effectively, the most of columnar crystals grow from substrate continuously, the biggest primary spacing of dendrites is about 35 μm and the microhardness of entity-wall increases obviously.

The probability analysis of dynamic distribution of beam positioning in high power laser facility is added to traditional stability design, and a stability analysis method based on dynamic distribution is proposed. Taking spatial filter in large laser facility as object, we discuss how to optimize its structural parameters by this method, with its optical parameters being constant. This method is aiming to constraint the relative stability of components in spatial filter, and it is different from the traditional method which is focused on the absolute stability of single components. Together with the traditional method, optimization can be achieved in dynamic range and distribution pattern of the beam at the same time, and a stable and reliable structure will be provided for facility operation.

Solar energy is the most abundant renewable energy among all kinds of energy sources, solar pumped laser can be the best choice in terms of the fully utilization of solar energy. The solar pumped laser with two stage sunlight concentration system is designed and constructed. A Fresnel lens with large diameter is adopted as a primary optical concentration device, and a cone type diffuse pumping chamber functions as a secondary concentrator is used to enhance the couple efficiency between the incident solar power and laser media. Output laser power is up to 2.85 W, with the use of Nd:YAG crystal as laser media, and 0.43% optical conversion efficiency is achieved. The performance of solar pumped laser is discussed by the concentration efficiency of Fresnel lens and the power distribution along the axis of laser rod in the cavity, as well as the laser characteristic. The reasons for low efficiency are discussed, and improvement approaches are presented.

A micro-channel phase-change heat sink has been developed for cooling high power continual laser diode (LD) based on coupling of boiling-cavitation in micro-channel and field synergy principle. The electron-optic conversion efficiency, output wavelength and the relation between input current and output power are measured experimentally when LD output power changes from 0 to 100 W. The cooling refrigerant is R134a. The thermal resistance of heat sink is measured as 0.211 ℃/W when the magnetic drive gear pump is operated at 23 r/s motor speed. Comparing with the previous heat sink, the thermal resistance of the micro-channel phase-change heat sink based on field synergy principle decreases significantly.

Experimental characterizations of the CaF2 substrates for applications of ArF excimer lasers are performed. The measured absorption for an excimer-grade CaF2 substrate with 5 mm thickness is equal to 922×10-6. The root-mean-square (RMS) surface ronghness measured by atomic force microscope (AFM) and white light interferometer (WLI) are 0.22 and 1.24 nm, respectively, and the corresponding calculated surface scattering losses are 0.005% and 0.25%, respectively. The emission of impurity of Ce3+ and Eu3+ ions in the ultraviolet (UV)-grade CaF2 substrates is detected and ascertained by fluorescence. No water molecular or other contamination on the surface of CaF2 is detected in Fourier transform infrared (FTIR) and Raman spectroscopy. The experimental results prove that laser calorimeters are suited to precisely measure the weak absorption of excimer-grade CaF2 substrates; the power spectral densities (PSDs) obtained by different measuring methods should be compared with each other and combined with the practical scattering losses to appropriately evaluate the surface roughness of CaF2 substrates; spectroscopy methods, such as fluorescence, FTIR and Raman spectroscopy, can effectively detect the trace impurities or defects in the CaF2 crystal and the contaminations on the surface of the polished CaF2 substrates.

The unavoidable defects exists in the optical component will modulate the phase and the amplitude of the beam propagate in the system. Based on the Fresnel diffraction integral, the propagation mode of the Gaussian beam modulated by the local phase is built and the analytical expressions for the intensity distribution and angular spectrum of a Gaussian beam modulated by finite phase modulated defects has been derived. The impact of the modulation depth and the size of the defects on the intensity distribution and angular spectrum of the beam modulated by phase modulated defects is studied. It shows that in the process of transmission the evolution of the light intensity is the same for different modulation depths and sizes of the defects. The deeper of the modulation depth of defects that modulated the beam, the higher of the intensity produced along the propagation process. The larger of the defect, the nearer of the proposition where produced the highest intensity from the defects location. The angular spectrum in the low frequency area become smaller and the angular spectrum in the high frequency area become greater with the increase of modulation depth and the size of the defect as well as the defect getting closer to the middle of the beam.

