Probe Beam Deflection Technique Research Articles

Probe beam deflection technique with liquid immersion for fast mapping of thermal conductance

Frequency-domain probe beam deflection (FD-PBD) is an experimental technique for measuring thermal properties that combines heating by a modulated pump laser and measurement of the temperature field via thermoelastic displacement of the sample surface. In the conventional implementation of FD-PBD, the data are mostly sensitive to the in-plane thermal diffusivity. We describe an extension of FD-PBD that introduces sensitivity to through-plane thermal conductance by immersing the sample in a dielectric liquid and measuring the beam deflection created by the temperature field of the liquid. We demonstrate the accuracy of the method by measuring (1) the thermal conductivity of a 310 nm thick thermally grown oxide on Si, (2) the thermal boundary conductance of bonded interface between a 3C-SiC film and a single crystal diamond substrate, and (3) the thermal conductivities of several bulk materials. We map the thermal boundary conductance of a 3C-SiC/diamond interface with a precision of 1% using a lock-in time constant of 3 ms and dwell time of 15 ms. The spatial resolution and maximum probing depth are proportional to the radius of the focused laser beams and can be varied over the range of 1–20 μm and 4–80 μm, respectively, by varying the 1/e2 intensity radius of the focused laser beams from 2 to 40 μm. FD-PBD with liquid immersion thus enables fast mapping of spatial variations in thermal boundary conductance of deeply buried interfaces.

Estimation of underwater acoustic direction-of-arrival using the probe beam deflection technique.

This paper proposes a method of estimating the underwater acoustic direction-of-arrival using several laser beams impinging on a propagating underwater acoustic wave. The deflection of the laser beam caused by the spatial variation of the optical refractive index, which is further due to the modulation of the acoustic wave, reflects the information of direction-of-arrival and is sensed by the position sensitive detector (PSD). The sensing of the minute displacement on the PSD, in fact, introduces an extra dimension in the depth direction, which is a significant advantage over the conventional piezoelectric sensing regime. The employment of the extra sensing dimension can overcome several shortcomings, represented by spatial aliasing and phase ambiguity, existing in the current direction-of-arrival estimating methods. In addition, the ringing phenomenon of the piezoelectric effect is greatly reduced in the proposed laser-based sensing regime. By the flexibility of placing the laser beams, a prototype of the hydrophone is designed and manufactured, and a series of testing is performed. The results show that, benefiting from the probe beam deflection technique and combining the rough estimate and fine calculation, the resolution of the underwater acoustic direction-of-arrival can be improved to better than 0.016°, which can support and reform many underwater applications such as underwater acoustic communication, underwater detection, and ocean monitoring.

Study of pulsed laser-induced heating in bio-plasmonic solution using combined photoacoustic and probe beam deflection technique: Thermoacoustic effects

We describe studies of the interaction of a pulsed Nd:YAG laser with bovine serum albumin (BSA) solution (i.e., S0) and S0 containing gold nanourchin (GNU) (i.e., S1: S0 + 0.1 ml GNU) using combined photoacoustic (PA) and probe beam deflection (PBD) techniques. The changes in absorbance and chemical bonds are studied by UV–Vis and near-FTIR spectroscopy. The results showed a decrease in absorbance of the bio-plasmonic solution, which further decreased by increasing the concentration. The PA pressure increased with fluence in the order of GNU > S0 > S1, and all exhibited a non-linear response at ≈9.5 J cm−2and reached a maximum at 12.5 J cm−2. No PBD was observed in S0 indicating the role of GNU in producing the heating effect. ∂n/∂T increased in the order of S2 > S1 > S0, respectively, where S2 is (S0 + 0.2 ml GNU). The absorbance of S0 and S1 increased after heating due to protein denaturation. For S1, surface-enhanced FTIR showed an increase in the intensity of most bands between 6320 and 6630 cm−1, and the band at 5264 cm−1, which likely corresponds to β-sheet structure, significantly diminished after heating. The collapse of cavitation and plasma shock waves produced significant acoustic transients, hence some photomechanical effects. The acoustic energy released after the collapse of bubbles at 1.8 and 12.5 J cm−2was calculated to be ≈140 μJ and 7 mJ, respectively, corresponding to 4% and 28% of the input optical energy being converted to sound energy in the early phase of the expansion.

