RESUMEN
High-resolution imaging is an important issue in various fields of scientific researches and engineering applications. Pseudothermal ghost imaging is one of the subfields of quantum imaging, providing new capabilities beyond conventional imaging methods. Also, it can provide a new viewpoint of imaging physical mechanisms. In this review, we explain the major ideas of pseudothermal ghost imaging, restricting the very important case of high-resolution imaging. We analyse the strategies which can significantly improve the image quality in pseudothermal ghost imaging. It may apply for merging it with common optical imaging methods in the extreme ultraviolet (XUV) or X-ray spectral regime for driving the applications to a wider audience in bioscience and nano-physics.
Ghost imaging, based on multiplexing, can help overcome specific kinds of noise. It can offer a way to alleviate the irreversible damage to the sample, because the object does not interact with the CCD camera. Pseudothermal light sources have a substantially higher flux, so the performance of the pseudothermal ghost imaging system can exceed those based upon parametric down-conversion sources. XUV and X-ray radiography are invaluable tools for the analysis of biological samples and in nano-physics. The pseudothermal ghost imaging can easily be transferred into the XUV and X-ray regime without a lens, whereas parametric down-conversion is restricted to the visible and infrared range. The main drawbacks of pseudothermal ghost imaging are longer acquisition times and the large number of measurements required for image recovery. At present, the resolution of microscopic ghost imaging has never reached the level of traditional microscopic imaging.
RESUMEN
Understanding the behaviour of matter under conditions of extreme temperature, pressure, density and electromagnetic fields has profound effects on our understanding of cosmologic objects and the formation of the universe. Lacking direct access to such objects, our interpretation of observed data mainly relies on theoretical models. However, such models, which need to encompass nuclear physics, atomic physics and plasma physics over a huge dynamic range in the dimensions of energy and time, can only provide reliable information if we can benchmark them to experiments under well-defined laboratory conditions. Due to the plethora of effects occurring in this kind of highly excited matter, characterizing isolated dynamics or obtaining direct insight remains challenging. High-density plasmas are turbulent and opaque for radiation below the plasma frequency and allow only near-surface insight into ionization processes with visible wavelengths. Here, the output of a high-harmonic seeded laser-plasma amplifier using eight-fold ionized krypton as the gain medium operating at a 32.8 nm wavelength is ptychographically imaged. A complex-valued wavefront is observed in the extreme ultraviolet (XUV) beam with high resolution. Ab initio spatio-temporal Maxwell-Bloch simulations show excellent agreement with the experimental observations, revealing overionization of krypton in the plasma channel due to nonlinear laser-plasma interactions, successfully validating this four-dimensional multiscale model. This constitutes the first experimental observation of the laser ion abundance reshaping a laser-plasma amplifier. The presented approach shows the possibility of directly modelling light-plasma interactions in extreme conditions, such as those present during the early times of the universe, with direct experimental verification.