共查询到20条相似文献,搜索用时 78 毫秒
1.
J. R. Schwesyg M. C. C. Kajiyama M. Falk D. H. Jundt K. Buse M. M. Fejer 《Applied physics. B, Lasers and optics》2010,100(1):109-115
Light absorption measurements of nominally undoped congruent lithium niobate crystals (CLN) as well as 5 mol% magnesium-oxide-doped
lithium niobate (MgO:LN) crystals were performed in the light wavelength range of 350 to 800 nm. Absorption spectra reveal
that—besides iron (Fe) impurities—chromium (Cr) impurities of less than 0.5 wt. ppm concentration contribute significantly
to the total optical absorption in the CLN crystals with a maximum of 0.035 cm−1 around 500 nm. The axial distribution of Cr within a CLN boule is examined, revealing that the bottom part of the boule contains
less Cr and therefore light absorption is reduced as well. In the case of the MgO:LN crystals, Cr impurities also contribute
significantly to the total optical absorption, which is on the order of 0.025 cm−1 for ordinarily polarized light and 0.015 cm−1 for extraordinarily polarized light around 500 nm. 相似文献
2.
We present a maximum-entropy model for the transport of waves through a classically chaotic cavity in the presence of absorption.
The entropy of the S-matrix statistical distribution is maximized, with the constraint 〈TrSS
†〉 = αn: n is the dimensionality of S, and 0 ≤ α ≤ 1. For α = 1 the S-matrix distribution concentrates on the unitarity sphere and we have no absorption; for α = 0 the distribution becomes a delta function at the origin and we have complete absorption. For strong absorption our result
agrees with a number of analytical calculations already given in the literature. In that limit, the distribution of the individual
(angular) transmission and reflection coefficients becomes exponential — Rayleigh statistics — even for n = 1. For n ≫ 1 Rayleigh statistics is attained even with no absorption; here we extend the study to α<1. The model is compared with random-matrixtheory numerical simulations: it describes the problem very well for strong absorption,
but fails for moderate and weak absorptions. The success of the model for strong absorption is understood in the light of
a central-limit theorem. For weak absorption, some important physical constraint is missing in the construction of the model. 相似文献
3.
4.
We describe a new technique to measure the UV/visible absorption spectrum of the ablated material during the laser pulse.
The technique utilizes the continuum emission from one laser produced plasma as a light source to measure the absorption properties
of a second laser produced plasma which is formed on a semi-transparent target with an array of 40 μm holes. A 6 ns, 1064
nm laser was used to ablate a Ag target and the plasma absorption was measured in the range 450–625 nm for a laser fluence
of 1 J cm−2. The total absorption cross-section is (0.5–1.5)×10−17 cm2 in the range 450–540 nm. By comparing the measured absorption with a calculation using the plasma spectroscopy code FLYCHK
it can be concluded that, in the wavelength region examined here, the absorption is mainly due to bound-bound transitions. 相似文献
5.
In this article, we propose an efficient and accurate compressive-sensing-based method for estimating the light transport
characteristics of real-world scenes. Although compressive sensing allows the efficient estimation of a high-dimensional signal
with a sparse or near-to-sparse representation from a small number of samples, the computational cost of the compressive sensing
in estimating the light transport characteristics is relatively high. Moreover, these methods require a relatively smaller
number of images than other techniques although they still need 500–1000 images to estimate an accurate light transport matrix.
Precomputed compressive sensing improves the performance of the compressive sensing by providing an appropriate initial state.
This improvement is achieved in two steps: 1) pseudo-single-pixel projection by multiline projection and 2) regularized orthogonal
matching pursuit (ROMP) with initial signal. With these two steps, we can estimate the light transport characteristics more
accurately, much faster, and with a lesser number of images. 相似文献
6.
De-Long Zhang Zhen Wang Ping-Rang Hua Edwin Yue-Bun Pun 《Applied Physics A: Materials Science & Processing》2010,100(4):1073-1081
Li-rich (Li-poor) vapor transport equilibration (VTE) treatments on a number of Z-cut 0.47 mm thick congruent MgO (5 mol%
in melt) : LiNbO3 crystals were carried out at 1100°C over different durations ranging in 1–172 (40–395) h. Neutron activation analysis shows
that neither Li-rich nor Li-poor VTE-induced Mg and Nb loss from the crystal occurred. The Li2O content in the crystal was measured as a function of VTE duration by the gravimetric method. The Li-rich/Li-poor VTE effects
on OH− absorption were studied in comparison with the as-grown crystal. The study shows that the Li-rich VTE results in OH− absorption band annihilation. After further oxidation treatment the band reemerges and peaks at the same wavenumber as that
of the as-grown crystal (∼3535.6 cm−1), showing that the MgO concentration in the Li-rich VTE crystal is still above the optical-damage threshold. The Li-poor
VTE causes OH− band shift to 3486.3–3491.6 cm−1, indicating that the MgO concentration in all Li-poor VTE crystals is all below the optical-damage threshold. Further successive
Li-rich VTE and oxidation treatments on the Li-poor VTE-treated crystal lead the band to shift back to 3535.6 cm−1, showing that the post Li-rich VTE brought the Li-poor VTE-treated crystal above the optical-damage threshold again. It is
found that the peaking position, band width, peaking absorption and band area of the absorption at ∼3486 cm−1 all increase monotonously with the decrease of the Li2O content arising from prolonged Li-poor VTE, and quantitative relationships to the Li2O content are established for the latter two parameters. The VTE effects on the OH− absorption are conducted with the VTE-induced OH− content alteration and charge redistribution. 相似文献
7.
