23 research outputs found
Acousto-optic laser optical feedback imaging
We present a photon noise and diffraction limited imaging method combining
the imaging laser and ultrasonic waves. The laser optical feedback imaging
(LOFI) technique is an ultrasensitive imaging method for imaging objects
through or embedded within a scattering medium. However, LOFI performances are
dramatically limited by parasitic optical feedback occurring in the
experimental setup. In this work, we have tagged the ballistic photons by an
acousto-optic effect in order to filter the parasitic feedback effect and to
reach the theoretical and ultimate sensitivity of the LOFI technique. We
present the principle and the experimental setup of the acousto-optic laser
optical feedback imaging (AO-LOFI) technique, and we demonstrate the
suppression of the parasitic feedback
The hypothesis of the moving comb in frequency shifted feedback lasers
International audienceThe use of frequency-shifted feedback (FSF) lasers in optical metrology is based on a unique coherence property: the appearance of beats in the noise spectrum at the output of a two-beam interferometer, whose frequencies vary linearly with the path delay of the interferometer. A description of the output of a FSF laser as a moving comb of optical frequencies is generally admitted to explain these specific coherence properties. Here starting from the model of a passive FSF cavity seeded by spontaneous emission we give a rigorous description of the time-spectrum properties of FSF lasers and show that the moving comb exists only in the limit of small frequency shift
Plenoptic microscope based on laser optical feedback imaging (LOFI)
We present an overview of the performances of a plenoptic microscope which
combines the high sensitivity of a laser optical feedback imaging setup , the
high resolution of optical synthetic aperture and a shot noise limited signal
to noise ratio by using acoustic photon tagging. By using an adapted phase
filtering, this microscope allows phase drift correction and numerical
aberration compensation (defocusing, coma, astigmatism ...). This new kind of
microscope seems to be well adapted to make deep imaging through scattering and
heterogeneous media
Pediatric DXA: technique and interpretation
This article reviews dual X-ray absorptiometry (DXA) technique and interpretation with emphasis on the considerations unique to pediatrics. Specifically, the use of DXA in children requires the radiologist to be a “clinical pathologist” monitoring the technical aspects of the DXA acquisition, a “statistician” knowledgeable in the concepts of Z-scores and least significant changes, and a “bone specialist” providing the referring clinician a meaningful context for the numeric result generated by DXA. The patient factors that most significantly influence bone mineral density are discussed and are reviewed with respect to available normative databases. The effects the growing skeleton has on the DXA result are also presented. Most important, the need for the radiologist to be actively involved in the technical and interpretive aspects of DXA is stressed. Finally, the diagnosis of osteoporosis should not be made on DXA results alone but should take into account other patient factors