Phage susceptibility testing and infectious titer determination through wide-field lensless monitoring of phage plaque growth.

The growing number of drug-resistant bacterial infections worldwide is driving renewed interest in phage therapy. Based on the use of a personalized cocktail composed of highly specific bacterial viruses, this therapy relies on a range of tests on agar media to determine the most active phage on a given bacterial target (phage susceptibility testing), or to isolate new lytic phages from an environmental sample (enrichment of phage banks). However, these culture-based techniques are still solely interpreted through direct visual detection of plaques.

Vascular bifurcation mapping with photoacoustic microscopy.

The detection of in cancer diagnosis is needed in the clinic. A change in the vascular bifurcation density is a biomarker for the sprouting activity. Here, ptical-esolution hotocoustic icroscopy is used for quantitative vascular bifurcation mapping in 2D after the creation of rtual bes out of furcations.

Photo-acoustic tomography based on laser optical feedback imaging of surface displacements.

We present how a laser optical feedback imaging (LOFI) setup can be used for the optical detection of ultrasound in photo-acoustic tomography (PAT). A PAT image is reconstructed by an inversion algorithm using surface displacement measurements made at several locations with our LOFI setup and following the optical irradiation with a pulsed Nd:YAG laser of a sample with absorbing inclusions. The width of the reconstructed inclusions and the signal-to-noise ratio (SNR) of the reconstructed images are first studied on the numerical model of a sample with three absorbing inclusions (i.

Multi-wavelength photo-acoustic microscopy in the frequency domain for simultaneous excitation and detection of dyes.

An optical-resolution photoacoustic microscope with modulated CW laser diodes allowing multi-channel imaging is presented that can be used for both imaging biological tissues and for targeted photo-dynamic therapy (PDT) varying the optical power and exposure time. The effects of this therapy are immediately monitored in order to optimize the time of irradiation. After the description of the experimental setup, and applications are presented on a synthetic sample and on the mouse ear using hemoglobin as endogenous and methylene blue as exogenous dye for imaging and PDT, respectively.

Ultrasound vibration measurements based on laser optical feedback imaging.

This paper examines the detection of ultrasound vibrations with nanometric amplitude by using a laser optical feedback imaging (LOFI) setup. By means of numerical simulations, we show typical examples of ultrasound vibrations having different temporal shapes (harmonic and transient), extracted from the laser output power modulation induced by the frequency-shifted optical feedback. Considering the laser quantum noise dynamic and the detection noise separately, we show that the simulated vibration noise is in good agreement with the theoretical prediction.

Prediction performance of reservoir computing systems based on a diode-pumped erbium-doped microchip laser subject to optical feedback.

Reservoir computing (RC) systems are computational tools for information processing that can be fully implemented in optics. Here, we experimentally and numerically show that an optically pumped laser subject to optical delayed feedback can yield similar results to those obtained for electrically pumped lasers. Unlike with previous implementations, the input data are injected at a time interval that is much larger than the time-delay feedback.

Nonlinear laser dynamics induced by frequency shifted optical feedback: application to vibration measurements.

In this article, we study the nonlinear dynamics of a laser subjected to frequency shifted optical reinjection coming back from a vibrating target. More specifically, we study the nonlinear dynamical coupling between the carrier and the vibration signal. The present work shows how the nonlinear amplification of the vibration spectrum is related to the strength of the carrier and how it must be compensated to obtain accurate (i.

Control of the differential interference contrast in reinjected bimode laser.

We have demonstrated, both theoretically and experimentally, that it is possible to control (i.e., to enhance or cancel) the contrast of the interference pattern appearing in the intensity images obtained with a laser optical feedback imaging (LOFI) setup using a bimode laser.

Phases of Talbot patterns in angular self-imaging.

The original Talbot (self-imaging) effect is observed in the vicinity of a grating of slits shined with a plane wave, and results in periodic images of the initial diffraction pattern (integer Talbot effect) and the appearance of images with a periodicity reduced by an integer factor (fractional Talbot effect). Most of the studies on Talbot effect so far have focused on the distribution of the intensity of the diffracted light. However, the phases of the Talbot images, obtained in both the integer and fractional self-imaging cases, can be calculated in a closed form and display interesting auto-correlation properties.

Laser optical feedback imaging controlled by an electronic feedback loop.

In autodyne interferometry, the beating between the reference beam and the signal beam takes place inside the laser cavity and therefore the laser fulfills simultaneously the roles of emitter and detector of photons. In these conditions, the laser relaxation oscillations play a leading role, both in the laser quantum noise, which determines the signal-to-noise ratio (SNR), and also in the laser dynamics, which determines the response time of the interferometer. In the present study, we have experimentally analyzed the SNR and the response time of a laser optical feedback imaging (LOFI) interferometer based on a Nd(3+) microchip laser, with a relaxation frequency in the megahertz range.

Demonstration of a plenoptic microscope based on laser optical feedback imaging.

A new kind of plenoptic imaging system based on Laser Optical Feedback Imaging (LOFI) is presented and is compared to another previously existing device based on microlens array. Improved photometric performances, resolution and depth of field are obtained at the price of a slow point by point scanning. Main properties of plenoptic microscopes such as numerical refocusing on any curved surface or aberrations compensation are both theoretically and experimentally demonstrated with a LOFI-based device.

Optimization of an autodyne laser interferometer for high-speed confocal imaging.

In autodyne interferometry, the beating between the reference beam and the signal beam takes place inside the laser cavity and therefore the laser fulfills simultaneously the roles of the emitter and the detector of photons. In these conditions, the laser relaxation oscillations play a leading role, both in the laser quantum noise that determines the signal-to-noise ratio (SNR) and also in the laser dynamics that determine the response time of the interferometer. In the present study, we have theoretically analyzed the SNR and the response time of a laser optical feedback imaging (LOFI) setup based on an autodyne interferometer.

