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Author

Frédéric Louradour

Bio: Frédéric Louradour is an academic researcher from University of Limoges. The author has contributed to research in topics: Laser & Femtosecond. The author has an hindex of 18, co-authored 114 publications receiving 1098 citations. Previous affiliations of Frédéric Louradour include Centre national de la recherche scientifique & Mauna Kea Technologies.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate a new technique for the direct, real-time, femtosecond scale temporal measurement based on the conversion of temporal information to the spectral domain.
Abstract: We demonstrate a new technique for the direct, real-time, femtosecond scale temporal measurement based on the conversion of temporal information to the spectral domain. The potential of the method has been experimentally investigated with an optical fiber spectral compressor device, first stretching and up-chirping the pulses in a prism dispersive delay line, and afterwards compensating the induced chirp by means of cross-phase modulation in a single-mode fiber. Spectro-temporal imaging (STI) reduces the problem of high-resolution temporal measurements to standard spectrometry.

105 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented a flexible, compact, coherent Raman and multimodal nonlinear endoscope (42 mm outer diameter, 71 mm rigid length) based on a resonantly scanned hollow-core Kagome-lattice double-clad fiber, which enables distortionless, background-free delivery of femtosecond excitation pulses and back-collection of nonlinear signals through the same fiber.
Abstract: Coherent Raman scattering microscopy is a fast, label-free, and chemically specific imaging technique that shows high potential for future in vivo optical histology However, the imaging depth in tissues is limited to the sub-millimeter range because of absorption and scattering Realization of coherent Raman imaging using a fiber endoscope system is a crucial step towards imaging deep inside living tissues and providing information that is inaccessible with current microscopy tools Until now, the development of coherent Raman endoscopy has been hampered by several issues, mainly related to the fiber delivery of the excitation pulses and signal collection Here, we present a flexible, compact, coherent Raman, and multimodal nonlinear endoscope (42 mm outer diameter, 71 mm rigid length) based on a resonantly scanned hollow-core Kagome-lattice double-clad fiber The fiber design enables distortion-less, background-free delivery of femtosecond excitation pulses and back-collection of nonlinear signals through the same fiber Sub-micrometer spatial resolution over a large field of view is obtained by combination of a miniature objective lens with a silica microsphere lens inserted into the fiber core We demonstrate high-resolution, high-contrast coherent anti-Stokes Raman scattering, and second harmonic generation endoscopic imaging of biological tissues over a field of view of 320 µm at a rate of 08 frames per second These results pave the way for intraoperative label-free imaging applied to real-time histopathology diagnosis and surgery guidance

103 citations

Journal ArticleDOI
TL;DR: In this article, a two-photon micro-endoscope capable of in vivo label-free deep-tissue high-resolution imaging through a very long optical fiber is presented.
Abstract: We present a two-photon microendoscope capable of in vivo label-free deep-tissue high-resolution fast imaging through a very long optical fiber. First, an advanced light-pulse spectro-temporal shaping device optimally precompensates for linear and nonlinear distortions occurring during propagation within the endoscopic fiber. This enables the delivery of sub-40-fs duration infrared excitation pulses at the output of 5 meters of fiber. Second, the endoscopic fiber is a custom-made double-clad polarization-maintaining photonic crystal fiber specifically designed to optimize the imaging resolution and the intrinsic luminescence backward collection. Third, a miniaturized fiber-scanner of 2.2 mm outer diameter allows simultaneous second harmonic generation (SHG) and two-photon excited autofluorescence (TPEF) imaging at 8 frames per second. This microendoscope’s transverse and axial resolutions amount respectively to 0.8 μm and 12 μm, with a field-of-view as large as 450 μm. This microendoscope’s unprecedented capabilities are validated during label-free imaging, ex vivo on various fixed human tissue samples, and in vivo on an anesthetized mouse kidney demonstrating an imaging penetration depth greater than 300 μm below the surface of the organ. The results reported in this manuscript confirm that nonlinear microendoscopy can become a valuable clinical tool for real-time in situ assessment of pathological states.

102 citations

Journal ArticleDOI
TL;DR: In this paper, the first experimental realization of image reconstruction in finite femtosecond laser-written waveguide arrays with segmentation is presented, where arbitrary field distributions can be imaged in one-dimensional as well as in two-dimensional geometries.
Abstract: We present the first experimental realization of image reconstruction in finite femtosecond laser-written waveguide arrays with segmentation. The results show that arbitrary field distributions can be imaged in one-dimensional as well as in two-dimensional geometries.

67 citations

Journal ArticleDOI
TL;DR: Passive mode-locking of a cw lamp-pumped Nd:YAG laser using nonlinear polarization switching in a type-II SHG crystal is reported in this paper.
Abstract: Passive mode-locking of a cw lamp-pumped Nd:YAG laser using nonlinear polarization switching in a type-II SHG crystal is reported. Light pulses with more than 5 W of average power and pulse duration shorter than 25 ps have been obtained at 1064 nm.

66 citations


Cited by
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Journal Article
TL;DR: In this article, a fast Fourier transform method of topography and interferometry is proposed to discriminate between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour generation techniques.
Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

3,742 citations

Book
04 Jan 2005

644 citations

Journal Article
TL;DR: In this article, the dynamics of mitochondrial distribution in hamster embryos at frequent intervals over 24 hours using two-photon microscopy (1,047 nm) while maintaining blastocyst, and even fetal, developmental competence.
Abstract: A major challenge for fluorescence imaging of living mammalian cells is maintaining viability following prolonged exposure to excitation illumination. We have monitored the dynamics of mitochondrial distribution in hamster embryos at frequent intervals over 24 h using two-photon microscopy (1,047 nm) while maintaining blastocyst, and even fetal, developmental competence. In contrast, confocal imaging for only 8 h inhibits development, even without fluorophore excitation. Photo-induced production of H2O2 may account, in part, for this inhibition. Thus, two-photon microscopy, but not confocal microscopy, has permitted long-term fluorescence observations of the dynamics of three-dimensional cytoarchitecture in highly photosensitive specimens such as mammalian embryos.

542 citations

Journal ArticleDOI
TL;DR: In this article, a review summarizes how insights from mesoscopic scattering theory have direct relevance for optical wave control experiments and vice versa, and the results are expected to have an impact on a number of fields ranging from biomedical imaging to nanophotonics, quantum information, and communication technology.
Abstract: Wave front shaping, the ability to manipulate light fields both spatially and temporally, in complex media is an emerging field with many applications. This review summarizes how insights from mesoscopic scattering theory have direct relevance for optical wave control experiments and vice versa. The results are expected to have an impact on a number of fields ranging from biomedical imaging to nanophotonics, quantum information, and communication technology.

492 citations

Journal ArticleDOI
TL;DR: In this article, a novel technique was developed with which waveguides can be directly written into various optical bulk materials using femtosecond laser pulses, which allows for the realization of a variety of innovative concepts which are not feasible using other fabrication methods.
Abstract: Over the last few years arrays of evanescently coupled waveguides have been brought into focus as a particular representation of functionalized optical materials, in which the dispersion and diffraction of propagating light can be specifically tuned Moreover, it turns out that the light evolution in these systems shares fundamental similarities to the quantum evolution of particle wavefunctions, so that waveguide arrays can act as a model system for emulating quantum mechanics Recently, a novel technique was developed with which waveguides can be directly 'written' into various optical bulk materials using femtosecond laser pulses, which allows for the realization of a variety of innovative concepts which are not feasible using other fabrication methods The aim of this tutorial is to give an introduction to this topic

482 citations