Deflection Signal Research Articles

Determination of the laser-induced damage threshold of bulk polymer samples at 1.06 mu m using the pulsed photothermal deflection technique

A pulsed Nd-YAG laser beam is used to produce a transient refractive index gradient in air adjoining the plane surface of the sample material. This refractive index gradient is probed by a continuous He-Ne laser beam propagating parallel to the sample surface. The observed deflection signals produced by the probe beam exhibit drastic variations when the pump laser energy density crosses the damage threshold for the sample. The measurements are used to estimate the damage threshold for a few polymer samples. The present values are found to be in good agreement with those determined by other methods.

Phase signal of optical beam deflection from single microparticles: Theory and experiment

The optical beam deflection (OBD) signal from a single microparticulate sample was theoretically derived for the photothermal response to an intensity-modulated excitation in the transverse experimental configuration. The dependencies of phase signal on the normal and transverse offsets of the probe beam were calculated and then experimentally verified. The OBD phase signal was chosen as a means of inspecting the particle interior, since it contains information about the heat source depth. The results showed that the phase signal was independent of the excitation beam power and that the surface absorbing layer thickness could be estimated from the phase variation using the modulation frequency. The possibility of correcting beam offsets by the phase signal was also considered.

The Ion Exchange Mechanism of Polypyrrole in Propylene Carbonate and Dimethylsulfite Based Electrolytes: An In Situ Probe Beam Deflection Study

In situ probe beam deflection (PBD) along with cyclic voltammograms have been used to monitor the ion exchange between polymer film and bulk electrolyte during the redox reactions of polypyrrole (PPy) in propylene carbonate (PC) and dimethylsulfite (DMSU) based electrolytes containing . During the reversible oxidation and reduction of PPy in PC, the PBD results confirmed that anion exchange takes place in the faradaic as well as in the pseudocapacitive part of the cyclic voltammogram. In the potential region where significant irreversible changes occur , the negative sign of the beam deflection signal during the positive scan shows expulsion of species; previous in situ Fourier transform infrared spectroscopic (FTIRS) results showed expulsion of anion‐containing species from the polymer. In DMSU based electrolyte, however, Li+ insertion/expulsion takes place during the reversible cycling of polypyrrole in the potential interval from 2.0 to 4.0 V vs. Li/Li+. In the latter electrolyte, up to one electron per pyrrole ring can be transferred reversibly which leads to a charge density of about 160 Ah/kg.

Photoelectrochemical processes at an n-type CdS: I single-crystal electrode as studied by photothermal laser beam deflection: Energy conversion efficiencies and Peltier heats

An expression is given for the potential dependence of the photothermal laser beam deflection signal (PDS) at a periodically illuminated n-type semiconductor electrode in a redox electrolyte solution. The expression can be used to obtain the maximal efficiencies of conversion of absorbed monochromatic optical energy to chemical or electrical energy ( n e m and L G m referring to the heat of reaction and to the Gibbs energy respectively for the hydrogen-producing photoelectrolysis mode, and light to electrical power conversion efficiency L G m for regenerative systems), the Peltier heat Q PE,e at the semiconductor-electrolyte junction and the internal quantum efficiency n a s of the photocurrent. Values of these quantities have been determined for oxidation of sulfite ( n e m = 0.21 and L G m = 0.12 for photoelectrolysis, n a s = 0.88 and Q PE,e, = -0.35 eV) and polysulfide ( n e m = 0.04, n a s = 0.74, Q PE,e = 0.13 eV and L G m = 0.07 for light to electrical power conversion) at the (0001) face of an approx. 3 mm 3 iodine-doped n-CdS single-crystal photoanode at 488 nm. The Peltier heat at the n-CdS-metal (In + Ga, Cu) contact was estimated as approx. 0.1 eV. The attempt to determine efficiency data by PDS for photoanodic oxidation of hexacyanoferrate(II) failed because of photocorrosion of the electrode. Results are discussed and compared with data from related photothermal studies employing various front- and back-surface techniques.

Determination of the position or speed of an object using pulsed laser photoacoustic beam deflection

We demonstrate here a method of measuring the position or speed of an object using photoacoustic beam deflection. Two laser beams are utilized: a pulsed one focused normally on the object and a continuous one parallel to the surface of the object. An acoustic wave generated by the pulsed laser is launched from the surface of the object and propagates through the air to the other beam where it deflects the beam. This deflection is measured by a position sensitive detector. The time-of-flight of the acoustic wave is determined from the zero crossing of the beam deflection signal. Multiplying this by the speed of sound gives the distance of the object from the probe beam.

Influence of carrier recombination on the pulsed photothermal beam deflection signal in semiconductors

The effect of carrier recombination on the thermal response of pulsed photothermal beam deflection (PBD) signal in Si is analyzed theoretically and experimentally. This effect appears in the form of small depression in PBD - signal time dependence at a depths closer to the thermal diffusion length. The carrier lifetime value is found to be evaluated from this depression time position.

Broadband ultrasonic absorption measurements using optical beam deflection.

