Route to Intelligent Imaging Reconstruction via Terahertz Nonlinear Ghost Imaging

Abstract

Terahertz (THz) imaging is a rapidly emerging field, thanks to many potential applications in diagnostics, manufacturing, medicine and material characterisation. However, the relatively coarse resolution stemming from the large wavelength limits the deployment of THz imaging in micro- and nano-technologies, keeping its potential benefits out-of-reach in many practical scenarios and devices. In this context, single-pixel techniques are a promising alternative to imaging arrays, in particular when targeting subwavelength resolutions. In this work, we discuss the key advantages and practical challenges in the implementation of time-resolved nonlinear ghost imaging (TIMING), an imaging technique combining nonlinear THz generation with time-resolved time-domain spectroscopy detection. We numerically demonstrate the high-resolution reconstruction of semi-transparent samples, and we show how the Walsh–Hadamard reconstruction scheme can be optimised to significantly reduce the reconstruction time. We also discuss how, in sharp contrast with traditional intensity-based ghost imaging, the field detection at the heart of TIMING enables high-fidelity image reconstruction via low numerical-aperture detection. Even more striking—and to the best of our knowledge, an issue never tackled before—the general concept of “resolution” of the imaging system as the “smallest feature discernible” appears to be not well suited to describing the fidelity limits of nonlinear ghost-imaging systems. Our results suggest that the drop in reconstruction accuracy stemming from non-ideal detection conditions is complex and not driven by the attenuation of high-frequency spatial components (i.e., blurring) as in standard imaging. On the technological side, we further show how achieving efficient optical-to-terahertz conversion in extremely short propagation lengths is crucial regarding imaging performance, and we propose low-bandgap semiconductors as a practical framework to obtain THz emission from quasi-2D structures, i.e., structure in which the interaction occurs on a deeply subwavelength scale. Our results establish a comprehensive theoretical and experimental framework for the development of a new generation of terahertz hyperspectral imaging devices.

Improving the performance of ghost imaging via measurement-driven framework

“…Considering the difficulty of generating quantum entanglement source, it was proved in theory and experiment that GI could be implemented with thermal and pseudo-thermal light [2][3][4][5][6][7][8] . In recent years, with the proposal of various GI schemes 6,[9][10][11] , GI has a bright application prospect in many related fields, such as remote sensing 12,13 , imaging through scattering media [14][15][16][17] , optical encryption 18,19 and terahertz imaging [20][21][22][23][24] .…”

Deterministic spatiotemporal focusing of terahertz waves through scattering media

“…37,38 The combination of nonlinear THz pattern generation and time-resolved field detection, in particular, has enabled the development of hyperspectral THz imaging with deeply subwavelength imaging resolution. 39 In essence, placing an object in the near-field of a nonlinear optical-to-THz converter makes it possible to produce terahertz illumination patterns with fine spatial features approaching the optical (i.e. the pump) diffraction limit.…”

Fast Terahertz Imaging Model Based on Group Sparsity and Nonlocal Self-Similarity

“…The information obtained from imaging at the Terahertz (THz) frequencies (0.1-10 THz) has received much attention in recent decades due to its unique properties [1][2][3][4][5][6]. Terahertz time domain spectroscopy (THZ-TDS) imaging is one of the most powerful techniques in the terahertz imaging field.…”