Photothermal therapies of nanophotohyperthermia and nanophotothermolysis utilize the light absorptive properties of nanoparticles to create heat and free radicals in a small localized region. Conjugating nanoparticles with various biomolecules allows for targeted delivery to specific tissues or even specific cells, cancerous cells being of particular interest. Previous studies have investigated nanoparticles at visible and infrared wavelengths where surface plasmon resonance leads to unique absorption characteristics. However, issues such as poor penetration depth of the visible light through biological tissues limits the effectiveness of delivery by noninvasive means. In other news, various nanoparticles have been investigated as contrast agents for traditional X-ray procedures, utilizing the strong absorption characteristics of the nanoparticles to enhance contrast of the detected X-ray image. Using X-rays to power photothermal therapies has three main advantages over visiblespectra wavelengths: the high penetration depth of X-rays through biological media makes noninvasive treatments very feasible; the high energy of individual photons means nanoparticles can be heated to desired temperatures with lower beam intensities, or activated to produce the free radicals; and X-ray sources are already common throughout the medical industry, making future implementation on existing equipment possible. This paper uses Lorenz-Mie theory to investigate the light absorption properties of various size gold nanoparticles over photon energies in the 1-100 keV range. These absorption values are then plugged into a thermal model to determine the temperatures reached by the nanoparticles for X-ray exposures of differing time and intensity. The results of these simulations are discussed in relation to the effective implementation of nanophotohyperthermia and nanophotothermolysis treatments.
Nanodrugs selectively delivered to a tumor site can be activated by radiation for drug release, or nanoparticles (NPs) can be used as a drug themselves by producing biological damage in cancer cells through thermal, mechanical ablations or charged particle emission. Radio-frequency (RF) waves have an excellent ability to penetrate into the human body without causing healthy tissue damage, which provides a great opportunity to activate/heat NPs delivered inside the body as a contrast agent for diagnosis and treatment purposes. However the heating of NPs in the RF range of the spectrum is controversial in the research community because of the low power load of RF waves and low absorption of NPs in the RF range. To resolve these weaknesses in the RF activation of NPs and dramatically increase absorption of contrast agents in tumor, we suggest aggregating the nanoclusters inside or on the surface of the cancer cells. We simulate space distribution of temperature changes inside and outside metal and dielectric nanopraticles/nanoclusters, determine the number of nanoparticles needed to form a cluster, and estimate the thermal damage area produced in surrounding medium by nanopraticles/nanoclusters heated in the RF field.
The use of nanoparticles in medical applications has been gaining momentum as antibody-conjugated nanoparticles are
becoming more and more feasible as a means of targeted delivery of various therapies. Irradiating nanoparticles with
light of strongly-absorbed wavelengths allows them to act as heat generation sites. Two therapies utilize these
nanoparticle heat sources to kill the target cells: nanophotohyperthermia, which heats the particles just enough to disrupt
cell function and trigger cell death; and nanophotothermolysis, which heats the particles to such extremes as to destroy
the cell membrane. The use of optical wavelengths in the range of 750-1100 nm has been to capitalize on the "optical
transparency window" of biotissues between the absorption peaks of hemoglobin in the visible end and water in the
near-IR. However, further research has shown that a plasmon resonance can greatly affect the absorption characteristics
of nanoparticles at the plasmon resonant frequency, allowing for increased absorption characteristics at desirable
wavelengths. Thus, other transparency windows may find use in a similar manner, such as nanoparticle heating by RF
waves. This paper presents the modeling of 3D thermal fields around nanoparticle absorbers in bone tissue for various
frequencies. A comparison of the heating effectiveness across multiple wavelengths is discussed for application to
nanophotothermolysis and nanophotohyperthermia treatments in or near biological hard tissue.
