Optical fiber probe based on spherical coupling of light energy for inner-dimension measurement of microstructures with high aspect ratios

An optical fiber probe, based on spherical coupling of light energy, is proposed to transform the lateral displacement of a spherical coupler into the deflection of a light energy center, while the light energy is transmitted in the reverse direction. Therefore, the shadowing effect of a microcavity can be eliminated. The probe has a high displacement sensitivity, allowing precision inner-dimension measurements of microstructures with high aspect ratios. Measurements of microholes and fuel injection nozzles indicate that, for a microstructure with an aspect ratio of up to 15:1, a probing force <1 μN, a resolution of up to 0.05 μm can be achieved using the proposed probe, which is easy to exchange and low cost.     

Ultrathin side-viewing needle probe for optical coherence tomography

We present the smallest reported side-viewing needle probe for optical coherence tomography (OCT). Design, fabrication, optical characterization, and initial application of a 30-gauge (outer diameter 0.31 mm) needle probe are demonstrated. Extreme miniaturization is achieved by using a simple all-fiber probe design incorporating an angle-polished and reflection-coated fiber-tip beam deflector. When inserted into biological tissue, aqueous interstitial fluids reduce the probe's inherent astigmatism ratio to 1.8, resulting in a working distance of 300 μm and a depth-of-field of 550 μm with beam diameters below 30 μm. The needle probe was interfaced with an 840 nm spectral-domain OCT system and the measured sensitivity was shown to be only 7 dB lower than that of a comparable galvo-scanning sample arm configuration. 3D OCT images of lamb lungs were acquired over a depth range of ~600 μm, showing individual alveoli and bronchioles.     

Real-space observation of nanojet-induced modes in a chain of microspheres

The three-dimensional real-space observation of photonic nanojet-induced modes in a chain of microspheres with different diameters is reported. The optical transmission properties of a chain of microspheres are studied by using high resolution finite-difference time-domain calculation. The photonic nanojet-induced modes in different chains of microspheres are measured by using a scanning optical microscope system with an optical-fiber probe. We observe the photonic nanojet-induced modes from optical microscope images for chains of 3 μm, 5 μm, and 8 μm microspheres deposited on a patterned silicon substrate. The incident beam can be periodically reproduced in chains of dielectric microspheres giving rise to lossless periodically optical focusing with period of two diameters. Detailed theoretical and experimental data on the transmission, scattering loss, and field-of-view are presented. This waveguide technique can be used in biomedical microscopy, ultra-precise laser process, microfluidics, and nanophotonic circuits.     

Some studies of BF2 and B+F implanted Silicon

Ion-implanted shallow junctions have been investigated using BE₂ (molecular ions) by the anodic oxidation method coupled with a four-point probe technique. BF₂ ions were implanted through screen oxide at doses of 3–5 × 10¹⁵ ions/cm² and energies of 25 and 45 keV which is equivalent to 5.6 keV and 10 keV of boron ions. The effect of energy, dose and annealing temperature on shallow junctions is presented in this paper. The shallow junctions in the range of 0.19 μm to 0.47 μm were fabricated.

The effect of fluorine on sheet resistivity of boron implanted silicon at various doses, treated with two-step and three-step annealing, is also presented for comparison in the paper.     

Parallel-plate RF resonator imaging of chemical shift resolved capillary flow

Magnetic resonance imaging has been introduced to study flow in microchannels using pure phase spatial encoding with a microfabricated parallel-plate nuclear magnetic resonance (NMR) probe. The NMR probe and pure phase spatial encoding enhance the sensitivity and resolution of the measurement. In this paper, ¹H NMR spectra and images were acquired at 100 MHz. The B₁ magnetic field is homogeneous and the signal-to-noise ratio of 30 μl doped water for a single scan is 8×10⁴. The high sensitivity of the probe enables velocity mapping of the fluids in the micro-channel with a spatial resolution of 13×13 μm. The parallel-plate probe with pure phase encoding permits the acquisition of NMR spectra; therefore, chemical shift resolved velocity mapping was also undertaken. Results are presented which show separate velocity maps for water and methanol flowing through a straight circular micro-channel. Finally, future performance of these techniques for the study of microfluidics is extrapolated and discussed.     

