The Principle of Invariance and Non-coherent Scattering

1970 ◽  
Vol 1 (8) ◽  
pp. 383-384
Author(s):  
J. N. Holt
Keyword(s):  
Coherent Scattering ◽  
Incident Radiation ◽  
Infinite Plane ◽  
Line Centre ◽  
Absorption And Emission ◽  
Plane Parallel ◽  
Scattering Factor ◽  
Isothermal Atmosphere

The purpose of this paper is to obtain an expression for the reflecting properties of a semi-infinite, plane parallel, isothermal atmosphere of scattering factor λ. The absorption and scattering of the incident radiation is assumed to be entirely due to transitions in two-level atoms, and the absorption and emission profiles are given by <f>(y), y being frequency from line centre in Doppler units.

The discovery of the Raman effect

1989 ◽  
Vol 43 (1) ◽  
pp. 1-23 ◽  
Keyword(s):  
Raman Effect ◽  
Rapid Development ◽  
Building Blocks ◽  
Incident Radiation ◽  
100Th Anniversary ◽  
Polyatomic Molecules ◽  
Transparent Medium ◽  
Selection Rules ◽  
Absorption And Emission ◽  
The World

C. V. Raman was born on 7 November 1888. A 100th anniversary • is a milepost, an occasion on which to review the best known of his contributions to science: the recognition that light scattered from a transparent medium includes wavelengths shifted from that of the incident radiation. It was realized from the outset that these shifts were due to an interaction, subtly different from the ordinary processes of absorption and emission, involving exchange of energy between radiation and the molecules of the medium. The discovery was promptly christened the Raman effect by Pringsheim (1), a phrase that caught on immediately and survives today. Its announcement in 1928 drew the attention of scientists around the world and ushered in a period of rapid development that brought the new spectroscopy onto a plateau where it remained, with few changes of substance, for practically a quarter of a century. For most purposes the experimental procedures were easily adapted from tried and true methods already in place for measurement of fluorescence: such instruments were put together from basic building blocks and examples already existed in a number of laboratories. The necessary theory, including selection rules and related symmetry considerations, emerged more gradually and several years elapsed before their framework was firmly in place. To some extent, however, this delay could be attributed to the greater attention now given to polyatomic molecules whose spectra had not been seriously addressed in the older forms of spectroscopy.

scholarly journals The diffraction of sound pulses IV. On a paradox in the theory of reflexion

1946 ◽  
Vol 186 (1006) ◽  
pp. 356-367 ◽  
Keyword(s):  
Detailed Examination ◽  
Simple Theory ◽  
Incident Pulse ◽  
Infinite Plane ◽  
Plane Parallel ◽  
Finite Distance ◽  
Limiting Case ◽  
Sound Pulses

Sommerfeld’s theory of diffraction, which has been discussed in detail in the preceding papers, is here applied to the elucidation of a certain paradox—the doubling of pressure at an infinite reflecting plane parallel to which a pulse is travelling, which is obtained if this is considered as a limiting case of reflexion. It is suggested that this paradox is an indication that the simple theory of the reflexion of plane pulses by an infinite plane, which is in any case only an approximation applying to parts of a reflector far removed from the edges, breaks down when the angle between the direction of propagation* of the incident pulse and the reflector becomes small. A detailed examination of the reflexion of plane pulses by a semiinfinite screen shows that when this angle becomes small, the diffracted pulse which emanates from the edge of the screen must be taken into account, so that the region in which the simple theory holds as an approximation moves away from the edge. In the limit, when the incident pulse travels parallel to the screen, the simple theory must be rejected at all points at a finite distance from the edge. Further examples of this mechanism are given by the reflexion of pulses by infinite wedges, some cases of which are also considered.

scholarly journals The Critical Frequency in the Stellar Pulsation Theory

1980 ◽  
Vol 58 ◽  
pp. 413-417
Author(s):  
Mine Takeuti
Keyword(s):  
Critical Period ◽  
Critical Frequency ◽  
Infinite Plane ◽  
Large Radius ◽  
Instability Strip ◽  
Plane Parallel ◽  
Stellar Pulsation ◽  
Running Wave

AbstractThe standing oscillation in an isothermal semi-infinite plane-parallel atmosphere has a critical frequency. The significance of critical frequency in the stellar pulsation is discussed briefly. The critical period is calculated for the cepheid instability strip. A star having relatively large radius compared with the mass should be examined by the criterion. The pulsational instability is reduced by the linear running wave.

Anomalous Scattering of Polarized X-Rays

1988 ◽  
Vol 143 ◽  
Author(s):  
David H. Templeton ◽  
Lieselotte K. Templeton
Keyword(s):  
Amorphous Materials ◽  
Incident Radiation ◽  
Single Element ◽  
Anomalous Scattering ◽  
X Rays ◽  
Single Chemical ◽  
Chemical States ◽  
Atomic Scattering ◽  
Scattering Factor ◽  
X Ray Absorption

AbstractSome elements in some chemical states exhibit strong dichroism and birefringence near x-ray absorption edges. The atomic scattering factor is a complex tensor. This polarization anisotropy has profound effects on the transmission and scattering of x-rays even when the incident radiation is unpolarized. The linear polarization of synchrotron radiation makes it easier to study the effects and to use them for new methods of structure determination. Several of these anomalous scattering tensors have been measured by absorption spectroscopy and in diffraction experiments. New polarization terms enter the calculation of diffraction intensities, with interesting consequences. Reflections forbidden by a screw-axis rule are observed in sodium bromate near the Br K edge and permit direct observation of the structure factor phases of their second order reflections. This technique is a method of selective diffraction in which atoms of single element in a single chemical state contribute to the signal, and it can reveal their positions with precision. These effects can be a handicap for some applications of near-edge anomalous scattering in the study structures of crystals and amorphous materials.

Photon escape probabilities in a semi-infinite plane-parallel medium

1984 ◽  
Vol 276 ◽  
pp. 691
Author(s):  
A. C. Williams ◽  
R. F. Elsner ◽  
M. C. Weisskopf ◽  
W. Darbro
Keyword(s):  
Infinite Plane ◽  
Plane Parallel ◽  
Escape Probabilities

scholarly journals The Hard X-ray Reflection on Cold Matter

1994 ◽  
Vol 159 ◽  
pp. 348-348
Author(s):  
E. Jourdain ◽  
J.P. Roques
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Cross Sections ◽  
Infinite Plane ◽  
Solar Abundance ◽  
X Ray ◽  
Direct Component ◽  
Plane Parallel ◽  
Γ Ray ◽  
Cold Matter

We have simulated the reflection on cold matter in a variety of situations to determine which informations can actually be inferred from observations. We modelled a semi-infinite plane parallel medium of solar abundance matter, semi-isotropically illuminated by a X/γ ray source. The spectra are calculated from a Monte-Carlo method without any approximation in the cross-sections. Θ is the angle over which the reflecting matter is seen (90°=face-on), Θ=all means a spatially integrated spectrum. Fref is the ratio of the reflected over direct component.

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