Through the influence of the He-Ne laser irradiation of 5 mW/mm2 He-Ne, 10.08 kJ/(m2·d) UV-B and the combination of the two on the seeding of winter wheat "Linyou 2018", the modification of apoptosis on the roots of seedling in different treatment days and each group are analyzed. The research results indicate that, the features of apoptosis are found in the roots of wheat seedling after enhanced UV-B irradiation, such as nuclear assembled, apoptopic bodies. Apoptosis in different treatment groups by flow cytometry are quantitative analyzed. The results also show that the number of apoptosis are increased after enhanced UV-B irradiation and the differences are obvious in the 5 th day. With the management of He-Ne laser after UV-B radiation, the number of apoptosis is less than that of the UV-B treatment group and decreases obviously. Therefore, the apoptosis of roots of wheat seedling induced by enhanced UV-B radiation can be remited partly by He-Ne laser irradiation.

A high frequency-stable laser source for Brillouin distributed optical fiber sensor (DOFS) is reported. A distributed-feedback (DFB) laser is used as the maser laser for optical fiber sensor measurement. Another DFB laser is used as the slave laser of which the frequency is tracked with the master laser. Thus the frequency difference of the two lasers can be locked at 11 GHz. With this source for distributed optical fiber sensing applications, the frequency of the beat frequency signal is only several million hertz. As a result, the noise can be decreased and the cost of the equipment will be reduced. The results indicate that the range of frequency is ±1 MHz.

A three-dimensional (3D) full-range complex Fourier domain optical coherence tomography (FDOCT) system based on sinusoidal phase-modulating method is developed for vivo imaging of human skin. A complex spectral interferogram is retrieved based on Fourier transform analysis and bandpass filter of phase-modulated interference spectra, which is recorded with sinusoidal phase modulation introduced during lateral beam scanning. With the system, the depth imaging range is doubled and the signal-to-noise ratio degrading with the lateral scanning is avoided. Also the system is suitable for vivo imaging. 3D vivo full-range OCT images of human skin is achieved with the proposed system. In the images, the stratum corneum, the epidermis and the upper dermis can be clearly identified. By optimizing the sampling number in one modulation period, the complex conjugate rejection ratio is improved, which is about 36 dB.

A 10 W diode pumped solid state (DPSS) laser is employed for through-transmission welding of polycarbonate to study the properties of weld joint. Optical microscope (OM), scanning electron microscope (SEM) and tensile machine are employed for analyzing the morphology of the welded joint, fracture and tensile-shear stress. The results show that under the condition of 8 W laser power, 50 kHz laser frequency, 350 mm/s scanning velocity and 0.1 mm scanning interval, the tensile-shear stresses of the samples are 44 MPa, which research 68% of the basic materials. Layering and pores in the welded joint are the main factors of low mechanical properties and different fracture mechanisms and with this approach we can get weld joint with good mechanical properties.

To solve the problem that truing and dressing of superabrasive grinding wheels are very hard, a method which is called "laser and mechanical compound truing and dressing" is used. Multiple-pulse finite element simulation is done to optimize laser parameters during laser rough trimming and reach a certain circular runout range of grinding wheels after laser rough trimming. Through simulation results, laser parameters of laser rough trimming are selected. Then, laser and mechanical compound truing and dressing experiments are done for bronze-bonded diamond grinding wheel which is just die-casting molding. Results show that if appropriate technological parameters are selected, laser and mechanical compound truing and dressing is an effective method.

ZrO2-13%Al2O3 (mass fraction) composite ceramic by laser engineered net shaping (LENS) with co-axial powder feeding is investigated on the titanium substrate. The effect of laser power and scanning speed on the macroscopic qualities (weight, height, surface and macrocrack) of ceramic by LENS is discussed, The dense、macrocrack-free ceramic thin-wall has been fabricated, the microstructure of ceramic has been evaluated using optical microscope, the composition distribution and the phase transformation before and after laser processing have been determinated by electro-probe microanalyzer (EPMA) and X-ray diffractometer (XRD). The results indicate that laser power and scanning speed have an important impact on the thickness of single layer and surface of ceramic, so good macroscopic qualities can be obtained by optimization of this two parameters. There may be two different macrocracks of horizontal and vertical by different laser powers and scanning speeds. The dense ceramic with fine dendritic crystal can be formed by the laser processing. Small amount of Al2O3 which mainly exists in the grain boundary is benefit to reduce cracks.

