In-situ flying height (FH) testing of the magnetic head in hard disk drives (HDD) plays an essential role in the commercial availability of high-density magnetic storage technology. A symmetrical common-path heterodyne interferometry is proposed, which utilizes a traverse Zeeman laser and a high-speed phase measurement technology. It takes the advantages of direct in-situ traceable measurement with high resolution (0.1 nm) and high sampling frequency (100 kHz). The errors introduced by rotation of disk and environmental disturbance can be adaptively compensated. The system is also suitable for the simulative FH measurement using glass disk. The experimental results show that it is able to clearly describe the FH modulation of less than 10 nm when the dynamic pitch of the rotating rigid disk is 1.2 μm.

An all-solid-state single frequency Nd:YVO4/KTP laser with high efficiency and high power is reported, with fiber-coupled laser diode (LD) end-pumping Nd:YVO4 crystal, ring resonator consisting of four mirrors, and KTP crystal intracavity frequency doubling. Based on the frequency-doubling theory of elliptical Gaussian beam under conditions of critical phase mathcing, an improved intracavity frequency-doubling conversion efficiency is obtained by tuning the orientation of Nd:YVO4 crystal and choosing appropriate polarizing direction for fundermental frequency light to make the walk-off plane of KTP crystal paralle to the sagittal plane of cavity. The peak output power of single frequency green laser reaches to 4.8 W and the optical-optical conversion efficiency equals to 25.5%, when the pumping power is 20 W. In comparison, when the walk-off plane is perpendicular to the sagittal plane, the conversion efficiency is 21.8%, and the maximal single frequency green laser output power is 4.1 W.

Using the propagation-circle and transform-circle graphic analysis, relation of axial-transfer to rotation, and then to axial-transfer has been developed and theoretically deduced based on axial-transfer invariability, which enriched the content of axial-transfer invariability. It was pointed out that the five-mirror cavity was a asymmetric cavity. And the design-scheme of modifying the five-mirror cavity to a nearly symmetrical cavity has been put forward based on axial-transfer to rotation to axial-transfer transform. As a result, the operation performance of the modified cavity was more stable.

Linewidth-narrowed, tunable spectrum can be obtained by external cavity feedback laser diode array (LDA). The external cavity is made up of fast axis collimator, collimating optical system and diffraction grating. Due to smile effect, each beam from emitter strikes the grating at a different angle, so the spectrum of each emitter has a different center wavelength and is expanded. All the emitters spectra compose the array spectrum whose width is increased by the smile effect. A spectrum filter is placed in the output branch to further narrow the spectrum. By this, the linewidth of LDA output is reduced from 2 nm to 0.12 nm with a tuning range of 12 nm (806～818 nm).

The output characteristics and their influence factors of continuous wave (CW) high power Yb3+-doped double clad fiber laser (YDCFL) are experimentally investigated. The results show that the slant angle of the dichroic mirror (DM) with respect to the fiber axes affects the threshold and the output power of the laser. The threshold increases and the output power decreases with the increase of the slant angle, however, such influences may be neglected if the slant angle is smaller than ±2°. The effective gain length of the doped fiber may also influence the threshold and the output power, and determine the lasing wavelength. The lasing wavelength shifts to longer wavelength as the effective gain length of the doped fiber increases.

An experimental and theoretical study on the wave clipping of 355 nm laser is conducted by using the laser induced plasma shutter technique. Five lenses with different focus are adopted to investigate the effects of the focus of lens and the laser pulse energies on pulse compression, and it is found that the best result can be obtained with the focus of 200 mm. While the focus of lens is 200 mm and the pulse energy is 160 mJ, the shortest pulse width of 3.47 ns is obtained. Under the ionization of the Cu pinhole and the atmospheric breakdown, the output pulse width can be further shortened to 2.11 ns. In addition, the measured atmospheric breakdown threshold induced by laser at 355 nm is in agreement with theoretical data.

SiO2-TiO2 planar waveguides on Si/SiO2 substrate were prepared by sol-gel method. A fiber laser was used to fabricate strip optical waveguides in the core layer of the planar waveguides by laser direct writing of the sol-gel coatings. The thresholds of laser power density for laser direct writing optical waveguides on the SiO2-TiO2 planar waveguides were studied systematically. Moreover, the relationships between the thresholds of laser power density and anneal temperature on sol-gel films were also discussed. The experimental results show that there are initial shrinkage threshold and damage threshold when laser direct writing strip optical waveguides on the SiO2-TiO2 coatings are fabricated by sol-gel technique. Both the two thresholds mentioned above increase with the anneal temperature on films respectively, but the increasing trend of the damage threshold is more prominent than that of the shrinkage threshold, which indicates a much smaller laser spot allowed in laser direct writing. Therefore, narrower strip optical waveguides in width can be fabricated in this situation. At last, the light propagation character of the strip waveguides was measured, the three-dimensional light propagation mode of the strip waveguides was confirmed.