The uniformity of focal-spot pattern is analyzed by the simulation employing spectral dispersion and distributed phase plate in the laser chain. The uncontrollability of intensity at non-sampling points in the distributed phase plate design causes the loss of uniformity. The simulation confirms the improvement of target irradiation by spectral dispersion; the nonuniformity of focal spot decreases from 58.30% to 19.50%. The relation between nonuniformity and integration time shows that the optimal integration time is 5~6 modulation periods of spectral dispersion. The high spatial frequency of focal spot caused by intensity at non-sampling points is reduced by spectral dispersion smoothing; the intensity fluctuation within 26.3 μm can be eliminated. The results above are confirmed by simulation and experiments, providing theoretical guidance for the next design of distributed phase plate combining with spectral dispersion.

Using the multi-photon nonlinear Compton scattering model and finite-difference time-domain (FDTD) algorithm, the influence of the filter wave of the plasma photonic crystals with tunable defect by the multi-photon nonlinear Compton scattering is studied. The results show that when the geometrical thickness of the plasma tunable defect is a constant, the transmission spectra frequencies of the defect mode are quickly moved to the high frequency direction along with the increases of the electric density in the plasma tunable defect by the multi-photon nonlinear Compton scattering, and its central frequencies nearly are linearly and quickly moved to the high frequency direction. When the geometrical thicknesses of the plasma tunable defect are increased, the central frequencies of the tunable defect mode are moved to the low frequency direction by the multi-photon nonlinear Compton scattering. The thickness is increased to the certain numbers, a higher tunable defect mode frequency than before Compton scattering is taken place on the upper part of the border of the band gap.

By using transfer-matrix method, optical properties of defect modes in one-dimensional photonic crystal containing a single defect layer with negative refractive index are studied. It is found that when the thickness of defect is increased, the frequency of defect modes can be changed presenting several stages. First stage is monotonously increased, second stage is a transitional process, and the third is monotonously decreased. These properties are different from those of the structure that defect layer has positive refractive index. Though the third stage is somewhat alike, but now defect modes move with greater speed. It is also found that in the whole process defect modes move faster than them in the structure containing a defect layer with positive refractive index.

Two beams of pumping up-conversion three-dimensional (3D) volumetric display which is based on a ZBLANPr, Yb fluoride glass are investigated. The lasers employed are infrared semiconductor laser with wavelength 960 nm and tunable Ti gem laser with wavelength of 820 nm, respectively. The two frequency up-conversion luminescence of Pr3+ ion is investigated. The relation between up-conversion fluorescence intensity, pumping lasers intensity, and ion doped concentration is analyzed, and the experimental conditions to realize the clear two frequency up-conversion 3D display are therefore obtained. ZBLAN glass is selected as two-frequency up-conversion 3D volumetric display foundation material for it has perfect phonon spectrum whose maximum phonon frequency is 580 cm-1; up-conversion fluorescence intensity increases linearly with augment of two beams of pumping lasers intensity when lasers intensity are very weak; optimal doped concentration of Pr3+ and Yb3+ ions are 0.5% and 1.5% mole fraction, respectively.

A new dondr-π-acceptor-π-donor Schiff base-ferrocene derivative is synthesized and characterized by 1H NMR and MS. The UV-vis absorption spectra of the materials are determined and the third-order optical nonlinearity is measured by optical path of degenerate four-wave mixing (DFWM) at wavelength of 800 nm and response time of 80 fs. The third-order nonlinear optical susceptibilities χ(3) of this compound is 3.67×10-13 esu and the second order hyperpolarizabilities γ of this molecule is 3.49×10-31 esu.The influence of molecular structure on the third-order optical nonlinearity is studied and the long conjugate chain, formation of accepor-donor structure can improve the third-order optical nonlinearity.

The energy storage in the Cr4+, Yb:YAG crystal amplifier is stimulated under the conditions of atom fraction thickness product 15%·mm and pumping density 20 kW/cm2 for different apertures and doped Cr4+ and Yb3+ densities, using the pumping dynamic model for Cr4+, Yb:YAG crystal amplifier. The results indicate that the density of energy storage decreases with the increasing of Yb3+ and amplifier aperture in absence of Cr4+; but the doped Cr4+ in Yb:YAG crystal affects on the energy storage in the amplifier. In some cases the maximum energy storage in amplifier increases first, then decreases with the increasing of Cr4+ density. Namely, for maximum energy storage there is an optimized Cr4+ density, which is determined by the Yb3+ density and aperture of amplifier.

