Light Beam Diameter Research Articles

Application of near-infrared spectroscopy for predicting the wood density of teakwood stands by increment cores and thin wood surface sampling

Density, as the most critical information for wood materials could be predicted by near-infrared (NIR) spectroscopy. Increment cores and thin wood samples of teakwood ( Tectona grandis) served as research materials for this new approach to sampling for NIR spectroscopy, explained in detail. Density data were combined with their NIR spectra data for analysis using cross-validation partial least squares regression as chemometrics to produce a density prediction model. A new approach of increment cores from teakwood stands for NIR spectroscopy measurements for density predictions resulting in a 0.34 coefficient of determination for cross-validation (R2CV) and 0.40 of R2CV for thin wood samples as the best result from the first derivative with 25 smoothing points of NIR spectra. The improvement from the previous research for density prediction accuracy resulted in an R2CV value of 0.55. The smaller diameter of the increment core sample than the NIR light beam's diameter and illuminated mixed surface (transversal and radial) are supposed to give weaker prediction accuracy by this new approach.

Effectiveness of 780 nm photobiomodulation as adjunct treatment for bone exposed fractures: A pilot study on radiograph, pain, and cytokines analysis.

The aim of this study was to evaluate the effectiveness of photobiomodulation with a 780 nm laser as an adjunct to surgical treatment in the regeneration of bone fractures. Twenty patients diagnosed with open fractures in the lower limbs were selected and randomly divided into two groups: control and LLLT. LLLT parameter: 780 nm, 0.04 cm2 of light beam diameter, 40 mW of power, 10 s per point, 0.4 J of energy, fluence of 10 J/cm2 and irradiance of 1 W/cm2. The evaluated data were: pain, using McGill scale, use of analgesics and anti-inflammatories, levels of cytokines TNF-α, IFN-γ, IL-1β, IL-10, and IL-17, and bone level regeneration. Data were analyzed using Wilcoxon and Mann-Whitney tests (5%). We can conclude that LLLT was effective as an adjuvant in the bone fracture regeneration process, altered IL-1β levels, reduced the use of analgesics and anti-inflammatories, reducing the pain pattern throughout the sessions.

Low-Power Photothermal Probing of Single Plasmonic Nanostructures with Nanomechanical String Resonators

We demonstrate the direct photothermal probing and mapping of single plasmonic nanostructures via the temperature-induced detuning of nanomechanical string resonators. Single Au nanoslits and nanorods are illuminated with a partially polarized focused laser beam (λ = 633 nm) with irradiances in the range of 0.26-38 μW/μm(2). Photothermal heating maps with a resolution of ∼375 nm are obtained by scanning the laser over the nanostructures. Based on the string sensitivities, absorption efficiencies of 2.3 ± 0.3 and 1.1 ± 0.7 are extracted for a single nanoslit (53 nm × 1 μm) and nanorod (75 nm × 185 nm). Our results show that nanomechanical resonators are a unique and robust analysis tool for the low-power investigation of thermoplasmonic effects in plasmonic hot spots.

Scanning Polymeric Waveguide Design of a 2-D Display System

Many small-scale display systems used in head-mounted displays (HMDs) create planar images by beaming light from an optical fiber onto deflectable or rotating mirrors. This mirror-based approach has a critical limitation: the hardware of mirror scanners and grating deflectors must be significantly larger than the light beam diameter to avoid undesirable clipping or diffraction effects. Typically, attempting to reduce the size of a conventional display device reduces pixel count by loss of resolution or field-of-view (FOV) of the device. In this paper, we propose a HMD system utilizing a microfabricated 2D optical scanner controlled by a field-programmable gate array (FPGA) that overcomes the size limitations of other systems while maintaining high resolution.

