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Abstract: Mott transitions in real materials are first order and almost always associated with lattice distortions, both features promoting the emergence of nanotextured phases. This nanoscale self-organization creates spatially inhomogeneous regions, which can host and protect transient non-thermal electronic and lattice states triggered by light excitation. Here, we combine time-resolved X-ray microscopy with a Landau-Ginzburg functional approach for calculating the strain and electronic real-space configurations. We investigate V2O3, the archetypal Mott insulator in which nanoscale self-organization already exists in the low-temperature monoclinic phase and strongly affects the transition towards the high-temperature corundum metallic phase. Our joint experimental-theoretical approach uncovers a remarkable out-of-equilibrium phenomenon: the photo-induced stabilisation of the long sought monoclinic metal phase, which is absent at equilibrium and in homogeneous materials, but emerges as a metastable state solely when light excitation is combined with the underlying nanotexture of the monoclinic lattice.

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Abstract: Vibrational microspectroscopy via Fourier transform infrared (FTIR) faces an experimental trade-off among the signal to noise ratio (SNR), acquisition time, spatial resolution, and sample coverage. This is mainly associated with broadband source type: e.g. low brightness thermal sources with high flux for large field of view imaging at low resolution, or low ´etendue of synchrotron radiation infrared (SRIR) for diffraction-limited scanning mi- croanalysis at high magnification.1 Adaptive optics (AO), in this case deformable mirror (DM), is a potent tool in tackling the problem by modulating the intensity of high brightness structured SRIR beam toward a homo- geneous field illumination for IR imaging at high magnification. The latter is required for an efficient coupling of SRIR source to a multi-pixel detector such as focal plane array (FPA).2 Additionally, DM enables to achieve different shapes, optimized for different Cassegrain IR objective. Regardless, the quality of the generated beam relies upon the performance of the adaptive elements, i.e. actuators and their linear and reproducible response to the applied voltage. Moreover, the beam shaping capability of a single DM in controlling light beam position and angle is limited by its actuators influence function. In this work, we implemented two DMs for intensity shaping for the complex SRIR beam. A variation of multi-conjugate AO is implemented to characterize the performance of DMs and their actuators transfer function at multiple locations. An IR sensitive microbolometer array has been optically conjugated to the focal plane of individual actuators and the far-field of DM, in order to probe the corresponding actuating response. By analysing each actuator’s response individually, a measure of linear independence, uniformity in response, and cross-coupling can be obtained in a spectral range, from visible to near and mid IR. Additionally, by assembling the vectorized version of each actuator response, the transfer matrix can be formed. This matrix describes the relationship between the actuation effect on the beam and the response of the IR microbolometer, at the given conjugate planes. Based on such discussion, we assess the stability of the deformable mirror for open-loop (i.e. without feedback) operation.

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Abstract: Infrared (IR) spectral imaging is a quantitative scientific technique for measuring both the molecular composition and its spatial distribution across large areas of materials. Synchrotron radiation (SR) enhances IR imaging with a broad spectral bandwidth unobtainable with a conventional laboratory source or laser (covering 10000 to 5 cm-1), while the high collimation and small size of the SRIR source provide a diffraction-limited microbeam. The use of a few micron-sized aperture for IR imaging has a clear advantage in SR in terms of spectral quality, due to the high spectral flux reaching microspots of the sample even at the lowest wavenumbers. In this article, we present IR imaging examples developed mostly in collaboration with the user community and the staff of the IR beamline MIRIAM (Multimode InfraRed Imaging And Microspectroscopy) at Diamond Light Source [1 G. Cinque et al., Synchrotron Radiation News 24(5), 24–33 (2011). [Taylor & Francis Online], [Google Scholar] ]. The layout of the MIRIAM beamline (B22) is shown in Figure 1. Optically, this is composed of a UHV vacuum vessel including a two periscope system each with two metal mirrors, allowing refocusing and overcoming a midway shield wall (not shown). From the right, the bending magnet source illuminates a first flat mirror (with a horizontal slot rejecting X-rays) that reflects the SRIR fan onto an ellipsoidal mirror. The SRIR is focused midway and collected by another ellipsoidal mirror that redirects it down onto a double flat mirror; this can be translated laterally to send the focused SRIR to either of the two end stations (or part of the beam to both) through wedged diamond windows. The two experimental end stations are composed of Bruker Vertex 80V in-vacuum Fourier Transform IR (FTIR) interferometers with Hyperion 3000 IR microscopes. The IR detectors are broadband or high-sensitivity MCT (mercury cadmium telluride; 100 μm or 50 μm pitch) for point-by-point microscopy, and photovoltaic MCT focal plane array (FPA) 64 × 64 pixel detectors for full-field imaging.

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Abstract: For the first time, infrared spectra on the sub-wavelength scale have been delivered by a synchrotron-radiation-induced thermal expansion technique. The novel experimental result was achieved by coupling an atomic force microscope (AFM) to an infrared (IR) beamline at the UK's national synchrotron facility, Diamond Light Source. Via broadband synchrotron illumination and an AFM sub-micron tip, molecular IR spectra were obtained by detecting a resonance-enhanced (RE) photothermal signal with spatial resolution beyond the diffraction limit. Together with results on synchrotron IR nanoscopy in scattering mode from the IR beamline at the Advanced Light Source two years ago, the Diamond photothermal nanoprobe approach moves vibrational analysis beyond the diffraction limit and into nanoscale absorption spectroscopy.