Andrei V. Pakoulev Vladimir Burtman 《Applied Physics A: Materials Science & Processing》2010,98(4):717-734
This paper focuses on the intrinsic charge transport in self-assembled monolayers (SAMs) and on the nature of transport in
organic systems, in which surface and bulk properties are undistinguishable due to scale of consistent materials. Developed
SAM-OFETs and photovoltaic (SAM-PVC) devices are characterized independently to study a role of charge delocalization both
in electrical and optical manifold. The dynamics of charge transport are determined and used to clarify a transport mechanism.
Taken together, these SAM devices provide a unique tool to study the fundamentals of polaronic transport on organic surfaces
and to discuss the SAM-OFET and SAM PVC performance. Vapor phase molecular self-assembly of 1, 4, 5, 8-naphthalene-tetracarboxylic
diphenylimide (NTCDI) having a rich π-stacking charge delivery system is used to enhance the performance of SAM-OFET and SAM PVC devices. Charge mobility in SAM-OFET
could achieve values of more than 30 cm2 V−1 s−1. The dynamics of charge transport in NTCDI-derived SAM-OFETs were probed using time-resolved measurements in an NTCDI-derived
photovoltaic cell device. Time-resolved photovoltaic studies allow us to separate the charge annihilation kinetics in the
conductive NTCDI channel from the overall charge kinetic in a SAM-OFET device. It has been demonstrated that tuning of the
type of conductivity in NTCDI SAM-OFET devices is possible by changing Si substrate doping. In addition, the possibility of
measuring transport in highly ordered SAM structures shines light on the polaron charge transfer in organic materials. Our
study proposes that a cation-radical exchange (redox) mechanism is the major transport mechanism in SAM nanodevices. The role
and contribution of the transport through delocalized states of redox active surface molecular aggregates of NTCDI are exposed
and investigated in this report. 相似文献
8.
I. S. Grudzinskaya Z. Ya. Kosakovskaya O. B. Ovchinnikov I. A. Chaban 《Acoustical Physics》2006,52(3):274-277
The optoacoustic effect is used to measure the coefficient of light absorption at a wavelength of 0.53 μm by a dense layer
of oriented carbon nanotubes on a quartz substrate. The value of the absorption coefficient is found to be equal to 3 × 106 m−1. This value is compared with the theoretical estimates and the estimate obtained from the reflection coefficient with the
use of the Kramers-Kronig relation. With the coefficient of light absorption being known, the optoacoustic effect allows one
to measure the film thickness at any point without destroying the film.
Original Russian Text Sc I.S. Grudzinskaya, Z.Ya. Kosakovskaya, O.B. Ovchinnikov, I.A. Chaban, 2006, published in Akusticheskiĭ
Zhurnal, 2006, Vol. 52, No. 3, pp. 330–334. 相似文献
9.
K. Ishida T. Matsuzaki K. Nagamine H. Kitazawa Y. Miyake E. Torikai 《Hyperfine Interactions》1991,65(1-4):1159-1165
A new type of beam transport system for secondary light charged particles (“Large Ω” Beam Course) has been constructed and
used to transport surface muons from the decay of pions produced in heavy-ion reactions at RIKEN Ring Cyclotron (RRC). In
an experiment carried out using a14N beam of 135 MeV/u and a carbon target of 0.9 g/cm2 thickness, the surface muon intensity obtained in 5×5 cm2 sample was around 100 1/s for 500 nA of the primary beam. This number may be increased by two orders if the energy were doubled. 相似文献
10.