In order to study the effect of laser shock processing (LSP) in high temperature environment, the K417 superalloy is treated by LSP with laser power density of 8.5 GW/cm2 and pulse width of 10 ns, and then the Vikers hardness of K417 is tested after heat treatment at 700 ℃, 800 ℃ and 900 ℃, respectively. The results show that the hardening effect is weakened at elevated temperature, but the average hardness of LSP region is obviously higher than that of non-LSP region. With the temperature increasing, the thickness of the LSP hardened layer shows a decreasing trend and the hardness in the depth direction is fitted with exponential function approximately. The hardness distribution on a single laser spot is related to the laser shock wave′s inequality which is induced by the laser spatial distribution. The research indicates that LSP can raise the K417 superalloy′s comprehensive properties under 800 ℃.

Repair path of 3D laser cladding remanufacturing is studied and generation algorithm automatically of repair trajectory is proposed based on equidistant parallel sections in order to conquer the shortages using on-line teach processing path for damaged parts of complex free-form surfaces in laser remanufacturing. The positions of laser beam scan points are decided according the intersection points of any equidistant parallel section planes and triangular mesh; the normal vector of the intersection point is calculated by interpolation to the two vertices′ normal vector after each vertex′s normal vector is acquired, thus the laser beam′s posture is obtained at the processing point. Practical experiments demonstrate that satisfying results are acquired by using this method, which has been applied in laser remanufacturing system.

W9Mo3Cr4V high speed steel is treated by composite technology of laser hardening and nitriding. The microstructure and properties of the sample after the composite treatment are investigated by means of X-ray diffraction, scanning electron microscopy, electron probe micro-analyzer, Vickers hardness tester, and friction wear testing machine. The results show that the surface modification layer consists of tempered martensite, retained austenite, Fe3N, Cr7C3, and M2C phases. Laser hardening obviously increases the depth of the nitrided layer, as a result of grain refinement, as well as production of high concentration microscopic defects. Compared to laser hardening and nitriding technologies, respectively, the composite treatment technology can effectively increase the hardness and wear resistance of the high speed steel.

A composite technology using laser driven flyer to form parts is proposed. Combined with the shearing mould, a top-hat NdYAG laser pulse (with 1064 nm wavelength) is used to shock copper foil with the thickness of 50 μm for getting high-quality flyer. The bulging parts and the ring parts with good forming property are finally obtained by high-speed flyer by means of forming mould. The mechanism and performance of laser driven flyer forming technology are studied, furthermore, the phenomenon and problems in the experiments are explored. This composite technology not only expands the application field of laser micro-forming, but also provides reference value on the research of forming microstructure of metal sheet under laser driven flyer.

Single walled carbon nanotubes and graphene oxide are deposited on glass and quartz by vertical evaporation method, respectively. By using single walled carbon nanotubes absorber, passively mode locked NdYVO4 laser is obtained. The maximum output power is 3.6 W, the slope efficiency is 31%, the pulse duration is 7.6 ps and the repetition rate is 75 MHz. By using graphene oxide absorber, passively mode locked NdGdVO4 laser is achieved. The maximum output power is 1.1 W, the slope efficiency is 11.3%, the pulse duration is 4.5 ps and the repetition rate is 70 MHz.

We demonstrate the all-fiber picosecond erbium-doped fiber lasers in which graphene oxide is used as the saturable absorber. The linear resonant cavity consists of a narrow band fiber Bragg grating and a graphene oxide saturable absorber mirror. When stable mode-locked pulses of the fiber laser occur at 22 mW incident pump power, the pulse repetition rate is 5.82 MHz and the measured pulse width is 87 ps. The spectral central wavelength is 1549.3 nm, the 3 dB spectral width is 0.06 nm and the signal-to-noise ratio is 66 dB.

