In-situ optical emission spectroscopy of laser-induced vanadium oxide plasma in vacuum

This study aims to analyze the elemental composition, and temporal- and spatial distributions of vanadium atoms and ions in the laser-induced vanadium oxide plasma under high vacuum using optical emission spectroscopy. Neutral atoms and singly charged V ions were detected under high vacuum in the emission spectra. The mean translational velocity of neutral V atoms in their first 25 mm propagation was estimated to be 15.7 km/s using the temporal- and spatial dynamics investigation of neutral V species in the plasma.     

离焦量对空气中YAG激光诱导Cu等离子体空间特性的影响

利用Nd:YAG脉冲激光在空气中烧蚀Cu靶,产生激光等离子体羽,通过改变离焦量获得相应的等离子体的空间谱;用光谱学方法分析了三种离焦量下空间谱线结构和空间等离子体的电子温度演化规律;并对等离子体光谱的特性和产生机制进行了讨论.结果表明:离焦量对等离子体的谱线强度、谱线结构、电子温度的空间特性都有影响,特征谱强度最大值出现在空间位置1.0mm附近,离焦量为-2mm时电子温度最高.     

Mid-infrared laser-induced superheating of water and its quantification by an optical temperature probe

Free-running thulium laser pulses (Cr:Tm:YAG, lambda = 2.01 microm, tp = 300 micros) were applied to a purified, degassed water sample and the resulting temperature rise was investigated by an optical temperature probe. The probe detected water reflectance index changes with temperature and also the onset of vaporization, which was found to occur in a superheat regime, at approximately 230 degrees C. The experimental data were compared with theoretical temperature calculations, and deviations of less than 20 degrees C were stated. The best agreement between theory and experiment was found for temperatures below 180 degrees C, defining by this the method's high accuracy limit. In conclusion, both the optical temperature probe and the presented calculations can help to improve dosimetry in pulsed IR laser applications by precise temperature measurement and prediction.     

Plasma-particle interactions in a laser-induced plasma: implications for laser-induced breakdown spectroscopy

The interaction between laser-induced plasmas and individual particles controls the rate of particle dissociation and subsequent atomic diffusion and emission processes, with implications for single-particle spectroscopy, as well as materials synthesis and other plasma sources. It is demonstrated through quantitative plasma imaging studies that discrete particles dissociate on a time scale of tens of microseconds within plasmas formed by 300-mJ Nd:YAG laser pulses. Significant spatial nonhomogeneity, as measured by localized atomic emission from particle-derived calcium atoms, persists on a comparable time scale, providing a measure of their average atomic diffusion rate of 0.04 m(2)/s. In addition, the resulting calcium atomic emission is explored using image analysis as well as traditional spectroscopic analysis.     

Optical aberrations of intraocular lenses measured in vivo and in vitro

Corneal and ocular aberrations were measured in a group of eyes before and after cataract surgery with spherical intraocular lens (IOL) implantation by use of well-tested techniques developed in our laboratory. By subtraction of corneal from total aberration maps, we also estimated the optical quality of the intraocular lens in vivo. We found that aberrations in pseudophakic eyes are not significantly different from aberrations in eyes before cataract surgery or from previously reported aberrations in healthy eyes of the same age. However, aberrations in pseudophakic eyes are significantly higher than in young eyes. We found a slight increase of corneal aberrations after surgery. The aberrations of the IOL and the lack of balance of the corneal spherical aberrations by the spherical aberrations of the intraocular lens also degraded the optical quality in pseudophakic eyes. We also measured the aberrations of the IOL in vitro, using an eye cell model, and simulated the aberrations of the IOL on the basis of the IOL's physical parameters. We found a good agreement among in vivo, in vitro, and simulated measures of spherical aberration: Unlike the spherical aberration of the young crystalline lens, which tends to be negative, the spherical aberration of the IOL is positive and increases with lens power. Computer simulations and in vitro measurements show that tilts and decentrations might be contributors to the increased third-order aberrations in vivo in comparison with in vitro measurements.     

