Doppler broadening

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

Subcycle Extreme Nonlinearities in GaP Induced by an Ultrastrong Terahertz Field.

Abstract: We report on the experimental observation of extreme laser spectral broadening and a change in optical transmission in gallium phosphite induced by $\text{25 }\mathrm{MV}/\mathrm{cm}$ terahertz (THz) single-cycle internal field. Such intense THz radiation leads to twofold transient modifications of the optical properties in the electro-optical crystal. First, the electric field provokes extensive cross-phase modulation via the ${\ensuremath{\chi}}^{(2)}$ and ${\ensuremath{\chi}}^{(3)}$ nonlinearities on a copropagating 50 fs near infrared laser pulse which turns into 500% spectral broadening. Second, we observe an instantaneous change of the optical transmission occurring at the THz field which is alleged to interband Zener tunneling and charge carrier density modification by impact ionization turning the semiconductor in a metal-like transient state. The presented scheme displays a pathway to coherently control the optical properties of semiconductors on an ultrafast time scale by a strong THz field.

Measurement of electronic splitting in PbS quantum dots by two-dimensional nonlinear spectroscopy

Abstract: Quantum dots exhibit rich and complex electronic structure that makes them ideal for studying the basic physics of semiconductors in the intermediate regime between bulk materials and single atoms. The remarkable nonlinear optical properties of these nanostructures make them strong candidates for photonics applications. Here, we experimentally probe changes in the fine structure on ultrafast timescales of a colloidal solution of PbS quantum dots through their nonlinear optical response despite extensive inhomogeneous spectral broadening. Using continuum excitation and detection, we observe electronic coupling between nearly degenerate exciton states split by intervalley scattering at low exciton occupancy and a sub-100 fs frequency shift presumably due to phonon-assisted transitions. At high excitation intensities, we observe multi-exciton effects and sharp absorbance bands indicative of exciton-exciton coupling. Our experiments directly probe the nonlinear optical response of nearly degenerate quantum confined nanostructures with femtosecond temporal resolution despite extensive line broadening caused by the finite size distribution found in colloidal solutions.

Efficient excitation of a mesospheric sodium laser guide star by intermediate-duration pulses

Abstract: Calculations of backscatter emission of mesospheric sodium atoms in a laser guide star that is excited by pulses ranging from 30-ns to 0.9-μs duration are described. The efficient use of such pulses at saturating irradiance values is shown to require ~3 GHz of spectral broadening to provide access to the full absorption spectrum of the D2 line. The broadening is provided by frequency modulation. A set of density matrices was used to account for all 24 hyperfine states and inhomogeneous Doppler broadening. At the broadband (3-GHz) saturation irradiance of 4 W/cm2, both linearly and circularly polarized laser beams are shown to produce emission rates exceeding 60% of the maximum possible rate-equation rate for the 0.9-μs pulses. As expected, circular polarization produced more backscatter than did linear polarization, but the enhancement never exceeded 1/3 in the calculations that are reported. A brief estimate of state precession in the Earth’s magnetic field suggests that achieving even this enhancement will require that the time scale for optical pumping be held to less than 1 μs, which will require the use of irradiances greater than 0.7 W/cm2 and spectral coverage of the full 3-GHz hyperfine-plus-Doppler absorption profile, at least until most of the population is pumped out of the F = 1 ground states.

Correction of intrinsic spectral broadening errors in doppler peak velocity measurements made with phased sector and linear array transducers

Abstract: Commercial duplex ultrasound systems primarily measure peak velocity of blood flow to provide important information in diagnosing vascular disease. However, due to errors caused by intrinsic spectral broadening (ISB), the accuracy decreases as the Doppler angle increases. In general, vascular technologists and surgeons keep the Doppler angle under 60°. Even at 60°, ISB can produce an overestimation of peak velocity as high as 40%. This would indicate the necessity of reducing the Doppler angle even lower than 60°. Since most vessels in the body run parallel with the skin surface and criteria requiring a Doppler angle of say 45° or less would be difficult to achieve. Using the transverse Dooppler equation as a correction for ISB, in conjunction with the classical Doppler equation, accurate peak velocity measurements were obtained at Doppler angles as high as 80°. Corrections were made using both phased sector and linear array transducters for steered and unsteered beams. However, for beams steered at large angles, 20° or more, corresponding to Doppler angles of

Spectral broadening of 112 mJ, 1.3 ps pulses at 5 kHz in a LG 10 multipass cell with compressibility to 37 fs

Abstract: The first-order helical Laguerre–Gaussian mode (also called donut mode) is used to improve the energy throughput of nonlinear spectral broadening in gas-filled multipass cells. The method proposed in this Letter enables, for the first time to the best of our knowledge, the nonlinear spectral broadening of pulses with energies beyond 100 mJ and is suitable for an average power of more than 500 W while conserving an excellent spatio-spectral homogeneity of ∼98% and a Gaussian-like focus profile. Additionally compressibility from 1.3 ps to 37 fs is demonstrated.