Biological hard tissues, such as those found in bone and teeth, are complex tissues that build a strong mineral structure
over an organic matrix framework. The laser-matter interaction for bone hard tissues holds great interest to laser surgery
and laser dentistry; the use of short/ultrashort pulses, in particular, shows interesting behaviors not seen in continuous
wave lasers. High laser energy densities in ultrashort pulses can be focused on a small irradiated surface (spot diameter is
10-50 μm) leading to rapid temperature rise and thermal ablation of the bone tissue. Ultrashort pulses, specifically those
in the picosecond and femtosecond ranges, impose several challenges in modeling bone tissue response. In the present
paper we perform time-dependent thermal simulations of short and ultrashort pulse laser-bone interactions in singlepulse
and multipulse (set of ultrashort pulses) modes of laser heating. A comparative analysis for both radiation modes is
discussed for laser heating of different types of the solid bone on the nanosecond, picosecond and femtosecond time
scales. It is shown that ultrashort laser pulses with high energy densities can ablate bone tissue without heating tissues
bordering the ablation creator. This reaction is particularly desirable as heat accumulation and thermal damage are the
main factors affecting tissue regrowth rates, and thus patient recovery times.
A stationary 2D axis-symmetric model able to evaluate the impurity distribution is developed by the finite element
method for single-crystal sapphire fibers grown from the melt by the edge-defined film-fed growth (EFG) technique. The
computations are carried out for two cases-one where the buoyancy is taken into account and the other where the
buoyancy is neglected-using different vertical temperature gradients kg in the furnace. The dependence of the impurity
distribution on kg and the Marangoni numbers Ma corresponding to the different surface tension gradients dγdT is
analyzed. Computations reveal critical Marangoni numbers Mac determined by the fluid flow behavior, and that a
smaller kg assures the best homogeneity of the crystal over a wide range of dγ/dT.
KEYWORDS: Chemical species, Diffraction, Optical engineering, Near field optics, Energy efficiency, Zone plates, Lens design, Particles, Physics, Near field
A simple focusing device is proposed for de Broglie matter waves—a diffractive lens, based on the optical effect of diffractive multifocal focusing of radiation. This matter-wave lens consists of two coaxial circular apertures in which the second aperture of smaller diameter is located where the Fresnel number of the first aperture is unity. It is shown that diffraction of a de Broglie matter wave by a system of two pinholes on an optical axis exhibits the multifocal focusing effect of matter waves in the near-field (Fresnel) zone, which creates a very intense, spatially localized beam of atoms. Theoretical predictions for the focusing efficiency of a neutral atomic beam by the diffractive lens are as follows. The spot diameter is ~0.1 µm, the ratio of focal and incident intensities is ~15, the focal length of the diffractive lens is in the range ~0.13 to 6 cm, the focusing depth is in the range ~15 to 30 cm, and the energy transmitting efficiency is ~30 %. For the relatively large diameters of the pinholes, 5.0 µm, the proposed configuration acts as a matter-wave lens with a large focal length and a long focusing depth.
The quality of the fiber depends to a considerable extent on homogeneity, i.e., on the distribution of both special added and detrimental impurities. A non-uniform distribution of such impurities along the fiber length and cross-section leads to non-uniform spatial, electrical and optical properties of the crystal. Variations of the concentration of impurities are determined by the processes that take place during the fiber manufacturing. In order to eliminate non-uniformities, crystal growth experts have concentrated on the analysis of the mass transport, heat transfer, impurity distribution and shape of the crystal-melt interface. In order to evaluate the dopant distribution, a stationary numerical model-including incompressible fluid flow in the Boussinesq approximation, heat and mass transfer, and surface tension-driven flows due to the temperature gradient along the liquid free surface (meniscus)-is developed using the finite element method. A two-dimensional axissymmetric model is implemented with COMSOL Multiphysics 3.3 software, and the Nd impurity distribution dependence on the pulling rate v0 and on the radius of the capillary channel Rcap in a LiNbO3 fiber grown from the melt by the EFG method is determined. Using this dependence, the optimal v0 and Rcap which assure the best impurity
distribution are chosen.