Novel calibration-free seedless velocimetry using laser-induced shockwave

Shockwave propagation from focused-laser-induced plasmas was characterized for implementing calibration-free seedless velocimetry. An emission-free probe beam deflection (EF-PBD) technique and short-gated shadowgraph/schlieren imaging were used for the investigation. Nanosecond laser pulses at 532 nm were focused to induce plasmas generating shockwaves from the focal point at atmospheric condition. A continuous-wave (CW) laser beam was set up to pass nearby for detecting the shock arrival at the beam location; the shock diverts the CW-laser beam, which is sensed by the photodiode. The EF-PBD was devised to minimize the influence of the plasma emission that affects the probe beam intensity measured by the photodiode. The probe beam was moved from the focal point to consecutive locations very close to the plasma (every 0.2 mm from 0 to 1.8 mm) for accurately measuring the shock speed in the region adjacent to the plasma. A point-explosion model was employed for predicting the shockwave propagation phenomenon. It was found that the ambient flow velocity around the plasma affects the shockwave arrival time on the probe beam, which suggests the feasibility of a seedless velocimetry technique. When the distance between the probe beam and the plasma is known, the velocimetry does not require calibration. The proposed velocimetry technique was tested successfully in a range of 30–180 m/s ambient flow.

Study of spatial thermal distribution of gold nanourchins in saline by combined transverse probe beam deflection and beam wavefront sensor: biomedical implications

Combined probe beam deflection (PBD) and wavefront sensor (WFS) technique are used to investigate the thermal distribution of gold nanourchins (GNU) in physiological saline (PS) using a low-power continuous NIR diode laser. Three different samples were prepared for the experiment: (S1) 0.5 mg/mL GNU only, (S2) 0.5 mL PS and 0.3 mL GNU, and (S3) 0.5 mL PS and 0.1 mL GNU. The laser transmission initially increases linearly as S3 > S2 > S1, but reaches a plateau and remains constant. The probe beam response in an adjective statistics process exhibited a stochastic behaviour at different positions and constant power in x- and y-directions. The beam view profiles showed a non-uniform intensity distribution and the addition of PS dramatically caused a blue shift indicating its cooling effect, S1 (20) warmer > S1(10) medium > S2 (20) cooler. S1 (10), S1 (20), and S2 (20) correspond to the samples irradiated with the laser power (mW) shown in the bracket. The peak-to-valley (PV) and root-mean-square (RMS) values demonstrated a non-linear intensity distribution during the scanning process. The greater PV values in deeper positions may well due to agglomeration, hence the sedimentation process. The Zernike coefficients with high absolute values represent the aberrations that cause the greatest distortion of the wavefront and found in the order of S2(20) > S1(10) > S1(20). This is consistent with PV wavefront slope and spatial period aberration relation. The opto-thermal coefficients were obtained as S2 (− 7.86 × 10−4) > S3: 0.5 mL PS and 0.1 ml GNU (− 6.3 × 10−4), respectively.

In Situ Characterization of Nanostructured Electrode Materials for Energy Conversion and Storage, Using Probe Beam Deflection Techniques

