Vicente Aboites

High repetition rate Q-switching of high power Nd:YVO4 slab laser

A high power, diode-side-pumped Nd:YVO4 laser with a grazing incidence cavity geometry was acousto-optically Qswitched at frequencies up to 500 kHz. In CW operation, the laser output power was 16.4 W at 30.5 W of diode pump, corresponding to optical conversion efficiency of 53.8%. In Q-switching operation, measurements were made of average output power, pulse duration, pulse energy and peak power as a function of Q-switching frequency. At 200 kHz repetition rate and pump power 30 W, the laser output had average power 15.9 W (optical conversion efficiency 53%), pulse duration 15 ns, pulse energy 80 lJ and peak power 5.3 kW. A numerical modeling of the Q-switched laser was performed and results compared with experimental data. 2003 Published by Elsevier Science B.V.

Powerful visible (530–770 nm) luminescence in Yb,Ho:GGG with IR diode pumping

Powerful visible luminescence in a Gadolinium Gallium Garnet (GGG) crystal, co-activated with Yb3+ (~15 at.%) and Ho3+ (~0.1 at.%) ions, is investigated under CW laser diode pumping (lambda = 938 and 976 nm). The main visible emission band is observed in the green with its peak at lambda ~540 nm) and measured to be about 10% with respect to Yb3+ IR luminescence (lambda ~1000 nm). Red (lambda ~650 nm) and near-IR (lambda ~755 nm) emission bands are also observed but are weaker (about 3-5%). Analysis of the crystal absorption and luminescence spectra allows one to conclude that Yb3+ - Ho3+ stepwise up-conversion is the mechanism explaining the phenomenon. Ho3+ ions embedded in the crystal in small concentration are shown to form an effective reservoir for energy transferred from the excited Yb3+ subsystem and to be an efficient source of the visible emission.

Shift of critical points in the parametrically modulated Hénon map with coexisting attractors

Abstract We study how the critical point positions change in the parametrically modulated Henon map with coexisting period-1 and period-3 attractors. In particular, a new type of scaling law is found coinciding with that evidenced by laser experiments. We show that resonance phenomena play a crucial role in deformation of attractors and their basins of attraction.

A polarisation-bistable neodymium laser with a Cr4+:YAG passive switch under the weak resonant signal control

Abstract A polarisation-bistable device is proposed based on the phenomenon of dependence of polarisation state of a Nd:YAG laser passively Q-switched with a Cr 4+ :YAG crystal upon relative orientations of the switch and an intracavity polariser. The device is shown to operate as an all-optical transistor. One of the main parameters (polarisation) of the neodymium laser can be controlled by the relatively weak signal delivered from a CW laser or laser diode, the wavelength of which falls into the Cr 4+ :YAG resonant absorption band. The parameters ranges for both the powerful neodymium and weak controlling lasers are found, for which the most reliable and effective operation of the device is expected.

Second-harmonic generation by Nd 3+ :YAG/Cr 4+ :YAG-laser pulses with changing state of polarization

We describe the passive Q-switching regime of a neodymium laser that contains a Cr4+:YAG saturable absorber inside the cavity. Two configurations of the laser cavity are modeled: the cavity containing a partial polarizer as an additional unit and the microchip laser cavity in which the functions of an active element and saturable absorber are combined in a single piece of a Nd3+:YAG/Cr4+:YAG crystal with reflecting facets. It is shown that both lasers are able to generate a giant pulse with a changing state of polarization. Both the kinetics of the state of polarization of the pulse and its impact on second-harmonic generation are treated numerically. We find that the up-conversion efficiency can be enhanced and that harmonic-pulse compression can be obtained by means of the proper orientations of the intracavity polarizing elements, for the first configuration, or by choosing the polarization of the longitudinal pump and angular orientation of the doubling crystal, for the second one. The ability of the doubling crystal to analyze the state of polarization of pulses with nonlinearly changing polarization is discussed.

Ce-doped and Ce/Au-codoped alumino-phospho-silicate fibers: Spectral attenuation trends at high-energy electron irradiation and posterior low-power optical bleaching

We report a study of attenuation spectra’ transformations in a couple of Cerium (Ce) doped alumino-phospho-silicate fibers (one of them codoped with gold (Au)), occurring under irradiation by a beam of high-energy β-electrons. The experimental data reveals an essential effect of β-irradiation upon the absorptive properties of the fibers, given by noticeable susceptibility of Ce ions in Ce3+/Ce4+ valence states to the treatment, arisen as growth followed by saturation of induced absorption. We also report posterior bleaching of the β-darkened fibers, also in terms of attenuation spectra’ transformations, at exposing them to low-power green (a He-Ne laser) and UV (mercury lamp) light, the effect never reported for Ce-doped fibers. It is shown that both phenomena are less expressed in Ce fiber codoped with Au than in Au-free one and that the spectral changes in the former are more regular and plain vs. irradiation dose and bleaching time. Possible mechanisms responsible for the phenomena and their impact at using such fibers for dosimetry and other applications are discussed.

Enhancing type-II optical second-harmonic generation by the use of a laser beam with a rotating azimuth of polarization

We propose a frequency converter which exploits laser pulses with changing state of polarization. The use of such pulses as a pump source for an extracavity doubling crystal is shown to result in the large conversion efficiency. These pulses can also provide a fairly good tool of monitoring the shape of the harmonic pulse. It is shown that temporal variations of the polarization direction experienced by the pump pulse in this system may cause considerable shortening of the harmonic pulse.

FWM interaction transfer matrix for self-adaptive laser oscillators

The FWM interaction transfer matrix for a self-adaptive laser resonator is deduced. The laser oscillator considered is made of a plane output coupler and an infinite nonlinear FWM medium in a self-intersecting loop geometry. This matrix can be used in different complex configurations to study the spatial evolution of a Gaussian beam.

Transient evolution and spatial mode size analysis of adaptive laser oscillators

We present a spatial mode analysis of a self-adaptive holographic laser oscillator formed by a non-linear medium in a self-intersecting loop geometry incorporating additional intracavity elements and a feedback mirror acting as output coupler. We used an ABCD transfer matrix approach for cavity elements, as well as the four-wave mixing (FWM) in the non-linear medium and demonstrate transient evolution, as well as self-consistent steady-state solutions for the fundamental mode configuration. We found that the transient case evolves to the self-consistent solution if one exists. We show the effects of intracavity lens focal length and position in the cavity, as well as the finite transverse dimensions of the non-linear medium, on the size of the self-consistent mode to find regimes for large mode size, good phase conjugate quality and low loss operation.

Generation of cnoidal waves by a laser system with a controllable saturable absorber

We demonstrate the cnoidal wave formation in a two-laser system with a saturable absorber in the cavity of one of the lasers. Another laser is used to activate the saturable absorber in order to control the pulse shape, width, intensity and frequency. Using the three-level laser model based on the Statz--De Mars equations, we show that for any value of the saturable absorber parameter there exists a certain modulation frequency for which the pulse shape is very close to a soliton shape with less than 5% error at the pulse base. Such a device may be prominent for optical communication and laser engineering applications.