KEYWORDS: Diffraction, Lens design, Chemical species, Near field optics, Near field, Particles, Information operations, Physics, Interferometers, Optical properties
Diffraction of a de Broglie matter wave by a system of two pinholes on an optical axis exhibits the multifocal focusing effect of matter waves in the near-field (Fresnel zone). The focusing, defocusing and refocusing phenomenon results from periodic phase changes at singular points, which are observed for the even Fresnel numbers, where the intensity is zero and the phase is undefined. As an on-axis observation point passes through a singular point, the nature of the wave in the neighborhood of the axis changes from that of a diverging wave to that of a converging wave, i.e., the wave refocuses. The amplitudes of the oscillations in the intensity and phase of the de Broglie wave depend on the ratio of the radii of the two apertures in the system. This effect of diffractive multifocal focusing of de Broglie waves can be used for designing a diffractive lens for matter-wave beams.
KEYWORDS: Chemical species, Diffraction, Information operations, Near field optics, Energy efficiency, Zone plates, Particles, Interferometers, Lens design, Physics
A simple focusing device is proposed for de Broglie matter-waves - a diffractive lens, based on the optical effect of
diffractive multifocal focusing of radiation. This matter-wave lens consists of two co-axial circular apertures in which
the second aperture of smaller diameter is located where the Fresnel number of the first aperture is unity. It is shown that
diffraction of a de Broglie matter wave by a system of two pinholes on an optical axis exhibits the multifocal focusing
effect of matter waves in the near-field (Fresnel) zone. The focusing, defocusing and refocusing phenomenon is
explained as resulting from periodic phase changes at singular points, which are points where the intensity is zero and
the phase is undefined. It is shown that the proposed matter-wave lens could create a very intense, spatially-localized
beam of atoms. Theoretical predictions for the focusing efficiency of a neutral atomic beam by the diffractive lens are:
the spot diameter is ~ 0.1 &mgr;m, the ratio of focal and incident intensities is ~ 15, the focal length of the diffractive lens is
in the range ~ 0.13.6 cm, the focusing depth is in the range ~ 15.30 cm, and the energy transmitting efficiency is ~
30%. For the relatively-large diameters of the pinholes, ⩾ 5.0 &mgr;m, the proposed configuration acts as a matter-wave lens
with a large focal length and a long focusing depth.
A promising avenue in the development of pulsed chemical HF/DF lasers and amplifiers is the utilization of a photonbranched
chain reaction initiated in a two-phase active medium, i.e., a medium containing a working gas and
ultradispersed passivated metal particles. These particles are evaporated under the action of IR laser radiation, which
results in the appearance of free atoms, their diffusion into the gas, and the development of the photon-branching process.
The key obstacle here is the formation a relatively-large volume (in excess of 103 cm3) of the stable active medium, and
filling this volume homogeneously for a short time with a sub-micron monodispersed metal aerosol, which has specified
properties. In this manuscript, results are presented for an extensive study of a gas-dispersed component of a H2-F2 laser
active medium, including novel techniques for the formation of a two-phase active medium with specified properties;
aerosol optics; degradation of the dispersed component; and beam stability of a chemically-active aerosol. These results
should help lead the way to creating powerful, reliable and inexpensive self-contained pulsed sources of coherent
radiation with high energy, high laser beam quality, and the possibility of scaling up the output energy.
A new mechanism is proposed for selective laser killing of abnormal cells by laser thermal explosion of single
nanoparticles - "nano-bombs" - delivered to the cells. Thermal explosion of the nanoparticles is realized when the heat
generates within the strongly-absorbing target more rapidly than the heat can diffuse away. On the basis of simple
energy balance, it is shown that the lower level of the threshold energy density of a single laser pulse required for
thermal explosion of solid gold nanospehere is about 40 mJ/cm2, which is well below the safety standard for medical
lasers (100 mJ/cm2) for healthy tissue and cells. The nanoparticle's explosion energy density can be reduced further (up
to 11 mJ/cm2) by using gold nanorods due to higher plasmon-resonance absorption efficiency of nanorods. Additionally,
the nanorods optical resonance lies in the near-IR region, where biological tissue transmissivity is the highest. Here, the
effective therapeutic effect for cancer cell killing can be achieved due to nonlinear phenomena, which accompany the
thermal explosion of the nanoparticles: generation of the strong shock wave with supersonic expansion of dense vapor in
the cell volume, producing sound waves and optical plasma.
