Probe Beam Deflection Research Articles

Thermal Conductivity of Single Carbon Fibers Using Photothermal Deflection Techniques

AbstractA modification of the transverse photothermal deflection technique is used to determine the thermal diffusivity of high-conductivity carbon fibers. A chopped, cw Ar-ion laser beam is focused to a point on the fiber to cause localized heating of the fiber and the surrounding transparent fluid medium. The fluid medium immediately adjacent to the fiber sample is probed with a weak He-Ne laser that grazes the fiber surface and is deflected by the synchronous thermal lens produced near the fiber surface. The pump laser is stepped along the length of the fiber to produce a photothermal signal that is proportional to the temperature gradient along the length of the fiber. The theory necessary to predict the magnitude and phase of the probe beam deflection as a function of distance along the fiber is derived. This signal can then be analyzed by a simple method to determine the thermal diffusivity of the carbon fiber.

Explosion of a liquid film in contact with a pulse-heated solid surface detected by the probe-beam deflection method

The threshold for explosive vaporization of a liquid layer on an opaque solid surface heated by an ultraviolet excimer pulsed laser is studied by a photoacoustic probe-beam deflection method. The probe beam traverses the liquid in the vicinity of the laser-heated liquid-solid interface. Below the explosion threshold, photoacoustic generation in the solid occurs only through a thermoelastic mechanism, which results mainly in shear waves that do not couple well into the liquid. Above the explosion threshold, photoacoustic pulses in the solid are also produced by explosive recoil, hence producing longitudinal pulses in the solid that couple well into the liquid after reflections. By setting the probe-beam refraction to detect longitudinal pulse echoes coupled back into the liquid, a sensitive detection of the explosive threshold can be established.

Quartz crystal microbalance and probe beam deflection studies of poly(1-hydroxyphenazine) modified electrodes

Quartz crystal microbalance (QCM) and probe beam deflection (PBD) were used to evaluate the exchange of mobile species (ions and solvent) during the redox reaction in poly(1-hydroxyphenazine) in aqueous acidic media. Both techniques indicate clearly two separate ion exchange steps with successive uptake and expulsion of ions and solvent molecules. The PBD and QCM results are consistent with a redox mechanism where protons are inserted in the first reduction step and anions are expelled in the second reduction step. During oxidation the process is inverted. At fast scan rates or potential jump experiments, however, QCM indicates a transient insertion of excess anions in the first oxidation step with a corresponding successive ion pair expulsion. Anion exchange at the more negative potentials involves a counter flux of solvent. Mass balance shows that the water content of the film is higher in its reduced state. The different processes are rationalized on the basis of electron/ion transfer coupled with protonation/deprotonation reactions and a potential pH diagram for the stability domains of the various states of the polymer is suggested.

LASER INTERFERENCE GRATING FOR SURFACE WAVE GENERATION

An optical method for generating and detecting periodic surface acoustic waves is described. The periodic source is created by splitting the beam from a Nd:YAG laser and recombining the beams at a sample surface to form an interference pattern. The periodic surface waves launched from the source are detected optically using either a modified Michelson interferometer or by laser probe beam deflection. In both cases the detection spot is smaller than the ultrasonic wavelength. Rayleigh waves in the 1–20 MHz frequency range can readily be generated and detected on thick aluminium samples (plate thickness greater than the wavelength). It is also possible to generate narrowband Lamb waves in plates which are thin compared to the wavelength, experimental and theoretical waveforms are presented for this case.

Anomalous CW thermal lens behaviour of uranyl ion in aqueous carboxylic acid media

A study of the thermal lens behaviour of the aqueous uranyl (UO 2+ 2) ion has been carried out using a two beam CW mode mismatched thermal lens spectrometer. Uranyl ion in 1 M HClO 4 exhibits normal thermal lens behaviour, however, with addition of carboxylic acids as part of the solute system anomalous behaviour is observed. The thermal lens slowly decays ( t 1 2 ≈ 3 s) to equilibrium and when the pump beam radiation is removed the thermal lens signal is reversed. Probe beam deflection measurements in the beam interaction volume indicate that this is caused by a refractive index gradient reversal. A possible mechanism for this phenomenon is proposed based on endothermic energy transfer and subsequent photodecarboxylation of the carboxylic acid (acetic acid) which removes energy from the centre of the beam interaction volume and this reverses the temperature gradient and hence refractive index gradient.