To obtain the optimized structure of photonic crystals with dispersion-free slow light, based on the traditional line-defect structure of photonic crystal waveguides, we introduce a novel type of slow light photonic crystal waveguide with a line defect which is surrounded by four rows of quadrate air holes, and optimize the structural parameters of the two rows of quadrate air holes. By means of the plane wave expansion (PWE) and 2D finite difference time domain (FDTD), our numerical analysis shows that, at the center wavelength of 1550 nm, our new design can present a wideband dispersion-free slow light, which in possession of a wavelength bandwidth of 8.34 nm, an average group index of 61 and a group velosity dispersion (GVD) of 104.

The crystalline Si films are prepared by pulsed laser deposition (PLD) in 10 Pa helium gas at room temperature. In experiments, substrates are located under ablated spot and paralleled to the axis of plume, at the same time, a vertical extra helium gas flow apart different distance from target surface is introduced above plume. The results of scaning electron microscope (SEM), Raman scattering and X-ray diffraction (XRD) indicate that nano-crystal grains formed in one area apart from target, the sizes first increase and then decrease with the addition distance from target surface. Size and position distribution of grains on substrates are analyzed. Combing with hydrodynamics model, nucleation division model, thermokinetic equation and rule of flat parabolic motion-like after formation of grains, nulcleation region width of 56.2 mm is calculated through numerical calculations.

With the purpose of meeting the special requirement of laser blinding weapons, choosing H4 as the material of high refractive index and YbF3 as the material of low refractive index, the film system is designed and optimized with the help of Macleod and TFCalc softwares. By adopting electron beam vaccum depositing method with the aid of ion assistant deposition technology, as well as using orthogonal matrix tests to adjust and optimize technological parameters of the materials, antireflection (AR) coatings on the substrate of sapphire to meet the demand are deposited. The transmittances at 532, 808, 905, 980 and 1064 nm are greater than 97%, and it makes the average transmittance over 92% in the 3~5 μm band. The laser induced damage threshold (LIDT) of AR coatings is further increased by adding inner barrier layer. This film can satisfy the requirement of many laser wavelengths at the same time, widening the range of its application and reducing the costs.

In a two-wavelength laser-diode (LD) sinusoidal phase modulating (SPM) interferometer, wavelength of LD is modulated by variation of its injection current (IC). However, the IC modulation results in both wavelength modulation and intensity modulation, which will cause a measurement error. A novel two-wavelength LD SPM interferometer is proposed. In order to eliminate the error caused by intensity modulation, phase of interference signal is calculated accurately by solving linear equations obtained with the interference signal processing. With the proposed method, measurement error decreases from 6 to 1 μm. Moreover, the proposed interferometer is combined with linear wavelength scanning interferometer (WSI) for absolute distance measurement. Experimental result indicates that an absolute distance measurement repeatability of 1 μm can be achieved over a range of 60 to 280 mm.

The fluctuation of laser brings many troubles when tunable diode laser absorption spectroscopy (TDLAS) is used in the real-time measurement of gases. For eliminating this influence, a novel method, in which a digital proportion integration differentiation (PID) algorithm and a software lock-in amplifier designed by using Lab-VIEW are employed, is introduced to lock the laser to the center of the absorption line. In order to test the system, three intimate absorption lines of methane near 1.653 μm are chosen by using fiber-coupled distributed feedback (DFB) diode laser. A 24-hour continuous measurement is implemented. Relative results are presented and discussed. The detection limit is lower than 1.8×10-8 while the second harmonic signal measurement is utilized. This method can be applied to the detection of trace gases by using other long path length cells (CEAS) or combustion diagnosis.

The laser induced breakdown spectroscopy (LIBS) has been used to synchronized detection the concentration of nitrogen, phosphorus, potassium in compound fertilizers. Applied the partial least squares (PLS) method on 10 selected samples which are known as the calibration samples to establish quantitative analysis regression models of different components. Then, use 5 untested samples to test the result of quantitative analysis regression models. Finally compare the predictive value with the reference obtained by the conventional inductively coupled plasma atomic emission spectrometry (ICP-AES) method. The result shows that the average relative errors (REP) are less than 8% mass fraction. The relative standard deviation (RSD) is less than 7% mass fraction. The detection limits (LOD) are 0.16%, 0.21% and 0.50% mass fraction. The experimental verify the applicability of the laser induced breakdown spectroscopy in synchronization rapid and accurate measurement of the three major fertilizer nutrients.