Resonator fiber optic gyro (R-FOG) is a novel optical sensor whose resonant frequency is changed due to the Sagnac effect. The digital closed-loop operation can eliminate the thermal drift in analog circuits and it will make the R-FOG system more flexible. Taking the resonant frequency deviation as the research object, a simple analytical model for the closed-loop locking technique is presented based on one-order inertial loop operation. Frequency locking technique in the digital closed-loop operation system is then studied. The optimum loop gain is achieved under a certain integral time constant. Using above optimum parameters, the loop is locked quickly and stably. Furthermore, the analysis is verified by experiments.

The relationship between the beam excursion error and the beam quality β factor of long-term exposure spot was analyzed with and without random wavefront error. The formula to calculate the beam quality β factor of long-term exposure spot with beam excursion error was given. The theoretic analysis and the numerical calculation results indicate that beam quality affected by beam excursion error was independent of the beam quality without beam excursion error, but relative to the criterion of the beam quality β factor and the obstructed ratio of optics system. The beam excursion error request in application was analyzed. The results indicate that the better the beam quality wanted, the smaller the beam excursion error needed.

Based on the analysis of advantages on laser thermal-stress forming (LTF) and laser peen forming (LPF), a laser pre-stressed compound peen forming of plate is presented, the technology combines heat stack action of continuous laser and shock wave action of pulse laser, so it combines heating effect and mechanics effect. At first, CO2 laser is used to scan SUS304 stainless plate which is 2 mm thickness according to special tracks to apply pre-load stress, the basic configuration is formed and residual stress is measured. ATOS-Ⅱ optical scan measure system is used to measure the contours of the plate′s surface after pre-forming, the reverse engineering software Imageware is used to establish virtual model of the plate. Then the interface between ABAQUS and Imageware is used to invert virtual model into finite element model, the optimum distribution of residual stress field is obtained through adjusting laser processing parameters and controlling tracks of laser peening by ABAQUS. Finally, the optimum laser parameters and processing condition are used for laser peen forming experiment. The results indicate that the anticipated shape is obtained, and both sides of the plate hold residual compressive stress field after laser pre-stressed compound peen forming.

Experiments of high power laser welding of Y gap ship plate have been performed using fast axial flow 10 kW CO2 laser, five-axial computer numerically controlled (CNC) table, St370-2 ship mild-steel plates and SG filling wire. Morphology and microstructure of laser welding seam have been widely examined by optical microscope (OM), scanning electron microscope (SEM) and X-ray diffractometer (XRD). It is shown that no crack full penetration welding in 12 mm thickness ship plate can be achieved at laser power of 8～10 kW and welding speed of 1 m/min. Comparing with submerged-arc welding (SAW), laser welding has a narrow seam width of 5 mm and a small heat-affected zone of 0.3 mm. Microstructure of fine martensite and a small amount residual austenite has been observed in the laser seam, which has a good synthesis mechanical obdurability. Mechanical tests of hardness of HV350, tensile strength of 536 N/mm2 and 180° cold bend without fracture have been measured.

The structures and particle size of Ni-P alloy film coated on single crystal silicon substrate by chemical deposition were observed with scanning electron microscope (SEM), and its residual stresses after chemical deposition were measured by X-ray diffraction (XRD). At the same time, residual stresses of Ni-P alloy film coated on silicon substrate by laser heat treatment were measured, and effects of residual stress of the film on wear property and interfacial bonding strength were analyzed. The experimental results showed that residual stresses of Ni-P alloy film coated on silicon substrate by chemical deposition are behaved as tensile stress, its residual stresses vary after laser heat treatment, and high tensile tress is changed into low tensile stress or compressive stress. The effect of residual stress of the film on its wear property is obvious, and its wear extent decreases with fall of residual stress. Bonding strength of the film-substrate system decreases with residual stress increase, and reasonable parameters of laser heat treatment may control residual stress of the film accurately, and increase bonding strength of the film-substrate.

To evaluate the feasibility of the laser rapid forming (LRF) technology for fabricating titanium coping, laser scanner was used to measure aluminium alloy die of abutment tooth and reconstruct its three-dimensional digital profile. The shape of coping was designed by computer based on the digital abutment tooth models. The processing parameters were established by employing orthogonal experimental design. Ten titanium copings were fabricated with LRF based on the coping data and the processing parameters, adhesive test of the titanium coping on the aluminium alloy die was made, and the fabricating precision of the LRF was evaluated through marginal adaptation test. Results showed that LRF technology could be used to fabricate titanium coping. Marginal adaptation test showed that the experimental data of gaps between fabricated copings were less than 120 μm which was accepted by clinical.