Synthetic aperture laser optical feedback imaging using a translational scanning with galvanometric mirrors.

In this paper we present an experimental setup based on laser optical feedback imaging (LOFI) and on synthetic aperture with translational scanning by galvanometric mirrors for the purpose of making deep and resolved images through scattering media. We provide real two-dimensional optical synthetic aperture image of a fixed scattering target with a moving aperture and an isotropic resolution. We demonstrate theoretically and experimentally that we can keep microscope resolution beyond the working distance.

Limitations of synthetic aperture laser optical feedback imaging.

In this paper we study the origin and the effect of amplitude and phase noise on laser optical feedback imaging associated with a synthetic aperture (SA) imaging system. Amplitude noise corresponds to photon noise and acts as an additive noise; it can be reduced by increasing the global measurement time. Phase noise can be divided in three families: random, sinusoidal, and drift phase noise; we show that it acts as a multiplicative noise.

Sensitivity of synthetic aperture laser optical feedback imaging.

In this paper, we compare the sensitivity of two imaging configurations, both based on laser optical feedback imaging (LOFI). The first one is direct imaging, which uses conventional optical focalization on target, and the second one is made by a synthetic aperture (SA) laser, which uses numerical focalization. We show that SA configuration allows us to obtain good resolutions with high working distance and that the drawback of SA imagery is that it has a worse photometric balance in comparison to a conventional microscope.

Heterodyne beatings between frequency-shifted feedback lasers.

Frequency-shifted feedback (FSF) lasers are potential candidates for long distance telemetry due to the appearance of beatings in the noise spectrum at the output of a homodyne interferometer: the frequencies of these beatings vary linearly with the path delay. In this Letter we demonstrate that these beatings also occur in the heterodyne mixing of two identical, but distinct, FSF lasers. This phenomenon is explained by the passive cavity model and is exploited to characterize the time-spectrum properties of FSF lasers.

Full analytical solution of Adapted Polarisation State Contrast Imaging.

We have earlier proposed a 2-channel imaging technique: Adapted Polarisation State Contrast Imaging (APSCI), which noticeably enhances the polarimetric contrast between an object and its background using fully polarised incident state adapted to the scene, such that the polarimetric responses of those regions are located as far as possible on the Poincaré sphere. We address here the full analytical and graphical analysis of the ensemble of solutions of specific incident states, by introducing 3-Distance Eigen Space and explain the underlying physical structure of APSCI and the effect of noise over the measurements.

Experimental comparison of autodyne and heterodyne laser interferometry using an Nd:YVO₄ microchip laser.

Using an Nd:YVO₄ 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.

Effect of speckle on APSCI method and Mueller Imaging.

The principle of the polarimetric imaging method called APSCI (Adapted Polarization State Contrast Imaging) is to maximize the polarimetric contrast between an object and its background using specific polarization states of illumination and detection. We perform here a comparative study of the APSCI method with existing Classical Mueller Imaging(CMI) associated with polar decomposition in the presence of fully and partially polarized circular Gaussian speckle. The results show a noticeable increase of the Bhattacharyya distance used as our contrast parameter for the APSCI method, especially when the object and background exhibit several polarimetric properties simultaneously.

Dynamical amplification of phase conjugation using a modulated optical feedback in a Nd:YVO4 laser.

We demonstrate an efficient dynamical amplification of phase conjugation in the gain medium of a diode-pumped Nd(3+)YVO4 solid-state laser via excitation of its relaxation oscillations. Consequently, enhancement in the modulated amplitude of the phase conjugate wave is observed with up to +30 dB compared to the classical homodyne approach.

Comparative study of autodyne and heterodyne laser interferometry for imaging.

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.

Self-aligned setup for laser optical feedback imaging insensitive to parasitic optical feedback.

We propose a new optical architecture for the laser optical feedback imaging (LOFI) technique which makes it possible to avoid the adverse effect of the optical parasitic backscattering introduced by all the optical interfaces located between the laser source and the studied object. This proposed setup needs no specific or complex alignment, which is why we can consider the proposed setup to be self-aligned. We describe the principle used to avoid the parasitic backscattering contributions that dramatically deteriorate amplitude and phase information contained in the LOFI images.

Phase sensitive optical near-field mapping using frequency-shifted laser optical feedback interferometry.

The use of laser optical feedback Imaging (LOFI) for scattering-type scanning near-field optical microscopy (sSNOM) is proposed and investigated. We implement this sensitive imaging method by combining a sSNOM with optical heterodyne interferometry and the dynamic properties of a B class laser source which is here used both as source and detector. Compared with previous near field optical heterodyne experiments, this detection scheme provides an optical amplification that is several orders of magnitude higher, while keeping a low noise phase-sensitive detection.

Resolution of a synthetic aperture laser optical feedback imaging using a galvanometric scanning.

We have improved the resolution of our laser optical feedback imaging (LOFI) setup by using a galvanometric scanning and two-dimensional angular synthetic aperture (SA) process. The experimental resolution of the classical LOFI images and of the SA LOFI images are compared for different working distances, and we show that the SA LOFI method is able to balance the degradation of the images resolution with increasing distance. We also show that the resolution of the SA LOFI images can be controlled by choosing the position of the galvanometric scanner between the laser and the target under investigation.

Two-dimensional synthetic aperture laser optical feedback imaging using galvanometric scanning.

We have improved the resolution of our laser optical feedback imaging (LOFI) setup by using a synthetic aperture (SA) process. We report a two-dimensional (2D) SA LOFI experiment where the unprocessed image (i.e.