Phase-resolved Method Research Articles

Phase-resolved photoacoustic spectroscopy to monitor dental plaque on tooth enamel

ABSTRACTDental plaque is a biofilm on the enamel surface of the teeth, formed by colonizing bacteria. It is essential to monitor the biofilm presence on the surface of the enamel of the teeth, since plaque is a reason for periodontal disease and dental caries. This paper proposes applying photoacoustic spectroscopy to monitor and the phase-resolved photoacoustic method to analyze the biofilm plaque on samples of human dental enamel facets. The biofilm growth occurred in the oral cavity environment at deposition time of 48 and 72 h. Photoacoustic ex vivo monitoring found that: (1) Photoacoustic spectroscopy is a helpful tool to identify the bactericidal effect on dental plaque; (2) the biofilm deposition provides an optical absorption of the Soret band at 410 nm and increase of hydroxyl absorption band; (3) the biofilm thickness by phase-resolved photoacoustic method is in agreement with the literature in situ measurements. These new knowledges may help in development of a greater practicality and safety equipment able to identify and quantify dental biofilm, which may be achieved with low-cost Soret-band light emitting diode as light excitation.

Photoacoustic viscoelasticity imaging dedicated to mechanical characterization of biological tissues

Since changes in mechanical properties of biological tissues are often closely related to pathology, the viscoelastic properties are important physical parameters for medical diagnosis. A photoacoustic (PA) phase-resolved method for noninvasively characterizing the biological tissue viscoelasticity has been proposed by Gao et al. [G. Gao, S. Yang, D. Xing, “Viscoelasticity imaging of biological tissues with phase-resolved photoacoustic measurement,” Opt. Lett. 36, 3341–3343 (2011)]. The mathematical relationship between the PA phase delay and the viscosity–elasticity ratio has been theoretically deduced. Moreover, systems of PA viscoelasticity (PAVE) imaging including PAVE microscopy and PAVE endoscopy were developed, and high-PA-phase contrast images reflecting the tissue viscoelasticity information have been successfully achieved. The PAVE method has been developed in tumor detection, atherosclerosis characterization and related vascular endoscopy. We reviewed the development of the PAVE technique and its applications in biomedical fields. It is believed that PAVE imaging is of great potential in both biomedical applications and clinical studies.

Spectroscopic study of Nafion® membrane as a function of water content by Phase-Resolved Photoacoustic Method

Nafion® membranes were developed by DuPont, a perfluorosulfonic acid/polytetrafluoroethylene copolymer. These membranes are hydrophilic and the water is preferentially sorbed into the clusters due to the hydrophobic character of fluorocarbon matrix. The sulfonic acid groups are chemically active and fixed within the Teflon polymer matrix. Thus, this first synthetic ionic polymer is chemically resistant and durable, making it useful for Proton Exchange Membrane fuel cells. In order to monitoring the groups -OH of the Nafion®, we used the Photoacoustic Spectroscopy phases. The optical absorption spectrum was determined for wavelengths of 800 to 2600 nm. The procedure was to measure the samples in different hydration times. Using the Phase-Resolved Photoacoustic method, it was possible to separate the contribution of –OH, of C=O and of methylene group. The phase lag as a water function behaviors found may be associated with structural changes induced by membrane hydration.

Polyvinylpyrrolidone Quantification in Paracetamol Using Phase-Resolved Photoacoustic Method

In this study, photoacoustic spectroscopy was used to quantify polyvinylpyrrolidone in paracetamol samples with different proportions of polyvinylpyrrolidone. Samples with 10%, 20%, and 30% of polyvinylpyrrolidone added to pure paracetamol were used. The results showed an increase in the intensity of the characteristic bands of polyvinylpyrrolidone centered at 1450 nm and 1170 nm; the intensity of these bands increased in relation to the concentration of polyvinylpyrrolidone. The phase-resolved photoacoustic method was applied in Photoacoustic spectra to provide further information. The results show that phase-resolved photoacoustic method can provide an alternative analytical method to detect different concentrations of polyvinylpyrrolidone in paracetamol samples.

