Experimental phase control of a 100 laser beam array with quasi-reinforcement learning of a neural network in an error reduction loop.

An innovative scheme is proposed for the dynamic phase control of a laser beam array. It is based on a simple neural network included in a phase correction loop that predicts the complex field array from the intensity of the induced scattered pattern through a phase intensity transformer made of a diffuser. A crucial feature is the use of a kind of reinforcement learning approach for the neural network training which takes account of the iterated corrections.

Shaping of amplified beam from a highly multimode Yb-doped fiber using transmission matrix.

The transmission matrix of an ytterbium doped multimode fiber with gain was measured. It was shown to vary owing to the pump power level. Amplified beam focusing, beam steering and shaping were demonstrated using the measured matrix for input wavefront shaping, with an efficiency similar to the case of a passive fiber.

Space-time adaptive control of femtosecond pulses amplified in a multimode fiber.

Ultrashort light pulse transport and amplification in a 1.3 m long step-index multimode fiber with gain and with weak coupling has been investigated. An adaptive shaping of the input wavefront, only based on the output intensity pattern, has led to an amplified pulse focused both in space (1/32) and in time (1/10) despite a strong modal group delay dispersion.

Efficient phase-locking of 37 fiber amplifiers by phase-intensity mapping in an optimization loop.

Coherent combination of laser beams from 37 fiber amplifiers in a tiled aperture configuration has been achieved thanks to an innovative iterative process. The high efficiency as well as the speed of the phase control demonstrated the relevance of the method for phase locking of a large array of fiber lasers.

Shaping the light amplified in a multimode fiber.

Propagation of light in multimode optical fibers usually gives a spatial and temporal randomization of the transmitted field similar to the propagation through scattering media. Randomization still applies when scattering or multimode propagation occurs in gain media. We demonstrate that appropriate structuration of the input beam wavefront can shape the light amplified by a rare-earth-doped multimode fiber.

Publisher's Note: Observation of Geometric Parametric Instability Induced by the Periodic Spatial Self-Imaging of Multimode Waves [Phys. Rev. Lett. 116, 183901 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.

Observation of Geometric Parametric Instability Induced by the Periodic Spatial Self-Imaging of Multimode Waves.

Spatiotemporal mode coupling in highly multimode physical systems permits new routes for exploring complex instabilities and forming coherent wave structures. We present here the first experimental demonstration of multiple geometric parametric instability sidebands, generated in the frequency domain through resonant space-time coupling, owing to the natural periodic spatial self-imaging of a multimode quasi-continuous-wave beam in a standard graded-index multimode fiber. The input beam was launched in the fiber by means of an amplified microchip laser emitting sub-ns pulses at 1064 nm.

One shot endoscopic polarization measurement device based on a spectrally encoded polarization states generator.

We report a novel technique for polarimetric characterization of samples through a flexible fiber endoscope, with a single shot measurement per pixel. The sample is simultaneously probed with a large diversity of polarization states, and both degree of polarization and linear retardance are determined thanks to specific processing of data. The probe polarization states are spectrally encoded on the 10 nm bandwidth of the source.

Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier.

Active coherent beam combination using a 7-non-coupled core, polarization maintaining, air-clad, Yb-doped fiber is demonstrated as a monolithic and compact power-scaling concept for ultrafast fiber lasers. A microlens array matched to the multicore fiber and an active phase controller composed of a spatial light modulator applying a stochastic parallel gradient descent algorithm are utilized to perform coherent combining in the tiled aperture geometry. The mitigation of nonlinear effects at a pulse energy of 8.

Pelvic radiation disease management by hyperbaric oxygen therapy: prospective study of 44 patients.

Pelvic radiation disease (PRD) occurs in 2-11% of patients undergoing pelvic radiation for urologic and gynecologic malignancies. Hyperbaric oxygen therapy (HBOT) has previously been described as a noninvasive therapeutic option for the treatment of PRD. the purpose of study was to analyze prospectively the results of HBOT in 44 consecutive patients with PRD who were resistant to conventional oral or topical treatments.

Experimental demonstration of passive coherent combining of fiber lasers by phase contrast filtering.

We report experiments on a new laser architecture involving phase contrast filtering to coherently combine an array of fiber lasers. We demonstrate that the new technique yields a more stable phase-locking than standard methods using only amplitude filtering. A spectral analysis of the output beams shows that the new scheme generates more resonant frequencies common to the coupled lasers.

Bragg-scattering conversion at telecom wavelengths towards the photon counting regime.

We experimentally study Bragg-scattering four-wave mixing in a highly nonlinear fiber at telecom wavelengths using photon counters. We explore the polarization dependence of this process with a continuous wave signal in the macroscopic and attenuated regime, with a wavelength shift of 23 nm. Our measurements of mean photon numbers per second under various pump polarization configurations agree well with the theoretical and numerical predictions based on classical models.

