Light field

About: Light field is a research topic. Over the lifetime, 5357 publications have been published within this topic receiving 87424 citations.

Ground-state depletion for subdiffraction-limited spatial resolution in coherent anti-Stokes Raman scattering microscopy

Abstract: We theoretically investigate ground-state depletion for subdiffraction-limited spatial resolution in coherent anti-Stokes Raman scattering (CARS) microscopy. We propose a scheme based on ground-state depopulation, which is achieved via a control laser light field incident prior to the CARS excitation light fields. This ground-state depopulation results in a reduced CARS signal generation. With an appropriate choice of spatial beam profiles, the scheme can be used to increase the spatial resolution. Based on the density matrix formalism we calculate the CARS signal generation and find a CARS signal suppression by 75% due to ground-state depletion with a single control light field and by using two control light fields the CARS signal suppression can be enhanced to 94%. Additional control light fields will enhance the CARS suppression even further. In case of a single control light field we calculate resulting CARS images using a computer-generated test image including quantum and detector noise and show that the background from the limited CARS suppression can be removed by calculating difference images, yielding subdiffraction-limited resolution where the resolution achievable depends only on the intensity used.

Nanofiber-based atom trap created by combining fictitious and real magnetic fields

Abstract: We propose a trap for cold neutral atoms using a fictitious magnetic field induced by a nanofiber-guided light field in conjunction with an external magnetic bias field. In close analogy to magnetic side-guide wire traps realized with current-carrying wires, a trapping potential can be formed when applying a homogeneous magnetic bias field perpendicular to the fiber axis. We discuss this scheme in detail for laser-cooled cesium atoms and find trap depths and trap frequencies comparable to the two-color nanofiber-based trapping scheme but with one order of magnitude lower power of the trapping laser field. Moreover, the proposed scheme allows one to bring the atoms closer to the nanofiber surface, thereby enabling efficient optical interfacing of the atoms with additional light fields. Specifically, optical depths per atom, σ0/Aeff, of more than 0.4 are predicted, making this system eligible for nanofiber-based nonlinear and quantum optics experiments.

Light- and electric-field-induced first-order orientation transitions in a dendrimer-doped nematic liquid crystal.

Abstract: Interaction of light and ac electric fields with a nematic liquid crystal (NLC) doped with nanosized second-generation carbosilane codendrimers containing terminal azobenzene fragments has been studied. A first-order Freedericksz transition in the linearly polarized light, accompanied by an intrinsic bistability in a wide region, was observed. An additional ac electric field decreases the light-induced Freedericksz transition threshold and narrows the bistability region. Light illumination transforms the second-order electric-field-induced Freedericksz transition to a first-order one. The width of the bistability region increases with the light wave intensity. The theory of the interaction of light and ac electric fields with the dendrimer-doped NLCs is developed taking into account an additional (with respect to the undoped nematic host) dependence of the optical torque on the angle between the director and the light field.

Compressive sensing of light fields

Abstract: We propose a novel camera design for light field image acquisition using compressive sensing. By utilizing a randomly coded non-refractive mask in front of the aperture, incoherent measurements of the light passing through different regions are encoded in the captured images. A novel reconstruction algorithm is proposed to recover the original light field image from these acquisitions. Using the principles of compressive sensing, we demonstrate that light field images with high angular dimension can be captured with only a few acquisitions. Moreover, the proposed design provides images with high spatial resolution and signal-to-noise-ratio (SNR), and therefore does not suffer from limitations common to existing light-field camera designs. Experimental results demonstrate the efficiency of the proposed system.

Strong-field approach to ultrafast pump-probe spectra: dye molecules in solution

Abstract: The ultrafast dissipative dynamics of molecular vibrations under the influence of strong laser pulses is studied in the framework of the density matrix theory. To circumvent any perturbational treatment of the molecule-radiation coupling the related equations of motion are solved directly with the inclusion of the light field. The theory is applied to the simulation of 20 fs two-color pump-probe experiments on the laser-dye IR 125 [S.H. Ashworth, T. Hasche, M. Woerner, E. Riedle and T. Elsaesser, J. Chem. Phys. 104 (1996) 5761]. It can be demonstrated that a three-level model of a S 0 , a S 1 , and a higher excited S n state completed by a single vibrational coordinate is sufficient to calculate the measured spectra. The main features of the spectra can be explained by the formation of a dynamical hole in the vibrational wave function of the electronic ground state. Its spatio-temporal oscillation and its dependence on the pump intensity is studied in detail.