Mode transition in a planar-coil inductively driven discharge caused by an external magnetic field

A hydrogen discharge inductively driven by a planar coil is studied by employing the phase resolved optical emission spectroscopy method, which permits observations not only on the stationary discharge structure but also of its time evolution over the cycle of the rf signal producing the discharge. Since the discharge is considered as a single element of a matrix source of negative hydrogen ions, it is equipped with an extraction device forming an additional grounded metal wall on the side opposite to that where the coil is positioned. Regarding use of a magnetic filter (a localized external magnetic field), the modifications in the discharge caused by the magnetic field have been studied. The results show: (i) transition of the discharge from a capacitive mode to an inductive one with the shift of the magnetic filter from the extraction device towards the coil, (ii) asymmetry both of the stationary and time-varying discharge structure of the inductive mode caused, respectively, by a diamagnetic drift and an -drift in the rf field, (iii) formation in the capacitive mode of the discharge of two electron beams, starting from the position of the magnetic filter, in addition to the beams well known as electron acceleration at the wall sheath expansion and (iv) asymmetry in the structure of the capacitive mode due to -drifts in the dc and rf fields.

Interferometric measurement of the temperature coefficient of the refractive index dn/dT and the coefficient of thermal expansion of Pr:YLF laser crystals

We report interferometric measurements of the temperature coefficient of the refractive index (dn/dT) and the coefficient of thermal expansion (α) of a praseodymium-doped yttrium lithium fluoride (Pr:YLF) crystal and of a fused silica reference sample. Our phase-resolved interferometric method yields a large number of data points and thus allows a precise measurement and a good error estimation. Furthermore, both dn/dT and α are obtained simultaneously from a single measurement which reduces errors that can occur in separate measurements. Over the temperature range from 20 °C to 80 °C, the value of dn/dT of Pr:YLF decreases from −5.2 × 10(−6)/K to −6.2 × 10(−6)/K for the ordinary refractive index and from −7.6 × 10(−6)/K to −8.6 × 10(−6)/K for the extraordinary refractive index. The coefficient of thermal expansion for the a-axis of Pr:YLF increases from 16.4 × 10(−6)/K to 17.8 × 10(−6)/K over the same temperature range.

Depth Profiles in Maize (Zea mays L.) Seeds Studied by Photoacoustic Spectroscopy

Photoacoustic spectroscopy (PAS) has been used to analyze agricultural seeds and can be applied to the study of seed depth profiles of these complex samples composed of different structures. The sample depth profile can be obtained through the photoacoustic (PA) signal, amplitude, and phase at different light modulation frequencies. The PA signal phase is more sensitive to changes of thermal properties in layered samples than the PA signal amplitude. Hence, the PA signal phase can also be used to characterize layers at different depths. Thus, the objective of the present study was to obtain the optical absorption spectra of maize seeds (Zea mays L.) by means of PAS at different light modulation frequencies (17 Hz, 30 Hz, and 50 Hz) and comparing these spectra with the ones obtained from the phase-resolved method in order to separate the optical absorption spectra of seed pericarp and endosperm. The results suggest the possibility of using the phase-resolved method to obtain optical absorption spectra of different seed structures, at different depths, without damaging the seed. Thus, PAS could be a nondestructive method for characterization of agricultural seeds and thus improve quality control in the food industry.

The cross-correlation in spectral domain based Doppler optical coherence tomography

We propose a cross-correlation method which is based on the cross-correlation of two adjacent A-scans of interferogram fringe for imaging the velocities of the blood flowing in vessels. The method was tested by measurements of the velocities of flowing particles within a glass capillary with known mean velocities. Mean standard deviations of flow velocities of the particles determined through the proposed method were compared to those by the conventional phase resolved method. I n vivo imaging of a mouse ear was performed and the Doppler flow velocity maps were reconstructed by both methods. The experimental results demonstrated that the proposed method can significantly suppress the phase noises caused by phase instabilities and improve the signal to noise ratio of blood flow map.

THE OCCURRENCE PROBABILITIES OF ROGUE WAVES IN DIFFERENT NONLINEAR STAGES

The occurrence probabilities of Rogue Waves in different nonlinear states are investigated based on high-order spectral method (HOSM), which is a direct phase-resolved numerical method. The focus is given to the occurrence probability of Rogue Waves in the nonlinear evolution stage where the Benjamin-Feir Instability is not the dominate mechanism due to the quartet resonance interactions for wave fields with a broad range in frequencies. The initial wave trains are generated from Stokes waves and two sidebands. Based on the simulation, we find that the Kurtosis evolves distinctly at three nonlinear stages and shows a weak relation to the probabilities of the Rouge Waves. We also introduce a simple Entropy formula, turning out to close a stable value.

