Research Highlights

Multidimensional Hyperspectral Imaging - route towards 4D terahertz imaging

This project comes from the understanding that the field-sensitive waveform detected in a Time-resolved Nonlinear Ghost Imaging setting (see below for more info) contains more information than just the refractive index of the object: it contains the "story" of how the light, generated from a point source, propagates inside the materials, from diffraction to reflection and absorption.

We have defined and employed a fundamental tool, i.e. inverse propagator, to analyze images of complex three-dimensional data acquired via TNGI, retrieving details of objects at a depth that would otherwise be invisible and paving the way for multidimensional (x,y,z,frequency) hyperspectral imaging. 

 Selected Publications:

• Olivieri, L., et al., Terahertz Nonlinear Ghost Imaging via Plane Decomposition: Toward Near-Field Micro-Volumetry. ACS Photonics 2023, 10 (6), 1726–1734. https://doi.org/10.1021/acsphotonics.2c01727  [COVER PAGE]

Selected Media outlets:

• “Scientists demonstrate terahertz wave camera can capture 3D images of microscopic world in major breakthrough” (2023) - Loughborough University Media Centre.

• “Major Breakthrough Reveals Terahertz Wave Camera Can Capture 3D Images of Microscopic World” (2023) TechnologyNetwork

• “This camera captures images of microscopic items hidden inside objects” (2023) Interesting Engineering

Microresonator-based Optical Frequency combs

In recent years, microresonator-based LASER cavities have raised great attention within the scientific community as they represent a viable technology for the development of integrated and portable quantum devices, e.g. atomic clocks. 

The laser light is generated by ground noise amplification inside a microresonator ring and is stabilised through a thoughtful balance of nonlinearities and dispersion.  The frequency comb generated is broadband with thin stable lines that provide the temporal reference. 

 Selected Publications:

• Cutrona, A., et al., Stability of Laser Cavity-Solitons for Metrological Applications. Appl. Phys. Lett. 2023, 122 (12), 121104. https://doi.org/10.1063/5.0134147   [COVER PAGE]

• Cutrona, A., et al., Nonlocal Bonding of a Soliton and a Blue-Detuned State in a Microcomb Laser. Commun Phys 2023, 6 (1), 259. https://doi.org/10.1038/s42005-023-01372-0 

• Bao, H.; Olivieri, L., et al., A. Turing Patterns in a Fiber Laser with a Nested Microresonator: Robust and Controllable Microcomb Generation. Phys. Rev. Research 2020, 2 (2), 023395. https://doi.org/10.1103/PhysRevResearch.2.023395

Time-resolved Nonlinear Ghost Imaging  (TNGI) 

Over the last two decades, photographing microscopic objects at terahertz frequencies (1 trillion cycles per second) has captured the scientific community's fascination. The Terahertz detected in a standard spectroscopic lab is a broadband pulse (0.1-3 THz), which contains the chemical information - e.g. vibrational and rotational resonances - of the target investigated, allowing non-invasive chemical discrimination. Extending this capability to a microscopic system is however challenging as light cannot be focused on a spot tighter than the wavelength itself - the "diffraction limit" of light. As terahertz wavelength ranges around 300 micrometers, standard imaging techniques would be limited in their resolution.

We developed a technique that combines time-resolved field-sensitive terahertz acquisition with a near-field nonlinear generation of terahertz radiation. The reconstruction procedure is inspired by the computational Ghost Imaging framework, where known patterns of light illuminate the sample and a single-element detector is employed to detect the overall transmitted field.  We demonstrated we are capable of breaking the diffraction limit of light - observing objetcs with microscopic details - while preserving the hyperspectral data of the samples.

 Selected Publications

• Olivieri, L., et al., Hyperspectral Terahertz Microscopy via Nonlinear Ghost Imaging. Optica 2020, 7 (2), 186. https://doi.org/10.1364/OPTICA.381035[ 

• Totero Gongora, J. S.; Olivieri, L., et al., Route to Intelligent Imaging Reconstruction via Terahertz Nonlinear Ghost Imaging. Micromachines 2020, 11 (5), 521. https://doi.org/10.3390/mi11050521

• Olivieri, L., et al., Time-Resolved Nonlinear Ghost Imaging. ACS Photonics 2018, 5 (8), 3379–3388. https://doi.org/10.1021/acsphotonics.8b00653   [COVER PAGE]