Both new and established technologies are explored in the pursuit of finding an efficient approach for diagnosing malignant melanoma skin cancer. The non-invasive sub-surface imaging technique of optical coherence tomography (OCT) is frequently applied in the ophthalmological clinic, but is still emerging within the field of dermatology. We present our work in testing two supercontinuum OCT systems for characterizing tape strips applied to skin cancer patients. Tape strips were collected in a clinical trial of 75 skin cancer patients at Bispebjerg Hospital, Denmark. After low-temperature storage, samples were scanned by a near-infrared OCT system and a mid-infrared OCT system of wavelengths 1.3 µm and 4 µm. We report on the scanning protocol and how the wavelength dependent OCT scans can be interpreted in order to target malignant melanoma characteristics.
Wind turbine blades are an important part of green wind energy production, but the blades are subject to manufacturing defects that lead to material erosion during their operation. Optical coherence tomography (OCT) is a useful tool for sub-surface non-destructive imaging in the few millimetre range. We present non-destructive inspection (NDI) characterisation of wind turbine blade samples with a MIR OCT system employing a supercontinuum laser source with central wavelength around 4 µm. In our inspection of the sub-surface of wind turbine blades to detect defects inside the coating, we hope to improve understanding in blade manufacturing and support the industry in achieving zero waste production.
The project was funded by the Horizon Europe, Grant Agreement No. 101058054 (TURBO) and No. 101057404 (ZDZW), and by VILLUM Fonden (2021 Villum Investigator project no. 00037822: Table-Top Synchrotrons).
The egg is world famous for its role in the evolution of life, religious traditions, culture and breakfast. With the latter, the chicken egg is the primary choice for which the production depends on careful inspection of each egg to ensure high quality. To make the inspection efficient, non-destructive inspection (NDI) techniques, which are of high speed, and that can potentially be implemented in the line of production, are in demand.
In this work, we present the first mid-infrared (MIR) optical coherence tomography (OCT) study of eggs. We apply both near-infrared- (NIR) and MIR OCT systems, of respective centre wavelengths of 1.3 µm and 4 µm. We inspect a quail egg and two chicken eggs, brown and white. The quail and chicken eggs present two different kinds of shells, both seen in structure and thickness.
Funding: Horizon Europe, Grant Agreement No. 101058054 (TURBO) and No. 101057404 (ZDZW). VILLUM Fonden (2021 Villum Investigator project no. 00037822: Table-Top Synchrotrons).
We report numerical and experimental studies of instabilities in a “noise-like pulse” dissipative soliton laser generating an output spectrum of 1000 nm bandwidth, and with two orders of magnitude variation in intracavity spectral width over one roundtrip. Simulations identify the origin of the laser instability as the sensitivity to noise of nonlinear soliton dynamics. Our experiments use real-time time and frequency domain measurements, and our simulations reproduce quantitatively both the full extent of intracavity supercontinuum broadening, as well as the probability distributions of temporal and spectral fluctuations, including rogue waves.
Numerical modelling based on purely scalar nonlinear Schröodinger equation propagation is applied to a dissipative soliton laser operating in the soliton-similariton regime and generating parabolic pulses. The model is shown to reproduce a range of instabilities that have been reported in recent experiments. Here, we study in detail the laser stability characteristics as a function of the parameters of the gain medium and the saturable absorber, allowing us to readily identify clear regimes where stable single solitons and soliton molecules are observed. Outside these regimes, we reproduce a wide range of instabilities linked with soliton molecule internal motion, soliton explosions and intermittence.
Supercontinuum generation in the long pulse regime exhibits large shot-to-shot spectral variation and chaotic time domain consisting of soliton peaks emerging with random statistics. Under particular conditions, the noise-seeded dynamics may lead to the generation of a small number of extreme red-shifted rogue solitons that are associated with highly skewed “rogue wave” statistics. To overcome the restrictions in the experimental measurements, we here use the techniques of machine learning to predict the peak power and temporal shift of extreme red-shifted rogue solitons from single-shot spectral intensity profiles of supercontinuum without any phase information. The possibility to combine machine learning approaches with real-time spectral measurements to obtain temporal characteristics information without direct time-domain measurements which are often complex and limited to specific regimes of operations offers completely new avenues for the study of ultrafast dynamics in general.
Ultrafast mode-locked lasers are well-known to display a rich variety of unstable dissipative soliton dynamics resulting from the interplay of nonlinearity, dispersion and dissipation. Although laser instabilities have been known and studied in depth for many years, their properties have recently received greatly renewed attention because of the development of time and frequency domain techniques that allow laser dynamics and instabilities to be measured in real-time. This has allowed the variations in circulating pulse characteristics to be examined on a roundtrip to roundtrip basis, providing a new window into understanding these instabilities and how they develop based on the cavity configuration being used.
A technique of this kind that has proven both straightforward to implement and powerful is the photonic time stretch or dispersive Fourier transform (DFT) which has been used in a number of important applications including the measurement of soliton rogue waves, modulation instability and supercontinuum noise. The DFT allows direct access to shot-to-shot measurement of the mode-locked fibre laser spectrum and, via computation of the associated autocorrelation function, can also provide complementary time-domain information in cases where multiple pulse states are observed.
In this paper, we report results of DFT measurements which have been used to reveal previously unreported behavior in a mode-locked fiber laser designed to operate with soliton-similariton dynamics. In particular, we observe instabilities including soliton explosions, chaotic evolution and oscillation in the relative phase of bound-state multi-pulse molecules, and what we believe to be a previously-unobserved regime of operation associated with the intermittent appearance of short-lived stable single pulses within of otherwise chaotic dynamics. Our results - obtained in a laser believed to be a particularly stable design - suggest that instabilities such as soliton explosions and intermittence are a universal feature of dissipative soliton systems transitioning from noise to stability.
We will review our recent work in real-time measurements of nonlinear instabilities including the use machine learning, as well as the observation of a range of instability processes in novel dissipative systems such as the soliton-similariton laser.
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