Nanostructured conductive materials of large surface area which are important in many areas of energy conversion and storage, including supercapacitors and fuel cells. While electrochemical techniques (e.g. cyclic voltammetry) assess the charge transfer processes at the electrode interface, the ion exchange process could only be inferred. Techniques of ion exchange determination, such as the electrochemical quartz crystal microbalance (EQCM) are of difficult application to porous electrodes since it requires fixing the porous material to the oscillating crystal. On the other hand, the techniques that monitor ion fluxes outside the electrode surface are able to study the actual ion exchange between a porous electrode and the electrolyte. Among them, Probe Beam Deflection (PBD) is a technique highly suitable to study porous electrodes.[1] The method uses a laser beam travelling parallel to the electrode surface which is refracted by the refractive index gradient associated with the flux of soluble species perpendicular to the electrode, at the center of the laser beam. Since the detection of beam position is optoelectronic, fast (ms) signals can be measured, unlike EQCM, allowing detecting transient phenomena. Since the flux is directly proportional to the surface area (like the current) the ratio of surface area to geometric pathlength (width of the electrode) assures large signal for porous electrodes. In this report, the study of different electrode materials using Probe Beam Deflection techniques is described. After a qualitative exploration using cyclic deflectometry, a continuous mass transport model is used to quantitatively evaluate the chronodeflectometric response.[2] First, the study of different porous glassy carbon materials is described. Then, PBD is applied to study mesoporous ordered Pt materials active in direct methanol fuel cells.[3] Finally, thin films of mesoporous oxides decorated with Au nanoparticles,[4] are investigated. The potential of minimum charge (PMC) can be determined and compared with the value measured by AC Impedance. Besides, transient phenomena like pH changes or effects on the coupled chemical reactions inside the pores can be easily detected. Therefore, a better understanding on the mass transfer in porous electrodes is obtained.

Time evolution of laser-ablation plumes and induced shock waves in low-pressure gas

We investigated correlations between the temporal evolutions of shock waves and plasma plumes generated by pulsed laser ablation of an aluminum target under various background gas pressures. Using a probe-beam deflection technique with a high-gain amplifier, we succeeded in detecting relatively weak shock waves in a thin gas with a pressure down to 200 Pa, which is considered to be a suitable condition for cluster formation. The behavior of the expanding plume was also observed using a high-speed framing camera and compared with that of the shock wave. The result shows that the shock front forms just ahead of the plume in the early expansion stages. The plume expansion rapidly attenuates with time and finally ceases, whereas the shock wave continues to propagate and gradually converts into a sound wave. The point-explosion blast wave model is able to estimate the transition of the temperature behind the shock front at low background pressures, giving valuable information for investigating the growth of clusters in the boundary region between the plume and background gas.

Probe beam deflection optical imaging of thermal and mechanical phenomena resulting from nanosecond electric pulse (nsEP) exposure in-vitro

Electric-field induced physical phenomena, such as thermal, mechanical and electrochemical dynamics, may be the driving mechanism behind bioeffects observed in mammalian cells during exposure to nanosecond-duration electric pulses (nsEP) in-vitro. Correlating a driving mechanism to a biological response requires the experimental measurement and quantification of all physical dynamics resulting from the nsEP stimulus. A passive and electromagnetic interference (EMI) immune sensor is required to resolve these dynamics in high strength electric fields. The probe beam deflection technique (PBDT) is a passive and EMI immune optical method for quantifying and imaging refractive index gradients in liquids and gases, both dynamic and static, with nanosecond temporal resolution. In this work, a probe beam deflection imaging system was designed to acquire 2-D time-lapse images of thermal/mechanical dynamics resulting from monopolar and bipolar nsEP stimulus.

Nanosecond pulsed laser nanostructuring of Au thin films: Comparison between irradiation at low and atmospheric pressure

Au thin films with tens of nm in thickness deposited on glass substrates were irradiated with nanosecond UV (355nm) laser pulses at atmospheric pressure and in vacuum conditions (∼600 and 10−5Torr). We studied the effect of the laser fluence (200–400mJ/cm2), thickness of the starting film (∼40–80nm) and surrounding pressure on the partial ablation/evaporation of the films and the morphology of the produced nanoparticles (NPs). The dynamics of NPs formation was studied by measuring in real time the transmission of the samples upon continuous-wave laser exposure, and by means of probe beam deflection technique. The ejection of material from the film as a result of the irradiation was confirmed by time-resolved shadowgraphy technique. Experiments show that the NPs diameter and their size distribution are smaller when the irradiation is performed in vacuum regardless the laser fluence and thickness of the started film. It is also shown that the plasmon band shifts to higher frequencies with lower background pressure. The optical measurements show that the films melt and ablate during the laser pulse, but the transmission of the irradiated areas continues changing during tens of microseconds due to ejection of material and solidification of the remaining gold. Our results indicate that partial ablation cannot be neglected in nanostructuration by ns-pulsed irradiation of thin films when their thickness is in the studied range.