A new method for improving accuracy of real-time three-dimensional (3D) measurement based on a composite grating is proposed. By analyzing the composite phase measuring profilometry (PMP), it is found that phase demodulation precision is related to filtering window choice when demodulating the deformed phase shift stripes from a deformed composite grating. By analyzing and comparing several common filtering windows, a new kind of filtering window which is combined Hanning and rectangular window together is designed. Because filtering precision is related to distribution of spectrum, by digital simulating Peaks-function object in 3D measurement based on a composite grating, distribution of optimized parameters of combined window is obtained. Using these data, the proper object in experiment to improve the accuracy of real-time 3D measurement based on a composite grating can be realized. Both simulating and actual experimental results prove the method′s effectiveness and practicability.

Severval camera pixels are usually corresponding to one projector pixel in three-dimensional (3D) imaging system using binary spatiotemporal encoded illumination. A novel method is proposed for subpixel image matching of camera and projector to increase the measurement precision and data density. The phase distribution of image captured by camera is obtained with sinusoid fitting on temporal direction, according to the binary spatiotemporal encoding strategy and the low pass filter characteristic of two-dimensional transfer function of measurement system. Because of the direct ratio of the phase distribution and projector pixel the corresponding point pairs between the image of projector and camera can be identified through the phase distribution with subpixel accuracy. The experimental results show that the measurement precision of the 3D imaging system is increased about one order of magnitude by using proposed method, and its measurement precision is similar with that of the phase measurement profilometry under the same experimental condition.

A high precision absolute radiance radiometer based on the ultroviolet (UV) standard detector is made up according to the complexity of the normal measurement of the spectral radiometric characteristics of the integrating sphere and the disadvantage of the huge uncertainty of the standard lamp in UV band. Calibration in three wavelengths is done so as to correct the curve of the aperture′s spectral radiance of the integrating sphere in 250~400 nm bands. Also the stability of the output, the uniformity of the aperture and the Lambert′s cosine characteristic of the integrating sphere are measured. The combined standard uncertainty in 280, 313 and 352 nm is 3.2%, 3.0% and 3.0% for the spectral radiance calibration and 1.7%, 1.6% and 1.6% for the stability of the output、the uniformity of the aperture and the Lambert′s cosine characteristic of the integrating sphere. Uncertainty analysis shows that research based on the absolute radiance radiometer is convenient, feasibility and has a higher precision in contrast to the traditional research of spectral radiance characteristics.

The influences of CCD pixel size, random noise and quantization series on contrasts of the interferogram after sampling and the moiré fringes are analyzed based on digital moiré phase-shifting interferometry. The effects of interference fringe′s spatial frequency on the phase measurement accuracy are analyzed and simulated in detail. The results indicate that with the increase of interference fringe′s spatial frequency, the contrast and the signal to noise ratio of moiré fringes will be worse with the influences of the process of CCD sampling, random noise and quantization series. Furthermore, the phase errors will be greater after phase-unwrapping. When the interference fringe′s spatial frequency is lower than 0.45 λ/pixel, the phase measurement accuracy can be better than π/50, which is equivalent to the optical path difference better than λ/100. This provides a theoretical quantitative basis for the further study of extending the measurement range of digital moiré phase-shifting interferometry.

Absolute test eliminates the errors of reference flats which limit the accuracy of interference measurement, so that the figure of optical surface can be measured with nanometer accuracy. We give a brief review and comparison of several mainstream absolute flatness test methods. And then the impacts of edge noise, figure grades of the flats under test, rotation angle error and rotation eccentricity, etc. on the measurement error of absolute test are analyzed respectively. The first 36 Zernike polynomial terms are used to construct the virtual flats under test. It is found that the measurement error is not sensitive to figure grades of the flats, resolution of interferogram and rotation angle error. However, it is sensitive to edge noise and rotation eccentricity. In an absolute test system, it is recommended that the alignment error of rotation axis is less than 2 pixel, and the ratio of central area is about 95%.

