Characterization of thermal modulation of electrical conductivity: a small volume absorbance measurement technique

1989 ◽  
Vol 67 (7) ◽  
pp. 1178-1186 ◽  
Author(s):  
Robert McLaren ◽  
Norman J. Dovichi
Keyword(s):  
Electrical Conductivity ◽  
Laser Beam ◽  
Laser Power ◽  
Spot Size ◽  
Electrode Spacing ◽  
Deuterated Water ◽  
Gaussian Laser Beam ◽  
Thermal Modulation ◽  
Absorbance Detection ◽  
The Difference

Laser-induced thermal modulation of electrical conductivity is a new photothermal method for the measurement of minute absorbance in sub-nanoliter liquid samples. In this paper, a model is presented for the technique. This model is based upon the interaction of a Gaussian laser beam with a cylindrical, homogeneous electrolytic resistor. Particularly simple results are produced if the laser beam spot size is much smaller than the diameter of the electrodes. The theory is verified with respect to the electrode spacing and to the laser power, spot size, and chopping frequency; the highest sensitivity occurs with low chopping frequency, high laser power, and small electrode spacing. The signal is independent of laser spot size, as long as the beam does not illuminate the electrode surface. The precision of the measurement is dominated by shot noise in the current flow through the electrolytic resistor. One point absorbance detection limits of 5.5 × 10−6 measured across the 76-μm diameter electrode wires are obtained in aqueous solution with a 5- mW helium–neon laser. With this instrument, the difference in the absorbance of water and deuterated water is easily determined at 632.8 nm. Keywords: thermal modulation of electrical conductivity.

scholarly journals Influence of Carbon Fiber Incorporation on Electrical Conductivity of Cement Composites

2020 ◽  
Vol 10 (24) ◽  
pp. 8993
Author(s):  
Ilhwan You ◽  
Seung-Jung Lee ◽  
Goangseup Zi ◽  
Daehyun Lim
Keyword(s):  
Electrical Conductivity ◽  
Electrical Resistivity ◽  
Carbon Fiber ◽  
Percolation Threshold ◽  
Cement Composite ◽  
Electrode Spacing ◽  
Cement Composites ◽  
Different Types ◽  
The Difference

This study investigated the effects of carbon fiber (CF) length, electrode spacing, and probe configuration on the electrical conductivity of cement composites. Accordingly, 57 different types of samples were prepared, considering three different CF lengths, five different CF contents, three different electrode spacings, and two different probe configurations. This research found that the influence of CF length on the electrical resistivity of cement composite depends electrode spacing. For the cement composite with wide electrode spacing of 40 mm, its resistivity decreased as increasing CF length as in the previous study. However, when the electrode spacing is 10 mm, which is narrow (10 mm), the resistivity of the cement composite rather increased with increasing CF length. The results implied that when an electrode is designed for the cement composite incorporating CF, the CF length should be short compared to the electrode spacing. The percolation threshold of CF measured by the two-probe configuration was 2% or more. This is higher than that measured by the four-probe configuration (1%). At a lower CF content than 2%, the two-probe configuration gave higher resistivity of the cement composite than the four-probe configuration. However, the difference coming from the different probe configurations was marginal as increasing the CF content.

Computer Simulation of Laser Induced Temperatures for the Laser Direct Writing technique

1987 ◽  
Vol 101 ◽  
Author(s):  
Didier Tonneau ◽  
Geoffroy Auvert
Keyword(s):  
Laser Power ◽  
Quartz Substrate ◽  
Equilibrium Temperature ◽  
Spot Size ◽  
Heat Diffusion ◽  
Laser Spot ◽  
Maximum Temperature ◽  
Substrate Thickness ◽  
Direct Writing ◽  
Gaussian Laser Beam

ABSTRACTLaser induced temperatures in substrates irradiated with a scanning gaussian laser beam were calculated by the finite element method. A quartz substrate of a given thickness and covered with a one - micron - thick silicon coating was assumed to be either placed on a heat sink or thermally insulated. The maximum temperature in the center of the laser spot was found to be proportional to the laser power for a spot size larger than the silicon thickness. Furthermore at a given laser power, the temperature decreased with increasing laser spot diameter and the time to reach the equilibrium temperature increases with the spot radius for radii less than the substrate thickness. The laser induced temperature was found to be affected by laser - scan speeds for speed values above the heat diffusion rate.

