Light Flux Measurements Research Articles

Frequency characteristics of basic mode oscillation at liquid-liquid interface of electrowetting liquid lens

A few microliters of oil and aqueous solution with same density encapsulated in a cylinder forms a spherical interface. In this paper, the frequency characteristics of the basic oscillation mode at the liquid-liquid interface inside the electrowetting lens is obtained by using the light flux measurement. It is found that the intrinsic frequency of the basic oscillation mode at the liquid-liquid interface changes accordingly with the amplitude of applied voltage, while the displacement of the center of the interface decreases with the increase of frequency. This work provides guiding for optimizing driving of the electrowetting liquid lens and other related microfluidic devices, and is also helpful to the study of forced oscillation of capillary wave in a cylinder.

Modeling the luminous intensity of Beijing, China using DMSP-OLS night-time lights series data for estimating population density

Various scientific researches were conducted to monitor human activities and natural phenomena with the availability of various night time satellite data such as Defense Meteorological Satellite Program (DMPS). Population growth especially in a faster growing economy like China is an important indicator for assessing socio-economic development, urban planning and environmental management. Thus, spatial distribution of population is instrumental in assessing growth and developmental activities in Beijing city of China. The satellite observation data derived from Defense Meteorological Satellite Program (DMSP) was utilized to estimate population density through the measurement of light flux with radiometric recording. The data was calibrated using C0, C1, C2 parameters before processing. Population density of Beijing city was estimated using light volume of this calibrated data. Regression analysis between urban population and light volume revealed high correlation (r2=0.89). Thus, population density can effectively be estimated using light intensity. The model used for estimating urban population density can effectively be utilized for other major cities of the world.

New functional capabilities of quartz for laser parameter measurements

This paper presents novel pyroelectric sensor design concepts for laser output measurements using a pyroelectric response induced in quartz. The proposed sensor design strategy relies on the relationship between the electric field configuration in a thermodynamically nonequilibrium crystal and the purpose-designed electrode geometry for light flux measurements. We describe various classes of pyroelectric sensors based on polarisation effects.

Organic Suspension Behavior of Rutile TiO<SUB>2</SUB> Nanoparticles with High Specific Surface Area

Sedimentation properties of the TiO2 nanoparticles with very high specific surface area (about 180 m 2 /g) based on the BET method have been investigated in various organic solvents. The TiO2 nanocolloid in the isopropyl alcohol displayed a considerably high electrostatic repulsive force, compared to that in other solvents, with negligible coalescence between the particles. Both the backscattered light flux measurements and scanning electron microscopy confirmed that in the cases of water, methyl alcohol and ethyl alcohol, a progressive sedimentation of the TiO2 particles was observed at the bottom due to a flocculation-induced particle growth, while a very stable TiO2 dispersion was observed in isopropyl alcohol. [doi:10.2320/matertrans.M2010245]

New bioreactor for in situ simultaneous measurement of bioluminescence and cell density

This article presents a new device devoted to the simultaneous measurement of bioluminescence and optical density of a bioluminescent bacterial culture. It features an optoelectronic bioreactor with a fully autoclavable module, in which the bioluminescent bacteria are cultivated, a modulated laser diode dedicated to optical density measurement, and a detection head for the acquisition of both bioluminescence and optical density signals. Light is detected through a bifurcated fiber bundle. This setup allows the simultaneous estimation of the bioluminescence and the cell density of the culture medium without any sampling. The bioluminescence is measured through a highly sensitive photomultiplier unit which has been photometrically calibrated to allow light flux measurements. This was achieved by considering the bioluminescence spectrum and the full optical transmission of the device. The instrument makes it possible to measure a very weak light flux of only a few pW. The optical density is determined through the laser diode and a photodiode using numerical synchronous detection which is based on the power spectrum density of the recorded signal. The detection was calibrated to measure optical density up to 2.5. The device was validated using the Vibrio fischeri bacterium which was cultivated under continuous culture conditions. A very good correlation between manual and automatic measurements processed with this instrument has been demonstrated. Furthermore, the optoelectronic bioreactor enables determination of the luminance of the bioluminescent bacteria which is estimated to be 6×10−5 W sr−1 m−2 for optical density=0.3. Experimental results are presented and discussed.

Statistical analysis of nonlinearly reconstructed near-infrared tomographic images: Part I--Theory and simulations.

Near-infrared (NIR) diffuse tomography is an emerging method for imaging the interior of tissues to quantify concentrations of hemoglobin and exogenous chromophores non-invasively in vivo. It often exploits an optical diffusion model-based image reconstruction algorithm to estimate spatial property values from measurements of the light flux at the surface of the tissue. In this study, mean-squared error (MSE) over the image is used to evaluate methods for regularizing the ill-posed inverse image reconstruction problem in NIR tomography. Estimates of image bias and image standard deviation were calculated based upon 100 repeated reconstructions of a test image with randomly distributed noise added to the light flux measurements. It was observed that the bias error dominates at high regularization parameter values while variance dominates as the algorithm is allowed to approach the optimal solution. This optimum does not necessarily correspond to the minimum projection error solution, but typically requires further iteration with a decreasing regularization parameter to reach the lowest image error. Increasing measurement noise causes a need to constrain the minimum regularization parameter to higher values in order to achieve a minimum in the overall image MSE.

