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The possibility to analyze transparent phase objects using femtosecond digital in-line holography is demonstrated. We show that the diffraction patterns produced by the diffraction of 20-fs pulses by pure phase objects can be advantageously processed by using the fractional Fourier transform. The optimal fractional orders lead to the longitudinal location of the phase object while the analysis of the reconstructed patterns leads to its diameter and to the value of the phase shift. Simulations and experimental results are in good concordance. This work shows new important applications of these reconstruction techniques in the domain of digital phase-contrast metrology. We further show that the use of femtosecond pulses results in a significant reduction of coherent noise. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate experimentally the intra-cavity generation of a coherent superposition of Laguerre-Gaussian modes of zero radial order but opposite azimuthal order. The superposition is created with a simple intra-cavity stop that creates equal losses for the two azimuthal modes, and we show that by adjustment of the stop we can produce modes up to azimuthal order 8. The fact that we have a coherent superposition rather than an incoherent superposition is verified by intensity measurements, propagation measurements and a decomposition of the field by an inner product executed on a phase-only spatial light modulator. Such fields have relevance in quantum information and optical trapping. [ABSTRACT FROM AUTHOR]

Vertical displacements on the SW–NE Têt fault (Eastern Pyrenees Axial Zone, France), which separates the Variscan Canigou-Carança and Mont-Louis massifs, were constrained using a thermochronologic multi-method approach. 40Ar/39Ar data from the granitic Mont-Louis massif record its Variscan cooling history and reveal no ages younger than Early Cretaceous, while the Canigou-Carança gneiss massif records systematically younger 40Ar/39Ar ages. These younger 40Ar/39Ar ages in the Canigou-Carança gneiss massif are the result of partial to total rejuvenation of argon isotopic systems related to a thermal flow coeval with the Cretaceous HT-BP metamorphism in the North Pyrenean Zone. Only the deepest rocks from the Canigou-Carança suffered this extensive Mid-Cretaceous thermal overprint probably due to differential burial around 4 km at that time. The post Mid-Cretaceous vertical displacements along the Têt fault are recorded by “low” temperature thermochronology using K-feldspar 40Ar/39Ar, zircon and apatite fission track and (U–Th)/He datings. The Mont-Louis granite samples experienced a long period of protracted cooling reflecting a lack of thermo-tectonic activity in this area from Late Palaeozoic to Early Cenozoic, followed by cooling from 55–60 Ma to Late Eocene at a mean rate of 15–20°C/Ma in the final stage. This cooling stage corresponds to Têt fault reactivation with a reversed component, promoting exhumation of the Mont-Louis roof zone contemporaneously with the south-vergent Pyrenean thrusting. In the Canigou-Carança massif, the main cooling event occurred from 32 to 18 Ma at a maximum rate of 30°C/Ma during Early Oligocene followed by a more moderate rate of 3°C/Ma from Late Oligocene to Early Burdigalian, coeval with the normal reactivation of the Têt fault in brittle conditions that accommodated the final exhumation of the massif during the opening of the Gulf of Lion. [ABSTRACT FROM AUTHOR]

We report the generation of self-similar highly stable femtosecond pulses from an ytterbium-doped double-clad fiber laser. Positively chirped parabolic pulses with 6.4-ps duration and more than 3.2-nJ energy are obtained. These pulses are extra-cavity compressed to 140 fs. Radio-frequency noise measurements show that this regime of emission ensures low-noise operation with less than 0.05% amplitude fluctuations. [ABSTRACT FROM AUTHOR]

We have investigated the generation of widely-separated bound pulses with a high power passively mode-locked Yb-doped double clad fiber laser. We report on the emission of bound pulses of 5 ps whose separation can exceed 180 ps. Pulses are further compressed extra-cavity to 140 fs, leading to pulse separations that can reach approximately 1300 pulse widths, while pulses remain bound. Scenarios leading to these regimes are detailed. RF analysis shows an important reduction of the amplitude noise of the laser when pulses bind together. Finally, we report on a new regime of multiple pulse emission of this fiber laser: stable co-emission of a single-pulse and a pair of bound pulses in the same cavity round trip. [ABSTRACT FROM AUTHOR]

The properties of an ytterbium-doped double-clad fiber laser, passively mode-locked by nonlinear polarization rotation are investigated in this work. Cartographies of mode-locking regime versus halfwave plates orientations are presented for several values of the total cavity dispersion and for different pump powers. Bistability between the continuous and the mode-locking regimes is pointed out. The effect of the total group velocity dispersion is described with a master mode-locking equation. [ABSTRACT FROM AUTHOR]

