Pulsed Photoacoustic Technique Research Articles

Study of erythrocyte sedimentation in human blood through the photoacoustic signals analysis

IntroductionIn this study, we utilized the pulsed photoacoustic (PA) technique to analyze globular sedimentation in whole human blood, with a focus on distinguishing between healthy individuals and those with hemolytic anemia. MethodsBlood samples were collected from both healthy individuals (women and men) and those with hemolytic anemia, and temporal and spectral parameters of PA signals were employed for analysis. ResultsSignificant differences (p < 0.05) were observed in PA metrics between the two groups. The proposed spectral analysis allowed significant differentiation within a 25-minute measurement window. Anemic blood samples exhibited higher erythrocyte sedimentation rate (ESR) values, indicating increased erythrocyte aggregation. DiscussionThis study underscores the potential of PA signal analysis in ESR assessment as an efficient method for distinguishing between healthy and anemic blood, surpassing traditional approaches. It represents a promising contribution to the development of precise and sensitive techniques for analyzing human blood samples in clinical settings.

Use of visible pulsed photoacoustic technique for the non-destructive measurements of absorption coefficients, thermal diffusion and viscosity properties of natural and clay-blended rubber nanocomposites

Use of visible pulsed photoacoustic technique for the non-destructive measurements of absorption coefficients, thermal diffusion and viscosity properties of natural and clay-blended rubber nanocomposites

Study of charge transfer mechanism of PEDOT polymer for detection of solid TEX and CL-20 explosives using pulsed photoacoustic technique.

We report the use of PEDOT polymer (poly (2, 3-dihydrothieno [3,4-b] dioxane-5,7-diyl) as a sensing medium for the detection of solid secondary explosives like TEX and CL-20 in solid form using pulsed photoacoustic (PA) technique under visible 532nm wavelength. The PEDOT polymer (poly (2, 3-dihydrothieno [3,4-b] dioxane-5,7-diyl) plays the role of an optode or an effective sensing medium for the detection of explosives when mixed in equal proportion and subjected to 532nm wavelength obtained from Q-switched Nd: YAG laser without any chemical treatment. The study reveals that one milligram of PEDOT is sufficient to initiate the charge transfer mechanism between the positive charge on the oxidized PEDOT and the lone pairs of electrons on the oxygen atoms of the nitro group of the explosives. The strength of the enhanced PA signal for TEX and CL-20 was of the order of 65.38 and 1.77 times, respectively. However, the same experiment was repeated with non-explosive samples such as NaNO2 and NaNO3, separately mixed with PEDOT. The obtained peaks of PA spectra were very weak, broaden and distorted in nature and occupies less than 3kHz frequency rage and 3.5 times less than the PA signal of pure PEDOT. The estimated minimum detection limit of the solid explosives, CL-20 and TEX were of the order of 0.33ng and 1.03ng, respectively.

FOTOACÚSTICA PULSADA APLICADA A LA DETERMINACIÓN DE UMBRALES DE ABLACIÓN LÁSER EN METALES

Se determinaron los umbrales de ablación láser de los metales cobre, oro y plata para la radiación láser de 1064 nm de un láser Nd:YAG de nanosegundos utilizándose la técnica fotoacústica pulsada para registrar las señales fotoacústicas producidas debido a la interacción del metal con los pulsos láser. Dichas señales se analizaron mediante correlación estándar y los cambios en la amplitud fotoacústica conforme aumento la fluencia láser. Los resultados indican que las señales fotoacústicas son muy sensibles a cambios físicos que experimenta una muestra solida debido a la interacción con pulsos láser, pudiendo diferenciarse claramente el cambio del régimen termoelástico al de ablación y por consiguiente el umbral de ablación. Los valores obtenidos para la fluencia umbral fueron: (1.71±0.08) J/cm2 para el cobre, (1.65±0.09) J/cm2 para el oro y (1.15±0.05) J/cm2 para la plata.