Light-emitting diodes as a light source for intraoperative photodynamic therapy.

The development of more cost-effective light sources for photodynamic therapy of brain tumors would be of benefit for both research and clinical applications. In this study, the use of light-emitting diode arrays for photodynamic therapy of brain tumors with Photofrin porfimer sodium was investigated. An inflatable balloon device with a light-emitting diode (LED) tip was constructed. These LEDs are based on the new semiconductor aluminum gallium arsenide. They can emit broad-spectrum red light at high power levels with a peak wavelength of 677 nm and a bandwidth of 25 nm. The balloon was inflated with 0.1% intralipid, which served as a light-scattering medium. Measurements of light flux at several points showed a high degree of light dispersion. The spectral emission of this probe was then compared with the absorption spectrum of Photofrin. This analysis showed that the light absorbed by Photofrin with the use of the LED source was 27.5% of that absorbed with the use of the monochromatic 630-nm light. Thus, to achieve an energy light dose equivalent to that of a laser light source, the LED light output must be increased by a factor of 3.63. This need for additional energy is the difference between a 630- and 677-nm absorption of Photofrin. Using the LED probe and the laser balloon adapter, a comparison of brain stem toxicity in canines was conducted. LED and laser light showed the same signs of toxicity at equivalent light energy and Photofrin doses. The maximal tolerated dose of Photofrin was 1.6 mg/kg, using 100 J/cm2 of light energy administered by laser or LED. This study concludes that LEDs are a suitable light source for photodynamic therapy of brain tumors with Photofrin. In addition, LEDs have the potential to be highly efficient light sources for second-generation photosensitizers with absorption wavelengths closer to the LED peak emission.

Errors and Error‐Avoidance in the Schottky Coupled Surface Photovoltage Technique

We have examined sources of error and techniques for error avoidance in Schottky barrier surface photovoltage measurements. In particular we have used a computer simulation approach to gauge the errors in the method A formalism, which is applied to analyzing constant open‐circuit voltage measurements, and in the method B formalism, which is applied to analyzing constant light flux measurements. As a result of this analysis, we have shown we can eliminate the extreme measurement precautions necessitated by method B through the use of a new method C formalism which is introduced here. We also show that, for measured diffusion lengths less than one‐third the sample thickness, the measurement is shown to be forgiving of the state of the back contact if that surface has flat or accumulated bands; however, if the back surface is rectifying, the range of the measurement validity can be affected by the magnitude of the front contact barrier height, even with the measured diffusion length less than one‐third the sample thickness.

Pulsed light flux measurement by a photodiode-operational amplifier pair

Pulsed light flux measurement by a photodiode-operational amplifier pair

Optimization of the photodiode-operational amplifier pair for weak light flux measurements

Optimization of the photodiode-operational amplifier pair for weak light flux measurements

Television-electronics study of faint astronomical objects

Advances in modern television detection techniques have resulted in a new and highly effective method for the study of astronomical objects. Its quantum efficiency approaches that of the instrument's input photocathode, the errors of light-flux measurement are in the tenths of a per cent, and use with on-line computers greatly reduces the time required to process observations. Practical use of the television techniques in the world's leading observatories has demonstrated its promise and produced qualitatively new results in studies of faint variable stars, x-ray sources, galaxies, quasars, and radio sources.

Experimental and Theoretical Comparison of Photon-Counting and Current Measurements of Light Intensity

The effect of gain variation on the integrated output-charge distribution of a photomultiplier tube is investigated experimentally and shown to be a predictable function of the multiplier single-electron response. Standardized or nonstandardized pulses recorded using either capacitive or digital storage are considered. Theoretical values for the moment-generating functions and variances (noise powers) of the charge distributions obtained in these four cases are given, and the role of these various distributions in determining the length of time required to achieve a given accuracy in a light-flux measurement is discussed. The experimental measurements adequately confirm the theoretical predictions. The work includes a critical discussion of the field of theoretical and experimental noise investigations in photomultiplier tubes with regard to their relevance in the present state of technology.

Interaction of Light with a Plant Canopy*

The Kubelka–Munk (K–M) theory has been applied to light interaction with leaves stacked in a laboratory spectrophotometer. The theory can also be applied to an actual field plant canopy. The K–M theory is a two-parameter generalization of the one-parameter Bouguer–Lambert, or Beer’s law, relation. The older theory accounts for transmittance of a medium but not for reflectance. The K–M theory, however, yields a theoretical value both for reflectance and transmittance. The K–M theory is applied in this paper to the reflectance and transmittance of stacked mature cotton leaves over the spectral range 0.5–2.5 μ. The standard deviation between theory and experiment, after known biases are calculated and removed from the data, is about 1%—a discrepancy well within experimental error. A procedure is developed to apply the K–M theory to an actual plant canopy. The method involves regression analysis to light flux measurements within a plant canopy. Differential coefficients are derived for use in both stacked-leaf and canopy applications.

Quantitative Evaluation of Spots on Paper Chromatograms. Light-Flux Measurement through Negative Printed Spots

Quantitative Evaluation of Spots on Paper Chromatograms. Light-Flux Measurement through Negative Printed Spots