All-optical optoacoustic microscopy based on probe beam deflection technique

Optoacoustic (OA) microscopy using an all-optical system based on the probe beam deflection technique (PBDT) for detection of laser-induced acoustic signals was investigated as an alternative to conventional piezoelectric transducers. PBDT provides a number of advantages for OA microscopy including (i) efficient coupling of laser excitation energy to the samples being imaged through the probing laser beam, (ii) undistorted coupling of acoustic waves to the detector without the need for separation of the optical and acoustic paths, (iii) high sensitivity and (iv) ultrawide bandwidth. Because of the unimpeded optical path in PBDT, diffraction-limited lateral resolution can be readily achieved. The sensitivity of the current PBDT sensor of 22μV/Pa and its noise equivalent pressure (NEP) of 11.4Pa are comparable with these parameters of the optical micro-ring resonator and commercial piezoelectric ultrasonic transducers. Benefits of the present prototype OA microscope were demonstrated by successfully resolving micron-size details in histological sections of cardiac muscle.

Ethanol extract of propolis as a protective coating for mild steel in chloride media

The anticorrosion performance of commercial extract of ethanolic propolis (EP)-coated mild steel samples immersed in a 3.5% w/v NaCl in neutral and near neutral media was evaluated by classical electrochemical and electrochemical probe beam deflection techniques. The functional groups and major components of the extract were identified by Fourier transform infrared spectroscopy and high-performance liquid chromatography, respectively. The extract and the major constituent identified in the extract, 3,5-diprenyl-4-hydroxycinnamic acid (DHCA), are poorly hydro-soluble in a neutral medium. The bare and coated carbon steel surfaces were characterized by scanning electron microscopy and atomic force microscopy before and after a saline immersion. The electrochemical response of the coated electrodes was compared with bare mild steel electrodes and all qualitative and quantitative data obtained supported the hypothesis that EP is a potential mild steel corrosion inhibitor. Although several flavonoids are known to have remarkable antioxidant properties and be effective metal corrosion inhibitors, this work is pioneering in its evaluation of the inhibitory capacity of a natural product whose main constituent is DHCA.

Photothermal study of RF-plasma polymerized hexamethyldisilazane thin films

Plasma polymerization by RF excited low pressure plasmas is a powerful technique for synthesizing thin films for a wide range of applications such in microelectronics, biomaterials and aeronautical industries. Among these applications plasma polymerized hexamethyldisilazane (HMDSN here in) is a promising material due its biocompatibility, optical and electrical properties. In the present paper, we reported the thermal diffusivity measurements of plasma polymerized HMDSN thin films using the probe beam deflection technique (PBD). The samples are thermally thin and optically transparent, with thicknesses ranging from 170 to 600nm, difficulting their thermal characterization by other photo-thermal techniques (photoacoustic and pyroelectric). PBD measurements were carried out with a diode (20mW, λ=640nm) and a HeNe (0.9mW, λ=632nm) laser, used as pump source and probe beam, respectively. The probe beam was focused close to the sample surface and its direction was perpendicular to the pump beam. The transverse PBD in skimming configuration is employed and the deflection signal is analyzed using the phase method for the determination of thermal diffusivity. The results show the decreasing of thermal diffusivity with the decreasing of film thickness. HMDSN film׳s thermal diffusivity values are reported in this paper for the first time being in the range of typical polymeric samples.