When airborne lidar is detecting the underwater target, the laser beam will be influenced by the wavy sea surface. Based on Monte Carlo method, the space distribution of photons on the target surface is quantitatively analysed and the space distribution and time distribution of the photons return which the sea-air interface are analysed. Simulation results show that the space distribution of photons at the target surface gradually deviates from Gauss distribution as the velocity of wind increases and the space distribution badly of the photons which return the sea-air interface deviates from Gauss distribution. The influence of wind velocity is no longer important. By computing the time distribution of photons which return the sea-air interface, it is found that when the wind velocity increases, the detection depth of lidar decreases.

The laser-diode (LD)-pumped passively Q-switched c-cut Nd:YVO4 self-Raman laser in which Cr4+:YAG crystal is taken as saturable absorber is investigated experimentally. By using Cr4+:YAG crystals with different initial transmissions and output couplers with different reflectivities at Raman laser in the experiment, the influences of the initial transmission and reflectivity on output characteristics of Raman laser are studied. The average output power, pulse repetition frequency and pulse width of Raman laser with respect to the pumped power are measured. The obtained maximum output average power of Raman laser is 370 mW at 4.8 W of pumped power and the corresponding conversion efficiency is 7.7%. The self-Raman laser can produce pulses in the sub nanosecond level, and the maximum single pulse energy and peak power are 54 μJ and 47 kW, respectively.

A cubic model of single-mode laser driven by quantum noise and nonlinear colored pump noise is founded, and the model is divided into amplitude Langevin equation (LE) and phase LE in polar coordinate. The approximate Fokker-Planck equation method is adopted to process the colored noise of phase LE, which makes the colored noise a Markovian process. Combined the equivalent phase LE which has been Markovian with phase locked conditions, the stable phase locked value is obtained. The effects of cross-correlation between the real and imaginary parts of pump noise and quantum noise on phase locked of single mode laser are discussed. Results reveal that the phase locked of laser is induced by the cross-correlation between the real and imaginary parts of quantum noise. However, the change of phase locked arises from the cross-correlation between the real and imaginary parts of pump noise or quantum noise.

The energy level diagram and absorption spectrum of Tm:YAP crystal and phase-matching properties of ZeGeP crystal are analyzed, and a middle-infrared optical parametric oscillator (OPO) under room temperature is presented. The wavelength of laser is 3.88, 4.00 and 4.14 μm, and the output power is 7.16 W at 10 kHz, the corresponding optical-optical conversion efficiency is up to 49.4%, and the slope efficiency is 48.9%. The single pulse width is 81.47 ns, the energy of single pulse is 0.71 mJ, the peak power of single pulse is 8.78 kW, the quality of middle infrared laser beam is 3.8(horizontal) and 4.0(vertical).

Frequency stabilized lasers are very important in many fields such as precision metrology and high resolution spectroscopy. A Nd:YAG laser (1064 nm) frequency stabilization scheme is reported. In this scheme, the laser frequency is doubled and stabilized at the R(56) absorption line of (32-0) band in the B-X system of molecular iodine based on digital proportion-integration-differentiation (PID) technique. The frequency stability reaches 10-9 and the frequency drift is less than 2 MHz in 1 h, which is far less than the Doppler-limited molecular absorption linewidth. This scheme can suppress the laser frequency drift effectively and minimize the large-amplitude random noise. It is proved simple and easy to implement.

An ultra-short ring-cavity Brillouin-erbium fiber laser (BEFL), whose cavity length is only 10 m, is demonstrated. The BEFL adopts a section of normal erbium-doped fiber (EDF) with a length of 4 m as the gain medium. Nonlinear Brillouin gain and linear erbium-doped fiber amplifier (EDFA) gain are both introduced into the EDF by using the Brillouin pump and the 980 nm pump outside the cavity, respectively. Experimental results demonstrate that the BEFL operats at single-longitudinal mode with a high signal-to-noise ratio (>40 dB), a low pump threshold (~20 mW), and a high output power (>10 mW). Moreover, the Brillouin pump not only decides the output wavelength of the BEFL, but also greatly affects its pump threshold and output power.