For studying the influence of impurity absorption on one-dimensional (1D) photonic crystal defect mode, the complex refractive index and Fabry-Perot interferometry are adopted, and variety feature of extinction coefficient with the transmissivity and reflectivity of defect mode in the impurity-doped 1D photonic crystal is calculated. The extinction coefficient has obvious influence on the transmissivity and reflectivity of defect mode. When the extinction coefficient increases from 0 to 0.03, the transmissivity and reflectivity of defect mode change from 1 to 0 and from 0 to 0.86 respectively. The width of defect mode in reflected wave will enlarge when the extinction coefficient increases, while the width of defect mode in transmitted wave turns constant when the extinction coefficient changes.

The focal plane intensity distribution, realized by the diffractive optical element (DOE) and the smoothing by spectral dispersion (SSD) technique, is theoretically analyzed based on the spatial frequency spectra. The focal plane intensity distributions of the DOE can be expressed as the sum of a series of sine and cosine functions with different harmonic spatial-frequencies and complex amplitudes, no matter whether the SSD technique is adopted or not. Theoretical analysis shows that the spatial frequency spectra are modulated by the SSD technique, and the modulation is determined not only by parameters of the SSD technique, but also by phase distribution of the DOE. The SSD technique smoothes the focal plane intensity distribution of the DOE. But to obtain good beam smoothing performance, the DOE should be optimized considering the parameters of the SSD technique. Finally the DOE is optimized at a certain choice of SSD parameters. The simulated results show that the tolerance of the DOE to incident wave-front distortion is improved with the use of the SSD technique.

Multi-order cascaded Raman fiber lasers (CRFLs) are analyzed by an analytical method from optical power coupling equation under steady states used to describe stimulated Raman scattering (SRS). According to the parity of cascaded number, the output power is deduced, and the optimal length of Raman fiber and reflectivity of output-coupler are also obtained when the maximum pump-to-Stokes conversion efficiency is reached. The output characteristics and conversion efficiency as a function of Raman fiber length and output-coupler reflectivity of a 5th-order Ge-doped CRFL have been calculated with the residual pump power reflected into the input-end of resonant cavity being ignored. The comparison of calculated results and the experimental data for the 5th-order CRFL has been made.

Based on the theories of the energy-transfer upconversion (ETU) effects in actively Q-switched solid-state lasers, coupling passively Q-switched rate equations including ETU parameters are established. The ETU effects in the Nd:YAG laser crystals and the Cr4+:YAG saturable absorbers are numerically simulated by a variation stepping Runge-Kuttaa method. The pulse energy and peak power are affected obviously at low pump power, and average power is affected obviously at high pump power. The effects of ETU on the pulse energy and peak power are decreased with the pump power increasing. And the effect to the pulse duration (full width at half maximum) and the repetition rate can be neglected with the pump power increasing. The numerical calculation results are coincident with the experiments.

In order to design the damage configuration of a cylindrical shell subjected to internal pressure and irradiated by laser beam in the laboratory, the estimation method of laser parameters on the shell-wall surface related to the damage configurations is theoretically studied. Neglecting the heat conduction in the direction of shell-wall surface, an analytical expression of temperature profile is obtained for the cylinder shell under laser-irradiation. According to the mechanical properties varying with temperature and internal pressure, analyses of the thermal crack formation, the thermal crack growth and the crack running are carried out. The laser parameters expression on the target surface is derived for the three kinds of damage configurations. Numerical calculation is performed for a 30CrMnSi-steel cylindrical shell, the numerical results accord with the experiment phenomenons. The results show that given the cylindrical shell properties and internal pressure, the damage configuration can be experimentally designed by the laser parameters choice.

To study the effect of laser flux on impulse coupling coefficient during laser aluminium target interaction at air ambient, by changing laser spot size on the target, the relationship between coupling coefficient and laser flux is achieved. The experimental results indicate that the coupling coefficient reaches to maximum when laser flux is 3.47×106 W/cm2, which agrees well with the theoretical result of 6.14×106 W/cm2. The two-dimensional model theory of laser supported detonation wave (LSDW) interacting with solid target is used to calculate the coupling coefficient. And the trends of theory and experiment are the same, but the two have prominent difference in values. The reason is that the laser spot is a little over large and the point blast model is not suitable to calculate the theory values.