Analyzing the Preparation and Properties of Silver Nanoparticles; A Photo-Acoustic Study

Metal nanoparticles have garnered recent attention due to their potential for use in various mechanical, electrical, chemical and optical applications. This study aimed to investigate the synthesis of silver nanoparticles using pulsed photo-acoustic (PA) spectroscopy techniques. The results indicated a linear relationship between absorbance and concentration. Additionally, stability of silver colloids was seen at room temperatures, with no aggregation. The nanoparticles were spherical and between 2-40 nm in diameter. Nanoparticle size and PA signal were inversely proportional. Furthermore, lack of nanoparticle stability was found to weaken the PA signal. Lastly, nanoparticle absorption was inversely proportional to fluorescence. Further studies are needed for exploring the rationale in the relationship between fluorescence and absorption of the nanoparticles.

Dual photoacoustic monitoring in laser ablation synthesis of silver nanoparticles to find in situ their fluence threshold formation

Abstract In this study, a dual pulsed photoacoustic technique was applied to monitor, in real time, the laser ablation synthesis in solution (LASiS) of silver nanoparticles. It was found that, at low optical fluence values, the ultrasound signal associated to the laser ablation process exhibited constant amplitude, independently of the ablation time. Further analysis confirmed that, under these conditions, the ablation process provided only suspended micro-sized Ag fragments. However, fluence values above 400 mJ cm−2 promoted the formation of nanoparticles, accompanied by amplitude changes in the photoacoustic signal. Determination of this threshold condition establishes a fingerprint in the photoacoustic signal that can be used to identify, in situ and in real time, the beginning of nanoparticle synthesis. Supplementary, the nanoparticle formation was also photoacoustically monitored during the ablation process introducing an additional laser pulse train of low fluence value propagating perpendicularly to the pulse train used for ablation. These laser pulses did not interfere with the nanoparticle LASiS process, but renders an ultrasound signal enhancement due to the surface plasmon resonance of metal nanoparticles. The characterization of the LASiS process through the photoacoustic technique can provide information about nanoparticle concentration and other synthesis features of interest.

Raman and time-resolved pulsed photoacoustic spectroscopy of solid trinitrotoluene in graphite mixture: For identification of double resonant optical phonon signatures

The optical phonon waves transfer mechanism between pure graphite (GP) and trinitrotoluene (TNT) using 1064 nm as an excitation wavelength based on the double resonant Raman effect and the pulsed photoacoustic (PA) technique has been investigated. The study was carried out at a different weight percentage of GP within TNT with respect to the two excitation wavelengths of 532 nm and 1064 nm (30 ps, 10 Hz, Q-switched Nd: YAG laser). The equal and double proportional matrix of the GP and TNT (solid samples) generate a strong PA signal with high quality factor (Q-factor) due to the interaction of optical phonons of GP and TNT in the same phase. The Raman spectra, recorded at 785 nm wavelength provides an insight on the pi-electron coupling between the GP and TNT. The obtained experimental results confirm that the pure GP and its derivatives, which have a SP2/SP3 hybridization, can be used to develop a new sensing optode for the detection and identification of explosive molecules in the visible and near-IR wavelengths range.

Elastic Evaluation of Poly(Lactic Acid) Electrospun Membranes Using the Pulsed Photoacoustic Technique

Fibrous membranes manufactured by electrospinning possess unique features such as a high porosity and large specific surface area, making them suitable for applications in tissue engineering. However, the determination of their mechanical behavior under different loading conditions remains one of the most difficult technical problems for researchers to overcome. While the tensile properties of this kind of membrane are commonly reported in the literature, few explorations of their properties in other directions have been reported. In this paper, the pulsed photoacoustic technique is employed to obtain the elastic constants of electrospun non-woven membranes, specifically in two directions (L, T). The electrospun samples are hybrid fiber membranes of poly(lactic acid) and hydroxyapatite (HA) nanoparticles at different concentrations. It is found that the concentration of HA nanoparticles determines the mechanical response of the membrane, where the nanoparticles act either as a reinforcement or as a mesh defect. The elastic constants ( $$E_{L}, E_{T}, G_{L}, G_{T}, v_{L}$$ , $$\nu _{T}$$ ) are obtained through velocity waves related to the stress–strain equations, using samples with two different geometries and considering the electrospinning mats as a transversely isotropic material. These values are compared to those acquired using macro-tensile testing equipment according to the ASTM D1708 standard.