We study theoretically and experimentally different methods to control the pulses emitted by solid-state lasers passively Q-switched by a saturable absorber. We explore one- and two-axis laser schemes allowing to control the pulse duration, which is ruled by the saturation powers of the transitions in the absorber and in the gain medium. In one-axis lasers, it is shown that the adjustment of the pump and laser beam sizes in the active medium and in the absorber provides an efficient means to control the pulse temporal shape and duration. Furthermore, a two-axis laser cavity supporting so-called forked-eigenstate operation permits to freely adjust the parts of the mode power which circulate in the gain medium and in the absorber. In this case, a lengthening of the pulse duration up to 500 ns is obtained with an increase of the average output power. The theoretical results obtained by using rate equations adapted to each cavity geometry are in close agreement with experiments performed on a diode-pumped Nd3+:YAG laser Q-switched by a Cr4+:YAG saturable absorber. The relevance of the different techniques to control the pulse durations in the framework of potential applications is discussed. [ABSTRACT FROM AUTHOR]

Provides information on a study which examined the compression properties of a side-pumped passively mode-locked Yb-doped double-clad fiber laser emitting subpicosecond pulse. Details on the experimental setup; Experimental results; Conclusion.

Abstract, A reverse saturable absorber is basically a classical saturable absorber exhibiting excited-state absorption. We investigate in this paper the dynamics of a laser with a reverse saturable absorber. A rate equation formalism is used to theoretically describe this laser, We first demonstrate, from a linear stability analysis, that excited-state absorption stabilizes the output intensity of a laser with a saturable absorber. Furthermore, the transient dynamics are considered. We show that, depending on the characteristic time associated with the reverse saturable absorber, the transient regime can depart considerably from the classical relaxation oscillations usually observed in single-mode class-B lasers. We observe in some cases a large reduction of the first peaks of the relaxation oscillations. [ABSTRACT FROM AUTHOR]

Polycrystalline silicon, widely used so far as current line material in microelectronics, has recently become a promising candidate for thin films devices (transistor, solar cell). In all these applications, low-temperature fabrication (< 600°C) will represent a significant progress. This was achieved through two ways : (i) by assisting the thermal decomposition of silane with a diode hf plasma ; the temperature threshold of polycrystalline deposition is decreased down to 350°C; (ii) by purely thermal deposition of an amorphous film at 620°C, then in situ recrystallization at 400°C through exposure to a hydrogen plasma, which on the other hand passivates the grain boundaries. We report the correlative variations of the grain size (x-ray), the residual short range disorder (Raman) and the H content (Elastic Recoil Detection) for these various poly-Si preparations. Posthydrogenation is shown to relax the Si matrix. The Raman line widening previously attributed to crystallite size below a few 10 Å is shown here to originate from residual short range disorder in the material. At this moment, poly-Si films obtained at low temperature exhibit higher residual disorder than those obtained from pure LPCVD at high temperature. Moreover, depending on the preparation, additional disorder is shown to appear at the surface and interface of all polycrystalline films. [ABSTRACT FROM AUTHOR]

Structure, phase composition and electrical conductivity of thin yttria-stabilized zirconia (YSZ) films deposited by electron beam evaporation on a silicon (1 0 0) substrate at different temperatures i.e. room temperature (r.t.), 700 and 830°C, as well as the quality of the YSZ–Si interface have been investigated. The phase composition was verified by Raman spectroscopy and by infrared (i.r.) transmission measurements. The structure of films changed in agreement with their electrical conductivity depending on the deposition temperature. Both structure and thereby electrical conductivity were influenced by the high concentration of Y2O3 stabilizer used and by the post-deposition thermal treatment of films. The deposition temperature was also important in determining the quality of the YSZ–Si interface and hence the accessible sweep of the surface potential. The capacitance–voltage characteristics of the metal–insulator–semiconductor (MIS) structures incorporating YSZ films measured at r.t. showed hysteresis and positive shifts of the flat-band voltages. © 1998 Chapman & Hall [ABSTRACT FROM AUTHOR]

We report passive harmonic mode locking of a high-power Yb-doped double-clad fiber laser. 680-fs, 48-pJ pulses are emitted at the repetition rate of 2.13 GHz, while the free spectral range of the cavity is 23.4 MHz. Results indicate a supermode suppression of more than 25 dB. [ABSTRACT FROM AUTHOR]

The case of a 34-year-old male patient with HIV infection referred for severe febrile pancytopenia is reported. Clinical and laboratory evaluations revealed acute hepatitis B infection and concomitant parvovirus B19 infection. The patient died just before treatment with immune globulin was to be administered. Parvovirus B19 has been found to cause a wide variety of hematologic disorders such as neutropenia, thrombocytopenia, pancytopenia, and hemophagocytic syndrome. The role of parvovirus B19 in the pathogenesis of bone marrow or liver involvement is briefly discussed. [ABSTRACT FROM AUTHOR]

Aluminophthalocyanines were encaged in different silica xerogel matrices. Nonlinear reverse-saturable absorption behavior was observed for both nanosecond and picosecond pulse excitation at 532 nm. In order to determine the relaxation paths of the molecules after optical excitation, we measured the evolution of the transmission of a continuous probe beam through the samples following absorption induced by a pump pulse. The transmission recovery was a few tens of microseconds. The fluorescence lifetime was about 10 ns. [ABSTRACT FROM AUTHOR]