Search

A speckle reduction apparatus is proposed by using an optical interferometer to introduce temporally changing interference fringes. With the help of the vibration of a mirror, diverse interference fringes and speckle patterns are added together in the intensity basis during the exposure time of the CCD camera, which result in a summed speckle image having lower speckle contrast. Experimentally, we have demonstrated the speckle reduction efficiency by this method, and compared with another approach by only using the modulation beam. The obtained speckle contrast is 0.66 after using both the modulation beam and the reference beam, which is lower than the 0.77 speckle contrast by only using the modulation beam. We conclude that the introduction of interference fringes helps the speckle reduction.

Frequency selective surface is a monolayer or multilayer 2D periodic structure which is composed of multiple resonance units scattering by a two-dimensional periodic array on dielectric layer. FSS can't absorb radio frequency energy, but can filter the frequency which is therefore applied in microwave technique or stealth technology. The relative research on curved FSS is relatively scarce since the curved FSS structure can be obtained only when FSS is attached on the materials surfaces of curved structures in engineering application. However, curved FSS is widely applied in practical engineering; therefore, the research on curved FSS structure has important significance. In this paper, a curved FSS structure model of Y-pore unit is established and numerical simulated by means of FDTD. The influence of curvature on FSS transmission characteristics is studied according to the analysis on the changing of radar cross section (RCS). The results show: the center frequency point of the plane band pass FSS structure drifts after the curve surface deformation of the structure; the center frequency point of the curved band pass FSS structure drifts with the changing of the curvature radius, i. e. with the decreasing of curvature radius, the frequency point drifts towards high points and the transmittance decreases. The design of FSS radome demands of accurate and stable center resonance frequency; therefore, the actual situation of curved surface should be considered in practical engineering application when band pass FSS is made into frequency selection filtering radome. The curvature radius should be long enough to avoid center frequency drifting and transmittance deceasing.

An array of diffraction gratings and a Random Phase Plate (RPP) are used to suppress laser speckle effect. Dynamic diffraction spots are generated on the surface of the RPP, after which the scattering lights are perceived by a detector. Speckle Contrast Ratio (CR) and Number of Independent Speckle Patterns (NISP) with different gratings rotation orientations ( θ ), gratings frequencies (grooves per millimeter: f ), diameters of laser beam ( D ), and distances between the array of diffraction gratings and the RPP ( Z ) are calculated based on ZEMAX simulations, and an optimized model is proposed.

We report a polymer based multiple diffraction modulator, in which PDMS (polydimethylsiloxane) is utilized as the actuation material, for speckle reduction. The properties of the PDMS are characterized based on its response time and deformability, which are the key properties concerned in this work. The structure dependent properties of PDMS are discussed. Using the described technique, the PDMS satisfy the system demand. The modulator is used to create real-time diffraction patterns by dynamic gratings formed by flexible PDMS. The diffracted light passes through a diffuser, which is placed after the modulator, and induces speckle patterns on the screen. Speckle-reduction is achieved by adding the time-varying speckle patterns in the integration time of the detector. It is observed that using the modulator which has two gratings, the speckle contrast ratio reaches to 50%, which shows fair agreement with the simulation.

Speckle is the constructive and destructive interference pattern observed from an optically rough surface when a highly coherent laser light is used as the illumination source. In this article, we present some methods to reduce the undesired laser speckle in laser display projector and show measurement results indicating reduction in speckle contrast obtained by using a dynamical flexible polymer-based diffraction grating phase modulator. Light is diffracted into multiple orders by the dynamic polymer diffraction grating. This diffracted light, after collection and homogenization, is used as the illumination source for displaying picture information. Due to the time-varying phase of the diffraction grating, the diffraction pattern changes thus creating time-varying speckle patterns on the rough screen. The time-varying speckle is captured by a CCD camera with appropriate integration time to mimic the averaging action of the human eye. Thus the time-integrated speckle is minimized by the intensity averaging of many independent speckle patterns. Different configurations of the diffraction grating along with random phase plate and beam combining lens were explored to ascertain the corresponding reduction in speckle contrast and its dependence on the time-period of the driving voltage of the diffraction grating.

We report on the photocurrent generated by nanometer grains embedded in hydrogenated amorphous silicon (a-Si:H), i.e., the hydrogenated nanocrystalline silicon (nc-Si:H) thin film. The embedded nanometer grains within the a-Si:H boundaries are found to be a narrow continuous energy band in the a-Si:H band-gap, from which the transitions can effectively generate the free electron-hole pairs, resulting in the observed high photocurrent. The high density of nanometer Si crystals is a good means to improve the photo current response, and the fabrication of the low-cost infrared photo detector by a single layer of nc-Si:H thin film on glass substrates is also expected.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diamond-like carbon (DLC) coated tips have been successfully applied in field emitter arrays, and scanning probe microscope (SPM) based nanofabrications. DLC deposition on tips is conventionally realized by thermal and plasma-enhanced chemical vapor deposition processes. In this study, we use laser-assisted method employing strongly enhanced near field around the tip apex for DLC deposition. DLC films were deposited on tungsten (W) tips under KrF excimer laser irradiation in a benzene solution and in a laser chemical vapor deposition (LCVD) chamber. Simulation results showed a highly localized optical field enhancement at the tip apex. There was also an optical-field gradient from apex to tip body. Experiment results showed that a locally confined DLC film was deposited based on energy dispersive X-ray (EDX) analysis. Raman spectra showed that at positions close to apexes, films tend to be more diamond-like. This implies that quality of DLC film varies according to local optical intensity along the tip. Hence, the deposition process was confirmed to be induced by the local near field generated by laser and nanotip interaction.

A novel spectrographic system with grazing incidence grating spectrograph for studying laser produced plasmas has been developed. Thecomplex system is composed of three units: a grazing incidence gratingspectrograph, 4 dimensions microadjustment equipment, and an aligningsystem with optical fibre bundle, electronic camera, TV monitor and lasertransit. The optical system, optoelectronic machinery system, experiment arrangement and results are discussed.1. INTRODUCTION The soft X—ray emission spectrum using a spectrographic system has received increasing attention, especially for plasma diagnostics and research soft X—ray diagnoses of high temperature plasma. The system described for use In spectroscopy experiments for laser plasma diagnostics is a combination with photographic detection and some units, allowing great versatility of performance. 2. OPT ICAL SYSTEM The spectral analysis of soft X—ray Is a challenge since one has to meet the requirements usually have to be over wavelength range X20—320 A.