Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere, which detects trace gases by analyzing the typical absorption waveband of narrow band molecules. The concentration of trace gases is retrieved through least-squares fits of reference absorbing cross section to the differential cross section. But in the application, for the superposition of noises on the absorption spectra, the measurement precision is affected. In the DOAS, denoising by polynomial smoothing filtering is the traditional method. Wavelet transform with soft threshold is put forward to reduce noises, which improves the precision of DOAS and declines the measuring limit, according to the comparison with experimental results.

A method to measure the grating parameters with the incident efficiencies ratio from both sides of the grating with the same wavelength is proposed. The proposed method has a higher precision than the original approach with the diffraction orders of m=±1 efficiencies ratio from one side of the grating. Firstly, by comparing the sensitivity of diffraction efficiency ratio to surface roughness under the condition of one side incidence and two-side incidence, it is found the former is more sensitive than the latter; secondly, the sine surface grating parameters are simulated for two-side incidence; finally, the volume phase holographic grating parameters are obtained experimentally more accurately. Meanwhile, the new method retains the advantage of the original method, such as no damage, simplicity and low cost.

A simple and practical method, moiré fringe method (MFM), for adjusting the light path of the pulse compression grating with a great aperture is introduced, with which the longitudinal precision of the conventional light path adjustment is improved. With the imaging formula of the holographic lens, the principle of the light path adjustment is deduced. With the primary aberration theory and relationship between the optical recording system and the diffraction wavefront aberration of the grating, it is concluded that the aberration of the moiré fringe is 0.4786λ, approximately twice of the diffraction wavefront aberration of grating. According to the above numerical relation, the diffraction wavefront aberration of the grating can be monitored. From the simulation, it is presented that, the wavefront aberration can be reduced to 0.06λ, corresponding to the longitudinal error of 0.007 mm.

According to fundamental principle of optical Fabry-Pérot cavity, the work principle and design project of optical fiber liquid-level sensor based on extrinsic and sensitive Fabry-Pérot cavity are analyzed. The experimental results indicate that the sensor possesses good characteristics of several periodicities output and partial linearity. But output intensity of the F-P cavity attenuates gradually with increase of cavity length, and the same length linear work intervals in different segments of output characteristic curve of the sensor correspond with different measurement ranges and sensitivities. The sensor can satisfy requirements for measuring different liquid-level by changing dimension of sensitive module in the sensing head. Precision of ±0.5 mm and minimal resolving power of 0.3 mm over a full range of 20 m are obtained. The sensor can be applied to measure liquid-level of flammable and explosive liquid accurately and has strong practicability.

For the single-drive Mach-Zehnder electrooptical modulator applied in radio over fiber (RoF) and sub-carrier multiplexing systems, the situation for two radio frequency signals inputs is discussed and an exact analytical solution for arbitrary order inter-modulation distortion (IMD) and harmonic terms is derived. The correctness of the analytical solution is approved by numerical results. Analytical results indicate that the third-order IMD is independent of the offset phase shift of the modulator and is only dependent on the modulation index of RF signals. In addition, when the applied offset voltage equals the half-wave voltage of the modulator, there are only even-order distortion terms. With the presented analytical expression, it is convenient to design the analog optical communication systems, precisely predict the nonlinear characteristics of the external modulator and optimize the system's performance.

In order to extend the application of the fiber couplers and develop the new function of fiber couplers, by utilizing the fused\|taper technology, a fiber coupler sensitive to wavelength is obtained. The couplers can split light beam and simultaneously is sensitive to wavelength. The experimental value agrees with the theoretical value. In experiment, the wavelength sensitivity of the coupler is maximized to be 17.86％/ nm. The coupler sensitive to wavelength is easy to be produced by the fused-taper technology and the peak wavelength of the coupling ratio can be well controlled. The coupler can be used to demodulate wavelength shift of fiber Bragg gratings (FBGs). When the Bragg wavelength of FBG agrees with the maximum sensitivity wavelength, the shift of the Bragg wavelength will influence coupling ratio of the coupler output. FBG with 1566.71 nm Bragg wavelength is demodulated by the self-made coupler. When the shift of wavelength reaches 1.80 nm, the coupling ratio varies about 20.34%. The demodulation system is simple and compatible with fiber device. It can be used in health monitoring for huge buildings.

