Sending femtosecond pulses in circles: highly non-paraxial accelerating beams

We use caustic beam shaping on 100 fs pulses to experimentally generate non-paraxial accelerating beams along a 60 degree circular arc, moving laterally by 14 \mum over a 28 \mum propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of non-paraxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic

Optical Coherence Spectro-Tomography by all-Optical Depth-Wavelength analysis

Current spectroscopic optical coherence tomography (OCT) methods rely on a posteriori numerical calculation. We present an alternative for accessing optically the spectroscopic information in OCT, i.e. without any post-processing, by using a grating based correlation and a wavelength demultiplexing system. Conventional A-scan and spectrally resolved A-scan are directly recorded on the image sensor. Furthermore, due to the grating based system, no correlation scan is necessary. In the frame of this paper we present the principle of the system as well as first experimental results

Astronomical photonics in the context of infrared interferometry and high-resolution spectroscopy

We review the potential of Astrophotonics, a relatively young field at the interface between photonics and astronomical instrumentation, for spectro-interferometry. We review some fundamental aspects of photonic science that drove the emer- gence of astrophotonics, and highlight the achievements in observational astrophysics. We analyze the prospects for further technological development also considering the potential synergies with other fields of physics (e.g. non-linear optics in condensed matter physics). We also stress the central role of fiber optics in routing and transporting light, delivering complex filters, or interfacing instruments and telescopes, more specifically in the context of a growing usage of adaptive optics.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June 2016, 21 pages, 10 Figure

Ultrafast turbidity compensation in the optical therapeutic window by three-wave mixing phase conjugation

International audienceImaging by phase conjugation through diffusing media is performed by using parametric amplification in a type II crystal, at a wavelength included in the therapeutic window. By nature, the method ensures imaging in a time far below the decorrelation time of in vivo biological tissues. A systematic comparison of performance with direct imaging is provided

Parallel Unstructured Mesh Adaptation Based on Iterative Remershing and Repartitioning

International audienceWe present a parallel unstructured mesh adaptation algorithm based on iterative remeshing and mesh repartitioning. The algorithm rests on a two-level parallelization scheme allowing to tweak the mesh group size for remeshing, and on a mesh repartitioning scheme based on interface displacement by front advancement. The numerical procedure is implemented in the open source ParMmg software package. It enables the reuse of existing sequential remeshing libraries, a non-intrusive linkage with thirdparty solvers, and a tunable exploitation of distributed parallel environments. We show the efficiency of the approach by comparing interface displacement repartitioning with graph-based repartitioning, and by showing isotropic weak-scaling tests and preliminary anisotropic tests

Direct machining of curved trenches in silicon with femtosecond accelerating beams

International audienceControl of the longitudinal profile of ablated structures during laser processing is a key technological requirement. We report here on the direct machining of trenches in silicon with circular profiles using femtosecond accelerating beams. We describe the ablation process based on an intensity threshold model, and show how the depth of the trenches can be predicted in the framework of a caustic description of the beam

Continuous wavelet transform ridge extraction for spectral interferometry imaging

The combination of wavelength multiplexing and spectral interferometry allows for the encoding of multidimensional information and its transmission over a mono-dimensional channel; for example, measurements of a surface's topography acquired through a monomode fiber in a small endoscope. The local depth of the imaged object is encoded in the local spatial frequency of the signal measured at the output of the fiber-decoder system. We propose a procedure to retrieve the depth-map by determining the signal's instantaneous frequency. First, we compute its continuous, complex-valued, wavelet transform (CWT). The frequency signature at every position is contained in the resulting scalogram. We then extract the ridge of maximal response by use of a dynamic programming algorithm thus directly recovering the object's topography. We present results that validate this procedure based on both simulated and experimental data

Making Summer Camp Inclusive: Staff Perspectives from Two National Youth-Serving Organizations

Organized out-of-school time (OST) activities can provide youth with developmentally enriching experiences. Summer camp is one such activity, offering opportunities for positive youth development and, in some cases, promoting socioemotional learning, character development, resilience, and academic and career-related outcomes (Garst et al., 2011; Henderson et al., 2007; Merryman et al., 2012; Whittington & Garst, 2018; Wilson & Sibthorp, 2018). Not all youth, however, have access to high-quality summer programs (Browne et al., 2019; National Academies of Science, Engineering, & Medicine, 2019). Furthermore, summer camps designed around the needs and interests of relatively privileged youth can create exclusive dynamics within camp spaces, potentially marginalizing those who are not members of the dominant group (Browne et al., 2019). Many organizations are recognizing these inequities and are seeking ways to create more inclusive programming (Fields, 2020). Despite efforts by many summer camps to become more diverse, equitable, and inclusive, few studies have examined what these efforts look like and what challenges and needs remain at a national level. Even less research has considered staff perceptions of these efforts, despite the fact that staff have a major role in shaping the camp environment. Drawing data from resident camp staff at two national youth-serving organizations, the purpose of this study was to identify 1) strategies staff use to create an inclusive summer camp environment; 2) challenges to creating an inclusive environment; and 3) what staff need to maintain and improve diversity, equity, and inclusion (DEI) efforts at camp