Pulsed Laser Stimulation Research Articles

Structural, optical and theoretical studies of 2,4-dichlorobenzoic acid benzamide in nonlinear optical applications using Z-scan technique

New organic 2,4-dichlorobenzoic acid benzamide co-crystal (DCBB) was successfully grown using slow evaporation solution growth technique. The formation of new DCBBco-crystals was taken and their structure and crystallinity were analyzed by single crystal and powder X-ray diffraction analyses. It shows that DCBB material in monoclinic structure with centrosymmetric space group of P21/c. The different vibrations, chemical bonding and chemical configuration of the co-crystal was studied through FTIR, Raman and 1H NMR spectroscopy. Optical transmittance is the basic requirement for the nonlinear optical application with a lower cutoff wavelength of about 320 nm as well as optical band gap value Eg is 3.84 eV. Photoluminescence spectrum showing two emission peaks of 403 and 550 nm by means of an excitation wavelength of 290 nm. The compound's thermal stability was up to 125 °C was analyzed by the thermal analysis. Vickers's micro hardness test was used for evaluating mechanical properties of DCBB, and the results showed that the material was classified as soft category (n = 2.54). Nonlinear optical characteristics of the sample under pulsed laser stimulation by Q-switched Nd:YAG laser with 532 nm wavelength. The presence of reverse saturable absorption peak exhibits 2-photon absorption process was confirmed by varying its intensity shows saturation intensity IS), nonlinear absorption coefficient (β) under pulse laser excitation. The optical limiting threshold determined by three different intensities were found to be 3.02×1012 (W/m2), 2.85×1012 (W/m2) and 1.44×1012 (W/m2) respectively. Theoretical investigations like density functional theory using B3LYP to calculate as well as determining non-linear optical characteristics of the DCBB complex.

A mathematical model for simulating photoacoustic signal generation and propagation in biological tissues

Photoacoustic (PA) medical imaging is a crossbred technique relying on light-induced ultrasonic waves due to the PA effect phenomenon recorded primarily in 1880 by A. G. Bell. Numerical simulation, also known as in-silico, studies assist scientists in minimizing incorrect PA experiments in both in-vitro and in-vivo. Numerical modeling techniques help to achieve a fast simulation process in contrast to pure mathematics alone. However, if a suitable facilitated mathematical model can be established prior to applying numerical modeling, it will be of great interest to the whole numeric model. Numerous mathematical equations, theorems, and propositions have been proposed to model the whole PA signal generation and propagation process in biological media. However, most of them are complicated and difficult to be understood by researchers, especially beginners. That’s why this paper was introduced. Our paper aims to simplify the understanding of the generation and propagation process of biomedical PA waves. We have developed a facilitated mathematical model for the entire process. The introduced developed mathematical model is based on three steps: (1) pulsed laser stimulation, (2) light diffusion, and (3) PA stress wave generation and propagation. The developed mathematical model has been implemented utilizing COMSOL Multiphysics, which relies on the finite element method (FEM) numerical modeling principle. The in-silico time-dependent study's results confirmed that the proposed mathematical model is a simple, efficient, accurate, and quick starting point for researchers to simulate biomedical PA signals' generation and propagation process utilizing any suitable software such as COMSOL multiphysics.

Quantitative beta autoradiography of a heterogeneous granulite sample and implications for luminescence dating

Beta dose rate heterogeneity is a known source of scatter in OSL measurement and equivalent dose distributions. Without proper methods to describe and account for it, it can contribute significantly to the uncertainties in OSL ages. For this reason, investigating the beta dose rate (β Dr) distribution is necessary to improve the dating of heterogeneous samples. Here we present a method for quantitative and high sensitivity autoradiographic imaging of beta dose rates. It is demonstrated using highly heterogeneous granulite rock samples. The accuracy and sensitivity of this method is improved using pulsed laser stimulation, and by underground exposure of samples in an ultra-low background environment. Results are calibrated using gamma (γ)irradiation and Monte Carlo simulation and have been validated using homogeneous dose rate standards. Combining analysis of autoradiography results and SEM backscattered images of the same samples allows determination of the dose rate distributions in the different mineral phases. A significant difference between the dose rate of K-feldspar grains obtained from the imaging and the dose rates calculated using methods commonly used in OSL dating is noted because of the clustering of grains in the sample. This represents a risk of bias in age determination in coarse grained rock samples which can be analysed using dose rate imaging methods. The beta Dr spatial distributions result in a significant dose scattering received by single grains, even compared to the total dose rate. The effect of such beta dose rate distributions on OSL dating of coarse-grained crystalline materials is discussed.