Ray-tracing simulation and simulating design for volume scattering integrated light guide plates are presented, with Monte Carlo sequential sampling method based on multiple Mie scattering theory. The effects of optical parameters, i.e. doped material, particle scale, concentration and geometrical structure of light guide plates, on the backlight performances, such as the output light intensity uniformity and illuminating angle, are considered, and primary verifying experiments and design evaluation are also presented. It is found that, the above parameters are sensitive and correlated, and plenty of optimizing simulation is necessary for light guide plate design scheme meeting practical demands. The uniformity of output light intensity is determined mainly by the deoped particle concentration, view angle by the light guide plate size and especially the scope angle of basal surface, and dispersion by the diameter of doped particle and refractivity, respectively.

Wavelength division multiplexing (WDM) used in an ultrashort pulsed digital micro-holographic system to record and represent ultrafast processing of femtosecond scale is reported.A BBO crystal is used to generate the harmonic wave of the incident laser wave, and both the basic and doubled frequency waves are separated, then time-delayed respectively and introduced to a Michelson's interferometer to record two sub-holograms with different spatial frequencies on a single frame of a CCD by means of WDM. In the experiment, an ultrafast dynamic process of air ionization induced by a single femtosecond laser pulse is holographically recorded, and both intensity and phase images of the digitally reconstructed images are obtained through Fourier transformation and digital filtering, which show clearly the dynamic process of the plasma forming and propagating, with a time resolution of femtosecond scale. The related parameters are, exposure time 50 fs, exposure interval of 400 fs, as well as exposure frequency of 2.5×1012 f/s.

A novel three-deimensional shape measurement method for specular surface, based on fringe reflection and phase shift is presented. A sinusoidal fringe is displayed on a plane monitor, and then the images will be recorded by a CCD camera after reflected by the tested and standard surfaces, respectively. The difference between the tested surface and standard surface is obtained as soon as the phase distributions are worked out by phase shift. Then the shape of the tested surface will be restored from the surface gradients, which is calculated by the relations between the tested gradients and phase difference of horizontal and vertical fringes. The measurement resolution of this method has also been discussed. Notablely, the computer-generated fringe will bring a no-error phase shift and make the shift of periods and directions more easily. A marked point is used to guide the phase unwrapping procedure. The experimental results of a tile surface are presented and prove its validity.

The inverse fringe projection technique using multi\|projectors simultaneously is proposed. Through the absolute phase measurement of the master object, different inverse fringes are generated for the different projectors placed in different directions. During the detection, the projectors project their inverse fringes simultaneously. If the object and master are identical, a standard sine fringe without shadow and break is got on the camera. If the object is deformed, the deformation becomes obvious, and can be evaluated quantificationally by simple Fourier transformation and phase unwrapping. Therefore, the detection of complex and discontinuous objects can be completed with only one fringe image, the problems of shadow and break are solved to a large extent, and consequently the fast online detection of this kind of objects is realized. The principle of this technique is expatiated, and the validity is proved by taking the system of two projectors for example. The analysis of error and requirement of application are also presented.

A method for instantaneous three-dimensional profile measurement of a continually vibrating cantilever beam is proposed. The moiré fringes containing the three-dimensional patterns information of a continually vibrating cantilever beam, generated by the interference of the grating lines and their shadows, are captured by a high\|speed CCD camera. Two light sources are used to enhance the illumination of the fringe patterns. Fourier transform method is adopted to analyze the time-sequence fringe patterns, and the outer extended interpolation is used to decline the phase error resulting from the leakage of the frequency. The phase unwrapping method is used to unwrap the phase in the dynamic process, the instantaneous three-dimensional profile is obtained and the continually vibrating process of the cantilever beam is reconstructed.