I. V. Fekeshgazi N. R. Kulish N. I. Malysh T. S. Sidenko V. M. Trukhan T. V. Golyakevich 《Journal of Applied Spectroscopy》2009,76(1):107-111
We studied the two-photon absorption coefficient (β) for cadmium diphosphide (CdP2) single crystals in the tetragonal modification vs. the polarization azimuth (φ) of the incident light for intensities close
to the optical breakdown (or optical damage) threshold for the crystal (11 MW/cm2). We have established that the value of βmax = 0.16 cm/MW is reached for φ = 0, i.e., for the ordinary wave. At the lasing frequency of a ruby laser, β⊥/β|| = 2.13, which suggests anisotropy of the two-photon absorption in the studied crystals. These dependences are needed for
design and fabrication of quantum electronics and nonlinear optics elements whose operation is based on the use of the two-photon
absorption effect for high radiation fluxes.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 117–121, January–February, 2009. 相似文献
11.
The aim of the current study is to simulate the laser photon through biological tissue during PDT therapy using Monte Carlo
simulation technique. The model is coded using MATLAB. Interaction of laser light with turbid medium e.g. human tissue depends
on the optical properties of the medium i.e. refractive index n, absorption coefficient μ
a
, scattering coefficient μ
s
and anisotropy factor g. Laser light transport through tissue is governed by the radiative transport equations based on absorption and scattering.
Direct sampling is used for step-size generation before interaction via absorption or scattering with the transmitting medium,
for deflection and azimuthal angle (θ and ϕ) when the scattering even occurs. The tissue medium considered is divided into
radial, axial and angular grid elements and an infinite narrow beam with normal incidence on the tissue is considered. The
laser light absorbance inside the tissue, reflectance at the top boundary of the tissue and transmittance at the bottom are
estimated and these quantities are shown varying radially and angularly. Results of reflectance, transmittance and fluence
are compared with the already published results to confirm the authenticity of our coding and these results are found to lie
at only 3–4% error. 相似文献
12.
M. A. Bolshov Y. A. Kuritsyn V. V. Liger V. R. Mironenko S. B. Leonov D. A. Yarantsev 《Applied physics. B, Lasers and optics》2010,100(2):397-407
A tunable diode laser absorption spectroscopy (TDLAS) technique and appropriate instrumentation was developed for the measurement
of temperature and water vapor concentrations in heated gases. The technique is based on the detection of the spectra of H2O absorption lines with different energies of low levels. The following absorption lines of H2O were used: 7189.344 cm−1 (E″=142 cm−1), 7189.541 cm−1 (E″=1255 cm−1), 7189.715 cm−1 (E″=2005 cm−1). Spectra were recorded using fast frequency scanning of a single distributed feedback (DFB) laser. A unique differential
scheme for the recording of the absorption spectra was developed. An optimal technique for fitting the experimental spectra
was developed. 相似文献
13.
L. Ciaffoni R. Grilli G. Hancock A. J. Orr-Ewing R. Peverall G. A. D. Ritchie 《Applied physics. B, Lasers and optics》2009,94(3):517-525
Diode laser technology coupled with a wavelength-conversion unit to produce mid-infrared narrow bandwidth laser light applicable
to trace-gas detection and with the potential for high-resolution spectroscopy is described. Quasi-phase-matched difference-frequency
generation (QPM-DFG) in a compact and fibre-coupled periodically poled lithium niobate (PPLN) waveguide module mixing 1063
and 1525-nm radiations has been adopted for generating 34 μW of 3.5-μm wavelength laser light. Optical detection methods,
including sensitive wavelength modulation spectroscopy and a rapid wavelength chirp technique, have been employed with a single-pass
cell to investigate methane and formaldehyde absorption profiles around 2855 cm−1, as proof of principle experiments for high sensitivity and resolution spectroscopy on atmospherically important molecules. 相似文献
14.
D. J. Hamilton M. G. D. Nix S. G. Baran G. Hancock A. J. Orr-Ewing 《Applied physics. B, Lasers and optics》2010,100(2):233-242
Optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) has been demonstrated by coupling a distributed feedback
diode laser to a ring cavity. Frequency-selected light decaying from the ring cavity is retro-reflected, inducing a counter-propagating
intra-cavity beam, and providing optical feedback to the laser. At specific laser-to-cavity distances, all cavity mode frequencies
return to the diode laser with the same phase, allowing spectra to be accumulated across the range of frequencies of the current-tuned
laser. OF-CEAS has been used to measure very weak oxygen isotopologue (16O18O and 16O17O) absorptions in ambient air at wavelengths near 762 nm using the electric-dipole forbidden O2
A-band. A bandwidth reduced minimum detectable absorption coefficient of 2.2×10−9 cm−1 Hz−1/2 is demonstrated. 相似文献
15.
K. O. Korovin E. Heinecke A. Patzer T. Liebig O. S. Vasyutinskii D. Zimmermann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):57-63
The first determination of translational anisotropy parameters β in the
photodissociation of NaI molecules in the spectral range
315–370 nm is reported. The anisotropy parameters were
determined by the analysis of Doppler resolved absorption profiles of
Na(2S1/2) atoms produced in the photodissociation of NaI by
linearly polarized light. The profiles were recorded for two orientations of
the photolysis light: parallel and perpendicular to the direction of the
probe beam. The value of the parameter β was obtained from a simultaneous fit
of the profiles. The role of the rotation of the parent molecules on the
branching ratio between parallel and perpendicular transitions in NaI during
dissociation is discussed. 相似文献
16.