scholarly journals Second-harmonic generation by relativistic self-focusing of cosh-Gaussian laser beam in underdense plasma

2015 ◽  
Vol 34 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Arvinder Singh ◽  
Naveen Gupta
Keyword(s):  
Differential Equation ◽  
Second Harmonic Generation ◽  
Laser Beam ◽  
Plasma Wave ◽  
Harmonic Generation ◽  
Second Harmonic ◽  
Spot Size ◽  
Gaussian Laser Beam ◽  
Self Focusing ◽  
Underdense Plasma

AbstractThis paper presents theoretical investigation of effect of relativistic self-focusing of cosh-Gaussian (ChG) laser beam on second-harmonic generation in an underdense plasma. Steep transverse density gradients are produced in the plasma by the electron plasma wave excited by relativistic self-focusing of ChG laser beam. The generated plasma wave interacts with the pump beam to produce its second harmonics. Following Jeffrey Wentzel Kramers Brillouin (J.W.K.B) approximation and moment theory the differential equation governing the evolution of spot size of laser beam with distance of propagation has been derived. The differential equation so obtained has been solved numerically by the Runge–Kutta method to investigate the effect of decentered parameter, intensity of laser beam as well as density of plasma on self-focusing of the ChG laser beam, and generation of its second harmonics. It has been observed that the peak intensity of the laser beam shifts in the transverse direction by changing the decentered parameter and a noticeable change is observed on focusing of the laser beam as well as on conversion efficiency of second harmonics.

scholarly journals Determination of 650nm wavelength for rapid detection of sickle cell anemia

2020 ◽  
Author(s):  
Noor Jadah ◽  
Imad Shamkhi
Keyword(s):  
Laser Beam ◽  
Sickle Cell ◽  
Sickle Cell Anemia ◽  
Laser Power ◽  
Spot Size ◽  
Transmitted Light ◽  
Power Meter ◽  
Hemoglobin Gene ◽  
Anova Table

Abstract Background Sickle cell anemia (SCA), is a type of inherited hemoglobin diseases, It is resulting from point mutation in the β-hemoglobin gene, that resulted from replacement of adenine with thymine, producing a phenotype of sickle hemoglobin (HbS). This paper represents a first try of hemo-photodiagnosis for such disorders using single wavelength, that absorbed by normal blood, so that any change in absorbance value interprets as pathological disorders of hemoglobin. Methods The proposed photobiosensor was designed according to Beer-Lamberts law. The system was involved diode laser of 650nm wavelength, with 100 mW output power, where the laser beam passed through a cuvette of blood sample, and then transmitted light emite to an optical lens to focus transmitted laser beam in to 2mm in diameter of laser spot size on optical sensor window of laser power meter detector that measure the amount of transmitted light in volts. Results The readings that displayed on LCD of laser power meter, had been analyzed using compare means values and ANOVA table of SPSS program. Conclusion The main conclusion that photobiosensor design was able to distinguish between experimental blood groups with respect to hemoglobin pathological conditions.

scholarly journals Long-Pulsed 1064 nm Nd:YAG Laser Treatment for Keloids and Hypertrophic Scars

2020 ◽  
pp. 271-278
Author(s):  
Rei Ogawa
Keyword(s):  
Energy Density ◽  
Laser Beam ◽  
Laser Therapy ◽  
Nd:Yag Laser ◽  
Laser Power ◽  
Vascular Diseases ◽  
Skin Surface ◽  
Spot Size ◽  
Hypertrophic Scars ◽  
Spot Diameter

AbstractThere are many therapeutic options for keloids and hypertrophic scars, including surgery, radiation, corticosteroids, 5-fluorouracil, cryotherapy, laser therapy, anti-allergy agents, anti-inflammatory agents, bleaching creams, and make-up therapies. In terms of laser therapy, we have used long-pulsed 1064 nm Nd:YAG laser to treat keloids and hypertrophic scars. This laser was developed for the treatment of vascular diseases, including inflammatory scars that exhibit neovascularization. The depth that is reached is determined by the spot size, the laser power, and the fluence: the larger the spot size, power, or fluence, the deeper the laser beam penetrates. The laser should generally be applied to the skin surface with the following standard treatment settings: a spot diameter of 5 mm, an energy density of 75 J/cm2, an exposure time per pulse of 25 ms, and a repetition rate of 2 Hz.