The phase-resolved photoacoustic method to indicate chemical assignments of paracetamol

In this work, the phase-resolved photoacoustic method was applied to provide specific information on the chemical assignments of paracetamol in the near-infrared region. Two broad bands, centered at 1370 and 1130nm, were well-resolved using this method, making it possible to assign the peaks centered at 1398, 1355 and 1295nm to a C–H combination from a CH3 structure and the peak at 1305nm to a C–H combination from the aromatic ring. This information represents a new finding in chemical studies regarding this medicament.

Probing the Plasma Sheath by the Continuous Mass Loss of Microparticles

A novel approach of using microparticles as probes for the sheath structure of radio-frequency discharges is presented. Starting with a heavy (large) particle confined deep in the plasma sheath, the ambient plasma causes a continuous mass loss, which increases the levitation height of the particle. It is shown that this process can be precisely monitored with the phase-resolved resonance method, which allows probing the force balance of the particle with high spatial resolution. The resulting force profile is in reasonable agreement with recent sheath models.

Advances in Doppler OCT.

We review the principle and some recent applications of Doppler optical coherence tomography (OCT). The advances of the phase-resolved Doppler OCT method are described. Functional OCT algorithms which are based on an extension of the phase-resolved scheme are also introduced. Recent applications of Doppler OCT for quantification of flow, imaging of microvasculature and vocal fold vibration, and optical coherence elastography are briefly discussed.

PROPERTIES OF FREAK WAVES INDUCED BY TWO KINDS OF NONLINEAR MECHANISMS

We investigate the dynamic and kinematic characteristics of freak waves using a direct phase-resolved nonlinear numerical method. The focus is on the understanding of the effects of different nonlinear wave-wave interactions on freak waves development and characteristics in the evolution process of modulated Stokes wave trains. Long time simulations of modulated Stokes wave trains, with different parameters, are obtained. Based on these simulations, we find that there are different kinds of freak waves in different time scales due to two kinds of different nonlinear mechanisms. One is the modulation instability and another related to the wave group interaction. Both the dynamic and kinematic characteristics of the different kinds of freak waves are distinct. Occurrence of freak waves (especially of large height) is usually correlated with broadband wave spectra.

Phase-resolved acoustic radiation force optical coherence elastography

Many diseases involve changes in the biomechanical properties of tissue, and there is a close correlation between tissue elasticity and pathology. We report on the development of a phase-resolved acoustic radiation force optical coherence elastography method (ARF-OCE) to evaluate the elastic properties of tissue. This method utilizes chirped acoustic radiation force to produce excitation along the sample's axial direction, and it uses phase-resolved optical coherence tomography (OCT) to measure the vibration of the sample. Under 500-Hz square wave modulated ARF signal excitation, phase change maps of tissue mimicking phantoms are generated by the ARF-OCE method, and the resulting Young's modulus ratio is correlated with a standard compression test. The results verify that this technique could efficiently measure sample elastic properties accurately and quantitatively. Furthermore, a three-dimensional ARF-OCE image of the human atherosclerotic coronary artery is obtained. The result indicates that our dynamic phase-resolved ARF-OCE method can delineate tissues with different mechanical properties.

An open and low-cost optical-fiber measurement system for the optical detection of oxygen using a multifrequency phase-resolved method

In this paper we present an open and low-cost optical-fiber measurement system for the optical detection of oxygen. A multifrequency phase-resolved method is proposed as the measurement technique in order to evaluate the oxygen-concentration-dependent phase-shift (or luminescence lifetime). Such evaluation is based on the operating principles of quadrature detection (also known as I/Q method), which may be entirely performed by digital signal processing. Theoretical aspects of the proposed methodology as well as the design and construction of the measurement system are discussed in this work. The system performance is assessed by characterization and evaluation of an oxygen-sensitive film (an oxygen-sensitive luminescent dye [Pt(II) meso-Tetra(pentafluorophenyl)porphine (PtTFPP)] immobilized into an oxygen-permeable polymeric matrix). These results are compared successfully with reference measurements obtained on the same sample using a conventional experimental setup based on a commercial lock-in amplifier. In this case, a measurement accuracy of <0.2 kPa oxygen partial pressure has been obtained over the measurement range of 0–20 kPa, for short periods of continuous measurement (<2 min), and at a room temperature of 21 °C.