Optical beam deflection method is used for real-time measurements of ultrasonic absorp tionin the frequency range 3 to 40 MHz in liquids. A laser beam is deflected by broad bandultrasonic pulse excited with a 1 MHz-quartz transducer, and the deflection signal is spectral analyzed. The dependence of the spectrum on sound-propagation distance gives absorption coefficients at several harmonic frequencies of the quartz. Absorp tionspectrum is obtained in benzene, o-xylene and carbon disulfide.

ミラージュ法及びＳＴＭによる銀上の鉛のＵＰＤ現象のＩｎ Ｓｉｔｕ検出

A study was carried out using photothermal deflection spectroscopy (PDS)-also known as the Mirage method-to detect underpotential deposition (UPD) of lead on silver. A laser beam for activation was first passed through a liquid electrolyte to be absorbed at the solid/liquid interface. The laser probe grazed the surface of the solid and was deflected by the gradient in the liquid, so that absorbed light heated the electrode surface causing a gradient in the refractive index of the liquid. Beam deflection was detected by a position sensitive detector as a photothermal deflection (PD) signal. The silver electrodes used were polycrystal, single crystal (111) and single crystal (100). For the (111) surface a very sharp UPD peak appeared in the current-potential curve and the corresponding PD signal also showed relatively abrupt changes. For the (100) surface, on the other hand the PD signal showed a two-step change and decay was relatively gentle.UPD was also investigated by electrochemical scanning tunneling microscopy, yielding in situ STM images of the electrode surface in the solution. After UPD, the surface stepline of the STM images changed slightly and the height of the steps decreased. In addition corrugations appeared on the surface.

Multishot ablation of polymer and metal films at 248 nm

The photoacoustic mirage effect technique was utilized to investigate excimer laser ablation of thin polymer (photoresist) and metal films. Layered systems, consisting of a photoresist-metal-SiO 2 structure, were ablated by KrF (λ = 248 nm) laser radiation at fluences up to 2 J/cm 2. For the photoresist layer a linear dependence of the deflection amplitude on the etch rate was found in the low fluence regime (≤ 0.7 J/cm 2). Significant changes in the deflection signal occured when the ablation passed the interface between subsequent layers. This effect can be used to distinguish between different layers. Therefore, shock wave monitoring in principle offers the possibility for an in situ control of laser thin film processing. Selective ablation of metal films from the SiO 2 layer is limited to fluences below 2 J/cm 2.

Photothermal beam deflection study of energy transfer from excited triplet states in fluid solution

Photothermal beam deflection spectroscopy was used to follow the decay of the lowest excited triplet state of benzophenone including energy transfer to biphenyl. Because of the simple step function time response of the beam deflection signal, we were able to extract two exponential functions from the heat accumulation waveform. From the results, we obtained a triplet—triplet energy transfer rate from benzophenone to biphenyl of k q = (4.6 ± 0.8) × 10 8 M −1 s −1. The triplet energy of biphenyl was also extracted from the results: E AT = 67 ± 0.5 kcal mol −1. From an analysis of the calorimetric amplitudes, we report the first photothermal observation of an endothermic energy transfer process from the triplet excited state of biphenyl to ground state benzophenone.

Laser-beam deflection measurements and modeling of pulsed laser ablation rate and near-surface plume densities in vacuum

Quantitative measurements of ablated material from the surface of polyethyleneterephthalate (PET) by 248-nm excimer laser fluences up to 10 J/cm2 are performed by HeNe laser-beam deflection in vacuum and by photoacoustic depth profiling in air. HeNe laser-beam deflection measures the density of gas phase material present in the ablation plume. Photoacoustic depth profiling is a nonintrusive diagnostic that directly measures the etch depths from laser ablation. A hydrodynamic model consisting of a centered rarefaction wave that reflects off the PET surface is shown to describe the laser deflection signals. From these measurements an estimate of the initial temperature of the ablated species is found.

Theory of optical beam deflection for single microparticles

A theory was developed for the optical beam deflection (OBD) signal generated from a single microparticle. From the thermal-diffusion equations, the temperature fields inside and outside the microparticle, which has a two-layer structure, was deduced. A three-dimensional theoretical treatment was established for the deflection signal of the probe beam passing through the temperature field formed by photothermal conversion of the excitation beam energy absorbed by the sample. The proprieties of the theoretical model and its results were confirmed by comparing the theoretical values of the frequency characteristics, probe beam offset dependencies, and particle size dependencies of the OBD signal with the experimental ones for 25–300-μm-radius microparticles. From the theory, the unique particle size dependencies and frequency characteristics of the OBD method for the single microparticle, i.e., higher sensitivity for smaller particles and at high frequencies, were identified as due to the microparticle surface curvature. The optimal experimental conditions in the OBD measurement of the single microparticle were also obtained using theoretical analysis.

Influence of probe absorption in the photothermal deflection technique

The photothermal deflection technique has been used to study thermal nonlinearity in samples of glasses doped with CdSxSe1−x microcrystals. The effect of the influence of probe beam absorption on deflection signal has been investigated from a theoretical point of view. Measurements have been performed showing the possibility of detecting very small changes of the probe beam absorption coefficient produced by the pump intensity.