Evaluation of thermal stability and time resolved acoustic fingerprint spectra of 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole

The paper reports the study of thermal stability and decomposition mechanisms of the newly synthesized phenyl series energetic molecule named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole (S5) using time resolved pulsed photoacoustic (PA) pyro analysis technique. The thermal PA spectra of the compound was recorded using a Q-Switched Nd-YAG laser (532nm, 7ns, 10Hz). TG-DTA technique was carried out for ascertaining the melting and decomposition temperature of the compound. The results of these two methods confirm that S5 is thermally stable in the range of 30–350°C. We have earlier reported that phenyl series 1,2,3-triazoles require high incident laser energy than that of benzyl series 1,2,3-triazoles [1]. However, our further investigation shows that the change in the position of principal functional groups affects the process of thermal decomposition. Also, the thermal stability of the compound is evaluated on the basis of quality factor (Q) of the PA cavity. Further, we have used GC–MS and FTIR techniques to identify some of the gaseous components released from the compounds.

Study of thermal decomposition mechanisms and absorption cross section of nitro-rich phenyl- and bis-series 1,2,3-triazoles.

This paper reports the investigation of thermal decomposition mechanisms and evaluation of thermally released NO2 from two newly synthesized high-energy materials named 1-(4-nitrophenyl)-1H-1,2,3-triazole (S8) and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine (S9) using time-resolved pulsed photoacoustic (PA) pyrolysis technique. The PA spectra were recorded between the 30°C and 350°C range and by varying the pressure of compounds vapor using 532 nm wavelength of pulse duration 7 ns at 10 Hz repetition rate obtained from Q-switched Nd:YAG laser pulses. The PA results were cross verified with thermogravimetric-differential thermal analysis data. The quality factor "&=&Q"&=& of the PA cavity was measured to test the thermal stability of the compound. In addition, we have ascertained the molecular density, absorption cross sections of high-energy materials vapor in terms of NO2. The corresponding values are of the order of 0.1-1.2×10(20) cm-3 and 0.5-6 kilobarn, respectively. These results once again confirm the close agreement between the radiative and nonradiative transitions data and established the role of NO2 during the thermal decomposition process.

Evaluation of thermal stability and acoustic fingerprint spectra of energetic 1,2,4-triazoles based on bond lengths of chemical substituents using pulsed photoacoustic technique

We investigated the effect of the bond lengths of the chemical substituents on the thermal stability of newly synthesized nitro rich 1,2,4-triazoles such as P-Me-DNPT, P-OMe-DNPT, and P-NH2-DNPT using pulsed photoacoustic pyrolysis technique.

Investigation of the thermal decomposition and stability of energetic 1,2,4-triazole derivatives using a UV laser based pulsed photoacoustic technique

The paper reports PA fingerprint spectra, thermal stability and efficiency as rocket fuel for nitro rich energetic materials labeled as p-Me-DNPT, p-OMe-DNPT and p-NH2-DNPT using UV 266 nm based pulsed photoacoustic pyrolysis technique between 30–350 °C range.

Photoacoustic determination of speed of sound in binary mixtures of water and ethyl and methyl alcohol

The speed of sound in binary aqueous solutions of two alcohols by means of the pulsed photoacoustic technique has been determined. Hereby an analysis of the relationships of excess thermodynamic properties of the mixture to the speed of sound in it is presented. It is also shown that neither the Grüneisen coefficient nor the absorption coefficient of the mixtures are additive functions of the composition. The advantage of this method of speed determination lies in its inherent simplicity and the good precision attained. It can be used in tomography of water in different phantoms and potentially in tissues of biological origin.