超小自聚焦光纤探头研究用场追迹数值模拟技术

研究场追迹数值模拟技术在超小自聚焦光纤探头设计与分析中的应用方法.首先,论述场追迹的概念及其基本原理;其次,论述场追迹在VirtualLab软件中的实现方法;最后,研究超小自聚焦光纤探头在基于场追迹的物理光学软件VirtualLab中的建模与分析方法,并进行仿真结果与实验结果的比较分析.结果显示,如设无芯光纤的长度为0.36 mm,自聚焦光纤透镜的长度分别为0.10,0.11和0.12 mm,计算所得的工作距离分别为0.75,0.63和0.51 mm,光斑尺寸分别为32,24和19 μm.理论计算结果与实验结果符合,表明基于场追迹的数值模拟技术是研究超小自聚焦光纤探头设计与分析方法的一个有效手段.     

Calculation of 3 μm probe transmission in p-Ge excited by a CO2 laser

We present a theory to describe the enhanced transmission of a weak tunable probe laser with a wavelength near 3 μm in the presence of a high-intensity saturating beam with a wavelength near 10 μm. The mechanism responsible for the increased transmission is the depletion of holes in the heavy-hole band by the saturating beam.     

Noise from small air jets and a quiet valve

Noise measurements of air jets of from 0·0794 to 0·635 cm diameter, with jet exit velocity varying from 54 to 244 m/s, to frequencies of 100 kHz are presented. Results are compared to those previously obtained for larger nozzles; acoustical power spectral density curves are found to be similar to those for the larger nozzles at like velocities. Results of a noise survey conducted near a 0·127 m line size quiet vent valve having approximately 20 000 square jets, 0·127 cm on a side are presented and found to agree with the laboratory nozzle noise data. Noise above a jet velocity of 120 m/s was found to be quadrupole in nature, while below this velocity dipole surface sound was observed; this surface noise is the noise of quiet valves, which operate at low velocities. It is estimated that a quiet valve jet of 0·025 cm diameter, with a velocity near 60 m/s will exhibit a peak acoustical power spectral density at frequencies beyond the range of human audibility.     

Langmuir Probe Diagnostics of a Low Temperature Non-Isothermal Plasma in a Weak Magnetic Field

This article presents measurements by a cylindrical Langmuir probe in the plasma of a DC cylindrical magnetron discharge át the pressure 1.5 Pa that aim at the experimental assessment of the influence of a weak magnetic field to the estimation of the electron density when using conventional methods of probe data interpretation. The probe data was obtained under the presence of a weak magnetic field in the range 1.10^?2?5.10^?2 T. The influence of the magnetic field on the electron probe current is experimentally assessed for two cylindrical probes with different radii, 50 μm and 21 μm. This assessment is based on comparison of the values of the electron density estimated from the electron current part with the values of the positive ion density estimated from the positive ion current part of the probe characteristic respectively by assuming that at the magnetic field strengths used in the present study the probe positive ion currents are possible to be assumed as uninfluenced by the magnetic field. For interpretation of the probe positive ion current two theories are used and compared to each other: the radial motion model by Allen, Boyd and Reynolds [10] and Chen [11] and the model that accounts for the collisions of positive ions with neutrals in the probe space charge sheath that we call Chen-Talbot model [8]. At lower magnetic field 3 · 10^?2 T the positive ion density values interpreted by using the Chen-Talbot model [8] are in better agreement with the values of electron density compared to those obtained by using the theory [10,11]; therefore the model [8] is used for calculation of the positive ion density from the probe data at higher magnetic fields. The comparison of the positive ion and electron density values calculated from the same probe data at higher magnetic fields shows that up to the magnetic field strength 4 . 10^?2 T with the probe 100 μm and up to 5 . 10^?2 T with the probe 42 μm in diameter respectively the decrease of the magnitude of the electron current at the space potential due to the magnetic field does not exceed the error limits that are usual for Langmuir probe measurements (absolute error ±20%).     

Efficiency of applying ammonium oxalate for protection of monumental limestone by poultice, immersion and brushing methods

Samples of cretaceous limestone have been treated with three application methods (poultice, immersion and brushing) using different concentrations of ammonium oxalate solution (AmOx) and varying treatment time in order to test the efficiency of surface and in-depth formation of a protective layer of calcium oxalate (CaOx). Synchrotron-based microanalytical techniques (SR-μXRD with 12.5 μm×7.5 μm (H×V) probe size, SR-μFTIR with 10 μm×10 μm and 8 μm×20 μm probe sizes) and laboratory μFTIR, XRD and SEM have been employed for analysis of the treated samples. Synchrotron-based techniques showed variations in the CaOx distribution along the surface on a micrometer scale. All treatments resulted in the development of a CaOx layer with a maximum thickness of approximately 40 μm. Application by the brushing method with 10 1-min applications with 5-min breaks during one hour showed a development of the calcium oxalate layer equivalent to the poultice treatment taking 10 h. This treatment could be preferred for large marble or limestone surfaces where poultice usage is economically not feasible.     

