Romeric Pobre | De La Salle University (original) (raw)

Papers by Romeric Pobre

Anticancer research, Jul 1, 2017

We present an analysis of the effects of pulsed electromagnetic fields (PEMF) with 3.3 MHz carrie... more We present an analysis of the effects of pulsed electromagnetic fields (PEMF) with 3.3 MHz carrier frequency and modulated by audio resonant frequencies on the MCF-7 breast cancer cell line in vitro using absorption spectroscopy. This involves a fluorescence dye called PrestoBlue™ Cell Viability Reagent and a spectrophotometry to test the viability of MCF-7 breast cancer cells under different PEMF treatment conditions in terms of the cell absorption values. The DNA molecule of the MCF-7 breast cancer cells has an electric dipole property that renders it sensitive and reactive to applied electromagnetic fields. Resonant frequencies derived from four genes mutated in MCF-7 breast cancer cells [rapamycin-insensitive companion of mammalian target of rapamycin (RICTOR), peroxisome proliferator-activated receptor (PPARG), Nijmegen breakage syndrome 1 (NBN) and checkpoint kinase 2 (CHEK2)] were applied in generating square pulsed electromagnetic waves. Effects were monitored through measur...

World Congress on Medical Physics and Biomedical …, 2007

We investigated thermal diffusion of Kerr nanobead under a tightly-focused laser beam. Kerr nanob... more We investigated thermal diffusion of Kerr nanobead under a tightly-focused laser beam. Kerr nanobeads refer to small beads whose refractive index is governed by n 2= n 2 (0)+ n 2 (1)| E* E|; where n 2 (0) is the linear component of the refractive index, n 2 (1) is the nonlinear ...

Optics …, 2008

A hollow-core microstructured polymer optical fiber was analyzed in the terahertz (THz) region. S... more A hollow-core microstructured polymer optical fiber was analyzed in the terahertz (THz) region. Spectral analysis of time domain data shows propagation of THz waves in both the hollow-core and the microstructured cladding with a time delay of approximately 20 ps. The frequency range and shift of the transmission bands between different sized waveguides suggested photonic bandgap or resonant guidance. Finite-difference time domain calculations agree relatively well to the experimental transmission results. Propagation losses were estimated to be as low as 0.9 dB/cm.

Applied optics, 2002

We determine the characteristics of the radiation force that is exerted on a nonresonant nonlinea... more We determine the characteristics of the radiation force that is exerted on a nonresonant nonlinear ͑Kerr-effect͒ rigid microsphere by a strongly focused Gaussian beam when diffraction and interference effects are significant ͑sphere radius a Յ illumination wavelength ͒. The average force is calculated from the surface integral of the energy-momentum tensor consisting of incident, scattered, and internal electromagnetic field vectors, which are expressed as multipole spherical-wave expansions. The refractive index of a Kerr microsphere is proportional to the internal field intensity, which is computed iteratively by the Rytov approximation ͑residual error of solution, 10 Ϫ30 ͒. The expansion coefficients for the field vectors are calculated from the approximated index value. Compared with that obtained in a dielectric ͑linear͒ microsphere in the same illumination conditions, we find that the force magnitude on the Kerr microsphere is larger and increases more rapidly with both a and the numerical aperture of the focusing objective. It also increases nonlinearly with the beam power unlike that of a linear sphere. The Kerr nonlinearity also leads to possible reversals of the force direction. The proposed technique is applicable to other types of weak optical nonlinearity.

Applied optics, 1997

We analyze the characteristics of the radiation force that is generated when a highly focused unp... more We analyze the characteristics of the radiation force that is generated when a highly focused unpolarized Gaussian beam interacts with a nonabsorbing microsphere whose refractive index exhibits a first-order dependence on the beam intensity. The behavior of the force exerted on the sphere is analyzed as a function of beam power, axial distance, sphere radius, refractive-index difference between the sphere and the surrounding liquid, and wavelength. The force characteristics are compared with those of the radiation force that is generated when the electro-optic Kerr effect is absent. Our results show that a reversal in the net force direction is introduced when the Kerr effect becomes significant, which occurs at sufficiently high beam intensities.

