Development of compact ultrafast fiber laser sources for nonlinear optical microscopy

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3D Imaging of Gems and Minerals by Multiphoton Microscopy

Many optical approaches have been used to examine the composition and structure of gemstones, both recently and throughout history. The nonlinear optical behavior of different gemstones has not been investigated, and the higher order terms to the refractive index represent an unused tool for qualifying and examining a stone. We have used a multiphoton microscope to examine the nonlinear optical properties of 36 different gemstones and demonstrate that it is a useful tool for imaging them three-dimensionally up to the millimeter scale below the sample surface. The polarization dependence of second harmonic generation signals was used to examine the crystal orientations inside the minerals.Comment: 9 pages, five figure

Graph-based Time-Series Anomaly Detection: A Survey

With the recent advances in technology, a wide range of systems continue to collect a large amount of data over time and thus generate time series. Time-Series Anomaly Detection (TSAD) is an important task in various time-series applications such as e-commerce, cybersecurity, vehicle maintenance, and healthcare monitoring. However, this task is very challenging as it requires considering both the intra-variable dependency and the inter-variable dependency, where a variable can be defined as an observation in time series data. Recent graph-based approaches have made impressive progress in tackling the challenges of this field. In this survey, we conduct a comprehensive and up-to-date review of Graph-based TSAD (G-TSAD). First, we explore the significant potential of graph representation learning for time-series data. Then, we review state-of-the-art graph anomaly detection techniques in the context of time series and discuss their strengths and drawbacks. Finally, we discuss the technical challenges and potential future directions for possible improvements in this research field.Comment: 19 pages, 4 figures, 2 table

Open-Set Multivariate Time-Series Anomaly Detection

Numerous methods for time series anomaly detection (TSAD) methods have emerged in recent years. Most existing methods are unsupervised and assume the availability of normal training samples only, while few supervised methods have shown superior performance by incorporating labeled anomalous samples in the training phase. However, certain anomaly types are inherently challenging for unsupervised methods to differentiate from normal data, while supervised methods are constrained to detecting anomalies resembling those present during training, failing to generalize to unseen anomaly classes. This paper is the first attempt in providing a novel approach for the open-set TSAD problem, in which a small number of labeled anomalies from a limited class of anomalies are visible in the training phase, with the objective of detecting both seen and unseen anomaly classes in the test phase. The proposed method, called Multivariate Open-Set timeseries Anomaly Detection (MOSAD) consists of three primary modules: a Feature Extractor to extract meaningful time-series features; a Multi-head Network consisting of Generative-, Deviation-, and Contrastive heads for capturing both seen and unseen anomaly classes; and an Anomaly Scoring module leveraging the insights of the three heads to detect anomalies. Extensive experiments on three real-world datasets consistently show that our approach surpasses existing methods under various experimental settings, thus establishing a new state-of-the-art performance in the TSAD field.Comment: 11 pages, 5 tables, 3 figure

Spontaneous forward Brillouin scattering in carbon disulfide

In recent years, guided acoustic wave Brillouin scattering has become an important tool in photonics, serving as the basis for everything from new forms of information processing to silicon lasers. Due to low losses and long interaction lengths, fiber optic systems offer an intriguing platform to harness these guided-wave light-sound interactions. However, within typical fiber optic systems these interactions are exceedingly weak—requiring complex microstucturing to yield appreciable light-sound coupling. Here, we enhance this light-sound coupling by using a CS2-filled liquid core optical fiber. Owing to tight confinement of the optical and acoustic modes within the fiber core, as well as the large electrostrictive response of CS2, this system yields an unprecedented forward Brillouin gain for a fiber optic system. To demonstrate this physics, we measure multipeaked spontaneous forward Brillouin scattering power spectra, yielding information about the fiber geometry, material properties, and acousto-optic coupling strength. To interpret these data, we simulate the spontaneous Brillouin scattering power spectrum for this fiber system. These results reveal that hybridized acoustic excitations within the fiber core and cladding produce this characteristic multipeaked power spectrum. In the future, the large forward Brillouin coupling, long interaction lengths, and low losses of liquid-core fibers may enable new forms of distributed sensing, lasers with customizable emission, and physics including continuum optomechanical cooling.Air Force Office of Scientific Research (AFOSR) [FA9550-15-1-0389]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Characterizing the transition dynamics for multi-pulsing in mode-locked lasers