When a periodic object with subwavelength structure is illuminated by normal incident monochromatic parallel light, evanescent waves occurs. For the quick attenuation of the evanescent wave, the object with subwavelength structure cannot be imaged properly by ordinary method . However, one-dimensional periodic object with subwavelength structure can be encoded by a grating so that homogeneous waves can be obtained. Passing through the optical system designed specially, the well-distributed waves with evanescent waves information is enlarged so that it can be recognised by CCD camera. After that, the homogeneous waves with evanescent waves information is decoded by a decoding grating, the information of the encoding grating is filtered, and the image of the object with subwavelength structure reappears in the image plane. The imaging technique based on the conventional optical setup is novel for superresolution image of object with subwavelength structure can be obtained. Theoretical analysis of the imaging process and experiment is given well by photonic method. It is designed that where the encoding and decoding gratings are placed, so does how to choose the tilt angles between the two gratings and the object. The low\|pass filters used in the novel technique are also discussed. The results of experiments demonstrate that the theory is valid.

The conversion from deflection tomography projection to phase tomography projection is analyzed, and an explicit expression corresponding to the conversion is presented. An error analysis is made to the reconstructed fields by filtered back-projection (DFBP) algorithm of deflection tomography. Results show that the effect of projection noise on the reconstructed fields is represented by a slope function related to the filter used in deflection tomographic filtered back-projection algorithm. So the deflection tomographic filtered back-projection algorithm is modified. Numerical simulation shows that the modified algorithm depresses the slope phenomena efficiently, while no obvious distortion is introduced to the reconstruction. Based on the modified algorithm, the three-dimensional reconstruction for density field of the real rocket exhausted plumes is carried out.

The inhomogeneous refractive index distribution of scattering medium is measured by combining computed tomography (CT) with optical coherence tomography (OCT). The refractive index distribution is reconstructed by CT technique and the needed projections in different directions are obtained by OCT system. This method gets advantages over traditional optical refractive index measurement method, focus tracking method simply based on OCT and optical path matching method which cannot measure inhomogeneous refractive index distribution of scattering medium. The refractive index distribution of a gradient refractive index bar is measured and a favorable result is obtained.

The crystal rotation method is usually used to measure the pretilt angle of liquid crystal molecules, but it is unsuitable to measure the pretilt angle of 20°～70°. In order to expand the range of applicability of crystal rotation method, we propose the pretilt angle measurement method to use prisms to assist the crystal rotation. A liquid crystal cell is located between two prisms, and the incident light enters from the former prism, passes through the crystal cell and exits from the back prism. We will get the incident angle on condition that the birefringence retardation is zero and the light transmission is maximal, and obtain the pretilt angle with optical geometry. The numerical simulation and experimental results show a feasibility of this method.

A new method based on photoelastic modulation technology for measuring retardation of a wave plate is presented. The theoretical analysis of the measurement principle and error of this method are given by using Miller matrix. The measurement setup is composed of laser source, polarizer, photoelastic modulator, wave plate to be measured, analyzer and photodetector. The retardation of the wave plate is computed by using the normalized fundamental frequency component and the second harmonic component of the detected signals. This method can measure the retardation of wave plate with a large spectral range from ultraviolet to infrared. The error of this method is less than 0.05°. The precision of measurement repeatability is less than 0.0048°, and the feasibility of the method is verified experimentally.

Although the traditional five-bucket phase-shifting algorithm possesses excellent accuracy, it isn't used in the practical length measurement because of the strict conditions of equal step length of phase shifting. Based on two-beam interference principle, a corrected five-bucket phase-shifting algorithm which possesses high accuracy with an arbitrary phase step in range of 10 nm is present. With the numerical simulation, it shows that the accuracy of the corrected algorithm is better than 0.001 phase period when the measuring error of the phase step is 1 nm and the measuring error of the signal is 0.1%, besides that, this algorithm does not need accurate equal step length of phase shifting. With higher reliability and higher accuracy, the corrected five-bucket phase-shifting algorithm is very valuable for the precision length measurement.