Journal of Photochemistry and Photobiology A-chemistry, 2006

We present terahertz (THz) emission of optically pumped 5-nm GaAs/AlGaAs multiple quantum wells (... more We present terahertz (THz) emission of optically pumped 5-nm GaAs/AlGaAs multiple quantum wells (MQWs) even at excitation energies below the bandgap. The excitation energy corresponding to the peak THz emission is red-shifted with respect to the photoluminescence (PL) and photoluminescence excitation peak. This is attributed to a transient bandgap renormalization that occurs on the same time scale as the generation of the THz transients. Moreover, an emission shoulder at ∼40 meV below the THz emission peak was observed. Deep level transient spectroscopy results do not indicate that this is due to electron traps. However, an indistinct LO phonon-related, below-bandgap PL feature was seen at low temperature that coincides well with the observed THz radiation feature. It is proposed that the THz action spectrum may be sensitive to phonon-mediated processes in contrast to more conventional optical spectroscopy techniques, albeit at room temperature.

JOSA B, 2009

Transmission characteristics of lens-duct, Cytop planar photonic crystal waveguide (PPCW) and hol... more Transmission characteristics of lens-duct, Cytop planar photonic crystal waveguide (PPCW) and hollow-core microstructured optical fiber were analyzed in the terahertz (THz) region. The lens duct was able to channel and couple the THz radiation into a Teflon waveguide with a loss of about 0.7 dB. Single-mode propagation and frequency-selective properties were achieved using PPCW whose central frequency is at 0.45 THz. Results of time-domain spectra of the hollow-core microstructured polymer optical fiber showed a difference of about 20 ps between the THz waves that propagated in the core and cladding. Frequency shift of the transmission bands between waveguides of different size suggested photonic bandgap guidance. Finite-difference time domain calculations agreed relatively well to the experimental results of PPCW and hollow-core fibers.

… on Lasers and …, 2006

Low-loss single-mode THz waveguiding using CYTOP, ... G. De Los Reyes1, A. Quema1, E. Estacio1, C... more Low-loss single-mode THz waveguiding using CYTOP, ... G. De Los Reyes1, A. Quema1, E. Estacio1, C. Ponseca Jr.1, R. Pobre2, R. Quiroga2, H. Murukami1, S. Ono1, N. Sarukura3, K. Aosaki4, Y. Sakane4, and H. Sato4 1Institute of Molecular Science, 38 Nishigonaka, ...

Applied physics …, 2006

A polymer-based, Cytop planar photonic crystal waveguide ͑PPCW͒ was designed for guiding terahert... more A polymer-based, Cytop planar photonic crystal waveguide ͑PPCW͒ was designed for guiding terahertz radiation. Results indicate that the propagation and coupling losses in the 0.2-1.1 THz range are relatively small for a sheetlike thickness design. Spectral analysis of the transmission data reveals frequency selectivity of the PPCW. Calculations of the spatial distribution of the terahertz electric field through the waveguide show evidence of single-mode propagation at a 0.45 THz central frequency. The highly transparent nature of Cytop from deep ultraviolet to the far infrared region indicates its potential use as an integral component in hybrid optics.

Semi-empirical calculations successfully predicted the terahertz (THz) absorption spectrum associ... more Semi-empirical calculations successfully predicted the terahertz (THz) absorption spectrum associated with intra- and intermolecular interactions in 1,4-dihydroxynaphthalene. Results are in excellent agreement with spectroscopy data in the 0.5-6 THz region using GaP wave THz source.

e-Journal of Surface Science and Nanotechnology, 2011

We investigate the adhesion mechanism of metal atoms (Al, Cu Ag, Au and Pt) on polyethylene terep... more We investigate the adhesion mechanism of metal atoms (Al, Cu Ag, Au and Pt) on polyethylene terephthalate (PET) using Density Functional Theory (DFT) and cluster models. The structural geometry of the basic unit of PET is optimized then a metal atom is made to approach this structure at different orientations while calculating the total energy of the system under B3LYP functional. Results show that Al atom binds strongly when oriented linear to C=O at a distance of 1.80Å. Orbital population analysis indicates that the good adhesion of Al at this orientation is due to the interaction of pz orbital of free oxygen in the carbonyl group and py orbital of Al atom. Binding is strongest for Al atom, followed by Pt, Cu, Ag, and Au, in decreasing order of adhesive strength.

Journal of Physics: Conference Series, 2008

Far infrared (IR) spectra of naphthalene and 1,4-dihydroxynaphthalene (1,4-naphthol) were measure... more Far infrared (IR) spectra of naphthalene and 1,4-dihydroxynaphthalene (1,4-naphthol) were measured in the region from 0.5 to 6.3 THz at room temperature using a GaP THz wave generator. Quantum chemical calculations were performed to obtain normal mode coordinates and frequencies for an isolated molecule case of naphthalene and 1,4-naphthol.