Detection of lead in water using laser-induced breakdown spectroscopy and laser-induced fluorescence

Laser-induced breakdown spectroscopy (LIBS) is a well-known technique for fast, stand-off, and nondestructive analysis of the elemental composition of a sample. We have been investigating micro-LIBS for the past few years and demonstrating its application to microanalysis of surfaces. Recently, we have integrated micro-LIBS with laser-induced fluorescence (LIF), and this combination, laser ablation laser-induced fluorescence (LA-LIF), allows one to achieve much higher sensitivity than traditional LIBS. In this study, we use a 170 microJ laser pulse to ablate a liquid sample in order to measure the lead content. The plasma created was re-excited by a 10 microJ laser pulse tuned to one of the lead resonant lines. Upon optimization, the 3sigma limit of detection was found to be 35 +/- 7 ppb, which is close to the EPA standard for the level of lead allowed in drinking water.     

Study of hydrogen and deuterium emission characteristics in laser-induced low-pressure helium plasma for the suppression of surface water contamination

An experimental study was conducted in search of the experimental condition required for the much needed suppression of spectral interference caused by surface water in hydrogen analysis using laser-induced low-pressure helium plasma spectroscopy. The problem arising from the difficulty in distinguishing hydrogen emission from hydrogen impurity inside the sample and that coming from the water molecules was overcome by taking advantage of similar emission characteristics shared by hydrogen and deuterium demonstrated in this experiment by the distinct time-dependent and pressure-dependent variations of the D and H emission intensities from the D-doped zircaloy-4 samples. This similarity allows the study of H impurity emission in terms of D emission from the D-doped samples and thereby separating it from the H emission originating from the water molecules. Employing this strategy has allowed us to achieve the large suppression of water induced spectral interference from the previous minimum of 400 microg/g to the current value of 30 microg/g when a laser beam of 34 mJ under tight focusing condition was employed. Along with this favorable result, this experimental condition has also provided a much better (about 6-fold higher) spatial resolution, although these results were achieved at the expense of reducing the linear calibration range from the previous 4 300 microg/g to the present 200 microg/g.     

Influence of the laser pulse duration on spectrochemical analysis of solids by laser-induced plasma spectroscopy

Quantitative analysis of aluminum and copper alloys by means of laser-induced plasma spectroscopy (LIPS) has been investigated for three representative laser pulse durations (80 fs, 2 ps, and 270 ps). The experiments were carried out in air at atmospheric pressure with a constant energy density of 20 J/cm2. Because the decay rate of the spectral emission depends on the laser pulse duration, the optimum detection requires an optimization of the temporal gating acquisition parameters. LIPS calibration (sensitivity and nonlinearity) and the limit of detection (LOD) are discussed in detail. While the LOD of minor elements embedded in alloy samples obtained by sub-picosecond or sub-nanosecond laser pulses are both time and element dependent, provided an appropriate temporal window is chosen, the optimum LODs (several parts per million (ppm)) prove to be independent of the laser pulse duration. Finally, it is found that for elements such as those detected here, gated LIPS spectra using picosecond or sub-picosecond laser pulses provide much better LOD values than non-gated spectra.     

Ultrasensitive liquid refractometer based on a Mach-Zehnder micro-cavity in optical fibre fabricated by femtosecond laser-induced water breakdown

Abstract

A Mach–Zehnder (MZ) micro-cavity with two symmetric openings in single mode fibre (SMF) was fabricated by femtosecond laser-induced water breakdown. The micro-cavity is rightly across half of the fibre core, and the opening size of the micro-cavity is 10 μm × 100 μm. The micro-cavity and the remaining half of the fibre core constitute two arms of the Mach–Zehnder interferometer (MZI). The MZI with micro-cavity immerged in water shows perfect interference spectrum due to the regular shape and smooth internal surface of the micro-cavity. The insertion loss is only –8 dB and the contrast of one MZI peak reaches more than 40 dB. The MZI with micro-cavity in SMF can be used as an ultrasensitive liquid refractometer as its ultrahigh refractive index (RI) sensitivity (14296.98 nm/RIU), high RI resolution (1 × 10^?5 RIU), good linearity (99.62%) and low temperature crosstalk (0.04 nm/°C).     