Defect modes will emerge in the emission spectrum as a defect is introduced in a photonic crystal, and such modes can be amplified to produce laser radiations. Based on the model that couples Maxwell's equations with the rate equations of electronic population, the spatial distribution and spectrum characteristics of the laser modes in a single-defect active photonic crystal are investigated by the finite-difference time-domain method, as well as the amplification of defect modes. The influences of the number of crystal periods and the thickness of the defect layer on amplification of defect modes are analyzed. The results show that the spectral property, resonance and radiation frequency, and spatial profile of defect mode depend directly on the medium parameters such as the number of crystal periods and the thickness of defect layer, which further influences the radiation threshold and saturation. The radiation threshold decreases and the saturated output increases when the number of crystal periods increases. Such a trend becomes weak when the number of the crystal periods is large enough and thus there exists an effective number for the crystal periods in the system.

Multifrequency dynamical theory of pulsed CO2 lasers is extended. By substituting optical field equations for optical intensity equations, a theoretical model for injection locking of pulsed CO2 lasers is presented. The output power, instantaneous frequency and gain coefficient are calculated with the classic fourth order Runge-Kutta method for different input signal intensity and detuning frequency. The mode-locking stability of injection-locked broad tuned TEA CO2 lasers is studied. Calculated results show that for frequency detuning of 600 MHz, the injected intensity should be two orders of magnitude larger than that at frequency center for stable injection locking. Theoretical results agree well with the published experimental data. Further study indicates that, when gas pressure is up to 106 Pa, for the same tuning range, the injection intensity is only about 10% higher than the intensity at frequency center.

A novel functional optical mapping procedure for brain is proposed, which is in a periodical mode and the period is much shorter than the duration of the homodynamic course. Under continuous-periodic stimulation, the neural response of cortical functional region enters a stable state. The mapping signals vibrate at the stimulation frequency round some level in state space, which can be detected by the spectral analyzing techniques, and the task related brain region can be determined by synthesizing the altitude and phase distribution of the spectrum. Hind-paw (HP) area of SD mouse with sciatic nerve stimulation is used as the neural model in the experiment, with red light with 605±10 nm wavelength for illumination. The vascular overspill phenomenon is weakened greatly, resulting in a reduction of pseudo-maps. The phase distribution indicates that response of contralateral HP area is temporally prior to that of ipsilateral HP area. The arterial-venous transit and local blood circulation are also discussed. It is found that when relatively high frequency stimulation is applied, the vessel net will resonate with the stimuli. The procedure presents more spatio-temporal information of cortical neural activation than traditional ones, and proves another valuable functional mapping technqiue.

Optical Doppler tomography (ODT) is a non-invasive and non-contact imaging technology which combines Doppler velocimetry with optical coherence tomography (OCT) for measuring blood flow velocity and blood vessel distribution in highly scattering biological tissue. The principle of phase-resolved ODT based on digital Hilbert transformation is described and verified by measuring polystyrene solution flow velocity through glass capillary and microchannels of biochip respectively. With measurement for the Doppler frequency shift of the polystyrene flowing through glass capillary, the curve of the velocity of flow is obtained. The obtained images with high spatial and velocity resolutions, demonstrates that the developed ODT system has promising value for future clinical applications.

Based on PFWc and AreaMTF metrics, which are objective and quantitative metrics of optical quality of human eyes, the influence of wavefront aberration of single Zernike modes on optical quality is investigated with the WRMS wavefront aberration of 0.05～1.00 μm. The results show that when a fixed amount of WRMS aberration is loaded into single Zernike modes, the optical quality of the central region of the pupil varies with the Zernike modes. The value of MPFWc of defocus (C4) and spherical aberation (C12) is minimum, but that of pentafoil (C15 and C20) is maximum. The value of area MTF of pentafoil is more than 0.94 in the case of WRMS wavefront aberration within the range of 0.05～1.00 μm, so its influence on optical quality can be ignored. Furthermore, the value of PFWc, as well as Marea MTF, decreases with rise of WRMS, but nonlinearly, and their decreased slopes become smaller as the WRMS value increases. Moreover, the influences of wavefront aberration of single Zernike modes on optical quality of human eyes are of great difference, the effect sequence of which is followed from the maxium to the miniumum by sphere, defocus, astigmatism, coma, trefoil, tetrafoil and pentafoil.