Electrochemical mass transport studied by probe beam deflection: potential step experiments

The deflection of a probing laser beam aligned parallel to a planar electrode was monitored during potential step experiments. The electrochemical systems investigated were Ag deposition and dissolution on Pt, the Fe(CN)3−/4−6 redox reaction on Pt and the electrochromic charge storage reaction in anodic iridium oxide (AIROF) films. The experimental probe beam deflection (PBD) transients can be simulated using simple models for the concentration profiles developed for mass transport controlled reactions. The results show that different approaches have to be used for mass transport controlled reactions and for reactions limited by a depletion of the reactant or reacting sites. The PBD transients measured for different beam distances allow the determination of the diffusion coefficients of the moving ions. In order to measure the diffusion coefficient of a single ion a supporting electrolyte has to be used. On the basis of the presented examples the relation between cyclic deflectograms and voltammograms is also briefly discussed.

Separation of bound and free carrier contributions to the refractive index change induced in II-VI semiconductors by femtosecond pulses

Time-resolved probe beam deflection and degenerate four-wave mixing (DFWM) have both been used to determine the temporal evolution of the refractive index changes induced in ZnSe and CdS0.75Se0.25 single crystals at T=300 K by lambda =620 nm, 120 fs pulses with irradiances (I) up to 500 GW cm-2. Negative refractive index changes which follow the pump pulse profile are attributed to virtual electronic transitions and two-photon resonances, while two-photon-generated hot carriers and their cooling rate determine the magnitude and temporal evolution of the refractive index change for probe delays up to 4 ps. No further evolution is observed up to 100 ps unless I>30 GW cm-2, in which case the refractive index appears to recover on a 10 ps timescale following carrier relaxation: the possible role of a threshold dependent recombination process in this recovery is discussed.

Stimulated Raman Gain Detected by Photothermal Beam Deflection for Selective Determination of Organic Compounds

The efficiency of the stimulated Raman gain scattering (SRGS) in liquids is sufficiently high to make the phenomenon useful as a means of chemical analysis. Quantitative and qualitative studies of stimulated Raman gain detected by photothermal probe beam deflection are presented with a major simplification in instrumentation for generating the Stokes probe beam. This technique is evaluated for the detection and quantitation of a model chlorinated hydrocarbon, 1,1,1-trichloroethane. With a very modest laser pulse energy of 1.5 mJ (average power of 1.5 mW) and a pathlength of 10 cm, the technique is useful for the noninvasive, real-time monitoring of SRGS-active compounds at the 10 mM level. Selectivity against 1,1,2-trichloroethane, 1,2-dichloroethane, trichloroethylene, ethylbenzene, and benzene is excellent. Direct identification and simultaneous determination of individual compounds in process and effluent streams could be attained without sampling, separations, or other pretreatment procedures.

Influence of the cation size on the charge compensation process in poly(1-naphthol) coated electrodes: Multiple internal reflection FTIR spectroscopy (MIRFTIRS) and probe beam deflection (PBD) study

The electrochemical oxidation-reduction process of poly(1-naphthol) (poly(NAP-1) film was studied by in situ FTIR spectroscopy and probe beam deflection techniques. On oxidation, the polymer film is positively charged and on reduction, it is in its neutral form. It is demonstrated that the charge compensation process depends on the electrolyte cation size. With bulky cations the role of the charge compensation is taken by the anion. With small cations a mixed contribution of anions and cations to the process is observed. Anion exchange is predominant at short periods (seconds) but cation exchange is also involved if one waits until equilibrium is established after several minutes.

Experimental and Theoretical Study of Concentration Distributions in a Model Pore Electrode: II . Mathematical Models and Comparison to Experiment

A two‐dimensional numerical model of mass transfer in a zinc model pore has been developed to interpret results obtained using the probe beam deflection technique. The concentrations and concentration gradients of the electrolyte species were calculated by the numerical model and were shown to provide good quantitative agreement with the experimental results. The combination of theoretical and experimental analyses led to an understanding of how the kinetic, geometric, and mass transport parameters determined the current and concentration distributions within the model pore electrolyte.

