Fast acquisition of reflectance spectra using wide spectral lines

We analyze a recently proposed technique for fast acquisition of the two-dimensional (2D) spatial distribution of reflectance spectra to figure out how much its ability of distinguishing almost similar spectra declines with increase of the spectral line bandwidth of the light source. This analysis was carried out using the experimentally measured reflectance spectra of four metameric samples and simulating the system response to an illumination by spectral lines with variable bandwidth. It was shown that the metameric samples are distinguishable even when the bandwidth of illuminating lines is 20–30 nm. A wider bandwidth allows implementation of simultaneous illumination of an object that leads to a diminution of the acquisition time of 2D-multispectral images due to both faster operation in the parallel mode of Light-emitting diodes (LEDs) switching and higher output power.     

Enhancing UV photosensitivity of ZnO UV nanosensor using electrical stimulation at megahertz frequency

We report a novel technique to enhance the ultraviolent (UV) photosensitivity of ZnO nanosensor with ZnO nanowires bridged on micromachined metallic electrodes. The experimental results reveal that the photoconductivity and the time response of the ZnO nanowire sensor with either Schottky or Ohmic contacts are significantly improved by electrifying the nanowire sensors using an alternating current at the frequency of megahertz. An integrated UV sensor incorporating ZnO nanowires with a constant current mode driving circuit is developed, which demonstrates promising sensitivity and time response to UV illumination with a low power consumption.     

Enhancing UV photosensitivity of a ZnO UV nanosensor using electrical stimulation at megahertz frequency

We report a novel technique to enhance the ultraviolet (UV) photosensitivity of a ZnO nanosensor with ZnO nanowires bridged on micromachined metallic electrodes. The experimental results reveal that the photoconductivity and the time response of the ZnO nanowire sensor with either Schottky or Ohmic contacts are significantly improved by electrifying the nanowire sensors using an alternating current at the frequency of megahertz. An integrated UV sensor incorporating ZnO nanowires with a constant current mode driving circuit is developed, which demonstrates promising sensitivity and time response to UV illumination with a low power consumption.     

Wide-field coherent anti-Stokes Raman scattering microscopy with non-phase-matching illumination

We have developed and tested a wide-field coherent anti-Stokes Raman scattering (CARS) microscopy technique, which provides the simultaneous imaging of an extended illuminated area without scanning. This method is based on the non-phase-matching illumination of a sample and imaging of a CARS signal with a CCD camera using conventional microscope optics. We have identified a set of conditions on the illumination and imaging optics, as well as on sample preparation. Imaging of test objects proved high spatial resolution and chemical selectivity of this technique.     

Quasi-confocal fluorescence sectioning with dynamic speckle illumination

We present a simple modification to a conventional wide-field fluorescence microscope that provides depth discrimination in thick tissues. The technique consists of illuminating a sample with a sequence of independent speckle patterns and displaying the rms of the resultant sequence of fluorescence images. The advantage of speckle illumination is that it provides diffraction-limited illumination granularity that is highly contrasted even in scattering media. We demonstrate quasi-confocal imaging in a mouse olfactory bulb labeled with green fluorescent protein.     

Resolution improvement by nonconfocal theta microscopy

We present a novel scanning fluorescence microscopy technique, nonconfocal theta microscopy (NCTM), that provides almost isotropic resolution. In NCTM, multiphoton absorption from two orthogonal illumination directions is used to induce fluorescence emission. Therefore the point-spread function of the microscope is described by the product of illumination point-spread functions with reduced spatial overlap, which provides the resolution improvement and the more isotropic observation volume. We discuss the technical details of this new method.     

Use of induced spatial incoherence for uniform illumination of laser fusion targets

We report a technique to achieve very uniform illumination of laser irradiated targets by inducing a controlled amount of transverse spatial incoherence in the output beam of a broadband laser. The spatial incoherence is created by imposing different optical delays upon different transverse sections of the beam, and choosing the delay increments to be larger than the laser coherence time t_c=1/δν. This technique may allow easy attainment of the pellet illumination uniformity required for laser fusion.     