scholarly journals Generation of second harmonics of intense Hermite–Gaussian laser beam in relativistic plasma

2019 ◽  
Vol 37 (01) ◽  
pp. 79-85 ◽  
Author(s):  
Jyoti Wadhwa ◽  
Arvinder Singh
Keyword(s):  
Differential Equation ◽  
Electric Field ◽  
Laser Beam ◽  
Second Harmonic ◽  
Incident Beam ◽  
Beam Width ◽  
Spot Size ◽  
Field Vector ◽  
Relativistic Plasma ◽  
Gaussian Laser Beam

AbstractIn this paper, the scheme of generation of second harmonics of incident electromagnetic wave having a Hermite–Gaussian intensity profile in an under dense relativistic plasma has been presented. The relativistic mass variation of electrons by the intense electric field of incident beam generates the density gradients in background plasma which further excites the electron plasma wave (EPW) at resonant frequency and coupling of the EPW with the incident beam results in the generation of second harmonics of incident beam. Propagation dynamics of the Hermite–Gaussian laser beam in plasma has been studied by the formulation of differential equation for the spot size of the laser beam with the help of method of moments. Numerical simulations have been carried out to solve the differential equation for the dimensionless beam width parameters. Solution of the nonlinear wave equation for the electric field vector of second harmonics of incident beam gives the expression for second-harmonic yield. It has been observed that second-harmonic yield is affected by the different modes of Hermite–Gaussian laser beam in relativistic plasma.

Monte Carlo Simulation of Light Distribution in Liver Tumors for 808nm Wavelength Laser

2011 ◽  
Vol 464 ◽  
pp. 663-667
Author(s):  
Guo Ran Hua ◽  
Hua Zhang ◽  
Ai Ping Qian ◽  
Cao Jun Lv
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Temperature Distribution ◽  
Laser Beam ◽  
Laser Power ◽  
Liver Tumors ◽  
Normal Liver ◽  
Action Time ◽  
The Difference ◽  
Interstitial Thermotherapy

Propagation of 808nm wavelength laser beam in liver tumors was simulated with Monte Carlo method. Based on the distribution of light in normal liver and liver tumors, the temperature distribution inside tissue under laser irradiation has been retrieved. Furthermore, the influences of laser power and action time on the temperature field were studied. The results show that the normal liver and liver tumors have different light absorption with laser beam. The difference of temperature distribution in tissues with the same laser power is useful to be applied in control the treatment of laser-induced interstitial thermotherapy for liver tumors.

scholarly journals Growth of spike in relativistic Gaussian laser beam in a plasma and its effect on third-harmonic generation

2017 ◽  
Vol 35 (1) ◽  
pp. 137-144 ◽  
Author(s):  
N. Ahmad ◽  
S. T. Mahmoud ◽  
G. Purohit
Keyword(s):  
Laser Beam ◽  
Beam Width ◽  
Spot Size ◽  
Main Beam ◽  
Gaussian Laser Beam ◽  
Third Harmonic ◽  
Single Beam ◽  
Self Focusing ◽  
Diffraction Divergence ◽  
Paraxial Ray

AbstractA paraxial ray formalism is developed to study the evolution of an on axis intensity spike on a Gaussian laser beam in a plasma dominated by relativistic and ponderomotive non-linearities. Ion motion is taken to be frozen. A single beam width parameter characterizes the evolution of the spike. The spike introduces two competing influences: diffraction divergence and self-convergence. The former grows with the reduction in spot size of the spike, while the latter depends on the gradient in non-linear permittivity. Parameter δ = (ωpr00/c) a00/(3.5 r00/r01) characterizes the relative importance of the two, where r01 and r00 are the spike and main beam radii, ωp is the plasma frequency, and a00 is the normalized laser amplitude. For δ > 1, the intensity ripple causes faster self-focusing of the beam; higher the ripple amplitude stronger the focusing. In the opposite limit, diffraction divergence increases more rapidly, slowing down the self-focusing of the beam. As the beam intensity rises due to self-focusing, it causes stronger generation of the third harmonic.

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