Experimental and Theoretical Study of Concentration Distributions in a Model Pore Electrode: I . Measurement of Two‐Dimensional Concentration Gradients in a Zinc Model Pore

The optical probe beam deflection technique has been employed to study two‐dimensional concentration gradients within the electrolyte of a zinc model pore. The model pore cell constructed for this study retains the small, confined geometry and two‐dimensional character of an actual pore within a porous zinc electrode. Refractive index gradients in the direction of the model pore axis showed that the concentration of zincate ion reaches a maximum between the model pore mouth and a position one‐fourth of the distance toward the pore root during the anodic oxidation of the zinc electrode. Also, the variation in the refractive index gradient normal to the electrode along the length of the zinc anode allowed us to calculate the local current density within the model pore.

Alteration of the ion exchange mechanism of an electroactive polymer by manipulation of the active site: Probe beam deflection and quartz crystal microbalance study of poly( aniline) and poly( N-methylaniline)

Alteration of the ion exchange mechanism of an electroactive polymer by manipulation of the active site: Probe beam deflection and quartz crystal microbalance study of poly( aniline) and poly( N-methylaniline)

Energy relaxation time in a gas mixture measured by a photothermal probe beam deflection technique

The deflection of a cw probe laser beam, which occurs in a gas mixture after the absorption of a short laser pump pulse, was experimentally studied inside the irradiated region in order to characterize the generation of photothermal and photoacoustic effects. The time varying component of the probe deflection was detected, and the results are presented as functions of pumping fluences, laser wavelengths and gas pressures. Numerical modelling of the thermo-acoustic dynamics leads to the definition of an effective energy relaxation time for SF6/Ar gas mixtures. An interesting nonlinear behaviour of this energy relaxation time is reported.

ChemInform Abstract: Probe Beam Deflection (PBD) Investigation of the Charge Storage Reaction in Anodic Iridium and Tungsten Oxide Films

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Direct In Situ Evidence for Proton/Anion Exchange in Polyaniline Films by Means of Probe Beam Deflection

Probe beam deflection (PBD) was used to monitor the ion exchange between polymer film and bulk electrolyte during the redox reaction in polyaniline in aqueous electrolyte (, , ). The PBD results clearly show that protons as well as anions are exchanged during the first oxidation process. Protons are exchanged at potentials below . The relative contribution of the proton to the overall process depends not only on the pH of the electrolyte but also on the nature of the specific anion present. While the participation of H+ could be observed in for a concentration of 0.5M a concentration of 1M was needed in . A simple model based on the protonation equilibria of leucomeraldine species is used to analyze the results quantitatively. The results are discussed in terms of previously proposed mechanisms of redox processes in polyaniline.

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.

The relation betweeen triplet lifetime and photoacoustic waveform detected by probe beam deflection

The photoacoustic (PA) signal waveform in a condensed phase with pulsed laser excitation is theoretically calculated. When there exist fast and slow deactivation processes from the excited state, the PA signal waveform depends upon the decay rate constant and the relative contribution of the slow decay process. The calculated result is confirmed experimentally by using the probe beam deflection technique to determine the quantum yield of triplet formation and the triplet lifetime of quinoxaline in benzene.

Excimer laser corneal ablation: Absence of a significant “incubation” effect

Pulse-to-pulse consistency of excimer laser etching of cornea has been examined via two noncontact techniques: photoacoustic probe beam deflection, and time-resolved excimer pulse reflectometry. These methods clearly document the incubation phenomenon accompanying excimer laser ablation of polymethyl-methacrylate and the absence of the effect during polyimide ablation. In comparison, results for corneal ablation indicate consistent tissue etching over a train of pulses. Consequently, incubation appears to have negligible impact on corneal ablation.

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.

The role of defects in laser surface damage thresholds of fluoride crystals

The energy of the acoustic pulse generated by laser-surface interactions and measured by probe beam deflection was used to investigate laser surface damage thresholds of fluoride crystals with optical quality. It was found that damage thresholds decrease with increasing density of surface states. The defect density also controls the energy absorption mechanism: for surfaces with few defects, like polished MgF2 and CaF2, avalanche breakdown occurs at above 1 GW/cm2, whereas for materials with lower damage thresholds, such as LiF, BaF2, and roughened or incubated surfaces of CaF2, multiphoton absorption across the band gap is observed.