A halo tester is designed to analyze the halo formation in low-light-level (LLL) image intensifiers and the influencing factors on halo size. The tester is used to collect a 0.1922-mm hole image directly using a CoolSNAPK4 charge-coupled device (CCD) in a darkroom under illumination conditions between 10 2 and 10 4 lx. The practical measurement result shows that the amplification ratio is 343.4. Then, the super second- and third-generation image intensifiers are placed after the hole, and the halo sizes of the hole images on the screens are determined as 0.2388 and 0.5533 mm, respectively.

In order to avoid stimulated Brillouin scattering and smooth the final focal spot that reaches the D-T capsule, spectral broadening is essential. However, the modulation of spectral structure might result in frequency-to-amplitude modulation (FM-to-AM) conversion. The spatial filter pinhole is used to cut off the high-frequency transmission laser, and to ensure the desired pass. Improper parameter of pinhole would lead a negative impact. Using the spatial filter pinhole, we analyze the characteristic of intensity modulation using several pinholes of improper parameters. We then compare these results with the intensity modulation obtained from an experiment. Experimental diagnosis and design of an appropriate pinhole parameter would be highly beneficial to the field of high-power lasers.

A dual-source distributed optical fiber sensor system with combined Raman and Brillouin scatterings is designed for simultaneous temperature and strain measurements. The optimal Raman and Brillouin signals can be separately obtained by adjusting the powers of the two sources using an optical switch. The temperature and strain can be determined by processing the optimal Raman and Brillouin signals. The experimental result shows that 1.7 ℃ temperature resolution and 60-με" strain resolution can be achieved at a 24.7-km distance.

LP01 and LP11 mode interferences in high-birefringence (Hi-Bi) panda fibers are theoretically and experimentally presented. The propagation characteristics of both the fundamental and second-order modes in Hi-Bi panda fibers are investigated, and the interference output intensity distribution of the LP01 and LP11 modes in panda fibers are thoroughly examined. An experiment is conducted to verify the feasibility of modal interference sensors. The results show that the two-lobe interference pattern of panda fibers generates energy exchanges when external strain is applied on the fiber. Moreover, Hi-Bi panda fibers can be used to design voltage sensors.

The effect of the diminution of the sensitizing intensity from initially high value on two-center recording is experimentally and theoretically investigated. A linear diminution of the sensitizing intensity is designed, and three different diminution rates are employed for the experimental investigation. The results show that the dynamic range can be improved by reducing the diminution rate of the sensitizing intensity. Compared with that of traditional two-center recording, the recording sensitivity obtained in the experiment is more improved when the maximum dynamic range is achieved. The effect of the diminution of the sensitizing intensity on grating uniformity and the effect of the initial sensitizing intensity on the recording sensitivity are theoretically investigated.

The reconstruction quality of in-line holography suffers from the superposition of twin images that have different foci but identical information content. We propose a phase retrieval method using two axially displaced holograms and a finite transmission constraint to eliminate the conjugate image. The simulation and experimental results demonstrate a better elimination effect and a faster rate of convergence compared with those of previously reported methods. Two holograms can be recorded simultaneously using two cameras, thus this technique can be used in real-time imaging.

Face-centered orthorhombic (FCO) sampling can be implemented more easily on CMOS image sensors than on other video acquisition devices. The sampling efficiency of FCO is the highest among all three-dimensional (3D) sampling schemes. However, interpolation of FCO-sampled data is inevitable in bridging human perception and machine-vision algorithms. In this letter, the concept of motion compensation is borrowed from deinterlacing, which displays interlaced videos on progressively scanned devices. The combination of motion estimation based on intrafield interpolated frames and motion-compensated interfield interpolation is found to provide the best performance by evaluating different combinations of motion estimation and interpolation.

Combining photoacoustic (PA) imaging with laser speckle (LS) imaging (LSI) can simultaneously determine total hemoglobin concentration (HbT), hemoglobin oxygen saturation (SO2), and blood flow rates. Thus, the co-registration of PA and LS images is important in physiological studies and pathological diagnosis. This letter presents a co-registration algorithm combining mutual information with the maximum between-class variance segmentation method (Otsu method). The mutual information and Otsu method are used to provide the registration measure criterion and image feature recognition, respectively. The evaluation results show that the registration function possesses a single maximum peak and high smoothness across the global co-registration district, indicating a robust behavior. Moreover, this method has good registration accuracy, and the fusion result simultaneously visualizes the separate functional information of two kinds of images.

We propose a method of generating orthoscopic elemental image array from a sparse camera array. A parallax image array obtained by a sparse camera array provides different perspectives of a real threedimensional (3D) scene, and has all the information the elemental image array needs. In-depth analysis of the generation method and the relationships between the sparse camera array and the elemental image array are presented. The experimental results demonstrate the correctness of the proposed method.

