A robust charge-coupled device (CCD) photoelectric autocollimator for outdoor use is designed and demonstrated. The influence of outdoor conditions on the signal-to-noise ratio (SNR) and imaging quality of the measuring system is experimentally analyzed. The pulse width modulation technology is applied to the automatic feedback control of the actively regulated illuminating light source of the measuring system to maximize SNR while avoiding image saturation. A Fourier phase shift method for subpixel estimation is adopted to achieve high-accuracy measurement in the presence of noises. Experimental results indicate that the technologies proposed here largely improve the measuring stability, dynamic range, and accuracy of the CCD photoelectric autocollimator used outdoors.

We report a 1 018-nm ytterbium-doped double-clad fiber laser pumped by 970-nm diode. A pair of fiber Bragg gratings with reflectivities of 99.9% and 9% at a center wavelength of 1 018.9 nm are employed as cavity mirrors. The ytterbium-doped double-clad fiber is a 2.6-m-long Liekki fiber. Laser output power of 7.5 W at 1 018 nm is obtained under the pump power of 59.2 W. The overall slope efficiency of the fiber laser is about 16%. This low slope efficiency is mainly due to the incomplete absorption of the pump power.

Ba impurity in potassium dihydrogen phosphate (KDP) is studied with the first-principle simulation method. The relaxed configurations and density of the states of KDP crystal with Ba impurity are calculated. We find that Ba can generate a K vacancy and an interstitial O-H unit for charge compensation. The band gap of KDP crystal narrowed down to about 3.9 eV, which is consistent with the experimental data from previously reported studies and indicates that Ba may be a source of low-damage threshold.

A laser power feedback control system that features fast response, large-scale performance, low noise, and excellent stability is presented. Some essential points used for optimization are described. Primary optical lattice experiments are given as examples to show the performance of this system. With these performance characteristics, the power control system is useful for applications in cold atom physics and precision measurements.

A method of locking the relative phase to provide stable constructive or destructive interference between the phase-modulated sidebands from a pair of phase modulators is demonstrated. It is discussed theoretically for optimal fringe visibility related to the phase noise from faulty system. After phase locking using the phase modulating and lock-in technique, the drift of the relative phase is focalized around +-0.0016 rad and the fringe visibility is restricted to 2×10?4.

A nanosecond square pulse fiber laser based on the nonlinear amplifying loop mirror (NALM) is numerically analyzed by the nonlinear Schr¨odinger equation. The fiber cavity with a NALM has a tendency to provide pulse shaping effect with nonlinearity increasing in the NALM, and the nanosecond square pulse is generated by the pulse shaping effect. The numerical results show that the stable square pulse can be obtained when the parameters of the NALM are chosen appropriately. The generated square pulses have flat top and no internal structure.

Diode-end-pumped continuous-wave (CW) Tm:YAP and Tm:YLF slab lasers are demonstrated. The a-cut Tm:YAP and Tm:YLF slabs with doping concentrations of 4 at.-% and 3.5 at.-%, respectively, are pumped by fast-axis collimated laser diodes at room temperature. The maximum CW output powers of 72 and 50.2 W are obtained from Tm:YAP and Tm:YLF, respectively, while the pump power is 220 W, corresponding to the slope e±ciencies of 37.9% and 26.6%, respectively.

A diode-side-pumped Tm,Ho:LuLiF laser at 2-1m wavelength obtained in a ring resonator and its amplification experiment are reported. At the maximum pump energy of 4.7 J available for the oscillator, the output energy per pulse for the oscillator decreases from 904 to 483 mJ in free running mode, and decreases from 106 to 68 mJ in Q-switched mode, with an increase of pump pulse repetition rate from 1 to 5 Hz. When considering the amplifier, 99-mJ Q-switched output energy is achieved at 5-Hz repetition rate.