In this paper we report on the state-of-the-art of the ultrashort (fs) laser pulse-driven surface microprocessing of materials [metals, semiconductors and dielectrics (glasses and polymers)]. We emphasize the advantages of fs time scale pulses of laser-matter interactions, e.g., no heat effects in laser-coupled outside zones in plasma breakdown below intensity scales. A two-temperature model (energy coupling between electronic and phonon subsystems), the role of
Dember effects, and ballistic transport are also considered.
It is shown theoretically and experimentally that when a Gaussian beam illuminates a bicomponent diffraction system with small Fresnel numbers, consisting of two plane screens with circular apertures on given optical axes, in a near zone of the second screen the effect of diffractive multifocal focusing of radiation is observed. In this case, the diffraction picture from the second screen in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by six times the value of the incident wave intensity. The proposed diffractive method allows the focusing of the wide-aperture beams without using classical refraction elements such as lenses and prisms, and it is applicable to both low-intensive and high-power radiation. The energy efficiency of diffractive focusing of Gaussian beams is as high as 70%. Such a method can improve the energy efficiency of the fiber coupling of diode lasers and can increase the intensity of radiation on a fiber exit up to a factor of ten.
KEYWORDS: Nickel, Silicon, Chemical lasers, Finite element methods, Argon ion lasers, Solids, Molecules, Atomic force microscopy, Cesium, Chemical vapor deposition
Experimental results of laser assisted chemical vapor deposition of nickel from Ni(CO)4 and theoretical treatment of deposition process are presented. The nickel deposition has ben realized by scanning of Ar+ laser beam (100 - 400 mW, (lambda) equals 515 nm and 488 nm) on Si surfaces in atmosphere of Ni(CO)4 with 0.2 - 2.0 mbars with scanning speeds of 20 - 700 micrometers /s. As a result homogeneous Ni lines on Si have been deposited with a typical volumetric growth rate of 250 micrometers 3/s and widths of 10 - 20 micrometers and thickness of 0.2 - 0.5 micrometers . The electrical resistivity of lines deposited was cca 7 (mu) (Omega) cm. The theoretical treatment includes computations of the temperature distribution in both gas- phase and solid substrate. The reaction rate is computed on base of local concentration and local temperatures, within the frame of finite element methods using triangles as a base of computing.
We have observed an appearance of a wavelike (ripple) structures on GaAs due to influence of ultrafast (fs) laser pulses. Optical and atomic force microscopy studies revealed the double wavelength characters of ripples inside and outside of the illuminated areas. Raman investigations showed the existence of zinc-blend to cubic transitions in crystalline symmetry at the peripherical part of the irradiated area.
Optical phonon modes in a semiconductor double heterostructure (DHS) are
examined within the continuum model. The interface modes found here can account
for the novel phenomena observed in right-angle Raman scattering. The Hamiltonian
for the electron interaction with phonon eigenmodes is derived and employed to
study polaronic effects in the DHS. The ls2p+transition energy of a
magnetopolaron bound to a hydrogenic impurity in the quantum well is calculated,
and excellent agreement with experiments is obtained.
New phenomena are observed theoretically in nonlinear optical responses of polydiacetylene-toluene sulfonate (PTS) irradiated by a strong laser beam. Within a two-level model of PTS the transient behavior of the induced susceptibility is investigated. Optical nutation is found and the optical Stark blue shift and bleaching are also found in qualitative agreement with experiments. In the steady state a new type of optical tristability mediated by phonons is found. A possible mechanism responsible for this tristability is discussed. 1 .
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