A polarization Fizeau interferometer based on birefringent thin film is presented. The interferometer adopts a birefringent thin film to obtain orthogonally polarized and strictly common-path reference and test beams. Advantages include ease of implementation on large-aperture interferometer, measuring test optics from long distance, and achieving high fringe visibility. The phase shift is obtained by combining a quarterwave plate and an analyzer. The concepts illustrated are verified experimentally.

A novel angle-resolved scatterometer based on pupil optimization for feature profile measurement in a photolithography process is proposed. The impact of image sensor errors is minimized by optimizing the intensity distribution of the incident light using a spatial light modulator. The scatterometry sensitivity of feature measurement at different polarization conditions is calculated using the rigorous coupled-wave and first-order analyses, and the reproducibility of the scatterometer is evaluated. The results show that the sensitivity and reproducibility of the angle-resolved scatterometer increase by 90% and 40% with pupil optimization, respectively.

GaInAs/AlGaAs comprehensive-strained three-quantum-well lasers with asymmetric waveguide are designed and optimized. With this design, the optical field in the transverse direction is extended, and a semiconductor laser with large spot is obtained. For a 300-\mu m cavity length and 100-\mu m aperture device under continuous wave (CW) operation, the measured vertical and horizontal far-field divergence angles are 12.2o and 3.0o, respectively. The slope efficiency is 0.44 W/A and the lasing wavelength is 917 nm. The equivalent transverse spot size is 3 \mu m for the fundamental transverse mode, which is a sufficiently large value for the purpose of coupling and manipulation of light.

A high-efficiency hybrid Brillouin/ytterbium fiber laser (BYFL) is demonstrated using a 41.5-cm-long highly ytterbium-doped fiber and a 10-m-long single-mode optical fiber. The BYFL operates at 1 052.92 nm, and the difference between it and the Brillouin pump (BP) wavelength matches the expected stimulated Brillouin scattering (SBS) Stokes shift. Its output power reaches 70.1 mW, which is more than seven times higher than the seeded BP power. The BYFL has an optical signal-to-noise ratio that is greater than 65 dB and has many potential applications, such as in controllable optical delay lines, sensing, and RF photonics.

In ring laser gyros (RLGs), dynamic lock-in, which results from information loss in the lock-in region, occurs when a constant sine bias is introduced. However, sampling some signals in the lock-in region for a particular duration allows the retrieval of lost information. It is demonstrated how dynamic lock-in and the flat region in the input-output curve near the zero angle rate can be eliminated after compensation.

Contrary to expectations, a measurement of the random walk in the ring laser gyro (RLG) as a function of laser power P shows that it is not consistent with the P^{-1/2} rule. In the experiment, the random walk and laser power are tested and recorded at different discharge currents. The random walk decreases with increasing power, but with a rate much less than the theoretical value according to current literature. In order to solve the inconsistency above, we derive the expression for the random walk in RLGs based on laser theory. Theoretical analysis shows that, accumulating effects of lower energy level due to its limited lifetime lead to additional quantum noise from spontaneous emission. Results show that the random walk in the RLGs consists of two components. The former decreases with increasing power according to the P^{-1/2} rule, whereas the other is power-independent. Thus far, the power-independent quantum limit has not appeared in the literature; therefore, the expressions for RLGs should be modified to describe the low-loss RLGs exactly, where the power-independent term takes a relatively larger proportion. The findings are significant to the further reduction of quantum limit in low-loss RLGs.

An antiresonant ring (ARR) interferometer configuration is introduced for the characterization of a continuous wave (CW) Nd:YAG laser output. The output of the ARR device is precisely characterized to determine the gain and loss of a laboratory CW Nd:YAG laser by using the Findlay-Clay approach. The ARR arm is then experimentally arranged inside the cavity of an arranged high power side-pumped CW Nd:YAG laser. A coated beam splitter with 50–50% reflectivity at normal incidence is placed inside the cavity to provide a wide range of reflectivity from 0 to 100%. This is performed by a rotatable stage and tilting the beam splitter by 10o with the steps of 0.05. By changing the input electrical power of the laser pump the variation of the output laser power is monitored for 20 individual reflectivity of ARR arm. Average pump threshold power of about 180 W is obtained. With the help of the derived equations and obtained threshold power, small signal gain and loss associated with the emerging beam is estimated. It is verified that the former is very dependent to the input parameters. Laser efficiency is also measures 5.6% which is quite comparable with the reported values.