Investigation of thermal stability and fingerprint spectra of energetic 1,2,3-triazole using pulsed photoacoustic pyrolysis technique

This paper reports on a comparative study of UV and visible radiation-based pulsed photoacoustic (PA) pyrolysis technique examining thermal stability and acoustic fingerprint spectra of a newly synthesized high-energy molecule named 1-(2,4-dinitrobenzyl)-4-nitro-1H-1,2,3-triazole (S6). The thermal PA spectra of S6 were recorded in temperatures ranging between 30 and 350 °C using second and fourth harmonic wavelengths (i.e., 532 and 266 nm), obtained from Q-switched Nd:YAG laser pulses of duration 7 ns at 10 Hz repetition rate. The PA results are further compared with TG–DTA data to understand the release mechanism of NO2 along with other gaseous by-products. The difference in thermal PA spectra of S6 which follows two different mechanisms, such as vibronic transition V–V and V–T relaxation in NO2 functional group, while electronic π* ← n transition in the entire molecule, is due to selection of visible and UV wavelengths. In addition, the effect of data acquisition time and incident laser energy has been examined in order to understand the behavior of acoustic modes of a PA cavity at the desired vapor temperature. The stability of the compound is also evaluated on the basis of thermal quality factor (Q), of PA cavity.

Study of thermal decomposition mechanisms and low-level detection of explosives using pulsed photoacoustic technique

We report a novel time-resolved photoacoustic-based technique for studying the thermal decomposition mechanisms of some secondary explosives such as RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), picric acid, 4,6-dinitro-5-(4-nitro-1H-imidazol-1-yl)-1H-benzo[d] [1, 2, 3] triazole, and 5-chloro-1-(4-nitrophenyl)-1H-tetrazole. A comparison of the thermal decomposition mechanisms of these secondary explosives was made by detecting NO2 molecules released under controlled pyrolysis between 25 and 350 °C. The results show excellent agreement with the thermogravimetric and differential thermal analysis (TGA–DTA) results. A specially designed PA cell made of stainless steel was filled with explosive vapor and pumped using second harmonic, i.e., λ = 532 nm, pulses of duration 7 ns at a 10 Hz repetition rate, obtained using a Q-switched Nd:YAG laser. The use of a combination of PA and TGA–DTA techniques enables the study of NO2 generation, and this method can be used to scale the performance of these explosives as rocket fuels. The minimum detection limits of the four explosives were 38 ppmv to 69 ppbv, depending on their respective vapor pressures.

Synthesis of silver nanoparticles by laser ablation in ethanol: A pulsed photoacoustic study

The pulsed photoacoustic (PA) technique was used to study the synthesis by laser ablation of silver nanoparticles (Ag-NPs) in ethanol. PA technique allowed to determine the production rate per laser pulse and concentration of synthesized Ag-NPs. The samples were produced by using a pulsed Nd:YAG laser with 1064nm of wavelength and 7ns of pulse duration. The laser pulse energy varied from 10 to 100mJ. Transmission electron microscopy micrographs demonstrated that the obtained nanoparticles were spherical with an average size close to 10nm. The absorption spectra of the colloids showed a plasmon absorption peak around 400nm. The PA analyses showed a significant reduction of the production rate of Ag-NPs during the first hundreds of laser pulses. For a higher number of pulses this rate was kept almost constant. Finally, we found that the root mean square (RMS) value of the PA signal was proportional to the laser pulse fluence on the target surface. Thus PA technique was useful to monitor the ablation process.