Estimation of shear wave velocity in gelatin phantoms utilizing PhS-SSOCT

We report a method for measuring shear wave velocity in soft materials using phase stabilized swept source optical coherence tomography (PhS-SSOCT). Wave velocity was measured in phantoms with various concentrations of gelatin and therefore different stiffness. Mechanical waves of small amplitudes (∼10 μm) were induced by applying local mechanical excitation at the surface of the phantom. Using the phase-resolved method for displacement measurement described here, the wave velocity was measured at various spatially distributed points on the surface of the tissue-mimicking gelatin-based phantom. The measurements confirmed an anticipated increase in the shear wave velocity with an increase in the gelatin concentrations. Therefore, by combining the velocity measurements with previously reported measurements of the wave amplitude, viscoelastic mechanical properties of the tissue such as cornea and lens could potentially be measured.

Xe irradiation-induced defects in CuInSe2 by phase resolved photoacoustic spectroscopy

We report a study on the optical properties of 40 keV Xe+ implants with a dose of 5 × 1016 ions/cm2 into p-type conducting CuInSe2 single crystals using the phase resolved method of the photoacoustic spectroscopy (PAS) technique. Photoacoustic spectra have been measured in the photon energy range 0.7 < hν < 1.4 eV prior and after implantation at various phase angles using a high resolution fully computerized spectrometer. Once the spectra separation is carried out, an analysis on the impact of Xe+ on the defect structure of CuInSe2 is presented. The results obtained here are discussed in the light of current reported literature.

Application of common transformers faults diagnosis methods on biodegradable oil-filled transformers

Due to environmental concerns regarding the use of mineral oil, biodegradable oil is increasingly being used as an alternative dielectric fluid. This paper presents results of experiments performed in the laboratory on the use of biodegradable oils for transformer application. The investigations cover two important diagnostic techniques for insulation assessment: (i) an investigation of partial discharge (PD) activity and characteristics in such oils and (ii) an investigation of the standard hydrocarbon dissolved gas products produced due to transformer faults. The fundamental aim of the investigation was to provide information as to whether the existing analysis techniques of PD fault pattern recognition and dissolved gas analysis methods, developed for mineral oil, are valid when used for insulation assessment with biodegradable transformer oil. The experiments were conducted on test samples to simulate three common types of transformer faults: low-energy PDs, high-energy arcing/sparking, and overheating. For the purpose of comparison, the same tests were performed using a mineral oil (Shell Diala MX) and a biodegradable oil (Envirotemp FR3). Also, each oil type was tested at three different moisture levels and with or without the presence of solid insulating materials (pressboard). PD activity was monitored using the standard IEC60270 phase-resolved analysis method. The fault gases produced were extracted and analysed by standard gas chromatography methods. Test results indicate that the PD phase resolved patterns are, in general, similar for the two oil types and thus existing PD pattern interpretations can be used to distinguish different types of PD faults, e.g. corona versus surface discharges. However, the values of various discharge quantities (PD magnitudes, repetition rate, current, etc) are very different under the same test condition. The quantities and the trend of dissolved gases for faults in biodegradable oil are substantially different compared with mineral oil. For the PD fault, biodegradable oil was found to release only a limited number of gases. For arcing and overheating faults, the main key gas produced is different between the two oils. Also, the presence of cellulosic materials such as pressboard influences the extent of hydrocarbon gases dissolved in the oil. It was found that for biodegradable oil, fewer amounts of gases are produced as the oil gets wetter.

Higher-order cross-correlation-based Doppler optical coherence tomography

A method based on higher-order cross-correlation is proposed to fetch the Doppler information on flow velocity within areas under low signal-to-noise ratio (SNR) by spectral domain optical coherence tomography. The proposed method is theoretically developed and validated by measurement of a moving mirror with known velocities. Standard deviations of flow velocities of the mirror under different SNRs are determined by the proposed method and compared with those by the modified phase-resolved method. Measurement of flowing particles within a glass capillary is also conducted, and Doppler flow velocity maps of the glass capillary are reconstructed by both methods. All experimental results demonstrate that the proposed method can significantly suppress noise, thus rendering it suitable for flow measurement under low SNR cases.

Analysis of the uncertainty in the measurement of electron densities in plasmas using the phase-resolved cutoff method

We have analysed the uncertainty of measured electron density using a phase-resolved wave cutoff probe and compared it with a previous cutoff probe. To determine the cutoff frequency (i.e. plasma frequency), we used the phase difference between two antennas of the cutoff probe and its slow time modulation instead of the transmittance used in the previous cutoff method. The phase-resolved cutoff method gives remarkable results under wide discharge conditions. The uncertainty of the phase-resolved cutoff method is much better than the previous cutoff method.