We consider experimentally and theoretically a refined parameter space near the transition to multi-pulse modelocking. Near the transition, the onset of instability is initiated by a Hopf (periodic) bifurcation. As cavity energy is increased, the band of unstable, oscillatory modes generates a chaotic behavior between single- and multi-pulse operation. Both theory and experiment are in good qualitative agreement and they suggest that the phenomenon is of a universal nature in mode-locked lasers at the onset of multi-pulsing from N to N + 1 pulses per round trip. This is the first theoretical and experimental characterization of the transition behavior, made possible by a highly refined tuning of the gain pump level

High-power picosecond fiber source for coherent Raman microscopy

We report a high-power picosecond fiber pump laser system for coherent Raman microscopy (CRM). The fiber laser system generates 3.5ps pulses with 6W average power at 1030nm. Frequency doubling yields more than 2W of green light, which can be used to pump an optical parametric oscillator to produce the pump and the Stokes beams for CRM. Detailed performance data on the laser and the various wavelength conversion steps are discussed, together with representative CRM images of fresh animal tissue obtained with the new source.Chemistry and Chemical Biolog

Analysis of spectral coverage and resolution performance in spectral focusing CARS spectroscopy

Conference on Lasers and Electro-Optics / Pacific Rim 2022, 31 August–5 September 2022, Sapporo Japan.Tipo evento: Congreso, Ámbito geográfico: Internacional no UE, Tipo de participación: Participativo - Ponencia oral (comunicación oral), Intervención por: Acceso por inscripción libre, Ciudad de celebración: Híbrido-Online, Entidad organizadora: Optical Society of America (OSA), Publicación en acta congreso: Si Con comité de admisión ext.: Si, Forma de contribución: Artículo científico.An open-code simulation tool for spectral focusing Coherent Anti-Stokes Raman Scattering (SF-CARS) spectroscopy has been developed for the analysis of spectral coverage and resolution performance. The main limitation has been found due to high-order dispersion and nonlinearities in laser source

Stimulated Raman Scattering Microscopy with a Robust Fibre Laser Source

Stimulated Raman scattering microscopy allows label-free chemical imaging and has enabled exciting applications in biology, material science and medicine. It provides a major advantage in imaging speed over spontaneous Raman scattering and has improved image contrast and spectral fidelity compared to coherent anti-Stokes Raman scattering. Wider adoption of the technique has, however, been hindered by the need for a costly and environmentally sensitive tunable ultrafast dual-wavelength source. We present the development of an optimized all-fibre laser system based on the optical synchronization of two picosecond power amplifiers. To circumvent the high-frequency laser noise intrinsic to amplified fibre lasers, we have further developed a high-speed noise cancellation system based on voltage-subtraction autobalanced detection. We demonstrate uncompromised imaging performance of our fibre-laser-based stimulated Raman scattering microscope with shot-noise-limited sensitivity and an imaging speed up to 1 frame $s^{−1}$.Chemistry and Chemical Biolog

Numerical evaluation of spectral coverage and spectral resolution in coherent Raman scattering spectroscopy using a broadband fiber laser source

We theoretically investigate the feasibility of using a fiber laser source for high resolution and broadband coherent Raman scattering (CRS) spectroscopy/ imaging employing spectral focusing technique. To accomplish this task, we have developed a simulation tool where the laser pulse parameters can be imported directly from any pulse propagation software using split-step Fourier method to evaluate the spectral resolution and spectral coverage of CRS spectroscopy. Thus, the simulation tool can accommodate optical pulses of arbitrary shape and central wavelength, being also a user-friendly and versatile open-source software. We validate the numerical simulation tool by comparing its results with published theoretical and experimental data. We then use the tool to study the feasibility of using an all-fiber laser source for high resolution CRS spectroscopy in both the C-H window and the fingerprint region. This tool has a broad scope of applications in multiple fields where CRS spectroscopy is useful such as biomedicine, materials characterization, and biological imaging.Comunidad de MadridAgencia Estatal de Investigació