The samples of zinc oxide nano-wires and hexagonal micro-rods are fabricated by using vapor phase transport method under the almost same conditions. Their morphology and the same crystal structures are examined and characterized by scanning electron microscopy and X-ray diffraction. The photoluminescence (PL) spectra of hexagonal samples, excited by 355 nm laser pulse with excitation power density (260 W/cm2), is measured and compared with those from nano-wires with the same exciting condition at room temperature. There are a more intensive broaden violet emission peaking at 393 nm, frequency spectrum broatening, the red shift of center wavelength and an almost disappearing green band emission in the PL of hexagonal rods while an emission peaking at 382 nm, flat green emission for wires samples. The difference of PL spectra between the two kinds of samples may be attributed to the enhancement of spontaneous emission in whispering gallery modes resonators (WGMRs) by theoretical analysis based on the theory of energy bands for semiconductors, emission from excitons, and Fermi golden rules. PL spectrum measuring experiments with higher excitation power density for the same samples are arranged to verify the theoretical analysis results, which fit with experimental results well.

The influence of nonlinear dispersion effects on modulation instability (MI) in nonlinear metamaterials (MMs) is investigated and some new instability phenomena are revealed. Firstly, a general expression for MI gain, taking account of the effects of arbitrary high-order nonlinear dispersions, is derived. It is shown that all even-order nonlinear dispersion not only deforms the original instability regions, but also may lead to the appearance of new instability regions; while all odd-order nonlinear dispersion always suppresses MI irrespective of their signs. Then, the influence of second-order nonlinear dispersion (SND) induced by dispersive magnetic permeability is further analyzed. It is found that SND not only leads to the occurrence of MI inaccessible in ordinary materials, but also opens up a new instability window with an infinite modulation frequency range and the gain value increases monotonically with increasing modulation frequencies.

Based on laser diameter-measuring technology, the measuring method on the cross-section diameter in fiber bundles and its wavelength of short-term irregularity is discussed. A contactless on-line measuring system and experimental scheme, including the selection of laser sensor and experimental materials, are plotted. The influence of feeding speed on the diameter, the unevenness and the mininum wavelength of the yarn and the results difference result from various methods are analysed experimentally. The results show that the system is feasible and has good reproducibility of the measured results. Moreover, the new system can extract the shorter wavelength feature on yarn short-term irregularity and the data analysis process can be efficiently automated.

For realizing two-dimensional angle measurement, PZT driving method is used to get dynamic interference fringes. According to ideal interference fringes, the relationships of fringe width, orientation angle and each phase of four-quadrant photoelectric detector are deduced with the method of numerical integration, and the approximation points of each quadrant phase are obtained. Moreover, the model between laser beam angle and the fringe shape is established. Ellipse least squares fitting algorithm is used to extract phase information from four quadrants detector. Recognition of width and orientation angle of the fringe is realized. Experimental results of two-dimensional angle measurement indicate that the method meets the requirement of high precision angle measurement. Even with the irregular shape of interference fringes or an inconsistent movement frequency of the worktable, the method can still keep high accuracy and good repeatability.

In order to improve the precision of laser spot position measurement, several key technologies are studied. Range-gated technology is studied to restrain laser backscattering caused by aerosol scattering. An asynchronous range-gated method based on four-quadrant detector is introduced. An improved blind deconvolution method used to process images afterwards is introduced, which serves to lower the impact of atmosphere turbulence on laser spot imaging. An image registration method based on objective area is introduced to eliminate the difference between visible camera and infrared camera. Recover the spot and find the laser spot position using Gauss surface fitting. The experimental results show that the precision of laser spot position is not more than 0.3 pixel.