The preparation of pyridine functionalized TbF3 nanoparticles are described in this report. Synthesized nanoparticles were characterized using the TEM, UV/Vis, FTIR and
photoluminescence spectroscopy. TEM micrograph reveals the nanorod shaped, uniform in size with a particles size in the range
of 20–30 nm. FTIR spectrum shown characteristic absorption bands of pyridine and a small intensity band at 411 cm−1 corresponding metal nitrogen ν(Tb–N) bonding. Uv-vis spectrum shown the characteristic absorption transitions of Tb3+ ion. A strong emission transition at 540 nm (5D4 → 7F5) was observed on excite by visible light at 414 nm. 相似文献
17.
E. E. Gorodnichev A. I. Kuzovlev D. B. Rogozkin 《Journal of Experimental and Theoretical Physics》1999,88(3):421-432
Small-angle multiple scattering of circularly polarized waves in disordered systems composed of large (larger than the light
wavelength) spherical particles is discussed. The equation for Stokes’s fourth parameter V — the difference between the intensities of the left-and right-hand polarized light — is shown to have the form similar to
that of the scalar transport equation for intensity I, the only difference being the presence of an additional “non-small-angle” term responsible for depolarization. In the case
of small-angle scattering, depolarizing collisions are relatively rare and, in contrast to the scalar case, the problem contains
an additional spatial scale, namely the depolarization depth. The polarization degree and helicity of the scattered light
are calculated for the case of purely elastic scattering and in the presence of absorption in the medium. For strong absorption,
depolarization is shown to follow the transition to the asymptotic regime of wave propagation. The features appearing in strong
(non-Born) single scattering are also discussed.
Zh. éksp. Teor. Fiz. 115, 769–790 (March 1999) 相似文献
18.
N. G. Borisenko A. A. Akunets A. M. Khalenkov D. Klir V. Kmetik E. Krousky J. Limpouch K. Masek Yu. A. Merkuliev M. Pfeifer V. G. Pimenov J. Ullschmied 《Journal of Russian Laser Research》2007,28(6):548-566
The velocities of energy transport in an undercritical plasma of polymer aerogel with and without copper nanoparticles were
measured. Transmission of the laser light through targets of different thicknesses such as submicron three-dimensional polymer
networks with densities below the critical value (0.13–0.52 N
cr) for a wavelength of 0.438 μm and intensity of (3–7)·1014 W/cm2 at a half-height pulse duration of 0.32 ns was studied. The transfer of a heating laser radiation was registered on the rear
side of the target. It ranged from a level of ∼0.5% for the thickness of a low-density layer of 400 μm and density of 9 mg/cm3 (mass per unit square of 0.36 mg/cm2) up to 50–60% for a thickness of 100 μm and density of 2.25 mg/cm3 (mass per unit square of 0.02 mg/cm2). The time dependences of the optical emission from the rear side of the targets were measured. They appear to be indicative
of the plasma dynamics in two-layer targets (polymer foam on Al foil) and enable the estimation of the absorption depth for
the laser light in an undercritical plasma.
__________
Translated from Preprint No. 8 of the P. N. Lebedev Physical Institute, Moscow (2007). 相似文献
19.
Light propagation in the digital head phantom for virtual near infrared spectroscopy and imaging is calculated by diffusion
theory. In theory, diffusion approximation is not valid in a low-scattering cerebrospinal fluid (CSF) layer around the brain.
The optical path length and spatial sensitivity profile predicted by the finite element method based upon the diffusion theory
are compared with those predicted by the Monte Carlo method to validate a practical implementation of diffusion approximation
to light propagation in an adult head. The transport scattering coefficient of the CSF layer is varied from 0.01 to 1.0 mm−1 to evaluate the influence of that layer on the error caused by diffusion approximation. The error is practically ignored
and the geometry of the brain surface such as the sulcus structure in the digital head phantom scarcely affects the error
when the transport scattering coefficient of the CSF layer is greater than 0.3 mm−1. 相似文献
20.
R. R. Vardanyan V. K. Dallakyan U. Kerst C. Boit 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2012,47(2):73-79
The different empirical models of light absorption in silicon by free charge carriers in near-infrared and infrared regions
are analyzed. An improved empirical model for free carrier absorption in silicon is developed. Results are obtained over the
wavelength range from 0.9 μm to 6 μm for n-type, and from 0.9 μm to 8 μm for p-type silicon. The new model is assessed ed by R
2 parameter and the sufficient fitting of the experimental data is presented. 相似文献