Application of the combined electrochemical quartz crystal microbalance and probe beam deflection technique in deep eutectic solvents

The electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) have been widely used to study interfacial processes in molecular solvent-based electrolytes. However, there has been limited use of the EQCM and none of PBD in room temperature ionic liquids, including deep eutectic solvents (DES). Here we explore the use of the combined EQCM/PBD technique to the study of Ag and Sn electrodeposition from a DES comprising a 1:2 mixture of choline chloride and ethylene glycol. While overcoming the effect of viscous loss in the acoustic wave (EQCM) part of the experiment is understood, the optical (PBD) technique fails to provide a meaningful response in slow scan rate voltammetric experiments; this contrasts sharply with the straightforward behaviour seen in aqueous media. Solution transport considerations reveal this to be a consequence of long surface-to-beam transit times in the viscous DES. The problem can be overcome by operating at scan rates 1-2 orders of magnitude slower, permitting application of this powerful technique to novel media of technological interest. The PBD responses reveal unanticipated chemical effects: multiple complexes in the Ag system and solubility limitations in the Sn system, neither of which is evident from the electrochemical or QCM responses.

Probe beam deflection technique as acoustic emission directionality sensor with photoacoustic emission source

The goal of this paper is to demonstrate the unique capability of measuring the vector or angular information of propagating acoustic waves using an optical sensor. Acoustic waves were generated using photoacoustic interaction and detected by the probe beam deflection technique. Experiments and simulations were performed to study the interaction of acoustic emissions with an optical sensor in a coupling medium. The simulated results predict the probe beam and wavefront interaction and produced simulated signals that are verified by experiment.

Optoacoustic Multispectral Imaging of Radiolucent Foreign Bodies in Tissue

Optoacoustic imaging is an emerging medical technology that uniquely combines the absorption contrast of optical imaging and the penetration depth of ultrasound. While it is not currently employed as a clinical imaging modality, the results of current research strongly support the use of optoacoustic-based methods in medical imaging. One such application is the diagnosis of the presence of soft tissue foreign bodies. Because many radiolucent foreign bodies have sufficient contrast for imaging in the optical domain, laser-induced optoacoustic imaging could be advantageous for the detection of such objects. Common foreign bodies have been scanned over a range of visible and near infrared wavelengths by using an optoacoustic method to obtain the spectroscopic properties of the materials commonly associated with these foreign bodies. The derived optical absorption spectra compared quite closely to the absorption spectra generated when using a conventional spectrophotometer. By using the probe-beam deflection technique, a novel, pressure-wave detection method, we successfully generated optoacoustic spectroscopic plots of a wooden foreign body embedded in a tissue phantom, which closely resembled the spectrum of the same object obtained in isolation. A practical application of such spectra is to assemble a library of spectroscopic data for radiolucent materials, from which specific characteristic wavelengths can be selected for use in optimizing imaging instrumentation and provide a basis for the identification of the material properties of particular foreign bodies.

Electroanalysis using modified hierarchical nanoporous carbon materials

The role of the electrode nanoporosity in electroanalytical processes is discussed and specific phenomena (slow double layer charging, local pH effects) which can be present in porous electrode are described. Hierarchical porous carbon (HPC) materials are synthesized using a hard template method. The three dimensional carbon porosity is examined using scanning electron microscopy on flat surfaces cut using a focused ion beam (FIB-SEM). The electrochemical properties of the HPC are measured using cyclic voltammetry, AC impedance, chronoamperometry and Probe Beam Deflection (PBD) techniques. Chronoamperometry measurements of HPC seems to fit a transmission line model. PBD data show evidence of local pH changes inside the pores, during double layer charging. The HPC are modified by in situ (chemical or electrochemical) formation of metal (Pt/Ru) or metal oxide (CoOx, Fe3O4) nanoparticles. Additionally, HPC loaded with Pt decorated magnetite (Fe3O4) nanoparticles is produced by galvanic displacement. The modified HPC materials are used for the electroanalysis of different substances (CO, O2, AsO3(-3)). The role of the nanoporous carbon substrate in the electroanalytical data is evaluated.

