Search results for "Attenuation coefficient"

Measurement of UV-induced absorption and scattering losses in photosensitive fibers

2018

UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery mode resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosen…

Laser-Calorimetric Study of Fundamental Absorption Edge in Pb,La(ZrTi)O3 (PLZT) Perovskite Ceramics

2000

The values of the light absorption coefficient of PLZT 10/65/35 ceramics at selected wavelengths have been obtained by laser calorimetric measurements. The absorption coefficient of the PLZT ceramics is an exponential function of the photon energy. Two values of characteristic Urbach energy have been found ΔE1 = 106 meV and ΔE2 = 238 meV. The first one is a characteristic of the potential of electron-phonon interaction of the optically excited transitions from the valence band to the conduction band and does not depend on lattice defects or admixtures. The other characterises the electron-phonon interaction at optical transitions between two localized electron states in the energy gap separ…

Optical determination of the oxygen content of YBa2Cu3O6+x thin films by IR reflectance and transmittance measurements

2001

Abstract Recent studies of the optical properties of YBa2Cu3O6+x (YBCO) single crystals by several authors have shown that the optical conductivity in the infrared spectral region is a sensitive function of the oxygen content of the samples. Infrared spectroscopy thus offers a possibility for oxygen concentration analysis and is an alternative to other methods such as (i) the X-ray determination of the length of the c-axis and (ii) spectroscopic ellipsometry at an electronic transition band centered around 4.1 eV whose strength decreases with increasing oxygen content. We explore the applicability of the IR optical method for the case of YBCO thin films of about 300 nm thickness which are e…

Study of magnesium and aluminum alloys absorption coefficient during Nd:YAG laser interaction

2007

International audience; In laser processes, the absorption factor of laser Nd:YAG by metals plays a very important role. In order to model laser welding, we need to know its evolution during the process. The theoretical calculation does not enable the prediction of the absorption factor in the case of a keyhole mode. It is difficult to predict the effect of plasma and recoil pressure on the shape of the keyhole. In this paper, an integrating sphere is used to determine the absorption factor during the laser process, which is carried out on two types of magnesium alloys (WE43 and RZ5) and an aluminum alloy. We obtain the evolution in time of the absorption factor according to different steps…

APPROXIMATION FOR THE ABSORPTION COEFFICIENT OF ATMOSPHERIC AEROSOL PARTICLES IN TERMS OF MEASURABLE BULK PROPERTIES

1976

Temperature dependence of refractive index and absorption coefficient of GaSe at 633 nm

1995

Abstract Measurements of the ordinary refractive index and the absorption coefficient ( E /t] to c axis ) of gallium selenide at 633 nm, in the temperature range [20,100] °C, are reported. Useful analytical approximations obtained after a least squares fitting process are provided, as well. These results are basic for any theoretical model of nonlinear and bistable optical devices based on GaSe.

Phonon contribution to the absorption of ultrasound in amorphous solids at moderately low temperatures

1998

Abstract Sound absorbtion in amorphous solids is considered to be due to the scattering of sound waves from the thermal phonons. It is shown that the dependence of the absorption coefficient on the temperature displays a maximum in the interval 10≲T≲100 K . The frequency dependence of the absorption coefficient is investigated. Numerical calculations for amorphous Mg and Zn illustrate the theoretical results.

Two-color holographic-grating formation in amorphous As_2S_3 films

1998

A detailed experimental study of the holographic gratings recorded in nonannealed amorphous As2S3 films by 514.5-nm light in the presence of 632.8-nm readout light is carried out. A strong influence of a continuous 632.8-nm readout is found. The dependences of the maximal first-order diffraction efficiency and the corresponding specific recording energy on the holographic grating period were studied in a wide range of periods from 0.40 to 70.0 μm for 2-yr-old films. The obtained results are discussed in terms of photoinduced structural changes, relaxational structural changes, photoinduced anisotropy, and photoinduced recharging of the localized states in the bandgap. The photoinduced sulph…

Mass absorption indices of various types of natural aerosol particles in the infrared

2010

The mass absorption index of aerosol particles has been measured in the 2-17-microm wavelength region. The measurements were performed on films of aerosol particles that were collected by an automatic jet impactor at polluted and various uncontaminated remote sites. All but marine aerosols possess strong absorption bands in the transparent part of the atmospheric long-wave spectrum, indicating marked influence of aerosol particles on the radiation budget of the atmosphere.

Laser ablation of a turbid medium : Modeling and experimental results.

2006

International audience; Q -switched Nd:YAG laser ablation of a turbid medium (paint) is studied. The optical properties (absorption coefficient, scattering coefficient, and its anisotropy) of a paint are determined with a multiple scattering model (three-flux model), and from measurements of reflection-transmission of light through thin layers. The energy deposition profiles are calculated at wavelengths of 532 nm and 1.064 $\mu$m. They are different from those described by a Lambert-Beer law. In particular, the energy deposition of the laser beam is not maximum on the surface but at some depth inside the medium. The ablated rate was measured for the two wavelengths and compared with the en…