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Doppler broadening

About: Doppler broadening is a research topic. Over the lifetime, 5509 publications have been published within this topic receiving 92552 citations.


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TL;DR: In this article, the spectral broadening of cholesteric liquid crystal films is described, and it is shown that both phase separation and in situ swelling are important mechanisms for the resulting film structure.
Abstract: This letter describes the spectral broadening of cholesteric liquid crystal films prepared from a blend comprising a cross-linkable liquid crystal polymer and a noncross-linkable low-molecular-weight liquid crystal. The bandwidth of the broadened reflection band can be increased by several times upon photopolymerization. The spectral broadening arises from the formation of gradient pitch across the film thickness. It is shown that both phase separation and in situ swelling are important mechanisms for the resulting film structure.

30 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the parabolic equation method to analyze the spectral broadening of monochromatic radio waves by density fluctuations near the sun and found that the three-dimensional density spectrum is close to the Kolmogorov spectrum (power law with spectral index of 11/3).
Abstract: Spectral broadening of monochromatic radio waves by density fluctuations near the sun is analyzed using the parabolic equation method. Application of the analysis to the 1968 Pioneer-6 spectral broadening observations yields indirect measurements of the density spectrum within 14 solar radii of the sun. For spatial wavenumbers of at least 0.0084 inverse km, the three-dimensional density spectrum is found to be close to the Kolmogorov spectrum (power law with spectral index of 11/3) and is consistent with interplanetary-scintillation and in situ spacecraft measurements farther from the sun. The magnitude of the density spectrum increases, but its shape remains the same during 'solar events' marked by increases in bandwidth.

30 citations

Journal ArticleDOI
TL;DR: In this article, the spectral and temporal characteristics of a coupled-cavity mode-locked (CCM) KCl:Tl color center laser where a 2.8m length of anomalously dispersive fiber was used in the control cavity were observed.
Abstract: The authors present experimental results on the spectral and temporal characteristics of a coupled-cavity mode-locked (CCM) KCl:Tl color center laser where a 2.8-m length of anomalously dispersive fiber was used in the control cavity. Under different operating conditions, both symmetrical and peak-featured spectra of the CCM laser were observed. Interrelationships between the spectral broadening and the cavity-length mismatch were determined experimentally. >

30 citations

Journal ArticleDOI
TL;DR: Positron lifetime and Doppler broadening experiments have been conducted in silicon which was subjected to various degrees of plastic deformation, and evidence is presented indicating the existence of the hexavacancy as mentioned in this paper.
Abstract: Positron lifetime and Doppler broadening experiments have been conducted in silicon which was subjected to various degrees of plastic deformation. With increasing plastic deformation (from 2.5 to 38%) the trapping rate per unit dislocation concentration decreased from about 8 × 1015 to 4.5 × 1015 s−1 as measured at room temperature. Two annealing stages were identified by isochronal annealing, one of which had an activation enthalpy of 3.2 to 3.8 eV as determined by isothermal annealing. Measurements in the temperature range 15 to 673 K show that the positron annihiliation parameters (lifetimes, intensities, and S-parameters) depend strongly on temperature and that the functional form of these dependencies is related to the state of annealing of the deformed samples. These results are disscussed in terms of the presence of vacancy clusters and dislocations, and evidence is presented indicating the existence of the hexavacancy.

30 citations

Journal ArticleDOI
TL;DR: In this paper, the annihilation characteristics of positrons in SiO2 films grown on Si substrates were studied by using monoenergetic positron beams, and it was found that about 90% of the positrons implanted into the SiO 2 film annihilate from positronium (Ps) states.
Abstract: The annihilation characteristics of positrons in SiO2 films grown on Si substrates were studied by using monoenergetic positron beams. Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured as a function of incident positron energy for SiO2 (166 nm)/Si specimens fabricated by thermal oxidation. From the measurements, it was found that about 90% of positrons implanted into the SiO2 film annihilate from positronium (Ps) states. This fact was due to the trapping of positrons by open‐space defects and a resultant enhanced formation of Ps in such regions. For the SiO2 film grown at 650 °C, the lifetime of ortho‐Ps was found to be shorter than that in the film grown at 1000 °C. This result suggests that the volume of open‐space defects in the SiO2 film decreased with decreasing the growth rate of the SiO2 film.

30 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202331
202290
2021122
2020134
2019128
2018122