Stochastic exciton-scattering theory of optical line shapes: Renormalized many-body contributions.

Spectral line shapes provide a window into the local environment coupled to a quantum transition in the condensed phase. In this paper, we build upon a stochastic model to account for non-stationary background processes produced by broad-band pulsed laser stimulation, as distinguished from those for stationary phonon bath. In particular, we consider the contribution of pair-fluctuations arising from the full bosonic many-body Hamiltonian within a mean-field approximation, treating the coupling to the system as a stochastic noise term. Using the Itô transformation, we consider two limiting cases for our model, which lead to a connection between the observed spectral fluctuations and the spectral density of the environment. In the first case, we consider a Brownian environment and show that this produces spectral dynamics that relax to form dressed excitonic states and recover an Anderson-Kubo-like form for the spectral correlations. In the second case, we assume that the spectrum is Anderson-Kubo like and invert to determine the corresponding background. Using the Jensen inequality, we obtain an upper limit for the spectral density for the background. The results presented here provide the technical tools for applying the stochastic model to a broad range of problems.

Towards Safe Infrared Nerve Stimulation: A Systematic Experimental Approach.

Neural activation by infrared nerve stimulation (INS) gains growing interest as a potential alternative to conventional electric nerve stimulation, since unambiguous advantages like contact-free operation, enhanced spatial selectivity and lack of (electrical) stimulation artifacts are promising for both future electrophysiological research and clinical application. For the systematic investigation of laser nerve activation, we recently introduced a novel experimental approach. Comprising a defined focused beam profile, it enables remote controlled, contact-free pulsed laser stimulation of the rat sciatic nerve, simultaneous to high-speed temperature measurement in vivo. Up to now, successful neural activation with single laser pulses (2 - 6 mJ) was observed in all performed experiments, however, it strongly depended on the particular nerve location. Hence, we depict the investigation of spatial dependency of the nerve response and identify `regions of excitability' on the nerve surface, that are highly susceptible to INS. By means of thermal imaging, we simultaneously monitored the nerve surface temperature, where we observed progressing temperature build-up during single pulse stimulation with repetition rates above 4 Hz. In this work, we present current results of our ongoing research.

In vivo auditory nerve stimulation with visible light

Background: Infrared laser stimulation has been proposed as an innovative method to elicit an auditory nerve response. Most studies have focused on using long-wavelength infrared ([Formula: see text][Formula: see text]nm) pulsed lasers with high water absorption coefficients. This paper sought to assess whether a short-wavelength laser (465[Formula: see text]nm) with an absorption coefficient as low as 10[Formula: see text][Formula: see text]cm[Formula: see text] would activate the auditory nerve and studied its potential mechanism. Method: Optical compound action potentials (OCAPs) were recorded when synchronous trigger laser pulses stimulate the cochlea before and after deafening, varying the pulse durations (from 800[Formula: see text][Formula: see text]s to 3600[Formula: see text][Formula: see text]s) and the amount of radiant energy (from 18.05[Formula: see text]mJ/cm2 to 107.91[Formula: see text]mJ/cm2). A thermal infrared imager was applied to monitor the temperature change of the guinea pig cochlea. Results: The results showed that pulsed laser stimulation at 465[Formula: see text]nm could invoke OCAPs and had a similar waveform compared to the acoustical compound action potentials. The amplitude of OCAPs had a positive correlation with the increasing laser peak power, while the latency of OCAPs showed a negative correlation. The imager data showed that the temperature in the cochlea rose quickly by about 0.3[Formula: see text]C right after stimulating the cochlea and decreased quickly back to the initial temperature as the stimulation ended. Conclusions: This paper demonstrates that 465-nm laser stimulation can successfully induce OCAPs outside the cochlea, and that the amplitude and latency of the invoked OCAPs are highly affected by laser peak power. This paper proposes that a photothermal effect might be the main mechanism for the auditory nerve response induced by short-wavelength laser stimulation.