The effect of shape, height, and interparticle spacing of Au nanoparticles (NPs) on the sensing performance of Au NP array is systematically investigated. Lengthening the major axis of elliptical NPs with the minor axis kept constant will cause the redshift of the local surface plasmon (LSP) resonance mode, enhance the sensitivity, and widen the resonance peaks. Larger height corresponds to smaller LSP resonance wavelength and narrower resonance peak. With each NP size unchanged, larger interparticle spacing corresponds to larger resonance wavelength and smaller full-width at half-maximum (FWHM). Moreover, duty cycle is important for sensitivity, which is largest when the duty cycle is 0.4.

An optical delay line of coupled resonator optical waveguide (CROW) compensated by photonic crystal waveguide (PhCW) is proposed. In the structure, etching the periodic holes around the waveguide of the ring resonator waveguide does not increase the size of the CROW. Theoretical studies and numerical models indicate that through careful design, CROW and PhCW exhibit different group velocity dispersion (GVD) properties at a certain frequency range. Optical signal can not only be compensated in terms of GVD, but can also be delayed with longer time period. Due to the propagation mode mismatch of the two structures, optical loss becomes inevitable.

A novel design and fabrication approach for a high fill-factor micro-electro-mechanical system (MEMS) micromirror array-based wavelength-selective switch (WSS) is presented. The WSS is composed of a polarization-independent transmission grating and a high fill-factor micromirror array. The WSS is successfully demonstrated based on the fabricated high fill-factor micromirror array. Test results show that the polarization-dependent loss (PDL) is less than 0.3 dB and that the insertion loss (IL) of the wavelength channel is about –6 dB. The switching function between the two output ports of WSS is measured. The forward switching time is recorded to be about 0.5 ms, whereas the backward switching time is about 7 ms.

A kind of highly birefringent quinquangular-core photonic crystal fiber (Q-PCF) structure is proposed and analyzed by full-vector finite element method (FEM). The modal field, effective index, and birefringence properties are investigated. From the numerical results, it is found that the birefringence of the new polarization-maintaining PCFs is at least five times larger than that of the standard highly birefringent hexagonal PCFs (H-PCFs) with the same hole pitch, hole diameter, and whole hole area as that of the new PCFs at 1 550 nm. Moreover, the modal field of the new PCFs could be better restricted than that of the standard highly birefringent H-PCFs; hence, the loss of fibers could be reduced.

A novel scheme is proposed, in which the aberrations in the off-axis holographic lenses used as demultiplexers are reduced to a low enough level for relatively small channel spacing. The scheme includes optimizing the recording and reconstruction geometries and collimating the reconstruction wave with a gradient-index lens. A demultiplexer operated in the 1 550-nm band with 5-nm channel spacing and ?\infty-dB crosstalk is obtained using the scheme. The channel spacing can be decreased to 2 nm by etching the cladding of the output fibers to a smaller size.

A single-frequency pulsed erbium-doped fiber (EDF) laser with master-oscillator power-amplifier configuration at 1 533 nm is developed. A short-cavity, erbium-doped phosphate glass fiber laser is utilized as a seeder laser with a linewidth of 5 kHz and power of 40 mW. The seeder laser is modulated to be a pulse laser with a repetition rate of 10 kHz and pulse duration of 500 ns. The amplifier consists of two pre-amplifiers and one main amplifier. The detailed characteristics of the spectrum and linewidth of the amplifiers are presented. A pulse energy of 116 1J and a linewidth of 1.1 MHz are obtained. This laser can be a candidate transmitter for an all-fiber Doppler wind lidar in the boundary layer.

A new transfer matrix method for long-period fiber gratings with coupled multiple cladding modes is proposed and numerically characterized. The transmission spectra of uniform and non-uniform longperiod fiber gratings are numerically characterized. The theoretical results excellently agree with the experimental measurements. Compared with commonly used methods, such as using the fourth-order adaptive step size control of the Runge-Kutta algorithm in solving the coupled mode equation, the new transfer matrix method exhibits a faster calculation speed.