The influence of aberrations at wide field of view on the optical system of human eyes cannot be neglected. The optical design software Zemax is used to construct the individual eye models for eight normal eyes. The individual eye model, which is optimized from actual wavefront aberrations measurement data, cornea parameter data and eye's axial lengths data, has the same optical characteristics with the actual eye. The variation trend of off-axis aberrations at temporal angles of vision (0°, 10°, 20°, 30°, 40°, 50°) with the field of view is analyzed based on individual eye model. The peripheral optical quality is poorer than the central optical quality and the oblique astigmatism and coma are the chief factors. Aberrations above the 4th order do not show an obvious variation with the angles of vision. The aberrations at wide field of view calculated from the individual eye model are in good agreement with those measured with a Hartmann-Shack wavefront sensor.

Spatiotemporal instability of ultrashort pulse beam propagating through cubic nonlinear dispersive media is studied by using an extended nonlinear Schrdinger equation (NLSE). Spatiotemporal focusing, self-steepening and Raman delayed response are identified. The linear stability theory are used to study the growth of small noise from the background of intense laser. It is found that Raman delayed response makes spatiotemporal instability occur in a wider spectrum region, even in an anomalous dispersion region of self-defoucsing media. Based on that, some characteristics about spatiotemperal instability have been studied.

Goos-Hnchen (GH) shifts of reflected and transmitted wave beams in frustrated total reflection structure occur simultaneously. Commonly, GH shift of frustrated-total-reflection in symmetric double-prism configuration is only of the order of the wavelength. It's difficult to measure it in experiment. According to Maxwell equations, the complex expressons of reflection coefficient and transmission coefficient are presented when the incident angle is less than the critical angle of prism-film interface but larger than the critical angle of prism-air interface in the thin-film enhanced frustrated total reflection configuration. The GH shifts of reflected and transmitted wave beams are investigated by stationary-phase approach. The results show that the GH shifts of reflected and transmitted wave beams are equal and can be modulated by changing the incident angle and thickness of thin film and air gap. When the incident angle is less than, but close to the critical angle of prism-film interface, the magnitude of the shifts is enhanced by a factor of 102 with given thickness of thin film and air gap.

Relying on dispersion equation, the refraction angles of wave vector and energy flow of TM wave at the interface between homogeneous right-handed material and hyperbolic uniaxial left-handed material are studied. In a large range of incident angle, the two refraction angles are not sensitive to that the smaller the optical axial angle is, the more evident the phenomena is and the range of the optical axial angle is given. This refraction phenomenon is caused by a negative principal index and anisotropy in hyperbolic uniaxial left-handed material. It is suitable for beam collimation, beam conformity and simple beam coupling. If TM wave is incident on the interface from a hyperbolic uniaxial left-handed material, the effect of superprism will be realized. Further, by analyzing the transmission coefficient, the possibility of above application is proven.

Considering the Debye-Hückel screening potential into Dirac equation, the plasma electron temperature and density effects on the energies of bound state 1s(2S1/2), 2s(2S1/2), 2p(2P1/2 and 2P3/2) for H-like ion C5+ are studied. A fitted formula, which estimates the bound state energies and ionization potential of H-like ion C5+ under different plasma conditions, is obtained. With this formula, the critical electron density of pressure ionization for bound levels is calculated, and agrees well with the data in previous literature. The results show that the energies of bound states increase with the increase of plasma electron densities or decrease of plasma electron temperatures. The relation between the logarithm of percentage shift of energy and the logarithm of plasma electron density or temperature is approximately linear. The results are useful in calculating the plasma ionization state distributions and plasma spectral simulations.