Mr. Markus Laubscher Profile

Markus Laubscher

at Ecole Polytechnique Fédérale de Lausanne

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Author

Publications (9)

Proceedings Article | 13 April 2005 Paper

A semi-analytical model accounting for multiple scattering in optical coherence tomography

Boris Karamata, Patrick Lambelet, Marcel Leutenegger, Markus Laubscher, Stephane Bourquin, Theo Lasser

Proceedings Volume 5690, (2005) https://doi.org/10.1117/12.590237

KEYWORDS: Optical coherence tomography, Mirrors, Multiple scattering, Light scattering, Sensors, Scattering, Motion models, Statistical modeling, Monte Carlo methods, Signal detection

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Proceedings Article | 1 July 2004 Paper

Light sources for optical cross-talk suppression in wide-field optical coherence tomography

Boris Karamata, Markus Laubscher, Patrick Lambelet, Tiemo Anhut, Theo Lasser

Proceedings Volume 5316, (2004) https://doi.org/10.1117/12.530337

KEYWORDS: Optical coherence tomography, Light sources, Scattering, Light scattering, Spatial coherence, Sensors, Mirrors, Interferometers, Speckle pattern, Mercury

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Proceedings Article | 14 June 2002 Paper

Video-rate high-resolution parallel optical coherence tomography

Markus Laubscher, Mathieu Ducros, Boris Karamata, Theo Lasser

Proceedings Volume 4619, (2002) https://doi.org/10.1117/12.470470

KEYWORDS: Optical coherence tomography, Signal detection, Microscopes, Femtosecond phenomena, Glasses, Detector arrays, Mirrors, Signal attenuation, Mode locking, Michelson interferometers

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Proceedings Article | 2 November 2001 Paper

High-resolution parallel optical coherence tomography in scattering samples

M. Laubscher, Mathieu Ducros, Boris Karamata, Stephane Bourquin, Theo Lasser

Proceedings Volume 4431, (2001) https://doi.org/10.1117/12.447442

KEYWORDS: Optical coherence tomography, Signal to noise ratio, Scattering, Image resolution, Signal detection, Laser scattering, Mirrors, Femtosecond phenomena, Glasses, Reflectivity

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Proceedings Article | 17 November 2000 Paper

ELP-OA: measuring the wavefront tilt without a natural guide star

Matthias Schoeck, Jean-Paul Pique, Alain Petit, Patrick Chevrou, Vincent Michau, Gilbert Grynberg, Arnold Migus, Nancy Ageorges, Veronique Bellanger, Francois Biraben, Ruy Deron, Hayden Fews, Francoise-Claude Foy, Claudia Hoegemann, Markus Laubscher, Daniel Mueller, Celine d'Orgeville, Olivier Peillet, Mike Redfern, Renaud Foy, Patricia Segonds, Richard Soden, Michel Tallon, Eric Thiebaut, Andrei Tokovinin, Jerome Vaillant, Jean-Marc Weulersse

Proceedings Volume 4125, (2000) https://doi.org/10.1117/12.409304

KEYWORDS: Telescopes, Stars, Sodium, Wavefronts, Adaptive optics, Modulation, Laser guide stars, Oscillators, Astronomy, Chemical species

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Proceedings Article | 16 August 2000 Paper

Polychromatic guide star: feasibility study

Renaud Foy, Jean-Paul Pique, Alain Petit, Patrick Chevrou, Vincent Michau, Gilbert Grynberg, Arnold Migus, Nancy Ageorges, Veronique Bellanger, Francois Biraben, Ruy Deron, Hayden Fews, Francoise-Claude Foy, Claudia Hoegemann, Markus Laubscher, Daniel Mueller, Celine d'Orgeville, Olivier Peillet, Mike Redfern, Matthias Schoeck, Patricia Segonds, Richard Soden, Michel Tallon, Eric Thiebaut, Andrei Tokovinin, Jerome Vaillant, Jean-Marc Weulersse

Proceedings Volume 4065, (2000) https://doi.org/10.1117/12.407359

KEYWORDS: Telescopes, Sodium, Stars, Oscillators, Adaptive optics, Modulation, Wavefronts, Chemical species, Photons, Laser guide stars

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Adaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS.

Proceedings Article | 7 July 2000 Paper

ELPOA: toward the tilt measurement from a polychromatic laser guide star

Proceedings Volume 4007, (2000) https://doi.org/10.1117/12.390401

KEYWORDS: Telescopes, Sodium, Oscillators, Adaptive optics, Modulation, Laser guide stars, Photons, Chemical species, Wavefronts, Atmospheric optics

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Adaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source, which is located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength of the observation, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. Several papers have addressed the problem of the sky coverage as a function of these parameters (see e.g.: Le Louarn et al). It turns out that the sky coverage is disastrously low in particular in the short (visible) wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (which is not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return- of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because approximately equals 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial or total sky coverage for the tilt, such as the dual adaptive optics concept, the elongation perspective method, or the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play.

Proceedings Article | 7 July 2000 Paper

PASS-2: quantitative photometric measurements of the polychromatic laser guide star

Matthias Schoeck, Renaud Foy, Jean-Paul Pique, Patrick Chevrou, Nancy Ageorges, Alain Petit, Veronique Bellanger, Hayden Fews, Francoise-Claude Foy, Claudia Hoegemann, Markus Laubscher, Olivier Peillet, Patricia Segonds, Michel Tallon, Jean-Marc Weulersse

Proceedings Volume 4007, (2000) https://doi.org/10.1117/12.390338

KEYWORDS: Laser guide stars, Telescopes, Sodium, Stars, Global system for mobile communications, Oscillators, Wavefronts, Adaptive optics, Calibration, Photometry

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Proceedings Article | 27 September 1999 Paper

PASS-2: photometry of the polychromatic laser guide star

Matthias Schoeck, Renaud Foy, Jean-Paul Pique, Michel Tallon, Patricia Segonds, Markus Laubscher, Olivier Peillet

Proceedings Volume 3762, (1999) https://doi.org/10.1117/12.363589

KEYWORDS: Laser guide stars, Sodium, Telescopes, Ultraviolet radiation, Pulsed laser operation, Mirrors, Wavefronts, Adaptive optics, Stars, Atmospheric corrections

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