Application of a polarized neutron microbeam to the investigation of a magnetic microstructure

The application of a neutron microbeam to the investigation of an internal magnetic microstructure has been demonstrated experimentally. The object of investigation is an amorphous magnetic wire 190 μm in diameter, with the axial and circular magnetic domains formed inside it. A narrow neutron microbeam with a width of 2.6 μm, which is formed by a three-layer film (a planar waveguide) serves as the probe for scanning with a high spatial resolution. The method of investigation is the neutron spin precession upon transmission through the sample.     

Numerical simulation of a gradient-index fibre probe and its properties of light propagation

In order to verify the properties of the light propagating through a gradient-index (GRIN) fibre probe for optical coherence tomography (OCT), numerical simulation using the optical software GLAD is carried out. Firstly, the model of the GRIN fibre probe is presented, which is consisted of a single mode fibre (SMF), a no-core fibre (NCF), a GRIN fibre lens and an air path. Then, the software GLAD is adopted to numerically investigate how the lengths of the NCF and the GRIN fibre lens influence the performance of the Gaussian beam focusing through the GRIN fibre probe. The simulation results are well consistent with the experimental ones, showing that the GLAD based numerical simulation technique is an intuitive and effective tool for the verification of the properties of the light propagation. In this paper, we find that on the conditions of a constant GRIN fibre lens length of 0.1 mm and an NCF length of 0.36 mm, the working distance of the probe will be 0.75 mm and the focus spot size is 32 μm.     

Combining transmission geometry laser ablation and a noncontact continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging

This paper describes the coupling of ambient pressure transmission geometry laser ablation with a liquid-phase sample collection into a continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging. The flow probe/emitter device was placed in close proximity to the surface to collect the sample plume produced by laser ablation. The sample collected was immediately aspirated into the probe and onto the electrospray emitter, ionized and detected with the mass spectrometer. Freehand drawn ink lines and letters and an inked fingerprint on microscope slides were analyzed. The circular laser ablation area was about 210 μm in diameter and under the conditions used in these experiments the spatial resolution, as determined by the size of the surface features distinguished in the chemical images, was about 100 μm.     

Simultaneous Measurement of Particle Size and Particle Velocity by the Spatial Filtering Technique

The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity.     

Experiments on the space and wavelength dependence of speckle

A comprehensive series of speckle experiments is described for opal glass diffusers ranging in thickness from 10 to 500 μm. Wavelength decorrelation measurements are made using a cw dye laser source; and accurate square-law detection is provided by the use of an optic-fiber, photomultiplier combination rather than film. For this diffuser set intensity distribution functions, polarized and unpolarized, are plotted. Second-order correlation functions are presented for different apertures, relating diffuser motion and probe motion. Remote texture determination using contrast ratio and frequency decorrelation is illustrated.     

Fiber-optic Fourier-domain common-path OCT

We experimentally and theoretically investigated the performance of a fiber-optic based Fourier-domain common-path optical coherence tomography （OCT）. The fiber-optic common-path OCT operated at the 840-nm center wavelength. The resolution of the system was 8.8 μm （in air） and the working depth using a bare fiber probe was approximately 1.5 mm. The signal-to-noise ratio （SNR） of the system was analyzed. OCT images obtained by the system were also presented.     

Rapid in-process measurement of surface roughness using adaptive optics

We present an in-process measurement of surface roughness by combining an optical probe of laser-scattering phenomena and adaptive optics for aberration correction. Measurement results of five steel samples with a roughness ranging from 0.2 to 3.125 μm demonstrate excellent correlation between the peak power and average roughness with a correlation coefficient (R(2)) of 0.9967. The proposed adaptive-optics-assisted system is in good agreement with the stylus method, and error values of less than 8.7% are obtained for average sample roughness in the range of 0.265 to 1.119 μm. The proposed system can be used as a rapid in-process roughness monitor/estimator to further increase the precision and stability of manufacturing processes in situ.     

Light Absorption Induced in Undoped-Silica-Core Panda-Type Birefringent Optical Fiber by Pulsed Action of Ionizing Radiation

The evolution of radiation-induced absorption (RIA) of light at λ = 1.55 μmis compared after pulsed action of ionizing radiation at different probe light power in an undoped-silica-core Panda-type birefringent optical fiber and in an isotropic optical fiber drawn from the same preform before embedding the stress-applying rods.High efficiency of RIA photobleaching by the probe light at λ = 1.55 μm is revealed in the birefringent fiber.