Time-resolved nonlinear ghost imaging

The spatial and temporal reconstruction of complex field distributions represents a critical challenge in a wide range of scenarios, ranging from photonics to ultrasound imaging [Err+15; Bor+02; Ber+12]. From practical stand point, it allows an enhanced form of hyperspectral imaging, a crucial task in many disciplines that enable the investigation into the bi-dimensional morphology of the absorption spectrum. [LF14; Mac12]. While these approaches are currently employed in microwave and ultra- sound imaging, they still represent a challenge in Photonics. At terahertz (THz) frequencies, the time-resolved full-wave measurements are en- abled by the Time-Domain Spectroscopy (TDS) technique, opening a plethora of different applications [SBB08; Gri+20; Che+20a; Yao+20; Cao+20; Lop+19; Gow07; Ngu+19]. In this frequency range, however, the lacking availability of field-sensitive cameras poses a technological limitation. As a result, imaging techniques that require a single- pixel detection have attracted interest in the THz community [Sha08; PB17; SB12; Gat+04a; Pit+95]. This class of approaches are currently known as Ghost Imaging (GI), because in its early demonstrations the imaging systems appeared to operate via photons that never interact with an object. As clarified in many following works, the GI image reconstruction is possible by correlating known spatial distributions of the patterns illuminating the object, with the single-pixel detection of the overall scattered power. In this thesis, I coin a new methodology for field-sensitive near-field imaging, namely the Time Resolved Nonlinear Ghost Imaging [Oli+18; Oli+20; TG+20; Oli+19]. This novel methodology relies on the correlation of nonlinearly generated THz pat- terns with a TDS detection, fusing the philosophy of the Ghost Imaging with all the requirements of time-domain field-imaging system. This new approach, presented in this thesis, is an advancement that requires novel understanding as well novel experiimental methodologies. These are here presented in the form of publications I have authored on the topic and recent developments still unpublished. The first chapter will explore the necessary background to approach the general topic from a general Physics and Photonics understanding.