Bidirectional reflectance distribution function (BRDF) data measurement is an important instrument to acquire information of target surface. The geometrical optics is used to establish theoretic model of laser BRDF. A model is designed to measure the scattering data with lasers, measuring equipments for laser energy density, etc. Under the same measurement condition, the sample and a diffuse reflection plate, whose scattering characteristic is known, are measured together to acquire scattering data of laser pulse. The 3D BRDF data is measured by turning the sample surface and keeping the measurement surface immobile. The 3D angles of measuring positions are computed. The model parameters are optimized using measurement data. The BRDF model of the sample is established. The measuring condition is easily constructed and it has a simple and convenient process. A new way is provided to research sample surface BRDF characteristic.

An experimental platform of good polarization control performance is designed for the fiber magneto-optical (MO) effect and four wave mixing (FWM), in which the states of polarization (SOPs) of input optical signal and the MO coupling coefficient of nonlinear fibers are respectively controlled by a self-made electromagnetic polarization controller (EMPC) and a fiber-embedded toroidal coil. The dependency of fiber FWM idler power on the SOP ellipticity of input signal is measured and the experimental data are consistent with the theoretical results. And then, the MO-FWM experiment is implemented and the variation of fiber FWM idler power with the applied magnetic field is obtained.

The cutoff properties of some lower-order modes of some nano silicon-on-insulator (SOI) waveguides with air cladding or SiO2 cladding are analyzed. Operation regimes of no mode, single mode, and two modes are obtained and demonstrated by using the cutoff wavelength and the waveguide width. The beat length, between the two modes with the same polarization in the two-mode regime, are shown as a function of the waveguide parameters. Two-mode interference and the effects of the birefringence as well as the temperature are discussed to show the potential applications of the SOI waveguides.

When free space optical communication system uses the atmosphere as a medium for information transmission, received signals are inevitably influenced by the atmospheric environment, atmospheric turbulence, background light factors, and so on. Considering that the atmosphere channel has a great influence on the laser atmosphere communication quality, a modulation/demodulation technology based on polarization parameters is proposed, and an atmospheric laser communication system based on polarization shift keying (PolSK) is designed. This system uses polarization shift keying modulation. In this modulation, two rotation states of circle polarization (left and right) are used for information transmission. In the receiver, the optical signal is detected with balance detection method. At the same time, the performance of the system is simulated. The results show that the modulation/demodulation techniques based on polarization parameters have unique advantages, such as anti-atmospheric interference, high data rate and low bit error rate. It will have broad prospects for development and application in future space laser communication.

In order to study the technology of optoacoustic communication between aerial platforms and underwater objects, a method of laser-generated sound with high repetition rate for underwater acoustic communication is presented in a thermal expansion mechanism. The narrow-band acoustic signal is calculated and validated by experimental results. n-frequency-shift keying (n-FSK) and n-multiple frequency-shift keying (n-MFSK) modulated signals are generated in this method. The in-water range, bandwidth and data rate are analyzed for different modulation methods based on existing laser technology. The performance of modulation method with high repetition rate is compared with existing method (modulation method with long pulse). The results show that this method can be used for communication of short range. Compared to n-FSK modulation, the performance of n-MFSK modulation is better on data rate but worse on in-water range. The in-water range of modulation method with high repetition rate is 1000 m, which is 40% further than that with long pulse for n-FSK modulation.

Electro-optic and voltage-controlled diffractive properties of Fe-doped potassium sodium tantalate niobate (FeKNTN) crystal are presented. This crystal is grown by the top seeded solution growth (TSSG) method and the Curie temperature is 15 ℃. Effective quadratic electro-optic (QEO) coefficient Reff is measured with the one-beam ellipsometric setup, and its Reff achieves as high as 1.05×10-15 m2/V2 near the Curie temperature which is about 19 times that of LiNbO3 under an electric field of 500 V/mm. Reff declines with the increasing temperature. The voltage-controlled diffractive property is measured by a two-wave mixing setup. When the external electric field increases from 0 to 900 V/mm, the diffraction efficiency increases firstly and decreases afterward, and reaches the maximum value of 80% at 700 V/mm. These results show that FeKNTN is a promising electro-optic crystal and voltage-controlled diffractive crystal.

