PhD Defence by Saher Junaid

Title: Upconversion based mid-infrared hyperspectral imaging

 

Supervisors

Supervisor: Peter Tidemand-Lichtenberg
Co-supervisor: Christian Pedersen

Co-supervisor: Professor Nicholas Stone, University of Exeter


Evaluation Board
Professor Karsten Rottwitt, DTU Fotonik
Professor Juan Capmany Francoy, Departamento de lngenieria de Comunicaciones, Universidad Miguel Hernandez , Spain
Associate Professor Franciscus Johannes Maria Harren, Institute of Molecules and Materials, Radboud University, The Netherlands

Master of the Ceremony
Senior Researcher Peter John Rodrigo, DTU Fotonik

Abstract:
Hyperspectral imaging in the mid-infrared spectral range is an emerging technology utilized for a multitude of applications, but its full potential is held back by the lack of sensitive mid-IR detectors. Nonlinear frequency upconversion offers a promising alternative to direct detection for room-temperature mid-IR spectroscopy and hyperspectral imaging.

In this work, upconversion based hyperspectral imaging has been demonstrated in the 1 to 10 µm spectral domain using different kinds of illumination sources narrowband\broadband, continuous wave\pulsed, such as globars, Quantum Cascade Lasers, Optical Parametric Oscillators and Supercontinuum sources. Nonlinear media such as Lithium Niobate (birefringent and quasi phase-matched) and Silver Gallium Sulfide have been exploited for sum frequency generation i.e. upconversion.

Large field of view and broad spectral coverage have been achieved using phase-match scanning techniques such as temperature and angle tuning of the nonlinear crystal. Post-processing techniques have been developed for the construction of upconversion hyperspectral cubes based on both narrowband and broadband light sources.

A video-frame rate upconversion imaging system is realized using a standard CCD camera, in synchronism with the crystal rotation of an upconversion system. This system is capable of acquiring 64 kpixels upconverted mid-infrared images in 2.5 ms, without the need for post-processing. This approach is generic in nature and constitutes a major simplification in realizing video-frame rate hyperspectral imaging in the mid-IR.

Based on this setup, a pilot study on oesophageal tissues samples from a tissue microarray, is presented, in the 3 to 4 µm wavelength range using computer assisted classification.  Comparing the stained sections evaluated by a pathologist to those obtained by either FTIR or upconversion hyperspectral 3 to 4 µm imaging based on machine learning shows great promise for future research pointing towards potential clinical translation.

In the last phase of the project, point-spread function engineering in the upconversion process is presented. Dark field imaging of static and dynamic near-infrared phase objects is demonstrated – resulting in edge-enhanced upconverted images. Through this scheme, the spiral phase filter operates at the pump wavelength rather than in the mid-IR signal wavelength which can potentially be broadband. This approach offers some advantages due to the lack of high-performance spiral phase filters and cameras operating at the signal wavelength (especially for mid-infrared objects). Furthermore, upconversion dark field imaging is extended numerically and experimentally from collinear to non-collinear interactions between signal and pump.

Tidspunkt

tir 26 feb 19
13:00 - 16:00

Hvor

Risø Campus

Building 112, auditorium Niels Bohr