Synthetic aperture microscopy for high resolution imaging through a turbid medium

We report on synthetic aperture microscopy through a highly turbid medium. We first recorded a transmission matrix for the turbid medium with an angular basis of 20,000 complex images covering 0.6 NA. This effectively converts the medium into a lens of the same NA. Distorted images of a target object are then taken at 500 different angles of illumination covering 0.6 NA. For each of the distorted images, the original object image is reconstructed from the transmission matrix by the recently developed turbid lens imaging (TLI) technique. All 500 reconstructed images are synthesized to enhance the NA to 1.2 and thereby generate an object image with twice the enhanced spatial resolution of the individual images. Our method of applying aperture synthesis for TLI makes it possible to enhance the resolving power without increasing the number of transmission matrix elements. This relieves the demand for data acquisition and processing that has impeded the practicality of TLI.     

Laser-Induced Silver Nanoparticles Deposited on Optical Fiber Core for Surface-Enhanced Raman Scattering

We report on surface-enhanced Raman scattering （SERS） probes based on silver nanopaxtieles which axe deposited on the core of the distal end of standard single mode fibers, by means of the very simple, versatile, and lowcost laser-induced nanoparticle technique. The morphological features of the Ag nanoparticles vary according to the experimental conditions such as laser power, illumination time, and concentration of the reaction solution. The SERS activity of the probes is demonstrated with the detections of rhodamine 6G aqueous solutions. The detections are made from both ends of the probes, i.e., in direct detection mode from the end with nanoparticles and in remote detection mode from the distal end, respectively.     

Study of an ultrahigh-numerical-aperture fiber continuum generation source for optical coherence tomography

The axial resolution of optical coherence tomography images is primarily dependent on the bandwidth of the illumination source. Continuum generation is one way to generate the single-mode, high-bandwidth light needed for point illumination. We present an inexpensive and easy-to-implement augmentation to a Ti:sapphire laser that widens the bandwidth from 20 to over 200 nm with commerically available ultrahigh-numerical-aperture fiber. This technique can provide a readily available broad-bandwidth source for researchers and a practical enhancement to a fiber-optic optical coherence tomography system.     

Polychromatic intensity point spread function of a birefringent lens

We study the intensity point spread function (IPSF) of a uniaxial birefringent lens sandwiched between two linear polarizers under broadband illumination having flat-top spectral profile. The optic axis of the birefringent crystal is perpendicular to the lens axis. For monochromatic input illumination, a low-power birefringent lens offers enhanced resolution under parallel-polarizers configuration and apodization under crossed-polarizers configuration with a single focus as well. At a relatively high value of birefringence parameter, the proposed system behaves as a double-focus lens. The present communication uses a novel technique to study the effect of polychromatic illumination on the imaging characteristics of birefringent lenses. The studies reveal that the imaging characteristics of the low-power birefrigent lens does not deteriorate considerably under polychromatic illumination. However, for a polychromatic beam with large bandwidth, the imaging behavior of the system having high birefringence parameter deviates appreciably from that under strictly monochromatic illumination. The said system even loses its inherent bi-focal nature due to depolarization of polarized polychromatic light upon passage through the birefringent crystal.     

尾流后向散射光功率衰减特性研究

依据Mie理论光散射在0°和180°有明显增强的结论,应用自行设计的模拟尾流后向散射光功率实验系统在632.8 nm He-Ne激光器直接照明和扩束后照明两种条件下,对模拟尾流后向散射光功率衰减特性进行了研究.结果表明,用后向散射光功率进行探测时,考虑到散射光在水中传播的衰减,对近距离分布的气泡,使用扩束光照明效果较好;对较远距离分布的气泡,使用细光束照明效果较好,其可探测的距离要比扩束光远.     

