Sorasak Danworaphong

Optical strain characteristics of holographically formed polymer-dispersed liquid crystal films

The optical strain characteristics of a reflective holographic-polymer dispersed liquid crystal are investigated. A spectral blueshift and induced polarization dependence are observed to occur with increasing strain. The spectral dependence on strain is explained by the Poisson contraction of the material and the polarization dependence is largely attributed to elongation of liquid crystal droplets. The material has potential use as an optical strain gauge.

Broadband evolution of phononic-crystal-waveguide eigenstates in real- and k-spaces

Control of sound in phononic band-gap structures promises novel control and guiding mechanisms. Designs in photonic systems were quickly matched in phononics, and rows of defects in phononic crystals were shown to guide sound waves effectively. The vast majority of work in such phononic guiding has been in the frequency domain, because of the importance of the phononic dispersion relation in governing acoustic confinement in waveguides. However, frequency-domain studies miss vital information concerning the phase of the acoustic field and eigenstate coupling. Using a wide range of wavevectors k, we implement an ultrafast technique to probe the wave field evolution in straight and L-shaped phononic crystal surface-phonon waveguides in real- and k-space in two spatial dimensions, thus revealing the eigenstate-energy redistribution processes and the coupling between different frequency-degenerate eigenstates. Such use of k-t space is a first in acoustics, and should have other interesting applications such as acoustic-metamaterial characterization.

Real-time imaging of acoustic rectification

We image gigahertz surface acoustic waves normally incident on a microscopic linear array of triangular holes—a generic “acoustic diode” geometry—with a real-time ultrafast optical technique. Spatiotemporal Fourier transforms reveal wave diffraction orders in k-space. Squared amplitude reflection and transmission coefficients for incidence on both sides of the array are evaluated and compared with numerical simulations. We thereby directly demonstrate acoustic rectification with an asymmetric structure.

Three-dimensional imaging of biological cells with picosecond ultrasonics

We use picosecond ultrasonics to image animal cells in vitro—a bovine aortic endothelial cell and a mouse adipose cell—fixed to Ti-coated sapphire. Tightly focused ultrashort laser pulses generate and detect GHz acoustic pulses, allowing three-dimensional imaging (x, y, and t) of the ultrasonic propagation in the cells with ∼1u2009μm lateral and ∼150u2009nm depth resolutions. Time-frequency representations of the continuous-wavelet-transform amplitude of the optical reflectivity variations inside and outside the cells show GHz Brillouin oscillations, allowing the average sound velocities of the cells and their ultrasonic attenuation to be obtained as well as the average bulk moduli.

Improving the voltage response of holographically-formed polymer dispersed liquid crystals (H-PDLCs)

Abstract We report a significant improvement in the switching voltage of holographic PDLCs. This is achieved by doping the prepolymer with small amounts of organic surfactants. The effect of these dopants on other important H-PDLC performance parameters is also investigated. Possible explanations for the reduction in switching voltage are discussed in relation to simple phenomenological switching models.

P-58: Diffuse H-PDLC Reflective Displays: An Enhanced Viewing-Angle Approach

We demonstrate a Holographic-Polymer Dispersed Liquid Crystal (H-PDLC) with an enhanced viewing-angle, formed by writing a diffuse hologram structure directly into our H-PDLC material. We model the diffuse H-PDLC reflectance by summing over the contributions of discrete grating domains of differing orientations. We use a normal distribution function to weight each orientation to describe the grating densities. SEM studies were performed to determine the morphologies and orientations of multiple gratings within the sample.

Improvement of the antifungal activity of Litsea cubeba vapor by using a helium–neon (He–Ne) laser against Aspergillus flavus on brown rice snack bars

The aim of this study was to improve the antifungal activity of the volatile Litsea cubeba essential oil and its main components (citral and limonene) on brown rice snack bars by applying He-Ne laser treatment. Different volumes (50-200 μL) of L. cubeba, citral or limonene were absorbed into a filter paper and placed inside an oven (18 L). Ten brown rice snack bars (2 cm wide × 4 cm long × 0.5 cm deep) were put in an oven and heated at 180 °C for 20 min. The shelf-life of the treated snack bars at 30 °C was assessed and sensory testing was carried out to investigate their consumer acceptability. A count of total phenolic content (TPC) and Fourier transform infrared spectroscopy (FTIR) on the properties of essential oil, citral, and limonene before and after the laser treatment was studied for possible modes of action. It was found that the laser treatment improved the antifungal activity of the examined volatile L. cubeba and citral with Aspergillus flavus inhibition by 80% in comparison with those of the control not treated with the laser. L. cubeba vapor at 100 μL with the laser treatment was found to completely inhibit the growth of natural molds on the snack bars for at least 25 days; however, without essential oil vapor and laser treatment, naturally contaminating mold was observed in 3 days. Results from the sensory tests showed that the panelists were unable to detect flavor and aroma differences between essential oil treatment and the control. Laser treatment caused an increase in TPC of citral oil whereas the TPC in limonene showed a decrease after the laser treatment. These situations could result from the changing peak of the aliphatic hydrocarbons that was revealed by the FTIR spectra.

Sonochemical Synthesis of Zinc Oxide Nanoparticles Using an Ultrasonic Homogenizer

Zinc oxide nanoparticles were synthesized using a commercial ultrasonic homogenizer in a sonochemical reaction between 0.05 M zinc nitrate and hexamethylenetetramine. The solutions in glass vessels of varying shapes i.e. cube, cylinder and sphere were sonicated with a 45 W 20 kHz ultrasonic pulse for 60 min under ambient conditions. The crystalline ZnO phase was confirmed by powder X-ray diffraction and scanning electron microscopy with average particle diameters around 70 nm from the three different vessels. These ZnO particles were smaller than those previously synthesized in ultrasonic baths and sonoreactors.

Internally excited acoustic resonator for photoacoustic trace detection.

The quantum-cascade laser can be used as an infrared source for a small portable photoacoustic trace gas detector. The device that we describe uses a quantum-cascade laser without collimating optics mounted inside an acoustic resonator. The laser is positioned in the center of a longitudinal resonator at a pressure antinode and emits radiation along the length of the resonator exciting an axially symmetric longitudinal acoustic mode of an open-ended cylindrical resonator. Experiments are reported with an 8-microm, quasi-cw-modulated, room-temperature laser used to detect N2O.

Probability of finding translucent flesh in mangosteen based on its electrical resistance and capacitance

Translucent flesh in mangosteens has been studied extensively in order to predict its presence in the fruit non-destructively. In this work, we propose the use of electrical parameters, capacitance and resistance of mangosteens, to determine the defect. The data are then analyzed employing logistic regression analysis to predict the probability for classification groups; in this case, those with and without translucent defect. The result from the logistic regression analysis reveals that the overall correctness of the prediction at 0.5 cut point is 87.3% which is competitive to those obtained by other means.