A linear distributed optical fiber sensor based on the principle of Sagnac interferometer is developed to detect pipeline leakage and locate leakage point in real-time. The traditional Sagnac interferometer is converted into in-line structure by using a Faraday rotator mirror, and the in-line structure is applied easily in perplexing pipelines. The representation of phase change caused by leakage is formulated for optic signal. The measuring principle and leaking source location method for the detection system are analyzed. An experiment is designed to detect leaking source and locate leaking source, and the leak is produced at 4.020 km from Faraday rotator mirror. The results verify that the system can realize leaking source detection and location accurately and the largest location error is less than 118 m.

A spectroscopic optical coherence tomography (OCT) system based on the principle of spectroscopic OCT was built, and the reflectance spectrum of multilayer film was measured. This method uses the Fourier transform to pick out the spectral information of OCT signals, and overcomes such limitations of existent film reflectivity measurement methods as lack of intuitionstic results and non-metrical surface interference. The gained spectral reflectivity matches well with the result calibrated by commercial instrument, and the mean square error turns out to be only 0.0488.

The refractive indices along arbitrary wave vector direction were analyzed in uniaxial crystal with buried optical axis. When the optical axis is in the plane of incidence,the reflectivity fitting functions of s- and p-polarized light are presented. Then, the changes of reflectivity with incident angle have been measured with a modified reflectivity scanner, in s- and p-polarized light for CaCO3 crystal respectively. Using a fitting of experimental data based on reflectivity fitting functions the two principal refractive indices were obtained, no=1.6559, and ne=1.4851. This technique does not need sample machining, and the accuracy reaches 0.0001. Otherwise,in the case of unknown optical axis, the optical axis direction was determined with the Brewster angles of the three crystal surfaces measured by using the improved Brewster angle technique.

A fiber-typed optical coherence tomography (OCT) based projected index computed tomography (PICT) system is reported. A water-filled glass tube with outer and inner diameters of 1.3 mm and 0.9 mm respectively is measured by the developed system. 180 projection data from the sample rotated at step resolution of 1 degree are collected, and its refractive index mapped image is then reconstructed based on convolution back projection algorithm. Experimental result with high spatial resolution shows that air, glass and water with different refractive indexes are properly discriminated and their boundaries are clearly resolved. Meanwhile, due to the utilization of information on refractive index distribution, geometrical distortions usually observed in conventional OCT images are avoided in the PICT image.

ZnSe and Na3AlF6 as two classical materials are composed of one-dimensional (1D) photonic crystal, and the medium of the defect is Na3AlF6. Using transfer matrix method, the optical transmission properties in 1D photonic crystals with defect is analyzed, and the band gap property of 1D photonic crystal is obtained. The transmission spectra of reference photonic crystal and measurement photonic crystal with or without adding strain is simulated numerically. The analysis shows that it is linear relationship between the longitudinal strain and wavelength of the peak of band gap. According to the corresponding relation, a new method of strain measurement is presented. The wavelength of the peak of band gap can shift because the linear expansion coefficient between substrate and photonic crystal is not equal and the medium reflection index varies along with the temperature. In order to compensate temperature error, a reference photonic crystal having the same structure as the measurement photonic crystal is introduced in the measurement system. And the temperature compensation with a reference photonic crystal is realized. The results show that the sensitivity of this measuring system is 6×10-4 nm/με and the measurement range is 0～2000 με.

For improving the measurement precision of the gain coefficient of semiconductor optical amplifier (SOA) and avoiding the influence of the optical spectrum analyzer′s resolution and noise, a Hakki-Paoli (HP) method combined with the wavelet denoise and deconvolution (HP-DD) process was presented. The HP-DD principle including deconvolution algorithm and wavelet denoise was analyzed. Based on the simulated amplified spontaneous emission (ASE) spectrum and measured ASE spectrum, wavelet denoise and deconvolution process were demonstrated to improve the precision of the measurement and the noise tolerance.

A simple cavity ring-down (CRD) technique based on an intensity-modulated continuous-wave (CW) diode laser is developed to determine simultaneously the reflectivities of the cavity mirror and the inserted planar mirror. The straight- and folded-cavity configurations with a same cavity length are established. Under both cavity configurations and with phase-locked technique, the amplitude and phase-shift of the first harmonic of the CRD signal are measured as a function of the modulation frequency covering an appropriate range. Effects of the system frequency response are eliminated in the data processing, and then the amplitude ratio and phase-shift difference between the two cavity configurations are fitted to an explicit theory to determine the reflectivities. The measurements are repeated with two cavity lengths, one of which is a 100 cm confocal cavity and the other a 110 cm stable cavity. The reflectivities of the cavity mirror and the inserted mirror are measured to be 99.784% and 99.668%, respectively, with an uncertainty in the order of 10-5.