Lasers and Electro- …, 2006

Terahertz (THz) radiation from p-type (100) InAs was investigated using time domain spectroscopy.... more Terahertz (THz) radiation from p-type (100) InAs was investigated using time domain spectroscopy. Azimuthal angle dependence measurements and the ambipolar mobility theory suggest the dominant THz radiation mechanism to be that of the surge current.

World Congress on Medical Physics and …, 2007

An extended nearest-neighborhood (ENN) tracking algorithm was appropriated in designing spatiotem... more An extended nearest-neighborhood (ENN) tracking algorithm was appropriated in designing spatiotemporal features of human gait kinematics under low illumination. Active markers in the form of light-emitting diodes (LEDs) were positioned at anatomical landmarks to ...

Applied physics …, 2007

The azimuthal angle dependence in the terahertz radiation power of ͑100͒ InAs under 1 T magnetic ... more The azimuthal angle dependence in the terahertz radiation power of ͑100͒ InAs under 1 T magnetic field is presented. Results show that although the dominant radiation mechanism is surge current, azimuthal-angle-dependent radiation due to the nonlinear effect is also observed. The twofold symmetry of the p-polarized terahertz radiation power was modified to a fourfold symmetry with the transverse magnetic field. Moreover, results exhibited fourfold symmetry for the s-polarized terahertz power even with no applied field. The anisotropic intervalley scattering of photocarriers is tentatively proposed as the origin of quadrupole response and the fourfold emission symmetry.

Ultrafast Optics V, 2007

Since the development of lasers that can produce ultrafast optical pulses several techniques in g... more Since the development of lasers that can produce ultrafast optical pulses several techniques in generating terahertz (THz) radiation have been reported. In partic-ular, InAs under magnetic field is considered to be the practical source since it provides intense THz radiation ...

Applied Physics …, 2005

An integrated optics called terahertz ͑THz͒ pigtail, which is comprised of an emitter, an optical... more An integrated optics called terahertz ͑THz͒ pigtail, which is comprised of an emitter, an optically transparent launching media, and a waveguide, is devised and fabricated. The InAs emitter under a 1 T magnetic field is coupled to the launching media using silicone grease, an index matching liquid. The launching media, a lens duct made from a polymer based on poly 4-methyl pentene-1 ͑commonly known as TPX͒, is designed based on the concept of guiding THz radiation into Teflon photonic crystal fiber ͑PCF͒ waveguide by means of total internal reflection. It is found that the constructed THz lens duct is able to channel and couple the THz radiation into the PCF waveguide with a loss of Ͻ1 dB. The results here show that the idea of using the THz pigtail can be a potential means of effectively directing THz radiation. Downloaded 27 Aug 2010 to 133.68.192.94. Redistribution subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions 151114-3 Diwa et al. Appl. Phys. Lett. 87, 151114 ͑2005͒ Downloaded 27 Aug 2010 to 133.68.192.94. Redistribution subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions

Optics communications, 2006

We calculate the radiation force that is exerted by a focused continuous-wave Gaussian beam of wa... more We calculate the radiation force that is exerted by a focused continuous-wave Gaussian beam of wavelength λ on a non-absorbing nonlinear particle of radius a ≪ 50λ/π. The refractive index of the mechanically-rigid particle is proportional to the incident intensity according to the electro-optic Kerr effect. The force consists of two components representing the contributions of the electromagnetic field gradient and the light scattered by the Kerr particle. The focused intensity distribution is determined using expressions for the six electromagnetic components that are corrected to the fifth order in the numerical aperture (NA) of the focusing objective lens. We found that for particles with a < λ/21.28, the trapping force is dominated by the gradient force and the axial trapping force is symmetric about the geometrical focus. The two contributions are comparable with larger particles and the axial trapping force becomes asymmetric with its zero location displaced away from the focus and towards the beam propagation direction. We study the trapping force behavior versus incident beam power, NA, λ, and relative refractive index between the surrounding liquid and the particle. We also examine the confinement of a Kerr particle that exhibits Brownian motion in a focused beam. Numerical results show that the Kerr effect increases the trapping force strength and significantly improves the confinement of Brownian particles.

Nonlinear Optics: …, 2007

The generation of intense terahertz (THz) radiation from InAs surfaces illuminated with ultrashor... more The generation of intense terahertz (THz) radiation from InAs surfaces illuminated with ultrashort optical pulses has been the subject of immense work in the past decade. Consequently, numerous studies have been conducted to explain the prevalent THz radiation mechanism in these ...