ABSTRACT
We propose a new method for measuring the phase and the amplitude of a short laser pulse that is based on shearing interferometry in the spectral domain combined with time gating. The method has several features in common with spectral interferometry for direct electric-field reconstruction, in particular, fast and direct reconstruction of the phase. Accurate measurement of the phase added to an 80-fs pulse by a block of F4 glass demonstrates the technique.
ABSTRACT
We discuss spectrotemporal measurements of laser diode pulses performed with a streak camera and a grating monochromator to yield a precise evaluation of chirping effects in Q-switched multimode emissions. We experimentally illustrate several causes of errors, depending on the grating size and period as well as on the adjustment of the collimating lens at the monochromator output. An analytical formula is derived that allows us to relate the chirp amplitude to the inclination of the modal structures in the streak image. Two configurations are proposed for a practical determination of the chirp amplitude in multimode emissions. Illustrations are provided with Q-switched AlGaAs laser diodes that exhibit chirp amplitudes larger than the mode spacing.
ABSTRACT
Intracavity phase locking and extracavity combination of the two emitted beams generated by a Nd:YAG laser longitudinally pumped by two fiber-coupled diode lasers are investigated. Phase locking is performed by a diffractive component located inside a confocal Fabry-Perot resonator. The coherent addition of the two synchronized beams in a single TEM(00) wave is made by a birefringent interferometer, with 96.8% energy yield. 610-mW output power was obtained in a single-lobed beam profile with 30.5% optical-to-optical conversion efficiency in the continuous-wave regime.
ABSTRACT
A laser profile consisting of 113 coupled Gaussian waves is obtained in a cw oscillator by use of a BaTiO(3) crystal as both an amplifying medium and a phase-conjugating mirror. Mutual locking of Gaussian waves is performed by a pair of spatial f ilters. One of them is a high-resolution holographic component; the other is an opaque screen with identical circular apertures.
ABSTRACT
We show that the proper use of a self-imaging confocal cavity can be a simple way to optimize the efficiency of optical pumping of solid-state lasers. In this type of resonator the transverse mode self-adjusts to fit the pumped volume optimally. Self-optimization of the mode size of a laser-diode pump Nd:YAG laser (54% slope efficiency) is demonstrated, and an intrinsic efficiency of 68% is measured.
ABSTRACT
We have developed techniques that permit broad spectral band interference fringes to be observed on a mode-by-mode basis, using long lengths of few-mode fiber without the detrimental effects of incoherent modal superimposition. Modes are spatially by a cladding etching technique. Mode orientation and polarization are preserved by using elliptical core fibers.
ABSTRACT
It has been predicted that an intense pump beam can induce the focusing of a weak probe beam at a different wavelength that is simultaneously propagating in a Kerr homogeneous material through cross-phase modulation. In Kerr-type nonlinear material, spatial solitons are the only stable waves able to propagate at high-intensity levels without leading to catastrophic breakdown. We propose the use of a soliton beam to induce the stable guiding of a probe beam. Experimental results obtained with picosecond pulses are reported that evidence spatial-solitoninduced guiding.
ABSTRACT
Color image transmission through a 1-D array of 150 parallel multimode optical fibers is demonstrated using chromatic encoding of both geometric and spectral structures of self-luminous incoherent sources. The spectroscopic encoding and decoding devices include infrared type echelette gratings working at high diffraction orders in the range of the visible wavelengths considered in these experiments (~0.45-0.75, microm). Very good image and color quality was achieved: 2.5 x 10(4) pixels, seven spectral components per pixel.
ABSTRACT
Two-dimensional color image transmission through a single multimode fiber using only passive spectroscopic components (echelette type diffraction gratings) will be demonstrated experimentally and discussed theoretically with two different performances: (a) nine image pixels, seven distinct colors per pixel; (b) about forty image pixels and three colors per pixel. The present technical limits will be discussed.
ABSTRACT
Real-time image correlation is achieved by coupling coherent Fourier spectra inside saturable absorbers. Previously described optical correlators using nonlinear susceptibilities are strongly limited by the angular selectivity of Bragg diffraction in thick interaction cells. We overcame these difficulties by a special 3-D arrangement of the interfering beams. High-quality quasi-real-time holographic images, enabling cross-correlationof photographic transparencies free of detection noise, are demonstrated.
ABSTRACT
This paper describes the principles and experimental implementation of a new optical technique based on Fourier analysis for second-order statistics of short coherent light pulses. Using only passive filtering operations, we obtained images of the autocorrelation functions of the optical fields of light pulses, derived from ode-locked Nd:YAG laser pulses, with 40-psec to 4-nsec duration. An application of the method to a shaped sequence of 40-psec pulses is reported.
ABSTRACT
A new technique for measuring the temporal transfer function of optical fibers is described. The method consists of placing the fiber under test in one arm of a Mach-Zehnder interferometer excited by a broadband source. The temporal impulse response is obtained from a holographic reconstruction. The method requires only short lengths of single-mode or multimode fibers (less than 1 m). We have measured a dispersion of 0.3 nsec/km.nm at 0.59 microm with a single-mode fiber, in good agreement with theory. The arrival times of the various modes of multimode fibers are resolved.
ABSTRACT
Chromatic and spherical aberration of Fresnel-zoned diffraction gratings may be of the opposite sign and the same magnitude as for glass lenses. This peculiarity is used to improve the stigmatism of single glass lenses in polychromatic radiation. Two types of compensation gratings are studied: point holograms reconstructed out of stigmatic conditions and holograms of the aberrating wave surface itself, reconstructed in the conjugate order.