Fluorescence reabsorption calculation and influence on solid-state optical cooling

The calculation model of fluorescence reabsorption and reemission with consideration of reflection on the boundary and material size using Monte Carlo method is proposed. To validate this stochastic model, experiments were conducted, and the calculated steady state spectra showed a good agreement with measurements. Using the absorption and fluorescence spectra of Yb-doped phosphate glass by careful measurements and corrections, we calculated the redshift in the observed fluorescence spectra and external quantum efficiency caused by fluorescence reabsorption and re-emission for the samples with the geometries of cylinder and cuboid. The calculation results show that the fluorescence reabsorption and re-emission have significant influence on the cooling efficiency. The calculation results also show that the cylinder with small waist beam incident (the incident light beam diameter is much less than the size of the sample, and goes through the center of the sample) is suitable for optical cooling.

Large-aperture neodymium-glass disk amplifier

An investigation was made of a neodymium-glass disk amplifier with a light beam diameter of 120 mm. When the pump energy density was 42 J/cm3 the stored energy was 0.26 J/cm3. A gain of 1.8 was obtained for a signal of 20 nsec duration and 2 J/cm2 density.

Effect of gaussian irradiance profile on the switching characteristics and the bit size of the fe/pc memory device

In the ferroelectric/photoconductor (FE/PC device, the effect of a gaussian irradiance profile is to give rise to a variable series resistance, in series with the ferroelectric. Low and high frequency hysteresis loops and the FE-switching transients are obtained as a function of series resistance for pulses of fixed amplitude and variable pulse width. Using a four-quadrant plot, the spatial distribution of the charge switched is estimated. Bit size is defined as the distance between the points where the switched polarization drops to half the amount of polarization switched at the center. The bit sizes are calculated for different photoconductor sensitivities and for different drive pulses. The sublinear lux-ampere characteristic of the photoconductor combined with the gaussian irradiance profile causes the recorded bit size to be larger than the light beam diameter.

High-Speed Facsimile Recording with Laser Light Sources

This paper describes improvements in facsimile receivers for newspaper transmission made by replacing conventional crater tube light sources with He-Ne laser lights. This replacement allows the system to operate at wider frequency bandwidth and provides stronger writing light intensity and longer system durability. The light intensity of the writing source is modulated by a Teglass acoustooptic modulator developed at the present laboratory and is operated under Raman-Nath mode of diffraction. Instabilities in the system have been corrected by a feedback loop using one of the two first-order diffracted lights as an intensity watcher. Experiments show that a filmed image with a transmission density of 3.9 and density rising time of 1μs can be obtained by using an acoustooptic modulator operated at a driving frequency of 40 MHz, an RF power of 300 mW, and an incident light beam diameter of 1 mm.

Effects of Ultrasonic Waves on Gaussian Light Beams with Diameter Comparable to Ultrasonic Wavelength

A theory is developed for diffraction of a Gaussian light beam by arbitrary periodic ultrasonic waves. Special attention is given the case of light beam diameter comparable to ultrasonic wavelength. The approach is essentially an extension of the simplified Raman-Nath theory for normal incidence of light and sound, but the results should predict the general behavior under conditions other than Raman-Nath and/or normal incidence. Criteria for considering the sound beam to be “thin” are considered.

Piezo-Optic Resonances in Crystals of the Dihydrogen Phosphate Type

Besides the Pockels effect, crystals of the dihydrogen phosphate type (symmetry class 4¯2 m) also exhibit an indirect electro-optic effect or piezo-optic effect. This effect is examined both experimentally and theoretically, and expressions for the spatial distribution, amplitude, and frequency response of modulation are derived for the case of a (zxt)0°-cut square plate. The frequency response is found to depend upon the light-beam diameter. The amplitude of the piezo-optic resonances is found to be nearly independent of frequency.

The influence of scintillation on the measurement of extinction with the photo-electric nucleus counter at very low concentrations

The variation of the initial setting of the galvanometer pointer when pure air or air containing only few nuclei is adiabatically expanded in the fog-tube of the photo-electric nucleus counter is described and explained by changes of the optical density of the air-column during expansion. The effect of this scintillation which interferes with the measurements of the extinction at very low concentrations can be eliminated either by using very narrow beams of collimated light in the illuminator of the counter or by selecting a light beam diameter so much smaller than the diameter of the sensitive surface of the photocell or of its diaphragm if used that the variations of the light beam due to scintillation are kept within the boundary of the sensitive surface.