329 research outputs found
Multi-imaging and Bayesian estimation for photon counting with EMCCD's
A multi-imaging strategy is proposed and experimentally tested to improve the
accuracy of photon counting with an electron multiplying charge-coupled device
(EMCCD), by taking into account the random nature of its on-chip gain and the
possibility of multiple photo-detection events on one pixel. This strategy is
based on Bayesian estimation on each image, with a priori information given by
the sum of the images. The method works even for images with large dynamic
range, with more improvement in the low light level areas. In these areas, two
thirds of the variance added by the EMCCD in a conventional imaging mode are
removed, making the physical photon noise predominant in the detected image.Comment: 19 page
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
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
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
Spherical light, arbitrary nonparaxial accelerating beams and femtosecond laser micromachining of curved profiles
International audienceWe review our recent results applying caustics wave theory to the generation of arbitrary curved accelerating beams and their use in the field of femtosecond laser materials processing. We report experimental realization of highly nonparaxial accelerating beams with circular, parabolic and quartic trajectories that extend over more than 95 degrees of arc as well as spherical optical fields. We also report femtosecond laser curved edge profiling
Micromachining along a curve: Femtosecond laser micromachining of curved profiles in diamond and silicon using accelerating beams
International audienceWe report femtosecond laser micromachining of micron-size curved structures using tailored accelerating beams. We report surface curvatures as small as 70 μm in both diamond and silicon, which demonstrates the wide applicability of the technique to materials that are optically transparent or opaque at the pump laser wavelength. We also report the machining of curved trenches in silicon. Our results are consistent with an ablation-threshold model based on calculated local beam intensity, and we also observe asymmetric debris deposition which is interpreted in terms of the optical properties of the incident accelerating beam
Filamentation of high-angle nondiffracting beams and applications to ultrafast laser processing
International audienceWe report on filamentation of nondiffracting beams and show that the intense light-matter interaction regime achieved on long distances allows for an enhanced control on ultrashort laser deep ablation
Implementing two-photon interference in the frequency domain with electro-optic phase modulators
Frequency-entangled photons can be readily produced using parametric
down-conversion. We have recently shown how such entanglement could be
manipulated and measured using electro-optic phase modulators and narrow-band
frequency filters, thereby leading to two-photon interference patterns in the
frequency domain. Here we introduce new theoretical and experimental
developments showing that this method is potentially a competitive platform for
the realization of quantum communication protocols in standard
telecommunication fibres. We derive a simple theoretical expression for the
coincidence probabilities and use it to optimize a Bell inequality.
Furthermore, we establish an equivalence between the entangled- photon scheme
and a classical interference scheme. Our measurements of two-photon
interference in the frequency domain yield raw visibilities in excess of 99%.
We use our high quality setup to experimentally validate the theoretical
predictions, and in particular we report a violation of the CH74 inequality by
more than 18 standard deviations.Comment: 19 pages, 3 figure
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