We propose a power spectrum analysis method to directly identify the time delay of a chaotic semiconductor laser with optical feedback. By measuring the radio frequency (RF) power spectrum of the chaotic laser and performing an inverse Fourier transform, we can easily unveil all the time delay signatures, regardless of whether the chaotic output is induced by single or multiple feedback. This method successfully retrieves the two time delay signatures from the power spectrum of a semiconductor laser with double-cavity feedback.

Based on the optical rotatory dispersion and zero reflection of the p-polarization light at the Brewster angle, a novel optical filter that employs only one NaBrO3 crystal and one polarizer are proposed and demonstrated. Performance of the optical filter is studied both theoretically and experimentally. Results show that the green light is becomes nearly extinct when the angles of the polarizer are set at 80o and 260o, whereas the red light becomes nearly extinct when the angles of the polarizer are set at 116o and 296o. Isolation of more than 8 dB can be achieved. The measured extinction ratios are 12.3 and 12.6 dB for green and red lights, respectively.

Designs of p-doped in quantum well (QW) barriers and specific number of vertically stacked QWs are proposed to improve the optical performance of GaN-based dual-wavelength light-emitting diodes (LEDs). Emission spectra, carrier concentration, electron current density, and internal quantum e±ciency (IQE) are studied numerically. Simulation results show that the e±ciency droop and the spectrum intensity at the large current injection are improved markedly by using the proposed design. Compared with the conventional LEDs, the uniform spectrum intensity of dual-wavelength luminescence is realized when a specific number of vertically stacked QWs is adopted. Suppression of electron leakage current and the promotion of hole injection e±ciency could be one of the main reasons for these improvements.

The virtual source for generation of rotational symmetric Lorentz-Gaussian (RLG) wave whose propagating dynamics present the rotational symmetry is identified. Closed-form expressions, including integral and differential representations, are derived for this kind of Lorentz-Gaussian (LG) wave, thereby yielding paraxial approximation of the RLG beam in the appropriate regime. From the spectral representation of this wave, the first three order corrections of nonparaxial approximations are determined for a corresponding paraxial RLG beam. Moreover, the relationship between the RLG beam and the Hermite-Gaussian beam is revealed.

This letter describes a method for calculating water-leaving radiance on smooth surfaces at different angles based on Fresnel law and the polarized measurements using an ASD FS3 spectroradiometer. The spectroradiometer is mounted on a goniometer so that it views the water surface from a height of several decimeters at different viewing angles through a linear polarizing filter. The incident angles equal the viewing angles. The water-leaving radiance spectra acquired by other methods are compared with the polarized measurements from the smooth water surface, and the radiance spectra obtained by the proposed method are found to be consistent with the results of the reference methods. The current study provides another effective technique for measuring water-surface reflectance via remote sensing. Moreover, the method does not avoid the sun glint during the detection of water-leaving radiance in cases where the viewing geometric position is clear.

Photoluminescence (PL) conversion of Si nanoparticles by absorbing ultraviolet (UV) lights and emitting visible ones has been used to improve the efficiency of crystalline Si solar cells. Si nanoparticle thin films are prepared by pulverizing porous Si in ethanol and then mixing the suspension with a SiO2 sol-gel (SOG). This SOG is spin-deposited onto the surface of the Si solar cells and dries in air. The short-circuit current as a function of Si nanoparticle concentration is investigated under UV illumination. The maximal increase is found at a Si concentration of 0.1 mg/mL. At such concentration and under the irradiation of an AM0 solar simulator, the photoelectric conversion efficiency of the crystalline Si solar cell is relatively increased by 2.16% because of the PL conversion.

Photocatalytic TiO2 thin film is prepared by sol-gel technique on microstructured silicon substrate produced by femtosecond laser cumulative irradiation. The photocatalytic activity is evaluated by the degradation of methylene blue (MB) solution under ultraviolet (UV) irradiation. For 6-ml MB solution with initial concentration of 3.0 \times 10^{-5} mol/L, the degradation rate caused by TiO2 thin film of 2-cm2 area is higher than 70% after 10-h UV irradiation. Microstructured silicon substrate is found to enhance photocatalytic activity of the TiO2 thin film remarkably. The femtosecond laser microstructured silicon substrate is suitable to support TiO2 thin film photocatalysts.

An electron beam is obtained using laser wakefield electron accelerator, and converted into a \gamma-ray source after undergoing bremsstrahlung radiation in a dense material. A quasi-monoenergetic structure is observed when the length of the plasma channel was modified. The structure has a 58-MeV peak energy, 15-mrad (full-width at half-maximum) divergence angle, and 340-pC charge. The \gamma-ray source generated by this high-quality electron beam is brighter and has higher spatial and temporal resolutions than other conventional sources. A \gamma-ray radiography demonstrational experiment is performed. Pictures of a ball with different layers made of different materials are taken. The results show a clear structure and density resolution.