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For given laser output power, object under investigation, and photodiode noise level, we have theoretically compared the signal-to-noise ratios of a heterodyne scanning imager based on a Michelson interferometer and of an autodyne setup based on the laser optical feedback imaging (LOFI) technique. In both cases, the image is obtained point by point. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity (i.e., directly on the detector), while in the autodyne configuration, the wave beating takes place inside the laser cavity and therefore is indirectly detected. In the autodyne configuration, where the laser relaxation oscillations play a leading role, we have compared one-dimensional scans obtained by numerical simulations with different lasers' dynamical parameters. Finally, we have determined the best laser for LOFI applications and the experimental conditions for which the LOFI detection setup (autodyne interferometer) is competitive compared to a heterodyne interferometer.

We describe a new method for imaging in three-dimensional turbid media, laser optical feedback tomography. This technique is based on the resonant sensitivity of a short-cavity laser to frequency-shifted optical feedback from ballistic photons retrodiffused from the medium. The advantage of the method is that the detector is the laser source itself, which provides optical amplification with self-aligned spatial and temporal coherent detection.

Using a Nd:YVO 4 microchip laser with a relaxation frequency in the megahertz range, we have experimentally compared a heterodyne interferometer based on a Michelson configuration with an autodyne interferometer based on the laser optical feedback imaging (LOFI) method regarding their signal to noise ratios. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity while in the autodyne configuration, the wave beating takes place inside the laser cavity and the relaxation oscillations of the laser intensity then play an important part. For a given laser output power, object under investigation and detection noise level, we have determined the amplification gain of the LOFI interferometer compared to the heterodyne interferometer. LOFI interferometry is demonstrated to show higher performances than heterodyne interferometry for a wide range of laser power and detection level of noise. The experimental results are in good agreement with the theoretical predictions.

International audienceWeprovideatheoreticalstudyoffrequency-shiftedfeedback(FSF)lasers,i.e.,laserswithaninternalfrequency shifter,seededwithamonochromaticwave.Theresultingspectrumconsistsinasetofequidistantmodes,labeled by n, whose phases vary quadratically with n. We prove the emergence of a temporal fractional Talbot effect, leading to generation of Fourier-transform-limited pulses at a repetition rate tunable by the parameters of the FSF cavity (cavity length and frequency shift per round trip), and limited by the spectral bandwidth of the laser. We characterize in detail the output field of this so-called “Talbot laser” and emphasize its specific intensity fluctuations.WeevidenceconnectionswithsomeaspectsofnumbertheorybytheappearanceofGausssumsand thetaseriesintheexpressionofthelaserfield.Ourpredictionsareinfullagreementwiththeexperimentalresults published in Guillet de Chatellus et al. [Opt. Express 21, 15065 (2013)]. Practical applications and limitations are discussed

Bubbles confined between the parallel walls of microchannels experience an increased drag compared to freestanding bubbles. We measure and model the additional friction from the walls, which allows the calibration of the drag force as a function of velocity. We then develop a setup to apply locally acoustic waves and demonstrate the use of acoustic forces to induce the motion of bubbles. Because of the bubble pulsation, the acoustic forces-called Bjerknes forces-are much higher than for rigid particles. We evaluate these forces from the measurement of bubble drift velocity and obtain large values of several hundreds of nanonewtons. Two applications have been developed to explore the potential of these forces: asymmetric bubble breakup to produce very well controlled bidisperse populations and intelligent switching at a bifurcation.

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We show both theoretically and experimentally that frequency-shifted feedback (FSF) lasers seeded with a single frequency laser can generate Fourier transform-limited pulses with a repetition rate tunable and limited by the spectral bandwidth of the laser. We demonstrate experimentally in a FSF laser with a 150 GHz spectral bandwidth, the generation of 6 ps-duration pulses at repetition rates tunable over more than two orders of magnitude between 0.24 and 37 GHz, by steps of 80 MHz. A simple linear analytical model i.e. ignoring both dynamic and non-linear effects, is sufficient to account for the experimental results. This possibility opens new perspectives for various applications where lasers with ultra-high repetition rates are required, from THz generation to ultrafast data processing systems.