A metal bellows-based fiber Bragg grating (FBG) accelerometer is proposed and experimentally demonstrated. The optical fiber (containing the FBG) is pre-tensioned, and the two ends of the optical fiber are fixed directly from the shell to the inertial mass. In this design, the FBG is uniformly tensioned to obtain a constant strain distribution over it. By employing this configuration, the FBG always has a sharp reflection characteristic with no broadening in its reflection spectrum during wavelength shifting. Dynamic vibration measurements show that the proposed FBG accelerometer has a wide frequency response range (5–110 Hz) and an extremely high sensitivity (548.7 pm/g). The two important indicators of FBG accelerometer can be tuned by the addition of mass to tailor the sensor performance to specific applications, identifying it as a good candidate for structural health monitoring.

The intelligent structural health monitoring method, which uses a fiber Bragg grating (FBG) sensor, is a new approach in the field of civil engineering. However, it lacks a reliable FBG-based accelerometer for taking structural low frequency vibration measurements. In this letter, a flextensional FBG-based accelerometer is proposed and demonstrated. The experimental results indicate that the natural frequency of the developed accelerometer is 16.7 Hz, with a high sensitivity of 410.7 pm/g. In addition, it has a broad and flat response over low frequencies ranging from 1 to 10 Hz. The natural frequency and sensitivity of the accelerometer can be tuned by adding mass to tailor the sensor performance to specific applications. Experimental results are presented to demonstrate the good performance of the proposed FBG-based accelerometer. These results show that the proposed accelerometer is satisfactory for low frequency vibration measurements.

An integrated microball lens fiber catheter probe is demonstrated, which has better lateral resolution and longer working distance than a corresponding bare fiber probe with diverging beam for Fourier domain optical coherence tomography (FDOCT). Simulation results are shown to gain the effect of the distance between the microball lens and the bare fiber to the focusing plane and beam width. The freedom of modifying the working distance and lateral resolution is shown. This is achieved by changing the gap distance between the single-mode fiber and the microball lens within the packaged surgical needle catheter without using an additional beam expander having a fixed length. The probe successfully acquired cross-sectional images of ocular tissues from an animal sample with the proposed miniaturized imaging probe.

Output nonlocality and nonclassicality for the two modes are investigated in an entanglement laser system. Within the framework of a quantum theory of multiwave mixing, nonlocality and nonclassicality are discussed according to the violations of Bell inequality and Cauchy-Schwarz inequality. It is found that both nonlocality and nonclassicality can be fulfilled in the outside cavity fields under certain conditions. It is also shown that there are some nonclassical states that do not show nonlocality.

The direct replication of W/Si supermirrors is investigated systematically. W/Si supermirrors are fabricated by direct current (DC) magnetron sputtering technology. After deposition, the supermirrors are replicated from the supersmooth mandrels onto ordinary °oat glass substrates by epoxy replication technique. The properties of the supermirrors before and after the replication are characterized by grazing incidence X-ray reflectometry (GIXR) measurement and atomic force microscope (AFM). The results show that before and after replication, the multilayer structures are almost the same and that the surface roughness is 0.240 and 0.217 nm, respectively, which are close to that of the mandrel. It is demonstrated that the W/Si supermirrors are successfully replicated from the mandrel with good performance.

By measuring the emission spectra and the fluorescence lifetime of the 4I13=2 state of Er3+ ions in Gd2SiO5 crystal at different temperatures, the effects of temperature on the spectra and the lifetime of the 4I13=2 state are investigated. When the temperature increases, the emission line width for the 4I13=2 -> 4I15=2 transition is broadened, and the main emission lines at 1 596, 1 609, and 1 644 nm shifte toward shorter wavelengths. The measured lifetime of the 4I13=2 state decreases from 13.2 to 8.4 ms with temperature increase from 13 to 300 K, which is mainly due to the temperature dependence of multiphonon relaxation between the 4I13=2 and 4I15=2 states and the changing population distribution among the Stark levels within the 4I13=2 state. The experimental results imply that low temperature condition is better for the ~1.6- \mu m laser output.