Soliton triads ensemble in frequency conversion: from inverse scattering theory to experimental observation.

We consider the spectral theory of three-wave interactions to predict the initiation, formation and dynamics of an ensemble of bright-dark-bright soliton triads in frequency conversion processes. Spatial observation of non-interacting triads ensemble in a KTP crystal confirms theoretical prediction and numerical simulations.

Pulse compression and fiber delivery of 45 fs Fourier transform limited pulses at 830 nm.

A specific scheme is used for fiber delivery of ultrashort pulses using conventional elements. Starting from a standard femtosecond Ti:Al(2)O(3) oscillator (150 fs @ 830 nm), perfectly compressed ultrashort pulses with a duration of 45 fs are produced at the output of a standard two meter long single-mode fiber. The setup allows compensating independently and simultaneously second and third orders of chromatic dispersion as well as management of self-phase modulation in the fiber.

Acute coronary syndrome and cerebral arterial gas embolism in a scuba diver.

Background: Pulmonary barotrauma is a rare but feared complication of scuba diving, with around 30% mortality.

Objective: We report an uncommon case of pulmonary barotrauma complicated by arterial gas embolism with both coronary and neurological ischemic injuries after scuba diving.

Case Report: A 46-year-old-man was admitted to our hospital for acute coronary syndrome and stroke following a scuba dive.

Velocity-locked solitary waves in quadratic media.

We demonstrate experimentally the existence of three-wave resonant interaction solitary triplets in quadratic media. Stable velocity-locked bright-dark-bright spatial solitary triplets, determined by the balance between the energy exchange rates and the velocity mismatch between the interacting waves, are excited in a KTP crystal.

Coherence properties of two fiber lasers coupled by mutual injection.

Phase locking of two fiber lasers is obtained by mutual injection. The coherence properties of this composite laser are analyzed. In the most general case, the radiations at the two output mirrors of the laser are not mutually coherent.

Fiber-optic device for endoscopic polarization imaging.

Polarization images were obtained using a flexible optical fiber device. The endoscopic technique is based on the real-time compensation of the birefringence of the standard fiber by means of a miniaturized Faraday rotator. Based on a Jones formalism analysis, specific signal processing allows one to extract both the phase retardation and the degree of polarization of the light backscattered by a remote target.

Discrete focusing in an optical fiber with a two-dimensional square array of coupled waveguides.

We report the experimental demonstration of "discrete focusing" inside a 60-cm-long optical fiber made of a 2D square array of coupled waveguides. The suitable input amplitude and phase distributions are imposed by using a spatial light modulator. Thus we demonstrate that focusing in a single core at the output by discrete propagation is possible despite some amount of transverse heterogeneities of the waveguide array.

Frequency generation and solitonic decay in three wave interactions.

We consider experimentally three-wave resonant nonlinear interactions of fields propagating in nonlinear media. We investigate the spatial dynamics of two diffractionless beams at frequency omega1, omega2 which mix to generate a field at the sum frequency omega3. If the generated field at omega3 can sustain a soliton, it decays into solitons at omega1, omega2.

[Aspirin in decompression sickness].

Objective: We have performed a survey on the use of aspirin in decompression sickness (DCS) treatment in French hyperbaric centers'. We also conducted a review of literature to determine if aspirin was beneficial to treat human victims of DCS.

Methods: Prospective observational study investigating French hyperbaric centers' prescription of aspirin to DCS' divers victims.

Spatial trapping of short pulses in Ti-indiffused LiNbO(3) waveguides.

We show numerically and experimentally that spatial trapping can be induced in quadratic media even if the pump pulse's duration is shorter than the group-delay mismatch between fundamental wave and second-harmonic components. The influence of phase mismatch and pulse power on the trapping effect is discussed. Spatial, temporal, and spectral behaviors that accompany self-trapped propagation are highlighted.

Passive phase locking of an array of four fiber amplifiers by an all-optical feedback loop.

We report the passive phase locking of an array of four fiber amplifiers in a unidirectional ring cavity. The feedback loop consists of a single-mode fiber that filters intracavity the far-field pattern of the four emitted beams. The pointing of the laser output can be managed by the intracavity filtering.

Tunable high-repetition-rate fiber laser for the generation of pulse trains and packets.

We report on a mode-locked erbium-doped fiber laser suited to the generation of high-repetition-rate pulse trains or packets. The two-arm interferometer resonator performs a spectral filtering leading to the emission of short pulse packets with a high repetition rate, adjustable up to 200 GHz. A continuous pulse train with a repetition rate of up to 6.