Optoacoustic effect is responsible for laser-induced cochlear responses

Optical stimulation of the cochlea with laser light has been suggested as an alternative to conventional treatment of sensorineural hearing loss with cochlear implants. The underlying mechanisms are controversially discussed: The stimulation can either be based on a direct excitation of neurons, or it is a result of an optoacoustic pressure wave acting on the basilar membrane. Animal studies comparing the intra-cochlear optical stimulation of hearing and deafened guinea pigs have indicated that the stimulation requires intact hair cells. Therefore, optoacoustic stimulation seems to be the underlying mechanism. The present study investigates optoacoustic characteristics using pulsed laser stimulation for in vivo experiments on hearing guinea pigs and pressure measurements in water. As a result, in vivo as well as pressure measurements showed corresponding signal shapes. The amplitude of the signal for both measurements depended on the absorption coefficient and on the maximum of the first time-derivative of laser pulse power (velocity of heat deposition). In conclusion, the pressure measurements directly demonstrated that laser light generates acoustic waves, with amplitudes suitable for stimulating the (partially) intact cochlea. These findings corroborate optoacoustic as the basic mechanism of optical intra-cochlear stimulation.

Near-Infrared Laser Stimulation of the Auditory Nerve in Guinea Pigs

Shenzhen Second People’s Hospital, Shenzhen, Guangdong 518035, P. R. China(Received November 17, 2015 : revised February 26, 2016 : accepted February 29, 2016)This study has investigated the feasibility of 980-nm low-energy pulsed near-infrared laser stimulation to evoke auditory responses, as well as the effects of radiant exposure and pulse duration on auditory responses. In the experiments, a hole was drilled in the basal turn of the cochlea in guinea pigs. An optical fiber with a 980-nm pulsed infrared laser was inserted into the hole, orientating the spiral ganglion cells in the cochlea. To model deafness, the tympanic membrane was mechanically damaged. Acoustically evoked compound action potentials (ACAPs) were recorded before and after deafness, and optically evoked compound action potentials (OCAPs) were recorded after deafness. Similar spatial selectivity between optical and acoustical stimulation was found. In addition, OCAP amplitudes increased with radiant exposure, indicating a photothermal mechanism induced by optical stimulation. Furthermore, at a fixed radiant exposure, OCAP amplitudes decreased as pulse duration increased, suggesting that optical stimulation might be governed by the time duration over which the energy is delivered. Thus, the current experiments have demonstrated that a 980-nm pulsed near-infrared laser with low energy can evoke auditory neural responses similar to those evoked by acoustical stimulation. This approach could be used to develop optical cochlear implants.Keywords : Cochlear implant, Pulsed near-infrared laser, Optical stimulation, Optical compound action potentialOCIS codes : (170.0170) Medical optics and biotechnology; (170.3890) Medical optics instrumentation

Electrical model of an inverter body-biased structure in triple-well technology under pulsed photoelectric laser stimulation

This study is driven by the need to optimize reliability and failure analysis methodologies based on laser/silicon interactions with an integrated circuit using a triple-well process. Nowadays, single event effect (SEE) evaluations due to radiation impacts are critical in fault tolerance and security field. The prediction of a SEE occurring on electronic devices is proposed by the determination and modeling of the phenomena under pulsed laser stimulation. This paper presents measurements of the photoelectric currents induced by a pulsed-laser on an inverter in a triple-well Psubstrate/DeepNwell/Pwell structure dedicated to low power body biasing techniques. It reveals the possible activation change of the parasitic bipolar transistors. Based on these experimental measurements, an electrical model is proposed that makes it possible to simulate the effects induced by photoelectric laser stimulation. Therefore this electrical model could be used as a tool for characterizing more complex CMOS circuits under photoelectrical laser stimulation.

The use of graphene in the self-organized differentiation of human neural stem cells into neurons under pulsed laser stimulation.

An effective and self-organized differentiation of human neural stem cells (hNSCs) into neurons was developed by the pulsed laser stimulation of the cells on graphene films (prepared by drop-casting a GO suspension onto quartz substrates). The effects of graphene oxide (GO) and hydrazine-reduced graphene oxide (rGO) sheets on the proliferation of hNSCs were examined. The higher proliferation of the cells on the GO was assigned to its better hydrophilicity. On the other hand, the rGO sheets, which have significantly better electrical conductivity than GO, exhibited more differentiation of the cells into neurons. The pulsed laser stimulation not only resulted in an accelerated differentiation of hNSCs into neurons (rather than glia), but also caused the self-organization of a radial neuronal network on the surface of the rGO sheets, due to the radial stress induced by the surface thermal gradient originating from the center of the laser spot. The higher thermal conductivity of the rGO sheets (compared to the GO sheets and the quartz substrate) provided better outward heat flow from the center of the laser spot, and consequently, prevented extra local heating at the position of the laser spot. These results can encourage further investigations into the advantages of graphene in the self-organized differentiation of hNSCs using pulsed laser stimulation.

