Doppler broadening

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

Nonresonant dielectric hole burning in neat and binary organic glass formers.

Abstract: Binary mixtures of the molecular glass former 2-picoline in oligostyrene, in which the dielectric response of 2-picoline exhibits a particularly broad distribution of correlation times, are investigated by nonresonant dielectric hole-burning (NDHB) spectroscopy and the results are compared with NDHB in neat systems, in particular, glycerol. It turns out that in both substance classes spectral selectivity is achieved, which indicates that dynamics is heterogeneous, i.e., slow and fast responses coexist in the material. However, in binary systems the position of the spectral modifications is completely determined by the spectral density of the pump field, and thus shifts linearly with burn frequency as expected, also at pump frequencies around the alpha-relaxation maximum. It is shown that in binary systems the lifetime tau(rec) of the spectral modifications is determined by the burn frequency omega(p) and exceeds its inverse by about one order of magnitude, indicating long-lived dynamic heterogeneity. The data are described in terms of a previously suggested model of dynamically selective heating, which was extended to include intrinsic nonexponential relaxation. It turns out that the spectral broadening in binary mixtures is not only due to pronounced dynamic heterogeneity, but partially also due to intrinsic broadening of the relaxation function.

Intensity and polarization dependences of the supercontinuum generation in birefringent and highly nonlinear microstructured fibers

Abstract: We present experimental results highlighting the physica mechanism responsible for the initial spectral broadening of femtosecond Ti:Sapphire pulses in a highly birefringent microstructured fiber having a small effective area. By rotating the input polarization and varying the injected power while monitoring the resulting changes in the output spectrum, we are bringing clear evidences that the initial broadening mechanism leading to a broadband supercontinuum is indeed the fission of higher-order solitons into redshifted fundamental solitons along with blueshifted nonsolitonic radiation.

Performance tests of Doppler ultrasound equipment with a string phantom.

Abstract: A detailed testing protocol has been developed for string phantom quality assessment performance measurements of Doppler equipment. General procedures have been developed for accurate setup of the string phantom prior to measurements, independent calibration of the string velocity, and compensation for degassed water in the tank. Detailed testing procedures were developed for important Doppler parameters. The dependence of spectral broadening on Doppler angle is demonstrated and a procedure given for minimizing its effect on Doppler velocity measurements. Doppler velocity calibration to better than 4% has been demonstrated even with degassed water in the tank with six high quality commercial pulsed Doppler systems.

Statistical performance evaluation and comparison of a Compton medical imaging system and a collimated Anger camera for higher energy photon imaging.

Abstract: In radionuclide treatment, tumor cells are primarily destroyed by charged particles emitted by the compound while associated higher energy photons are used to image the tumor in order to determine radiation dose and monitor shrinkage. However, the higher energy photons are difficult to image with conventional collimated Anger cameras, since a tradeoff exists between resolution and sensitivity, and the collimator septal penetration and scattering is increased due to the high energy photons. This research compares imaging performance of the conventional Anger camera to a Compton imaging system that can have improved spatial resolution and sensitivity for high energy photons because this tradeoff is decoupled, and the effect of Doppler broadening at higher gamma energies is decreased. System performance is analyzed by the modified uniform Cramer–Rao bound (M-UCRB) algorithms based on the developed system modeling. The bound shows that the effect of Doppler broadening is the limiting factor for Compton camera performance for imaging 364.4 keV photons emitted from 131I. According to the bound, the Compton camera outperforms the collimated system for an equal number of detected events when the desired spatial resolution for a 26 cm diameter uniform disk object is better than 12 mm FWHM. For a 3D cylindrical phantom, the lower bound on variance for the collimated camera is greater than for the Compton imaginer over the resolution range from 0.5 to 2 cm FWHM. Furthermore, the detection sensitivity of the proposed Compton imaging system is about 15–20 times higher than that of the collimated Anger camera.

A new measurement of the 429 keV 15N(p, αλ) 12C resonance. Applications of the very narrow width found to 15N and 1H depth location

Abstract: The unexpectedly narrow width Γp = 120 eV or ΓN15 = 1.8 keV of this resonance opens quite new possibilities for its use in 15N or 1H depth location and for hydrogen adsorption studies using 15N beams. Resonance depth profiling of 15N is possible with much better near-surface depth resolution than thought until recently. In 1H resonance depth profiling the indeep background originating from the surface contamination peak is also much smaller than previously assumed. These features are illustrated by 15N self-diffusion experiments in NbN films and by 15N adsorption experiments on copper single crystals in ultrahigh vacuum. The strong effect of Doppler broadening on the actual ultimate near-surface depth resolution of hydrogen depth profiling with 15N beams is discussed as well as the use of this resonance for the direct measurement, based on the Doppler effect, of the vibration speed distribution of hydrogen atoms adsorbed on clean surfaces.