We calculate the sound velocity and the damping rate of the collective excitations of a 2D fermionic superfluid in a non-perturbative manner. Specifically, we focus on the Anderson–Bogoliubov excitations in the BEC-BCS crossover regime, as these modes have a sound-like dispersion at low momenta. The calculation is performed within the path-integral formalism and the Gaussian pair fluctuation approximation. From the action functional, we obtain the propagator of the collective excitations and determine their dispersion relation by locating the poles of this propagator. We find that there is only one kind of collective excitation, which is stable at T = 0 and has a sound velocity of v F / 2 for all binding energies, i.e., throughout the BEC-BCS crossover. As the temperature is raised, the sound velocity decreases and the damping rate shows a non-monotonous behavior: after an initial increase, close to the critical temperature T C the damping rate decreases again. In general, higher binding energies provide higher damping rates. Finally, we calculate the response functions and propose that they can be used as another way to determine the sound velocity.
As Terahertz (THz) technology becomes more prominent in the imaging industry, there is a rising need for improved reconstruction techniques for THz tomographic imaging. Conventional reconstruction techniques yield artifacts for limited data problems, hindering further analysis of the reconstruction. In this paper, we explore a discrete reconstruction algorithm for Terahertz tomography, which exploits prior knowledge on the gray levels in the imaging data of the object to obtain high quality reconstructions. Simulations show that, compared to THz-SIRT reconstruction, the discrete THz algorithm (THz-DART) generates more accurate reconstructions, especially when only a small number of projections or projections acquired within a limited angular range are available.
In this paper, we study the application of a ray tracing technique to terahertz (THz) computed tomography (CT). We evaluate its accuracy by comparing the resulting sinograms with the ones simulated with a Born series approximation.
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