Speckle noise reduction in digital holography by use of multiple polarization holograms

A novel speckle reduction technique for digital holography is proposed. Multiple off-axis holograms are recorded using a circularly polarized illumination beam and a rotating linearly polarized reference beam. The speckle noise in the reconstructed images is suppressed by averaging these fields. We demonstrate the effectiveness of this technique experimentally and conduct additional statistical evaluation.     

Lensless digital holographic microscope with light-emitting diode illumination

We demonstrate the operation of a digital in-line microscope with LED illumination. We show with a practical example that, for typical setups, the limited temporal coherence and the spatial incoherence of the source do not affect the resolving power of the system. On the contrary, important advantages are obtained in terms of signal-to-noise ratio and alignment simplification.     

高功率激光聚焦均匀照明靶面的验证

由正六边形的球面透镜列阵和一个非球面的主聚焦透镜组成的聚焦系统,用于改善高功率激光(10~(12)W)聚焦照明靶面的均匀性,得到实验上的证明.文中报道了采用这个聚焦系统进行的激光驱动高压冲击波实验,显示出了均匀照明对改善激光冲击波平面性的良好的效果.     

High-fidelity image reproduction using angular distribution of reflected spectral intensity

A method to reproduce images of an object under various observation conditions is presented. In this method, a series of multispectral images is captured by rotating the object under a point light source of which spectral power distribution and the position are known. The captured images are decomposed into diffuse and specular reflection component images based on the dichromatic reflection and the Lambertian models. Next, the incident angle of the illumination light and the angle between viewing direction and regular reflection are calculated based on observation geometry. Finally, the image under observation geometry is synthesized using the light-ray rearrangement technique. The experiments are carried out using two-dimensional objects, leather and fabric. Most of the synthesized images are shown to be the same as the images actually captured under the assumed illumination geometry, even if the object has complex reflection like fabric for which it is difficult to apply the reflection model used in computer graphics.     

Measurement technique for characterizing odd aberration of lithographic projection optics based on dipole illumination

A dipole illumination based measurement technique for measuring odd aberration of lithographic projection optics is proposed. In the present technique, odd aberration is extracted from the image displacements at multiple illumination settings. Theoretical analysis of the impact of illumination profile on the measurement accuracy is presented. By use of dipole illumination, the image displacement variation range that determines the measurement accuracy is enlarged. Using lithographic simulator PROLITH, the measurement accuracies of odd aberration under conventional illumination and dipole illumination are compared. The simulation results show that the measurement accuracy of odd aberration increases significantly when dipole illumination is used.     

Design and performance of an excimer-laser based optical system for high precision microstructuring

We report on the design of an excimer-laser based system for high precision micromachining of spinnerets using a mask imaging technique. Both the illumination and imaging unit are optimized for specified demagnification ratios of 5 and 15, respectively. Detailed investigations were performed to measure the resolution, depth of focus and the sensitivity for the position accuracy of the substrate depending on illumination parameters. A special test mask for measuring the resolution in combination with a new definition of measurement procedure is used. SEM views of ablation results with high machining quality are presented.     

Design and performance of an excimer-laser based optical system for high precision microstructuring

We report on the design of an excimer-laser based system for high precision micromachining of spinnerets using a mask imaging technique. Both the illumination and imaging unit are optimized for specified demagnification ratios of 5 and 15, respectively. Detailed investigations were performed to measure the resolution, depth of focus and the sensitivity for the position accuracy of the substrate depending on illumination parameters. A special test mask for measuring the resolution in combination with a new definition of measurement procedure is used. SEM views of ablation results with high machining quality are presented.     

High-efficiency volume hologram recording with a pulsed signal beam

We present an efficient photorefractive volume hologram recording technique with a pulsed signal beam and continuous reference-beam illumination. The grating envelope can be simply controlled by manipulation of the duty cycle of the signal beam. Thus, for any grating coupling strength and different initial reference-signal intensity ratios, the diffraction efficiency can be maximized with this technique and can be greatly increased in comparison with that of the conventional recording technique.