Fourth-order optical aberrations and phase-space transformation for reflection and diffraction optics

One can derive fourth-order optical ray deviations for a mirror or grating from the optical path function by using the analytical code REDUCE. Some of the aberrations are discussed for normal-incidence and grazing-incidence monochromators. The nonlinear transformation of light from the source to the image plane of a mirror or grating is represented by a transformation matrix. The optical properties of a combination of several optical elements are given by the product of the matrices of the individual optical elements. The matrix elements can be interpreted as optical aberrations. A program has been written that optimizes a complete beam line with respect to various optical aberrations by minimizing an appropriate cost function that is built from a weighted sum of the matrix elements.     

Conditions for correction of linear and quadratic field-dependent aberrations in plane-symmetric optical systems

The Abbe sine condition and the recently developed pupil astigmatism conditions provide a powerful set of relationships for describing imaging systems that are free from aberrations that have linear and quadratic dependence on field, to all orders in the pupil. We have proved both of these conditions and applied them to axisymmetric imaging systems. We now extend our approach to plane-symmetric systems. Still using Hamilton's characteristic functions, we derive the general sine conditions and the pupil astigmatism conditions that describe plane-symmetric systems that are free of all aberrations with linear and quadratic field dependence.     

Miniature endoscope for simultaneous optical coherence tomography and laser-induced fluorescence measurement

We have designed a multimodality system that combines optical coherence tomography (OCT) and laser-induced fluorescence (LIF) in a 2.0-mm-diameter endoscopic package. OCT provides approximately 18-microm resolution cross-sectional structural information over a 6-mm field. LIF spectra are collected sequentially at submillimeter resolution across the same field and provide histochemical information about the tissue. We present the use of a rod prism to reduce the asymmetry in the OCT beam caused by a cylindrical window. The endoscope has been applied to investigate mouse colon cancer in vivo.     

Acoustic characterization of microbubble dynamics in laser-induced optical breakdown

A real-time acoustic technique to characterize microbubbles produced by laser-induced optical breakdown (LIOB) in water was developed. Femtosecond laser pulses are focused just inside the surface of a small liquid tank. A tightly focused, high frequency, single-element ultrasonic transducer is positioned so its focus coincides axially and laterally with this laser focus. When optical breakdown occurs, a bubble forms and a pressure wave is emitted (i.e., acoustic emission). In addition to this acoustic signal, the microbubble is actively probed with pulse-echo measurements from the same transducer. After the bubble forms, received pulse-echo signals have an extra pulse, describing the bubble location and providing a measure of axial bubble size. Wavefield plots of successive recordings illustrate the generation, growth, and collapse of cavitation bubbles due to optical breakdown. These same plots also can be used to quantify LIOB thresholds.     

High-precision methods and devices for in situ measurements of thermally induced aberrations in optical elements

An optical system that comprises two devices for remote measurements, a broadband optical interferometer and a scanning Hartmann sensor, is described. The results of simultaneous measurements with both devices and the results of numerical modeling of sample surface heating are presented.     

Two-beam interferometer for measuring aberrations of optical components with axial symmetry

We present a concept of interferometric testing, believed to be novel, that can be applied to measuring aberrations of optical components that have rotational symmetry. The optical configuration uses two coherent, collimated wave fronts that are tilted to impinge upon the optical component being tested such that one beam is on axis and the other is off axis. For small tilt angles the two aberrated wave fronts can be considered to be carrying the same aberrations. Furthermore, the off-axis beam is displaced along a direction orthogonal to the optical axis of the component. Interference between the two aberrated wave fronts produces a fringe pattern that is similar to a lateral shear interference pattern. Moiré fringes are obtained by spatial beating of the interference pattern with a CCD TV camera array. Under such conditions it is possible to subtract most of the linear carrier that is intrinsically present in the resultant fringe pattern owing to the large defocus aberration and tilt.     