Applied Technology in Evoked Auditory Response <i>In Vivo</i> Animal Cochlea by 980nm Pulsed Laser Light

Optical cochlear implant is an emerging applied technology of stimulating auditory neurons by using pulsed laser light as a stimulus to evoke neural activity instead of electrical currents. Laser stimulation has more potential in accuracy and high frequency resolution than electrical stimulation. In this paper we demonstrated a fiber laser system (980nm) to irradiate on guinea pig cochlear in vivo for the first time. The pulsed laser stimulation successfully evoked auditory nervous impulse, similar to acoustic stimulation. And the performance under different laser pulse intensity and pulse width is further tested and discussed. The results show that the 980nm pulsed laser stimulation with microsecond level width is effective and safe to evoke auditory response. Photoacoustic or photothermal effects maybe the main mechanism. In the end, we put forward some prospects of the applied technology in cochlear implant.

Electrical modeling of the photoelectric effect induced by a pulsed laser applied to an SRAM cell

This abstract presents an electrical model of an SRAM cell exposed to a pulsed Photoelectrical Laser Stimulation (PLS), based on our past model of MOS transistor under laser illumination. The validity of our model is assessed by the very good correlation obtained between measurements and electrical simulation. These simulations are capable to explain some specific points. For example, in theory, a SRAM cell under PLS have four sensitive areas. But in measurements only three areas were revealed. A hypothesis was presented in this paper and confirmed by electrical simulation. The specific topology of the cell masks one sensitive area. Therefore the electrical model could be used as a tool of characterization of a CMOS circuits under PLS.

New Combined Approach for the Evaluation of the Soft-Errors of Complex ICs

In this paper, we propose to investigate the relevance of a combined use of the methodologies commonly used to estimate the fault tolerance of complex integrated circuits (IC) towards radiation effects, in order to propose a clear procedure for estimating this sensitivity. As presented, each of the well-known methodologies is relevant to provide a particular type of result: the pulsed laser stimulation (PLS) to analyze the device memory layout as well as to validate the test set up thanks to fault injection, the accelerator test to evaluate the static soft-error rate (SER), and the Statistical Fault Injection (SFI) to determine the derating factor due to the circuit and the application. Nevertheless, taken separately, none of them is suitable to exhaustively assess the SER at application level in complex ICs. This paper presents an accurate methodology coupling those techniques applied on a STRATIX IV FPGA target with an embedded Nios II Soft-Core running different applications.

Pulsed wavelength-dependent laser stimulation of the inner ear

Article Pulsed wavelength-dependent laser stimulation of the inner ear was published on September 6, 2012 in the journal Biomedical Engineering / Biomedizinische Technik (volume 57, issue SI-1-Track-P).

Infrared light excites cells by changing their electrical capacitance.

Optical stimulation has enabled important advances in the study of brain function and other biological processes, and holds promise for medical applications ranging from hearing restoration to cardiac pace making. In particular, pulsed laser stimulation using infrared wavelengths >1.5 μm has therapeutic potential based on its ability to directly stimulate nerves and muscles without any genetic or chemical pre-treatment. However, the mechanism of infrared stimulation has been a mystery, hindering its path to the clinic. Here we show that infrared light excites cells through a novel, highly general electrostatic mechanism. Infrared pulses are absorbed by water, producing a rapid local increase in temperature. This heating reversibly alters the electrical capacitance of the plasma membrane, depolarizing the target cell. This mechanism is fully reversible and requires only the most basic properties of cell membranes. Our findings underscore the generality of pulsed infrared stimulation and its medical potential.