A novel way to maintain resorcinol–formaldehyde porosity during drying: Stabilization of the sol–gel nanostructure using a cationic polyelectrolyte

The formation of monolithic porous carbon having a BET surface area of ca. 725 m 2/g is achieved by carbonization of a resorcinol/formaldehyde (RF) resin prepared in the presence of a cationic polylectrolyte (polydialyldimethylammonium chloride, PDADMAC). The porosity of the resin is maintained during air drying due to the stabilizing effect of a cationic polyelectrolyte on the sol–gel nanostructure. While carbon made of RF resins prepared in the presence of cationic polyelectrolyte show a large surface area, those prepared in the presence of a negatively charged polyelectrolyte (poly(styrenesulfonate), PSS), a neutral hydrophylic polymer (poly(vinyl alcohol), PVA) or in the absence of polymeric additives renders carbon materials having negligible surface areas (<10 m 2/g). It seems that positively charged polymer stabilizes the negatively charged resin nanoparticles, suggesting a new mechanism of action for cationic species in porous RF formation. The method simplifies greatly the fabrication of porous carbon by making unnecessary to use complex (e.g. supercritical) drying procedures. It also does not require long curing times and cumbersome solvent exchange. Avoiding the use of organic solvents makes the process friendlier to the environment. The carbon material presents large electrochemical specific capacitance ( ca. 210 Fg −1 in acid media and 110 Fg −1 in neutral media) making it suitable for supercapacitor applications. The ion exchange properties, related with the double layer charging/discharging processes are investigated using Probe Beam Deflection techniques.

In Situ Calorimetry at Metal−Electrode Liquid Electrolyte Interfaces As Monitored by Probe Beam Deflection Techniques

A probe beam deflection method that allows for the heat generated or absorbed during an interfacial proces to be determined in situ is herein described. These optical measurements are performed using a collimate laser beam propagating parallel to the interface through the back of a flat, optically transparent ZnSe crystal that supports a very thin film of a metal electrode in contact with the electrolyte solution. Analysis a experimental data collected for a Au electrode in sulfuric acid aqueous solutions using numerical simulation were found to be consistent with the release of ~375 kJ/mol upon formation of a monolayer of Au oxide This value is very similar to the value observed using the same methodology for the reduction of the A oxide layer under otherwise the same experimental conditions.

采用光偏转法研究激光等离子体冲击波

Laser probe beam deflection technique is used for the analysis of laser-induced plasma shock waves in air and distilled water. The temporal and spatial variations of the parameters on shock fronts are studied as functions of focal lens position and laser energy. The influences of the characteristics of media are investigated on the well-designed experimental setup. It is found that the shock wave in distilled water attenuates to an acoustic wave faster than in air under the same laser energy. Good agreement is obtained between our experimental results and those attained with other techniques. This technique is versatile, economic, and simple to implement, being a promising diagnostic tool for pulsed laser processing.

Probe beam deflection studies of nanostructured catalyst materials for fuel cells

Probe beam deflection (PBD) techniques, both as cyclic voltadeflectometry (CVD) and chronodeflectometry (CD), were applied for the first time to the study of the electrochemistry of nanostructured Pt materials which are commonly used as electrocatalysts in fuel cells. The electrochemical surface reactions, including faradaic processes, double layer charging and specific anion adsorption were easily detected. Quantitative analysis of the chronodeflectometric data made possible to elucidate the dynamics of double layer charging in such materials and to determine the potential of zero charge (pzc) of the metal present either as a monolithic mesoporous material or as metal nanoparticles supported on carbon. The electro-oxidation of CO, adsorbed on nanostructured Pt, was also studied by CVD and CD being able to detect the formation of CO2 and H3O+ related with the nucleation and growth process which controls the rate of CO stripping. The interplay of Pt oxide formation and COad electrooxidation, both in potential and time, was detected indicating possible application of the technique to other electrocatalysts.