In order to study the light field statistical property when the laser is scattered by rotated diffuser, combining the statistical model of multi-pixel photon counter (MPPC), the Fano factor which describes the photons fluctuation is gained through adopting the second-order momentum and average value of the photon statistics. Then, the curve fitting of the Fano factor produces the number of thermal modes μ and the parameter B which is the combination of the gain coefficient γ and the cross-talk probability ε for the photo-detector. The experimental results are as follows. The number of thermal modes for the echo signal increases from 289 to 1229 when the driving voltage increases from 20 to 1280 mV, and the increasing speed decreases with the increase of driving voltage for the diffuser. The parameter B can reflect the variance of cross-talk probability between the neighbouring pixels due to the coefficient γ which is a constant during the course of measurement. The results suggest that the cross-talk probability decreases when the rotating velocity increases (the increase of the driving voltage). The curve fitting of the Fano factor only gives the qualitative description of the cross-talk, while there is no information of the gain coefficient in the fitting. The quantitative analysis of gain coefficient and cross-talk probability can be achieved through the research of the third-order momentum for the arriving photons.

Electronically controlled liquid-crystal gratings have advantages such as small volume and agile optical beam steering in satellite laser communication and laser radar. However, the key issue for performance evaluation of liquid-crystal gratings is to obtain the modulated beam wavefront by it. Conjugation phase shifting interferometry measuring liquid-crystal gratings wavefront is presented. In the experiment, the measured far-field intensity is in accordance with the theoretic analysis on near-field wavefront. This technology shows a new beam steering control method with near-field wavefront measurement.

The characteristics of beat-frequency signal (BFS) and the detection performance of the frequency-modulated continuous-wave (FMCW) coherent lidar are influenced by speckle noise. In order to estimate the impact and improve the system′s property, the scattered field is simplified utilizing geometrical optics approximation. The impact model of BFS affected by speckle field is derived by Monte Carlo simulation, and the optical antenna′s aperture is optimized. The system experiment is carried out, and the results demonstrate that the BFS intensity has a negative exponential relationship with the ratio of the surface-roughness height to the square of light wavelength, and it decreases more rapidly with weak scattering surfaces. The experimental results are in good agreement with the theoretical analysis and numerical simulation results. After system optimization, the BFS with speckle noise can be detected effectively, and the system′s range and velocity measurement errors are less than 1 cm and 0.05 cm/s, respectively.

For the problem of the big errors in the calculation of atmospheric attenuation under water fog weather, starting from the physical phenomena of water fogs weather, through the revision of the existing model, a more precise and reasonable model was proposed. And using the proposed model, the performance of free space optical (FSO) communication system was analyzed, the simulated results pointed out that the relative errors caused by the existing model can′t be ignored. The work can provide a theoretical basis for the evaluation and estimation of FSO communication system and other related domain in water fogs weather.

A novel scheme of multi-wavelength (4×40 Gb/s) all-optical 3R regeneration is presented by using a fiber optical parametric amplifier (FOPA) with degraded data signals as the pump, which is different in mechanism from previous regeneration schemes. It is demonstrated that, this scheme restrains the noise on both "1" bit and "0" bit very well. The clock extraction is based on wavelength conversion and a Fabry-Perot (F-P) filter with a high Q value of 1000. And the jitter of the recovered clock is only 180 fs. In the multi-wavelength decision unit, the orthogonal polarization as well as bidirectional injection is employed to avoid crosstalk among the four degraded signals. Finally, this scheme realizes that, the signal to noise ratios of the four regenerated signals are improved by 2.21, 2.79, 2.72, 1.99 respectively.

A novel technique for the generation of millimeter-wave (mm-wave), i.e., frequency sextupling technique, is theoretically analyzed and experimentally demonstrated. The proposed technique is comprised of two cascaded dual-electrode Mach-Zehnder modulators (MZMs). The first MZM, biased at the minimum transmission, is only used for odd-order optical harmonic generation, and then a second MZM, biased at the maximum transmission, suppresses all odd-order optical harmonics. As an example, a 10 GHz radio frequency (RF) signal, which drives the MZMs, is considered; and a mm-wave signal at 60 GHz, i.e., a frequency sextupler, is obtained. Compared with the conventional techniques without optical band-pass filter, the generated mm-wave signal is robust to fiber chromatic dispersion. The proposed technique is verified by experiments.

Spatial resolution is an important technical parameter for terahertz (THz) imaging system. To measure the resolution characteristic of the imaging system, a Siemens star for resolution measurement is prepared according to ISO 12233. By imaging the Siemens star, multidirectional square wave response for different spatial frequencies can be deduced from the imaging results, thus obtaining the system′s modulation transfer function (MTF). Resolution measurement experiment based on the Siemens star is carried out on a THz reflection-mode scanning imaging system. The system′s resolution capability is measured and analyzed. The measurement result shows that the system′s resolution is 1.273 lp/mm, and the resolvable line width is 0.393 mm, which is consistent with the measurement result by knife edge method. The study demonstrates that the Siemens star offers a convenient approach to measure the system′s imaging resolution capability. The system′s resolution upper limit can be obtained precisely and directly.