Time-resolved measurements of optically stimulated luminescence of Al2O3:C and Al2O3:C,Mg

This study investigates the components of the optically stimulated luminescence (OSL) signal from enhanced aluminum oxide doped with carbon and magnesium (Al2O3:C,Mg), a new material developed for optical data storage and nuclear track detection. The objective is to understand the OSL properties of Al2O3:C,Mg in comparison to Al2O3:C (the most commonly used OSL detector) and to explore the potential of Al2O3:C,Mg for applications in luminescence dosimetry. The study includes continuous-wave OSL (CW-OSL) and time-resolved OSL (TR-OSL) measurements under pulsed laser stimulation. The results show that the OSL emission from Al2O3:C,Mg is similar to Al2O3:C, but the UV emission at 330 nm attributed to F+ centers is more intense in Al2O3:C,Mg than in Al2O3:C. Moreover, we observed a delayed UV emission with a luminescence lifetime of ∼3 ms which can be explained by the influence of shallow traps related to thermoluminescence (TL) peaks below room temperature.

Spatial extent of cochlear infrared neural stimulation determined by tone-on-light masking

Artificial neural stimulation is widely used in clinic, rehabilitation, and research. One of the limitations of electrical stimulation is the current spread in tissue. Recently, pulsed mid-infrared laser stimulation of nerves has been investigated as an alternative stimulation method. The likely benefits of infrared neural stimulation (INS) include spatial selectivity of stimulation, noncontact mode of operation, and the lack of stimulation artifact in simultaneous electrical recordings. The hypothesis for this study is that INS of the cochlear spiral ganglion at low pulse energy is as spatially selective as low-level tonal stimulation of the cochlea. Spatial selectivity was measured using a masking method. An optical pulse with fixed optical parameters was delivered through a 200-μm diameter optical fiber. An acoustic tone, variable in frequency and level, was presented simultaneously with the optical pulse. Tone-on-light masking in gerbils revealed tuning curves with best frequencies between 5.3 and 11.4 kHz. The width of the tone-on-light tuning curves was similar to the width of tone-on-tone tuning curves. The results indicate that the spatial area of INS in the gerbil cochlea is similar to the cochlear area excited by a low level acoustic tone, showing promising results for future use of INS in implantable cochlear prostheses.

Timing analysis of scan design integrated circuits using stimulation by an infrared diode laser in externally triggered pulsing condition

This paper presents a new timing analysis methodology for clock driven scan design integrated circuits, based on externally triggered pulsed laser stimulation. The laser pulse can easily be shifted to time windows of interest in reference to clock and scan pattern. It is demonstrated that the technique is able to identify the most sensitive signal condition for fault injection with a time resolution correlated to the signal switching time, offering new opportunities to failure analysis.

Pulsed Mid-Infrared Laser Stimulation of the Auditory Nerve in the Gerbil: Implications for Cochlear Implants

Light can artificially stimulate nerve activity in vivo and has the advantage of a higher spatial selectivity relative to that which can be obtained with electrical stimulation. An increased spatial selectivity of stimulation could improve the function of neuroprosthetics, such as cochlear implants, whose performance is limited by overlapping electric fields from neighboring electrodes. The studies reported here investigated optical stimulation of nerves in the gerbil auditory system. Pulsed, infrared light was used to elicit compound action potentials (CAPs) from the gerbil cochlea in vivo. Penetration depth was varied by changing the wavelength of irradiation, to select the tissue depth of stimulation. Experiments showed no immediate damage to the cochlea when optically stimulating at 400Hz for several hours. Immunohistochemical staining for the protein c-FOS revealed spatial specificity of the optically stimulated cochleae: only the spiral ganglion cells directly in the optical path revealed c-FOS staining, indicating that they were stimulated. In contrast, c-FOS staining of electrically stimulated cochleae demonstrated electric current spread. An electrophysiologic measurement of the spatial specificity of optical stimulation was conducted with tone-on-light masking experiments. Results from tone-on-light masking studies revealed tuning curves that were similar in extent to tone-on-tone tuning curves.

Special features of formation of plasma torch under conditions of hybrid laser-arc welding

This paper is devoted to analytical description of processes occurring in hybrid discharge plasma under conditions of laser-arc welding with deep melting. The axially symmetric boundary layer approximation is used to solve the problem on the outflow of a jet of hot metal vapor into an atmosphere of cold protective helium gas in view of the compressibility of gas mixture and of the bulk heat release during absorption of laser radiation in plasma. In so doing, the degree of ionization of plasma is determined from the solution of kinetic problem in the approximation of constant collision frequencies for a helium-iron mixture without the assumption of local thermal equilibrium. A series of experiments in the interferometry of plasma torch under conditions of pulsed laser stimulation of metal targets are performed to confirm the obtained results.