Search results for "absorption."
showing 10 items of 2682 documents
Infrared photoluminescence of preexisting or irradiation-induced interstitial oxygen molecules in glassySiO2and α-quartz
1998
A sensitive technique for detecting interstitial ${\mathrm{O}}_{2}$ molecules in ${\mathrm{SiO}}_{2}$ is demonstrated by measuring their infrared $\stackrel{\ensuremath{\rightarrow}}{a}X$ luminescence at 1272.2 nm under a Ti-sapphire laser excitation into the ${\mathrm{O}}_{2}\stackrel{\ensuremath{\rightarrow}}{X}b$ absorption band at 765 nm. Contrary to the case of ${\mathrm{O}}_{2}$ trapped in inert gas matrices, the visible emission of ${\mathrm{O}}_{2}$ corresponding to the direct $\stackrel{\ensuremath{\rightarrow}}{b}X$ transition is not found. Examination of different neutron- and gamma-irradiated glassy ${\mathrm{SiO}}_{2}$ and \ensuremath{\alpha}-quartz samples reveals radiation-in…
Generation and excitation of point defects in silica by synchrotron radiation above the absorption edge
2010
We report photoluminescence measurements carried out on amorphous SiO{sub 2} upon excitation by synchrotron light. Exposure of the as-grown material to above-edge light at low temperature induces the formation of nonbridging oxygen hole centers (NBOHC), localized in a thin layer below the surface limited by the penetration depth (tens of nm) of impinging light. After concluding the exposure to 11 eV light, stable defects are revealed by observing their characteristic 1.9 eV photoemission band excited at 4. 8eV. The local concentration of induced defects, supposedly formed by nonradiative decay of excitons, is very high (close to approx10{sup 21} cm{sup -3}) and independent of the previous h…
<title>PLZT ceramics as optical phantom for simulation of light scattering in eye segments and other biological tissues</title>
1999
ABSTRACT Coefficients of light absorption ta and scattering for biological tissues lie within a broad range - minimum ones forhealthy eye tissues up to higher values (fe. t a 0.3 cm and i = 40 cm' at 633 nm for muscle tissues ) for other andmainly turbid tissues. The specific feature of the transparent PLZT ceramics (having absorption t a > 0. 1 cm in the visible and in the near infrared spectrum range) is electrically controlled light scattering. The present work reports onexperimental results of the light transport and backscattering for PLZT 9/65/35 (Pb091La009Zr065Ti035O3). We proposePLZT ceramics with fast and continuously controllable light scattering as an optical phantom for photon …
Reflection-refraction effects on light distribution inside tubular photobioreactors
2017
One of the main parameters affecting autotrophic algae cultures is photon absorption distribution inside the photobioreactor. This clearly depends on the geometry of both the radiation source and the photobioreactor, as well as on algae suspension optical properties. In this work the local volumetric rate of photon absorption LVRPA in a cross-section of a horizontal-pipe photobioreactor was investigated by means of simplified Monte Carlo simulations. In particular, the fate of a number of photons perpendicularly hitting the photobioreactor circular section was simulated in relation to different values of algae concentration. The model takes into account refraction/reflection phenomena at th…
Strong optical nonlinearities in gallium and indium selenides related to inter-valence-band transitions induced by light pulses
1997
A nonlinear optical effect is shown to occur in gallium and indium selenides at photon energies of the order of 1.5 eV. It corresponds to transitions from a lower-energy valence band to the uppermost one when a nonequilibrium degenerate hole gas is created in the latter by a laser pulse. This inter-valence-band transition is allowed by crystal symmetry. Its oscillator strength is estimated through the $f$-sum rule and turns out to be about two orders of magnitude higher than that of the fundamental transition. The intensity of this effect is stronger when the pump pulse photon energy is close to that of the inter-valence-band transition; a condition that can be fulfilled only in indium sele…
X-ray absorption and Raman spectroscopy studies of tungstates solid solutions ZncNi1-cWO4 (c=0.0-1.0)
2020
G.B. acknowledges the financial support provided by the State Education Development Agency for project No. 1.1.1.2/VIAA/3/19/444 (agreement No. 1.1.1.2/16/I/001) realized at the Institute of Solid State Physics, University of Latvia. A.K. and A.K. would like to thank the support of the Latvian Council of Science project No. lzp-2019/1-0071. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.
In situ tuning of a photonic band gap with laser pulses
2008
We report on light-induced optical tuning of colloidal photonic crystals doped with gold nanoparticles (Au-nps). By resonantly exciting the Au-np surface plasmon absorption with picosecond pulses at 0.53 micron in a standard pump-probe setup, we observed permanent changes in the stop band resonance around 1.7 micron, with blue wavelength shifts as large as 30 nm and associated to a nanoparticle reshaping. Fine tuning was achieved by controlling either the pulse energy or the irradiation time.
Optical investigation of the OH− groups in the LiNbO3 doped by copper
2019
Doping ions and OH− groups absorption bands spatial profiles were investigated for the case of congruent LiNbO3 single crystal grown by Czochralski technique. Doping was performed after the crystal...
The “accumulation effect” of positrons in the stack of foils, detected by measurements of the positron implantation profile
2013
The profiles of positrons implanted from the radioactive source 22Na into a stack of foils and plates are the subject of our experimental and theoretical studies. The measurements were performed using the depth scanning of positron implantation profile method, and the theoretical calculations using the phenomenological multi-scattering model (MSM). Several stacks consisting of silver, gold and aluminum foils, and titanium and germanium plates were investigated. We notice that the MSM describes well the experimental profiles; however when the stack consisting of silver and gold foils, the backscattering and linear absorption coefficients differ significantly from those reported in the litera…
High-temperature X-ray absorption spectroscopy study of thermochromic copper molybdate
2019
Financial support provided by Scientific Research Project for Students and Young Researchers Nr. SJZ/2017/5 and SJZ/2018/1 realized at the Institute of Solid State Physics, University of Latvia is greatly acknowledged. The work was also supported by philanthropist MikroTik and administrated by the University of Latvia Foundation . The experiment at the Elettra synchrotron was performed within the project No. 20150303 .