A modified algorithm for tracking laser Doppler vibrometer (TLDV) is introduced to measure the vibration of rotating objects. The proposed algorithm unlike the old algorithm for TLDV can be used when the speed of the object to be tracked varies continuously or alternating in a small range. The proposed algorithm is to use encoder only as a position sensor. The position from the encoder is used to calculate the driving signals to the galvanometers. To verify the proposed method, experimental modal analysis of the circular plate in stationary and rotating cases are made.
This paper reports the measurement of elastic constants between two DNA strands that are simultaneously hybridized by
a third target-DNA linker. Two probe-DNA strands that are immobilized on fluorescent beads and a target-DNA linker
formed a hybridized assembly through the Watson-Crick based pairing. Elastic constants of the resulting assembly were
measured using a force calibrated dual optical trap. This study can be used to detect the existence of a target-DNA linker
with a specified nucleotide sequence, indicating its potential use in DNA biosensors.
KEYWORDS: Near field, Near field optics, Optical lithography, Glasses, Near field scanning optical microscopy, Polymers, Nanoprobes, Light sources, Process control, Nanolithography
Near field optical nano patterning was investigated using azobenzene based amorphous molecular glass material, which shows fast response to the light and higher diffraction efficiency for short irradiation time compared to common azo polymers. Optical patterning was performed using NSOM equipped with a He-Cd laser as the light source and a cantilever with 100 nm aperture diameter. Macroscopic motion of photoresponsive materials containing azobenzene groups was useful to fabricate the well defined nano structures such as dots and line array without nanomask and development process by control of irradiation time and scan speed.
Highly photosensitive organic phototransistors (OPTs) with an organic thin film transistors configuration based on a biphenyl end capped fused bithiophene oligomer (BPTT) and copper phthalocyanine (CuPC) were prepared. The measured maximum responsivity and the ratio of photocurrent to dark current (IPh/IDark) in BPTT and CuPC OPTs were 82 A/W, 2 A/W and 2.0 × 105, 1000 under 365 nm UV light with 1.55 mW/cm2, respectively. The prepared OPTs showed a photocurrent response similar to the photo to current conversion efficiency (IPCE) spectrum of BPTT and CuPC. The main mechanisms responsible for photocurrent amplification in the devices were examined by comparing theoretical and measured data. The photovoltaic (turn-on) and photoconductive effect (turn-off) of the OPTs were determined by fitting to theoretical equations. The findings confirmed that the operation of the OPTs followed as photo-voltaic (turn-on state) and photo-conductive (turn-off state) behaviors.
We report a novel all-fiber, maskless lithograpic technology to form various concentric grating patterns for micro zone plate on azo polymer film. The proposed technology is based on the interference pattern out of the cleaved end of a coreless silica fiber (CSF)-single mode fiber (SMF) composite. The light guided along SMF expands into the CSF segment to generate various circular interference patterns depending on the length of CSF. Interference patterns are experimentally observed when the CSF length is over a certain length and the finer spacing between the concentric rings are obtained for a longer CSF. By using beam propagation method (BPM) package, we could further investigated the concentric interference patterns in terms of intensity distribution and fringe spacing as a function of CSF length. These intereference patterns are directly projected over azo polymer film and their intensity distrubution formed surface relief grating (SRG) patterns. Compared to photoresist films azo polymer layers produce surface relief grating (SRG), where the actual mass of layer is modulated rather than refractive index. The geometric parameters of the CSF length as well as diameter and the spacing between the cleaved end of a CSF and azo polymer film, were found to play a major role to generate various concentric structures. With the demonstration of the circular SRG patterns, we confirmed that the proposed technique do have an ample potential to fabricate micro fresnel zone plate, that could find applications in lens arrays for optical beam formings as well as compact photonic devices.
A novel photonic crystal in which the refractive index of the interstitial void region in a colloidal crystal is gradually changed with respect to the specific direction of the crystal was proposed. This was achieved by infiltrating polymers using the interfacial-gel polymerization with high refractive index dopants. Therefore, the resulting colloidal photonic crystal has a gradually varying stop-band at different positions of the crystal when the incident light was normal to the [111] crystallographic axis. This structure could be a kind of tunable photonic crystals based on the positional variations. The optical properties and potentials for other photonic applications will be investigated.
We fabricated all-optical polymer devices such as Mach-Zehnder modulator and 1x2 switch using a polymer doped with photoresponsive dyes. The refractive index change of the photoresponsive dyes by irradiation of light was utilized to fabricate switching and modulation devices. All-optical Mach-Zehnder modulator and switch are demonstrated which are composed of a polymer waveguide doped with the dyes in the core and a thick light blocking metal layer on the
waveguide. The metal layer was opened on one arm of the Mach-Zehnder modulator and 1x2 Y-branch switch, so that only one arm could be irradiated by control light, thus allowing a changing of refractive index. The optical modulator and switch exhibited an extinction ratio of about -12 dB and a crosstalk of -14 dB at a wavelength of 1.55 μm respectively. A simple kinetic model developed to delineate the refractive index change in the dye doped polymer film was applied to predict the evolution of the modulation characteristics. We have also fabricated polymeric wavelength filters with Bragg grating. The surface relief grating was formed using an azobenzene polymer film and used as an etch mask to transfer the pattern to polymer waveguides by reactive ion etching (RIE). The grating period was 5OO nm and the depth was 3O nm with 10-mm-long grating length. A crosstalk of -20 dB at the Bragg wavelength and the 3-dB transmission bandwidth of 0.2 nm were obtained from the device.
Surface relief gratings were photofabricated on various polymer films containing azobenzene groups in the side chain or in the main chain. Formation of the surface relief gratings on the polymer was very sensitive to the polymer structures. The surface gratings were produced on the polymers containing photoisomerizable azobenzene groups. Recording of the gratings was strongly dependent on the polarization of the beams. The localized variations of magnitude and polarization of the resultant electric field in the film are essential to the formation of the surface relief gratings. Large surface modulation (greater than 6000 angstrom) and high diffraction efficiency (greater than 40% into each of plus or minus 1 order) were obtained under optimal recording conditions. The diffraction efficiency of the surface relief grating was dependent only on the total light energy incident on the film. The surface pattern resulting from straight edge diffraction mapped the negative first derivative of the intensity distribution. Fabrication of various multiple gratings on the same spot of the polymer films were demonstrated. Fourier blazed gratings were also fabricated. The resulting surface pattern was a simple superposition of all the interfering recording waves.
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