Amorphous SiN/amorphous Si/amorphous SiN sandwiched structures with two different thicknesses of amorphous Si are prepared by plasma-enhanced chemical vapor deposition. Raman spectra demonstrate the formation of Si quantum dots (QDs) when the laser energy is above 320 mJ and the sizes can be controlled as small as 2.8 nm and 4.7 nm, which suggests that the size-controllable Si QDs can be formed due to constrained confined effect in sandwiched structures. Room temperature electroluminescence (EL) can be detected when the applied voltage is above 10 V, and the intensity varies under different laser energies. The EL spectrum peaks are at 680 nm (2.8 nm QDs) and 720 nm (4.7 nm QDs) which are attributed to the radiative recombination of injected electrons and holes within the Si QDs.

In order to improve the pump beam homogeneity of high-power solid-state laser, the basic theory of beam homogenization with imaging and non-imaging beam integrator systems is analyzed. Mainly from three aspects, i.e., spot size, maximum incident angle and spot homogeneity, performances of both beam integrator systems are compared in detail. The analysis shows that imaging beam integrator system not only provides better homogenization effect and reduces the requirement of beam collimation than non-imaging beam integrator system, but also can change the distance between two microlens arrays in order to extend its applicable field. After passing through the imaging beam integrator system, the spot inhomogeneity of laser diode stacks is less than 10% in the illumination area.

Based on optical architecture of LIFE laser driver in USA, Ndglass, YbYAG, YbS-FAP, YbCaF2 are chosen as the laser material candidates. And with their material properties, the pump and energy storage process of the main-amplifier is simulated. According to the results, the influence of media aperture, pump intensity, pump pulse width and media temperature on the performance of laser driver are analyzed, and optimal design parameters of the main-amplifier with each laser materials are acquired. After judging the feasibility of application of those materials to a laser driver required for inertial fusion energy, the qualification of an ideal material is presented, supplying basis for searching the suitable laser materials.

After analyzing the cause of the phenomenon of heaping thinner and uneven thickness in the wall thickness when coaxial inside-beam powder feeding laser cladding is used in the accumulation of variable diameter solid, we propose to control the amount of defocus layer by layer to compensate the pool of liquid metal loss and to keep the cladding layer width. Through a large number of experimental data, we demonstrate the relationship between the variation of defocus amount and slope of the variable diameter solid, and thus in the accumulation process the control of defocus amount can be changed in real time according to the variable rotary slope. By real-time controlling the amount of defocus, and correspondingly controlling the amount of the powder feeding and laser power, a few typical variable diameter rotating solid with good surface quality and uniform thickness are got. The molded parts show fine microstructure and excellent mechanical properties. The hardness of the molded parts is measured, the overall hardness is higher than that of the substrate and evenly distributed.

This paper investigates laser bonding of silicon and Pyrex7740 glass by finite element method (FEM) simulation, self-design of apparatus and experimental research, test and characterization of bonding results. Based on a theoretical heat transfer two-dimensional (2D) model, a three-dimensional (3D) numerical simulation of laser bonding silicon and glass with laser power 20~48 W is conducted using ANSYS FEM softwave. Simulation results include temperature field and melted bonding depth which predicts the bonding threshold power is 28 W. A laser bonding apparatus with laser spot diameter of 150 μm and laser power of 30 W is designed to achieve good bonding. Shear force test shows that the bonding strength is 5.2 times of that of anodic bonding, while helium leak test on hermeticity of bonding samples observes average leakage rate of about 9.29×10-9 Pa·m3/s, which is the same order of magnitude as anodic bonding. From energy dispersive spectroscopy (EDS) line scanning laser bonded Si/glass interface cross section, the thickness of transition layer is 9 μm under 30 W laser, which agrees with the simulation results.

