Non-radiating sources: fundamental and higher-order anapole states in all-dielectric nanostructures

Non-radiating sources are radiationless electromagnetic states characterized by vanishing scattering in the far-field and robust energy localization in the near field. Initially developed in quantum mechanics and astrophysics to model elementary particles noninteracting with the electromagnetic field, non-radiating states have gained a prominent role in nanophotonics following the experimental demonstration of anapole states. This chapter provides an overview of the theoretical foundations and critical milestones in investigating optical anapole states and their application in subwavelength dielectric nanostructures, discussing past results and present challenges.</p

Deterministic terahertz wave control in scattering media

Scattering-assisted synthesis of broadband optical pulses is recognized to have a cross-disciplinary fundamental and application importance. Achieving full-waveform synthesis generally requires means for assessing the instantaneous electric field, i.e., the absolute electromagnetic phase. These are generally not accessible to established methodologies for scattering-assisted pulse envelope and phase shaping. The lack of field sensitivity also results in complex indirect approaches to evaluate the scattering space–time properties. The terahertz frequency domain potentially offers some distinctive new possibilities, thanks to the availability of methods to perform absolute measurements of the scattered electric field, as opposed to optical intensity-based diagnostics. An interesting conceptual question is whether this additional degree of freedom can lead to different types of methodologies toward wave shaping and direct field-waveform control. In this work, we theoretically investigate a deterministic scheme to achieve broadband, spatiotemporal waveform control of terahertz fields mediated by a scattering medium. Direct field access via time-domain spectroscopy enables a process in which the field and scattering matrix of the medium are assessed with minimal experimental efforts. Then, illumination conditions for an arbitrary targeted output field waveform are deterministically retrieved through numerical inversion. In addition, complete field knowledge enables reconstructing field distributions with complex phase profiles, as in the case of phase-only masks and optical vortices, a significantly challenging task for traditional implementations at optical frequencies based on intensity measurements aided with interferometric techniques.</p

Terahertz nonlinear ghost imaging via plane decomposition: Towards near-field micro-volumetry: Fig.2. US temporal movie

 Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging (TNGI) methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally-resolved, field-sensitive detection to ‘refocus’ an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with sub-wavelength resolution, discussing the range of applicability of our technique. </p

Concurrent terahertz generation via quantum interference in a quadratic media

The strive for efficiency in the generation of terahertz (THz) waves motivates intense research on novel field–matter interactions. Presently, THz generation via quadratic crystals remains the benchmark thanks to its simple and practical deployment. An interesting problem is whether new mechanisms can be exploited to elicit novel generation approaches and forms of control on the THz output in existing systems. THz generation via quantum interference (QI) leverages a third-order nonlinear response under resonant absorption, and it has been recently explored to access surface generation in centrosymmetric systems. Its deployment in standard THz quadratic sources can potentially create a physical setting with the concurrence of two different mechanisms. Here, THz generation via QI in noncentrosymmetric crystals concurrent with phase-matched quadratic generation in a bulk-transmission setting is demonstrated. Beyond investigating a new physical setting, it is demonstrated that conversion efficiencies much larger than those typically associated with the medium become accessible for a typically adopted crystal, ZnTe. An inherent control on the relative amplitude and sign of the two generated THz components is also achieved. This approach provides disruptive boost and management of the optical-to-THz conversion performance of a well-established technology, with significant ramifications in emerging spectroscopy and imaging applications. </p

Dataset for Concurrent terahertz generation via quantum interference in a quadratic media

Dataset to accompany the paper    "Concurrent terahertz generation via quantum interference in a quadratic media." The dataset is provided in a .fig format which contains the figures for the paper. The file format also contains the datasets for each of the figures.</p

Terahertz nonlinear ghost imaging via plane decomposition: Towards near-field micro-volumetry: Fig.3. MGI temporal movie

Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging (TNGI) methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally-resolved, field-sensitive detection to ‘refocus’ an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with sub-wavelength resolution, discussing the range of applicability of our technique. </p

Terahertz nonlinear ghost imaging via plane decomposition: Towards near-field micro-volumetry: Fig.3. MGI spectral movie

Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging (TNGI) methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally-resolved, field-sensitive detection to ‘refocus’ an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with sub-wavelength resolution, discussing the range of applicability of our technique. </p

Terahertz nonlinear ghost imaging via plane decomposition: Towards near-field micro-volumetry: Supplementary information

Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging (TNGI) methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally-resolved, field-sensitive detection to ‘refocus’ an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with sub-wavelength resolution, discussing the range of applicability of our technique. </p

Terahertz nonlinear ghost imaging via plane decomposition: Towards near-field micro-volumetry

Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging (TNGI) methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally-resolved, field-sensitive detection to ‘refocus’ an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with sub-wavelength resolution, discussing the range of applicability of our technique.</p

Terahertz nonlinear ghost imaging via plane decomposition: Towards near-field micro-volumetry: Fig.2. US spectral movie

 Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging (TNGI) methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally-resolved, field-sensitive detection to ‘refocus’ an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with sub-wavelength resolution, discussing the range of applicability of our technique. </p