Influence of Mn impurity on formation of secondary phases and optical properties of ZnO NPs

ZnO:Mn nanoparticles with various Mn concentrations (1–7%) were synthesized by a simple chemical method at low temperature. Structural and optical properties of as synthesized samples were investigated by X-ray diffraction (XRD), UV–vis absorbance, and photoluminescence (PL) spectrophotometers, respectively. XRD patterns of the ZnO:Mn nanocrystals indicate that in low Mn concentrations (1 and 3%), the ZnMn₂O₄ nanoparticles are formed, whereas in high Mn concentrations (5 and 7%), more Mn atoms replace Zn atoms in crystalline lattice, so that Mn₃O₄ is formed. It is also found that the size of the ZnO:Mn nanocrystals increases from 7.82 to 76.07?nm with increasing Mn concentration from 1 to 7%. Band gap energy of the samples, calculated by extrapolation of (αhν)² versus hν curves, shows a decrease in band gap with increasing the Mn concentration from 1 to 7%. The size of nanoparticles calculated by effective mass approximation model is nearly in accordance with the one calculated by Scherrer formula. The PL spectra of low Mn concentration ZnO:Mn nanoparticles indicate a weak green emission which vanishes in highly Mn concentrated ZnO:Mn samples.     

Influence of cell shape and aggregate formation on the optical properties of flowing whole blood

We studied the influence of shape and secondary, or intercellular, organization on the absorption and scattering properties of red blood cells to determine whether these properties are of any practical significance for optical evaluation of whole blood and its constituents. A series of measurements of transmittance and reflectance of light from bovine blood in a flow cuvette was conducted with a 650-900-nm integrating sphere at shear rates of 0-1600 s(-1), from which the influence of cell orientation, elongation, and aggregate formation on the absorption (mu(a)) and the reduced scattering (mu(s)') coefficients could be quantified. Aggregation was accompanied by a decrease of 4% in mu(s)' compared with the value in randomly oriented single cells. Increasing the degree of cell alignment and elongation as a result of increasing shear rate reduced mu(s)' by 6% and mu(a) by 3%, evaluated at a shear rate of 1600 s(-1). Comparison with T-matrix computations for oblate- and prolate-shaped cells with corresponding elongation and orientation indicates that the optical properties of whole blood are determined by those of its individual cells, though influenced by a collective scattering factor that depends on the cell-to-cell organization. We demonstrate that cell morphological changes must be taken into consideration when one is conducting whole blood spectroscopy.     

Biocatalytically induced formation of cupric ferrocyanide nanoparticles and their application for electrochemical and optical biosensing of glucose

The enzymatically controlled growth of cupric ferrocyanide nanoparticles in the presence of glucose oxidase, its ferricyanide electron acceptor, and copper ions is described. The biocatalytically stimulated growth of these nanoparticles on the surface of carbon-paste electrodes results in an amplified electrochemical detection of the glucose substrate. This concept can readily be expanded for monitoring a wide range of biocatalytic processes involving the ferricyanide electron acceptor.     

DNA-assisted binding of microspheres on glass substrates and their laser-induced release

DNA hybridization has been increasingly adopted in materials sciences due to its complementary nature of single stranded DNAs. This unique property could be potentially used in the realization of 2 dimensional (2D) arrays of colloidal microspheres as a precursor to further build more complicated superstructures. In order to precisely understand this DNA-assisted assembly of colloidal particles, we quantitatively assessed the surface density of grafted and hybridizing accessible DNA oligomers on both substrate and colloidal particles. The DNA grafting densities were determined by UV–Vis of dye-functionalized complementary DNA oligomers, in conjunction with theoretical models. The variations of the concentration of hybridized DNA as a function of parameters such as the number of DNA base pairs (bp), the length of spacer and the size of sphere were also investigated to determine the immobilization strength of colloidal microspheres on the substrate. Dehybridization of the particle was conducted by utilizing a focused laser beam. These results were also compared with the particle hybridization energies and modeled according to the sum of DNA bindings as a function of the number of hybridized bases.