We present the dynamics of microparticle launching and loading into optical traps in air. To address repeatable launching and loading of particles into the trap remained as a stubborn obstacle to realization of robust trapping systems, we investigated launching and trapping mechanism, analyzing particle trajectories during the three phases of particle loading: vibration and launching from a substrate, entrainment into the trap with dissipation, and steady state trapping. We identify characteristics that can be exploited to enable more repeatable launching, including in situ measurement of adhesion or natural frequency and the existence of stable subharmonic modes of particle vibration.
We simulate the dynamics of particle motion during launching and loading into optical traps to enable strategies for controlled loading of optical traps in vacuum. Particle dynamics during trap loading are simulated in air and compared to measured trajectories to validate particle behavior at measured launch velocities. The simulated dynamics are analyzed in both ballistic (vacuum) and diffusive (air) regimes to determine the forces required so that particles can be trapped stably. These results provide a foundation for developing control algorithms to reliably launch and load particles into optical traps in vacuum, and examples of controllers will be presented.
We present a reflective Fourier ptychographic microscopy (FPM) with a deep ultraviolet (DUV) laser and a high numerical aperture objective for sub-100nm imaging of an opaque target used in semiconductor device manufacturing. An aperture scanning illumination system designed for a laser with high energy fluence is implemented for angle-varied illumination. Performance of the DUV FPM is evaluated and compared to conventional DUV microscopy by imaging a series of molybdenum silicide (MoSi) multiline with a minimum linewidth of 80 nm, showing that contrast enhancement ratio increases as the linewidth of the target decreases.
A coherent averaging method was applied to the speckle variance algorithm with a akinetic swept-source OCT system and compared with the case of magnitude averaging to find that the contrast of the OCT angiography image increased.
In breast-conserving surgery, an optical wire is a useful surgical guiding tool to optically locate small lesions within the breast tissue. However, the use of a long silica glass fiber as the optical wire can be burdensome to patients because of its stiffness and nonbiocompatibility. We investigate the use of a biocompatible fiber for light localization in tissue. A surgical suture with a diameter of 400 μm and a few centimeters long is employed as the biocompatible optical waveguide to transport the visible laser light to the inner tissue site. Optical location is confirmed with glow ball-like red laser illumination at the tip of the suture embedded within a fresh chicken breast tissue. Effective optical power coupling to the suture is made by using a double-cladding fiber coupler. From this preliminary result, we realize practical light localization with biopolymer waveguides.
We present the real-time stroboscopic full-field optical coherence tomography (FF-OCT) system that is based on graphics processing unit (GPU). The basic configuration of the proposed FF-OCT system was the Linnik interferometer. While scanning of a reference mirror in the axial direction, a series of the transverse sectional image was captured with a 2-dimensional CCD camera. To get a depth-resolved 3-D image, the light source of OCT was turned on and off like a stroboscope at the Doppler frequency of the OCT system. The CCD camera used in experiment operated at a rate of 200 frames per second, but the Doppler frequency was ~kHz. To overcome the slow operation of the CCD camera below the Doppler frequency, the light source was operated in the stroboscopic mode. In addition, lock-in detection technique was utilized in order to avoid the dissolution of the coherent signals during the integration time of the CCD camera. Furthermore, the Doppler frequency shift due to nonlinear scanning motion of the reference mirror was monitored by using an auxiliary interferometer and then fed back to the light source driver so that the strobe frequency was always matched with the Doppler frequency of the OCT system. For the real-time 3-D rendering, we used a graphics processing unit.
We present a single-channel detection-based polarization-sensitive full-field optical coherence tomography (PS-FF-OCT) for simultaneous acquisition of high-resolution OCT and linear retardance images. A linearly polarized sub-10-fs laser was used as a broadband light source for the OCT system. A bi-stable polarization switching device, composed of a ferroelectric liquid crystal cell and an analyzer, was employed to get the horizontal and the vertical polarization components of a full-field interference signal. The time-switched two perpendicular interference signals were sequentially recorded by a single charge-coupled device camera, then processed to extract en-face functional images of a biological sample. The rat tail tendon was imaged ex vivo to confirm the imaging feasibility of the proposed system, which showed axial and transverse resolutions of 2 and 1.3 μm, respectively.
We present biomimetic antireflective AlInP nanostructures fabricated by inductively coupled plasma etching using Ag etch masks, which were easily formed by spin-coating Ag ink and subsequent sintering process on a hotplate without any lithography process and complicated equipments, for compound semiconductor based solar cell applications. This lithography-free technique is a simple, cost-effective, and high throughput method. The fabricated AlInP nanostructures demonstrated drastically reduced the hemispherical reflectance and solar-weighted reflectance (SWR) compared to that of bulk AlInP in the wavelength range of 300-870 nm. The incident angle-dependent SWR of the AlInP nanostructures remained below 4% up to an incident angle of 50°. Therefore, the biomimetic antireflective AlInP nanostructures fabricated by using the lithography-free method hold great potential for use in compound semiconductor based solar cell applications.
We present a birefringence analysis method based on polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) for distinguishing pearls. To cope with the round shape of general pearls, a rotation stage was used for the sample scanning. With the system, the birefringence of several cultured pearls including south sea, Akoya, freshwater cultured pearls, and imitation pearls are analyzed and compared. Interestingly, PS-SS-OCT surely shows well developed birefringence patterns of phase retardation and fast axis orientation with the cultured pearls, whereas the pattern does not appear in the imitation pearls. In addition, the intensity image can help to distinguish the cultured pearls. Therefore, PSSS-OCT enables a more accurate interpretation for identifying the cultured pearls from imitation pearls.