Study of thermal stability and acoustic fingerprint spectra of phenyl and benzyl triazole derivatives using time resolved pulsed photoacoustic pyro analysis technique

The paper reports the use of pulsed laser based photoacoustic (PA) pyro analysis technique to study the thermal decomposition, stability and acoustic fingerprints of nitro rich phenyl and benzyl triazole derivatives. Two compounds named as 1-(3-methoxy-2,6-dinitrophenyl) -1H-1,2,3-triazole (S10) and 1-(4-methoxy-3,5-dinitrobenzyl)-1H-1,2,3-triazole (S4) are studied using visible 532nm and UV 266nm wavelengths, respectively, obtained from Q-switched Nd:YAG laser of 7ns pulse duration and repetition rate 10Hz. These compounds are also subjected to the thermo gravimetric–differential thermal analysis (TG–DTA) technique. The obtained results of pulsed PA and TG-DTA techniques are used to understand the thermal stability and decomposition mechanism of HEMs. We have also evaluated the thermal quality factor ‘Q’ which plays very important role to test the thermal stability of the S4 and S10 irrespective of incident laser wavelengths.

A pulsed photoacoustic technique for studying red blood cell sedimentation

This study shows the capability of a pulsed photoacoustic (PA) technique to measure red blood cell sedimentation and aggregation processes in vitro . Red blood cells are the main source of absorption in blood. The PA signal is proportional to the sample’s optical absorption coefficient, and hence, dynamic changes in the sample can be monitored by analyzing the PA pulse amplitude and pulse arrival time. Optical coherence tomography (OCT) is used as a parallel method for comparison. Diluted whole blood and different concentrations of washed red blood cells were used as samples. The pulsed PA technique is suitable for monitoring changes in sedimentation velocity when dextran is added to the sample. When the measurement section with the fastest sedimentation rate was selected for analysis, a more than 10-fold increase in the sedimentation rate, induced by dextran, was found with both the PA and OCT techniques. The PA pulse delay was found to be a more reliable measure of changes in the sample than the PA signal amplitude.

Study of acoustic fingerprinting of nitromethane and some triazole derivatives using UV 266 nm pulsed photoacoustic pyrolysis technique

We report a comparative study of acoustic fingerprints of nitromethane, nitrobenzene and some nitro rich triazole derivatives using pulsed photoacoustic technique. UV 266nm wavelength i.e. Fourth harmonic of Q-switched Nd: YAG laser having pulse duration 7ns and 10Hz repetition rate is employed to record the time resolved PA spectrum. The PA fingerprint is produced due to absorption of incident UV light by molecule itself and photo dissociation of nitromethane and nitrobenzene at room temperature while in case of triazole it is attributed to the combination of thermal and photo-dissociation process. The entire dissociation process follows the root of cleavage of C-NO2 bond to produce free NO, NO2 and other by product gases due to π∗←n excitation. In addition, we have studied the thermal stability criteria of nitro rich triazoles based on the quality factor of acoustic resonance frequencies of the PA cavity. We have also studied the effect of data acquisition time to ascertain the decay behavior of HEMs samples.

Thermal stability study of nitro-rich triazole derivatives using temperature dependent time resolved pulsed photoacoustic (PA) technique

The paper reports the pulsed laser based photoacoustic pyrolysis technique to study the thermal stability of novel nitro-rich 1H-1,2,3-triazole derivatives of high energy materials (HEMs) for the first time. We have employed 532nm wavelength, 7ns duration pulses at 10Hz repetition rate obtained from Q-switched Nd:YAG laser system to record the time resolved temperature dependent PA spectra in a specially designed PA pyrolysis system. The study has been carried out between the 30 and 350°C temperature range. Thermally stable HEMs are insensitive to temperature and they release very small amount of volatile compounds such as H2O, NO2, and NO at high temperatures. The combined results obtained from PA and TG–DTA techniques open a new channel to understand the molecular dynamics of HEMs which is responsible for energy storage mechanism of these compounds in terms of free NO2 at different temperature ranges. In addition, the experimental findings lead to develop a new tool to scale the efficiency of these molecules as a fuel.