Dr. Francesca Braglia Profile

Dr. Francesca Braglia

at Prometheus Srl

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Publications (3)

Proceedings Article | 9 October 2019 Presentation + Paper

Ghost imaging in the frequency domain with a high brilliance coherent monochromatic source: a novel approach to extend spectroscopy sensitivity beyond detectors limits

M. Chiarini, A. Parini, F. Braglia, L. Braglia, S. Braglia, S. Farabegoli, A. Artoni, A. Desalvo, G. Bentini

Proceedings Volume 11159, 1115904 (2019) https://doi.org/10.1117/12.2532244

KEYWORDS: Photons, Interferometers, Erbium, Sensors, Waveguides, Photodetectors, Imaging spectroscopy, Fourier transforms, Spectroscopy, Silicon

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Ghost imaging is an active technique that implies using a time-varying structured illumination source to image a target without spatially-resolving measurements of the light beam that interacts with the target. Traditionally, a beam splitter is used to create two highly correlated beams, such that the signal interacts with the target and is then measured by a single pixel detector, while the reference is directly measured by a spatially resolving detector. This approach allows to implement ghost imaging in the space domain, nevertheless also temporal and frequency domains can be addressed^1,2, allowing to extract the pertinent information. In particular, ghost imaging in the frequency domain has been recently applied to extract spectral information from a target object by means of Fourier Transform Interferometry^3,4. In this work we illustrate and discuss the results of interaction-free measurements on an Er³⁺ doped nonlinear crystal, placed in one arm of an interferometer, obtained by using only non-interacting photons. Our equipment is a wave-guided solid state device, exploiting an integrated quantum photonic circuit that is equivalent to an Asymmetric Nonlinear Mach-Zehnder Interferometer. The experiment was performed by using a 250mW monochromatic 980 nm laser source that allowed exciting an Er:LiNbO₃ waveguide, placed in one of the arms of the asymmetric interferometer. The interferograms were obtained by varying the signal in the time domain by using a LiNbO₃ undoped waveguide in the opposite branch of the interferometer and recorder with a standard Si p-i-n detector, provided with a pass band filter (975nm ± 25nm) thus blocking all photons except the pump ones. The data were analyzed with conventional Fast Fourier Transform Techniques. The application of this approach allowed to recover information in the frequency domain, in particular, despite the monochromatic characteristics of the detected signal, we could recover the whole spectroscopy of the energy levels of the Er³⁺ doped crystal. The role of the converted photons was evidenced by the fact that, by using a radiation source that does not interact with the dopant (1320nm Laser), only the line of the source is recovered by the FFT handling of the interferograms. An important aspect to remark is that the obtained spectral distribution addressed also the IR part of the spectrum where the applied detector (Si p-i-n) is blind. In this view, this methodology opens the possibility to extend sensitive spectral measurements in spectral regions where detectors show poor responsivity.

Proceedings Article | 9 October 2019 Presentation + Paper

Theoretic approach to ghost imaging in the frequency domain performed by means of a high brilliance coherent monochromatic source

M. Chiarini, A. Parini, F. Braglia, L. Braglia, S. Braglia, S. Farabegoli, A. Artoni, A. Desalvo, G. Bentini

Proceedings Volume 11159, 1115905 (2019) https://doi.org/10.1117/12.2532307

KEYWORDS: Photodetectors, Fourier transforms, Erbium, Sensors, Phase shifts, Imaging spectroscopy, Interferometers, Spectroscopy, Nomenclature, Nonlinear crystals

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Ghost imaging is a novel non-conventional technique allowing to generate high resolution images by correlating the intensity of two light beams, neither of which independently contains sufficient information about the spatial distribution and shape of the object. The first demonstration of ghost imaging used light in double photon state, obtained from spontaneous parametric down-conversion. Owing to the entanglement of the source photons, the proposed theory required quantum descriptions for both the optical source and its photo-detection statistics¹. However, subsequent experimental and theoretical considerations^2,3 demonstrated that ghost imaging can be performed also with thermalized light, utilizing either CCD detector arrays or photon-counting detectors, thus admitting to a semi-classical description, employing classical fields and shot-noise limited detectors. This has generated increasing interest^4-6 in establishing a unifying theory that characterizes the fundamental physics of ghost imaging and defines the boundary between classical and quantum domains. In this view, we exploited recent progress obtained through the application of Fourier Transform Techniques to demonstrate ghost imaging in the frequency domain, in order to measure a continuous spectrum by using a highly brilliant and coherent monochromatic source. In particular, we demonstrate the application of this ghost imaging technique to broadband spectroscopic measurements by means of interaction free photon detection. The experimental apparatus and the collected data are described in a dedicated work⁷. In this paper, we consider the theoretical aspects underlying the proposed Spectroscopic technique. In particular, two alternative theoretical models are presented. In one case, a statistical approach (semi-classical) is applied, where the states of the sampling beam are considered, whereas in the other case a pure quantum treatment is carried on, by describing the interaction of vacuum states generated by photon conversion processes. Both theoretical models, though carried on by means of a complementary formalism, lead to equivalent results and offer a physical interpretation of the collected experimental data. The application of these results offer novel perspectives for remote sensing in low light conditions, or in spectral regions where sensitive detectors are lacking.

Proceedings Article | 9 October 2019 Presentation + Paper

Sensor for security and safety applications based on a fully integrated monolithic electro-optic programmable micro diffracting device

G. Basti, G. G. Bentini, M. Chiarini, A. Parini, A. Artoni, F. Braglia, S. Braglia, S. Farabegoli

Proceedings Volume 11159, 1115907 (2019) https://doi.org/10.1117/12.2532107

KEYWORDS: Sensors, Safety, Electro optics, Molecules, Sensing systems, Explosives, Gases, Digital libraries, Computer security, Field spectroscopy

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