Optical traps provide tight confinement and very long storage times for atomic gases. Using a single focused
beam from a CO2 laser, we confine a mixture of spin-up and spin-down fermionic 6Li atoms, achieving storage
times of ten minutes, and evaporative cooling to quantum degeneracy in seconds. A bias magnetic field tunes
the gas to a collisional (Feshbach) resonance, producing extremely strong spin-pairing. This system now tests
current many-body predictions for high-temperature superconductors, universal interactions in neutron stars,
and hydrodynamic flow of quark-gluon plasmas, a state of matter that existed microseconds after the Big Bang.
For the first time we are able to observe the time-resolved Wigner function of enhanced backscatter from a random medium using a novel two-window technique. This technique enables us to directly verify the phase-conjugating properties of random media. An incident divergent beam displays a convergent enhanced backscatter cone. We measure the joint position and momentum (x, p) distributions of the light field as a function of propagation time in the medium. The two-window technique allows us to independently control the resolutions for position and momentum, thereby surpassing the uncertainty limit associated with Fourier transform pairs. By using a low-coherence light source in a heterodyne detection scheme, we observe enhanced backscattering resolved by path length in the random medium, providing information about the evolution of optical coherence as a function of penetration depth in the random medium.
We demonstrate the measurement of path-length-resolved optical phase space distributions as a new framework for exploring the evolution of optical coherence in a turbid medium. This method measures joint transverse position and momentum (i.e., angle) distributions of the optical field, resolved by optical path length in the medium. The measured distributions are related to the Wigner phase space distribution function of the optical field, and can provide complete characterization of the optical coherence in multiple scattering media. Optical phase space distributions are obtained as contour plots which enable a visual as well as quantitative method of characterizing the spatial coherence properties and wavefront curvature of the input and scattered fields. By using a broad-band source in a heterodyne detection scheme, we observe transmission and backscatter resolved by path length in the random medium, effectively providing timing resolution. New two-window heterodyne detection methods permit independent control of position and momentum resolution with a variance product that surpasses the uncertainty limit associated with Fourier transform pairs. Hence, high position and angular resolution can be simultaneously achieved. These techniques may provide new venues for using optical coherence in medical imaging.
We demonstrate the measurement of path-length-resolved optical phase space distributions as a new framework for exploring the evolution of optical coherence in a turbid medium. This method measures joint transverse position and momentum (i.e., angle) distributions of the optical field, resolved by optical path length in the medium. The measured distributions are related to the Wigner phase space distribution function of the optical field, and can provide complete characteristics of the optical coherence in multiple scattering media. Optical phase space distributions are obtained as contour plots which enable a visual as well as quantitative method of characterizing the spatial coherence properties and wavefront curvature of the input and scattered fields. By using a broad-band source in a heterodyne detection scheme, we observe transmission and backscatter resolved by path length in the random medium, effectively providing timing resolution. New two-window heterodyne detection methods permit independent control of position and momentum resolution with a variance product that surpasses the uncertainty limit associated with Fourier transform pairs. Hence, high position and angular resolution can be simultaneously achieved. These techniques may provide new venues for using optical coherence in medical imaging.
We explore enhanced backscatter from a random medium using time-resolved optical phase space measurement, i.e. measurement ofjoint position and momentum (x, p) distributions of the light field as a function of propagation time in the medium. Enhanced backscatter is a coherent effect and is not predicted by radiative transport theories. By using a low-coherence source in a heterodyne detection scheme, we observe enhanced backscattering resolved by path length in the random medium, effectively providing timing resolution. Such time-resolved studies are important for exploring the evolution of optical coherence as a function of penetration depth in the random medium. Optical phase space methods provide a visual as well as quantitative method of characterizing the spatial coherence properties and wavefront curvature of the input and scattered fields. These techniques may provide new venues for using optical coherence in medical imaging.
We use heterodyne detection to characterize the Wigner phase space distribution W(x,p) of an optical field in position x and momentum p. Using a low coherence source, this method is used to obtain optical phase space distributions for various photon path lengths in a multiple scattering medium. These techniques may find important applications in analyzing and enhancing images obtained in coherence tomography as well as in characterizing low coherence sources.
We use heterodyne detection to characterize the Wigner phase space distribution W(x,p) of an optical field in position x and momentum p. This method yields smoothed Wigner phase space distributions directly as contour plots and can be applied with either coherent or low coherence light sources. The measured phase space distributions are used to characterize the light sources and to study light propagation in multiple scattering media. These techniques may find important applications in understanding and enhancing images obtained in coherence tomography.
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