Based on a three-layer polysilicon surface micromachining process and some experience formulas of adaptive optics, an electrostatically actuated microelectromechanical systems (MEMS) deformable mirror (DM) with 16 actuators and continuous surface is designed and fabricated. Both static and dynamic characteristics of the prototype are tested using a scanning white light interferometer ZygoNewView7300. The result from the static test shows that the displacement of the actuator is 0.667 μm at 150 V, the interaction between the neighboring actuator is 9%, and the position repeatability of the surface of DM is 10%. At the same time, the result from the dynamic test shows that the response time of the prototype is less than 30 μs and a cosine curve is observed under a sine driving signal. The resonance frequency of the actuator is about 36 kHz. This type of DM can be used for free space optical communication, laser beam shaping, wavefront correction, projection, biomedical imaging and human eye aberration correction.

To cool and focus the Cr atoms, the laser frequency must be locked to the 425.55 nm 7S3→7P04 transition of 52Cr in the research of Cr atom deposition. A see-through Cr-He hollow cathode discharge cell is designed and fabricated to sputter the atom vapor of Cr. Polarization spectroscopy is applied to lock the laser frequency. This technique not only simplifies the experimental equipment but also increases the efficiency. A high signal-to-background ratio dispersion signal is obtained without any modulation device or lock-in amplifier. This signal is used as error signal to lock a frequency-doubled Tisapphire laser to the 7S3→7P04 transition of 52Cr. A frequency fluctuation of ±295 kHz for more than one hour is achieved. The experimental results show that this technique is feasible to lock laser frequency to transitions of metals with high melting point.

In order to explore the physiological response and tolerance mechanism of Bacillus subtilis after exposure to formaldehyde, laser tweezers Raman spectroscopy (LTRS) is employed to perform the experimental process in which germinated spores (g. spores) are stressed with different concentrations of formaldehyde for 2 h. The results show that both vegetative cells and g. spores have tolerance to formaldehyde, but the growth and physiological effect of g. spores stressed by different concentrations of formaldehyde are dissimilar. A lag phase of characteristic spectrum involved with various biomacromolecules is observed while g. spores are exposed to 0 mmol/L of formaldehyde medium from 0 to 0.5 h, subsequently, the Raman spectra peaks tend to rapidly ascend from 0.5 to 2.0 h. Characteristics and trend of Raman spectra variation are all from ascending to descending while g. spores are exposed to 0.4, 0.8, and 1.0 mmol/L of formaldehyde medium respectively for 2 h, and the corresponding inflexion of Raman spectra causes various components in vivo to decline where the time points are 1.5, 1.0, and 0.5 h, respectively. The analytic results of Raman spectra display that various components in vivo decrease gradually after 1.5 h while g. spores are stressed by 0.4 mmol/L of formaldehyde, implying that g. spores are harmed mildly. While g. spores are in 0.8 mmol/L formaldehyde medium, the band of nucleic acid decreases slowly at the very start, indicating that DNA cannot duplicate in the whole process. The bands of membrane phospholipids and C-S (protein) stretching mode descend obviously after formaldehyde stress for 0.5 h, which suggested formaldehyde could break down the membrane lipid hydrocarbon chains. While g. spores are in 1.0 mmol/L of formaldehyde medium, the high formaldehyde concentration makes a severe stress effect on cells, the content of biological macromolecules drops significantly after 0.5 h leading to cells deterioration gradually.

A experimental study of widely tunable periodically poled MgOLiNbO3 (PPMgLN) optical parametric oscillator (OPO) is presented. The laser diode (LD) end-pumped acousto-optically (A-O) Q-switched NdYVO4 laser was used as the pump source of OPO. The OPO resonator consisted of a two CaF2 concave mirror linear cavity. By varying temperature (30~80 ℃) and poling periods (29.0~31.5 μm) of PPMgLN crystal, the signal wavelength was tunable in the range of 1450~1700 nm as well as the idle wavelength was tuned from 2849.0~3989.4 nm. The measured full width at half maximum ( FWHM) of the output signal and idler ware were about 0.58 and 4 nm or less, respectively. The results indicate that the experimental data agrees well with the calculated tuning curve.