The competition between electron localization and de-localization in Mott insulatorsunderpins the physics of strongly-correlated electron systems. Photo-excitation, which redistributes charge between sites, can control this many-body process on the ultrafast In Mott insulators, conductivity at low energies is prevented by repulsion among electrons.This state is fundamentally different from that of conventional band insulators, in which Bragg scattering from the lattice opens gaps in the single particle density of states. The electronic structure of Mott insulators is, therefore, sensitive to doping. Photo-excitation, in analogy to static doping, can trigger large changes in the macroscopic properties viii .However, the coherent physics driving these transitions has not been fully observed because the many-body electronic dynamics are determined by hopping and correlation processes that only persist for a few femtoseconds.We report measurements of coherent many-body dynamics with ultrafast optical spectroscopy in the one-dimensional Mott insulator ET-F2TCNQ. Several factors make this possible: ET-F2TCNQ has a narrow bandwidth (~ 100 meV), which corresponds to hopping times of tens of femtoseconds; the material has a weak electron-lattice interaction; we use a novel optical device producing pulses of 9 fs at the 1.7 m Mott gap; we study this physics in a one-dimensional system, allowing the evolution of the many-body wavefunction to be calculated and compared with experimental data. The characteristics of this new peak are time dependent, as visualized in Fig. 2c, where we have normalized the reflectivity at each time step. Two contours are shown in Fig. 2c. On the blue side, a prompt red-shift and recovery of the resonance is observed, whereas the red side shows a longer-lived component, containing a damped oscillatory response at 25 THz. StaticRaman data on ET-F2TCNQ does not show any equivalent features, strongly suggesting that the oscillation is not due to coherent phonons, but of an electronic origin xiv .To investigate such dynamics, we used a one-dimensional Mott-Hubbard Hamiltonian for a half-filled chain, with N = 10 sites, with electron hopping, t, and onsite and nearest neighbourCoulomb repulsion U and V, where, c †l, and cl, are the creation and annihilation operators for an electron at site l with spin , nl, is the number operatorand nl = nl, + nl,. We described the initial state, where  represents a many-body wavefunction with one electron per site and total spin-vector . This reflects the fact that, at room temperature, charges are localized, but posses no magnetic ordering.We calculate the static optical conductivity (see methods section) to find values of U, V and t that provide the best fit to the experimental results. The best fit, shown in Fig. 3c (t = -200 fs), gave U = 820 meV, V = 100 meV and t = 50 meV. It was not possible to fit the optical conductivity using U and t alone and inter-site correlation energy, V, was needed xv .These static parameters were used to fit to the...

Ultrafast optical parametric amplifiers (OPAs) can provide, under suitable conditions, ultra-broad gain bandwidths and can thus be used as effective tools for the generation of widely tunable few-optical-cycle light pulses. In this paper we review recent work on the development of ultra-broadband OPAs and experimentally demonstrate pulses with durations approaching the single-cycle limit and almost continuous tunability from the visible to the mid-IR.

We present wavefront sensorless adaptive optics (WSAO) Fourier domain optical coherence tomography (FD-OCT) for in vivo small animal retinal imaging. WSAO is attractive especially for mouse retinal imaging because it simplifies optical design and eliminates the need for wavefront sensing, which is difficult in the small animal eye. GPU accelerated processing of the OCT data permitted real-time extraction of image quality metrics (intensity) for arbitrarily selected retinal layers to be optimized. Modal control of a commercially available segmented deformable mirror (IrisAO Inc.) provided rapid convergence using a sequential search algorithm. Image quality improvements with WSAO OCT are presented for both pigmented and albino mouse retinal data, acquired in vivo.

Adaptive optics is rapidly transforming microscopy and high-resolution ophthalmic imaging. The adaptive elements commonly used to control optical wavefronts are liquid crystal spatial light modulators and deformable mirrors. We introduce a novel Multi-actuator Adaptive Lens that can correct aberrations to high order, and which has the potential to increase the spread of adaptive optics to many new applications by simplifying its integration with existing systems. Our method combines an adaptive lens with an imaged-based optimization control that allows the correction of images to the diffraction limit, and provides a reduction of hardware complexity with respect to existing state-of-the-art adaptive optics systems. The Multi-actuator Adaptive Lens design that we present can correct wavefront aberrations up to the 4th order of the Zernike polynomial characterization. The performance of the Multi-actuator Adaptive Lens is demonstrated in a wide field microscope, using a Shack-Hartmann wavefront sensor for closed loop control. The Multi-actuator Adaptive Lens and image-based wavefront-sensorless control were also integrated into the objective of a Fourier Domain Optical Coherence Tomography system for in vivo imaging of mouse retinal structures. The experimental results demonstrate that the insertion of the Multi-actuator Objective Lens can generate arbitrary wavefronts to correct aberrations down to the diffraction limit, and can be easily integrated into optical systems to improve the quality of aberrated images.