A-plane GaN films are deposited on (302) \gamma-LiAlO2 substrates by metalorganic chemical vapor deposition (MOCVD). The X-ray diffraction (XRD) results indicate that the in-plane orientation relationship between GaN and LAO substrates is [010]LAO//[0001]GaN and [203]LAO//[1100]GaN with 0.03% and 2.85% lattice mismatch, respectively. Raman scattering results indicate that the strain in the films decreases along with the increase in the thickness of the films. In addition to the band edge emission at 3.42 eV, defects-related luminescence at 3.35 eV is observed in the photoluminescence (PL) spectra. The cathodoluminescence (CL) spectra indicate that the 3.35-eV emission is related to the V pits.

The roles of laser-induced defects and native defects in multilayer mirrors under multi-shot irradiation condition are investigated. The HfO2/SiO2 dielectric mirrors are deposited by electron beam evaporation (EBE). Laser damage testing is carried out on both the 1-on-1 and S-on-1 regimes using 355-nm pulsed laser at a duration of 8 ns. It is found that the single-shot laser-induced damage threshold (LIDT) is much higher than the multi-shot LIDT. In the multi-shot mode, the main factor influencing LIDT is the accumulation of irreversible laser-induced defects and native defects. The surface morphologies of the samples are observed by optical microscopy. Moreover, the number of laser-induced defects affects the damage probability of the samples. A correlative model based on critical conduction band (CB) electron density (ED) is presented to simulate the multi-shot damage behavior.

A new removal optimization method called submerged jet polishing (SJP) is reported. Experiments are conducted to obtain the removal shape. Results of SJP indicate that a Gaussian shape removal function can be obtained and that the removal rate is sensitive to variations in the standoff distance. SJP is applied to the corrective figuring of a BK7 optical glass. The flatness is improved from photovolatic (PV) 0.066 \lambda to 0.024 \lambda (\lambda=632.8 nm) after three iterations, and the root mean square (RMS) value is improved from 0.013 \lambda to 0.00395 \lambda. The experimental result indicates that SJP has a capability for ultra-precision figuring and can be applied in polishing complex-shaped surfaces.

A method of clarifying bioaerosol particles is proposed based on T-matrix. Size and shape characterizations are simultaneously acquired for individual bioaerosol particles by analyzing the spatial distribution of scattered light. The particle size can be determined according to the scattering intensity, while shape information can be obtained through asymmetry factor (AF). The azimuthal distribution of the scattered light for spherical particles is symmetrical, whereas it is asymmetrical for non-spherical ones, and the asymmetry becomes intense with increasing asphericity. The calculated results denote that the 5o–10o scattering angle is an effective range to classify the bioaerosol particles that we are concerned of. The method is very useful in real-time environmental monitoring of particle sizes and shapes.

Femtosecond (fs) pulse laser ablation of silicon targets in air and in vacuum is investigated using a time-resolved shadowgraphic method. The observed dynamic process of the fs laser ablation of silicon in air is significantly different from that in vacuum. Similar to the ablation of metallic targets, while the shock wave front and a series of nearly concentric and semicircular stripes, as well as the contact front, are clearly identifiable in the process of ablation under 1￡105 Pa, these phenomena are no longer observed when the ablation takes place in vacuum. Although the ambient air around the target strongly affects the evolution of the ablation plume, the three rounds of material ejection clearly observed in the shadowgraphs of fs laser ablation in standard air can also be distinguished in the process of ablation in vacuum. It is proven that the three rounds of material ejection are caused by different ablation mechanisms.

A camera-based model is established to predict the total difference for samples of metallic panels with effect coatings under directional illumination, and the testing results indicate that the model can precisely predict the total difference between samples with metallic coatings with satisfactory consistency to the visual data. Due to the limited amount of testing samples, the model performance should be further developed by increasing the training and testing samples.