Detection of superconducting transitions of multi-phase (Bi,Pb)-Sr-Ca-Cu-O ceramics by photothermal deflection technique

Superconducting transitions, believed to correspond to the 2223 phase and the 2212 phases, of high T c multi-phase (Bi,Pb)-Sr-Ca-Cu-O superconductors were observed by the photothermal deflection (PTD) method. The deflection signal Φ was found to change anomalously at transition temperature ranges corresponding to but not exactly equal to those observed by reistance measurements. Using a semi-quantitative analysis of previous theoretical results, and based on our Φ- T data, specific heat jumps are found at relatively well-defined temperatures. Our study indicates that the PDT method is a sensitive way of studying bulk superconductivity properties of ceramics. Improvements to our prototype setup are, however, necessary for higher precision measurements to be made.

Surface Curvature Effect on Optical Beam Deflection Signal from a Single Microparticulate Sample

A three-dimensional theoretical treatment was established for the photothermal deflection signal from a two-layered single microparticulate sample. The proprieties of the analytical results were confirmed by comparing the theoretical values of the frequency characteristics with the experimental ones. This theory suggests that the microparticle surface curvature localizes the temperature field and enhances its gradient, resulting in unique size dependences of sensitivity for the beam deflection signal, i.e. more sensitivity for smaller microparticles.

Single-chip video processing system

A video display processing system has been developed which offers many advantages compared to analog or conventional digital systems. Its system architecture opens digital video processing towards multi-standard and multi-media applications. An advanced CMOS technology allows economic integration of high-quality TV processing on a single chip. Analog video is input to the color decoder module. It performs analog-to-digital conversion followed by all digital multi-standard demodulation and filtering. Output is YUV and synchronized in an orthogonal sampling pattern. In the display processor the processing from YUV to RGB and the digital-to-analog conversion takes place. Both horizontal and vertical deflection signals are provided. A very flexible high-quality interface supports many features and keeps the system open for TV evolution towards new standards (enhanced-definition TV with a ratio of sixteen to nine) or other displays (100 Hz, proscan, or liquid crystal).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mechanistic investigations of redox polymer-coated electrodes using probe-beam deflection and cyclic voltammetry

Optical probe-beam deflection signals, together with cyclic voltammograms, have been used to analyse the electron-transfer process at electrodes coated with [Ru(bpy)2ClPVP]Cl, polyaniline and poly(1-hydroxyphenazine). With this technique it is possible to determine if anions or cations are used as the charge-compensating ions in the electron-transfer process. The electron transfer at [Ru(bpy)2ClPVP]Cl was shown to be accompanied by a simple counter-ion diffusion process. The known electron-transfer mechanism of polyaniline was confirmed and a plausible mechanism for the electron transfer of poly(l-hydroxyphenazine) has been proposed. The additional information (direction of concentration gradients) obtained by a simple probe-beam deflection experiment is extremely useful in the analysis of reaction mechanisms at redox polymer-coated electrodes.

Probe beam deflection investigation of the charge storage reaction in anodic iridium and tungsten oxide films

The electrochromic charge storage reaction in anodic iridium oxide films (AIROF) was investigated in aqueous electrolytes using the probe beam deflection (PBD) technique in combination with cyclic voltammetry. In add electrolyte (1 M HClO 4 for iridium and 1 M H 2SO 4 for tungsten) the sign of the PBD signal shows clearly that protons are ejected from the oxide film into the bulk electrolyte during oxidation. In basic electrolyte (1 M LiOH, 1 M NaOH) OH − ions are consumed during the oxidation reaction in the AIROF. The PBD signal for the main oxidation peak in the cyclic voltammogram was measured for iridium at different pHs. The change in sign of the beam deflection signal, indicative for one or the other reaction, occurs around pH 4 (±0.5). The coloration of the AIROF in acid was monitored by means of photothermal deflection spectroscopy (PDS) and the results are in good agreement with published reflectivity data.

Collinear photothermal deflection spectroscopy with light-scattering samples

An analytical model that incorporates effects of light scattering was developed for dual-beam photothermal deflection spectroscopy. Thermal gradients induced by a modulated excitation beam deflect an optical probe beam which was treated as being of finite dimensions. Mechanisms by which thermal gradients produce refractive index gradients are discussed, with an explicit expression for dn/dT being derived. Experimental studies with suspensions of small latex particles in Nd(3+) solutions demonstrated that the model accurately predicts both the shape of the deflection signal and the attenuation of the signal due to light scattering. The absolute magnitude of the observed signal is approximately predicted by theory.

Optical beam deflection signal from a single microparticle

The optical beam deflection (OBD) method was applied to the measurement of a single microparticle, and the signal from one resin microparticle of 200–600 μm in diameter could be detected. Based on the frequency characteristics and size dependence of the OBD signal, this method was found to be more sensitive for a smaller particle, and more effective than the photoacoustic method. Theoretical considerations showed that these characteristics were attributable to the enhancement of the temperature field gradient due to the curvature of the microparticle.