We present polarization-sensitive full-field optical coherence tomography (PS-FF-OCT), which is based on a bi-stable polarization switch (BSPS) device. The proposed PS-FF-OCT is a Linnik type interferometer, and allows getting both the birefringence-induced phase retardation and the intensity images of specimens with high resolutions using a pair of micro objectives and a BSPS device. Two orthogonal polarization states are formed with a regular time interval by the BSPS device that changes the polarization direction of light in a short time by switching its optic axes. Therefore, both the horizontally polarized light signal and the vertically polarized light signal from the sample can be detected with a single CCD camera. For getting a phase retardation image in real-time, the BSPS device is phase-locked with the CCD camera. The proposed method makes easy implementation of the PS- FF-OCT system without the needs of complex alignment process of using two identical CCD cameras. The experimental results confirm the feasibility of the system.
Optical coherence tomography (OCT) has been developed particularly for biomedical and industrial fields owing to the
advantage of in vivo real time optical imaging with a micro-scale high resolution. Depending on specific imaging
purposes, various dedicated OCT systems have been proposed and implemented. We present the recent achievements of OCT systems and their applications such as monitoring of cross-sectional biological specimen, discrimination of living human breast cancer cells, and characterization of wet pad surface in chemical mechanical polishing (CMP) process.
We present an optical tweezer technique assisted full-field optical coherence tomography (FF-OCT) system. The
proposed scheme enables ultrahigh-resolution OCT imaging of a floating object optically trapped by single-beam
gradient force in medium. The set up consists of a Linnik type of white light interference microscope combined with an
optical tweezer system. The optical trap is formed by tightly focusing a 1064 nm Q-switching pulsed laser beam with a
microscope objective lens of high numerical aperture (1.0 NA) in sample arm of the OCT interferometer. This co-sharing
of probe channel between two of systems enables concurrent actions of trapping and OCT imaging for the sample. OCT
imaging of the sample in depth can achieve by positioning the coherence gating with displacement of reference arm in
the OCT interferometer. To demonstrate the efficacy of the system, micron-sized dielectric particles and living cells in
solution are simultaneously trapped and optically sliced with cellular resolution.
A fiber optic sensor based on the wavelength division multiplexer coated with a palladium (Pd) thin film is designed for
hydrogen gas detection. The sensing mechanism of this sensor is measuring the wavelength shift that is induced by the
evanescent field interaction with the refractive index change of Pd film when it absorbs hydrogen.
An optical interferometric system for the simultaneous measurements of physical thickness and refractive group index is
implemented. The proposed system is based on a spectral-domain optical low coherence interferometry with two sample
probes facing to each other. The two-probe approach enables simultaneous measurements of thickness and group index
of a transparent sample. The average measurement errors were ~0.112 % in the physical thickness and ~0.035 % in the
group index, respectively.
We report the fabrication and performance of the 2x2 photonic crystal fiber (PCF) splitter that was designed as a single
mode splitter at the 800 nm optical band and used as the beam splitter for a spectral domain optical coherence
tomography system. The PCF splitter has been made by coupling PCFs to a planar lightwave circuit (PLC) splitter chip.
The PLC splitter chip was fabricated to have a single mode property at the 800 nm wavelength band and the PCFs were
securely connected to the PLC chip through PCF block arrays having lithographically fabricated V grooves. The core
size of the splitter chip was about 5 μmx5 μm and the core-cladding index difference was about 0.15 %. With the
implemented PCF PLC splitter, we have obtained a low excess loss of 1.2 dB at 850 nm and a low polarization-dependent
loss of 0.19 dB. With the proposed 2x2 PCF splitter, optical coherence tomography images of pearls were
successfully obtained.
KEYWORDS: Optical coherence tomography, Luminescence, Cladding, Imaging systems, Fluorescence spectroscopy, Tissues, Skin, Single mode fibers, Signal detection, In vivo imaging
We report a combined swept source optical coherence tomography (SSOCT) and fluorescence spectroscopy (FS) system
for multimodal measurements of biochemical information and internal structures with fast imaging speed. The FS probe
composed of a double clad fiber (DCF) coupler is adopted into the single mode fiber based SSOCT system. Here, the
DCF coupler acts as a FS system as well as a multifunctional probe for the SSOCT-FS system. The performances of the
single-unit SSOCT-FS system is confirmed by monitoring the fluorescence signal from photosensitizer in cancerous
region of in-vivo rat and by imaging the internal structures of same region with speed of 40 frames/sec.
We propose a simple but compact hydrogen sensor based on Fabry-Perot (FP) type all fiber interferometer. The proposed
sensor consists of two cascaded FP cavities formed with hollow core fiber (HOF) cavity, which is mainly used to
compensate the influence of the unstable source power, and multi mode fiber (MMF) cavity coated with palladium as a
sensing part. The experiment result shows that the exposed 4% hydrogen gas can be detected by the variation of
interference fringe contrast with respect to optical property change of the palladium.
We demonstrate a high temperature sensor by using an intrinsic photonic crystal fiber (PCF) based Mach-Zehnder
interferometer. Air hole collapsed regions inside the PCF act as coupler between the core and cladding modes which
form the two arms of the interferometer. The temperature measurements are obtained by measuring the shift in the peaks
of the interference signal. The experiments confirm the reliability, repeatability and hysteresis. The small amount of
hysteresis and deviation in the repeated experiments are within the experimental errors.
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