In order to realize the alignment of primary and secondary mirrors in large aperture telescopic system and improve optical imaging quality, a new method for adjusting comparative position and pose between primary and secondary mirrors is introduced named high-precision alignment machining. Other than a traditional method of adjusting washer, the method can eliminate astigmatism aroused from inclination between primary and secondary mirrors, and coma aberration aroused from secondary mirror′s eccentricity at the same time. The method reduces the alignment difficulty markedly and avoids systemic instability. In addition, a new method for primary and secondary mirrors test is established by combination of interference auto-collimating tests and cross wire application which replaces optical axis. The alignment and test′s result from the Φ520 mm primary and secondary mirrors shows that root-mean-square (RMS) value of wave aberration hardly changes before and after assembling, and is entirely less than 0.03λ (λ=632.8 nm), axial angles swaying in primary and secondary mirrors are 0.72″ and 2″, respectively, the verticalities of two mirrors optical axis and respective frames are less than 0.005 mm, primary and secondary mirrors′s concentricity is less than 0.01 mm, and the RMS value of the system is less than 0.7λ after interation, which achieves design requirements.

The traditional detection methods for these regions of interest in high resolution remote sensing image generally search the whole image on the basis of prior knowledge, which leads to high computational complexity. A new fast detection algorithm based on human visual characteristic for these regions of interest in high resolution remote sensing image is proposed. The new algorithm based on visual attention model applies spatial dimension reduction strategy to confirm these focuses of visual attention. According to the positions of focuses of visual attention, the new algorithm describes these relevant regions of interest in the original remote sensing image. The experimental results show that the new algorithm could not only have the lower computational complexity, but also avoid image segmentation and feature detection for the whole image and improve the detection efficiency of regions of interest in high resolution remote sensing image.

The accuracy of measurement is affected by the variation of water vapor concentration when a quartz enhanced photo-acoustic spectroscopy (QEPAS) is used for real-time trace-gas monitoring. A QEPAS based methane sensor is developed at 1.653 μm and the influence of water vapor on the performances of QEPAS methane sensor including second harmonic signal, resonance frequency, Q factor are investigated experimentally. Measurements are carried out under different absolute humidities which are obtained by bubbling method combined with hygrometer at atmosphere pressure. The results suggest that the water vapor could impact both on relaxation time of methane and the parameters of quarts tuning fork in practical application. The smallest detective mass concentration of the sensor is found to be about 0.57 mg/m3 at different atmosphere pressures with an absolute humidity of 2.34%.

A near-infrared fiber-type Raman spectrum detection system with low cost and simple configuration, which is based on the surface enhanced Raman scattering (SERS) effect, is reported. This system uses a near-infrared laser diode as the excitation light source. By improving the background suppression ratio of the excitation light, suppressing the Raman noise caused by the excitation laser propagating along the fiber, and eliminating the residual excitation light reflected from the nano-sample surface with cascaded wavelength-division-multiplexing couplers, the SERS spectrum for 4-aminothiophenol is successfully measured with an InGaAs avalanche photo diode detector in photon counting mode instead of the expensive near-infrared photomultiplier or near-infrared charge-coupled device. The fiber-type Raman spectrum detection system may have advantages of simple configuration, miniaturization, low cost and remote detection.

A fluorescence spectroscopy method of classification for phytoplankton populations is developed based on the high-frequency component of wavelet transform. Three-dimensional (3D) fluorescence spectra of 52 species are projected onto the wavelet function and a series of high-frequency components (cd1~cd6) are obtained. The characteristic points are chosen by the standard deviation and used to form new feature vectors. These feature vectors are analyzed by Bayesian discrimination and cd3~cd6 components are selected as the optimal feature vector for differentiation with the discriminant accuracy rate as a standard, based on which, nonnegative least squares (NNLS) method is introduced to establish the discrimination technique. The technique is used to identify algal species at both the division and the genus level and the correct discrimination rates (CDRs) are 95.5% and 85.7%, respectively. For the actual mixture samples (the mixed proportions are 100%, 75%, 25%), the CDRs are 100%, 90.9%, 53.3% with the relative contents of 79.7%, 68.3%, 17.5%, respectively at the division level and the CDRs of the dominant species (75%) is 81.2% at the genus level. For the water samples from mesocosm experiment and the Jiaozhou Bay, the method can be used to realize the identification of phytoplankton population and estimate the relative abundance of different classes at the division level effectively.