1,720,975 research outputs found
Spontaneous improvement of spatial coherence and frequency locking in high-pump-power multimode lasers
No full textBy using the time average of amplitude products we are able to identify changes in the dynamical complexity and the spatial coherence of a multimode laser. We find that there are cases in which as the pump increases, the dynamical complexity decreases and the spatial coherence improves. In some limiting cases the complexity is reduced to zero and the beam is completely coherent spatially. We show that these phenomena are caused by phase synchronization of the mode amplitudes and that they can be observed using slow detectors.<br/
Pattern formation in lasers with Fabry-Perot cavities and hard-edge diffraction
No full textWe show that the presence of cylindric metallic objects, such as waveguides and apertures, inside lasers with Fabry-Perot cavities modifies considerably the symmetry of these systems. This, in turn, changes the structure of the patterns that can be observed and could lead to the use of patterns as a way of studying properties of the scattering objects
Combined effects of polarization and non-paraxial propagation on pattern formation
No full textWe show analytically that the presence inside an optical cavity of a polarizer and a hard diffracting object, for example, a circular aperture or waveguide, reduces the symmetry of the system from cylindrical to rectangular. As a consequence, patterns with concentric rings of bright or dark spots made up by modes whose azimuthal indexes are not multiples of one another, appear when the zero-field solution becomes unstable. These types of bifurcations are anomalous if the symmetry is cylindrical and therefore indicate the presence of polarization effects induced by diffraction. As an example of this type of system, we investigate numerically the bifurcations of a ring laser with a metallic duct and a polarizer inside the optical cavity
Explicit centre manifold reduction and full bifurcation analysis for an astigmatic Maxwell-Bloch laser
No full textUsing an explicit centre manifold reduction, we set up a general framework to study the bifurcations of nearly degenerate modes of a rather general laser model. We then apply it specifically to the study of interactions of two modes of a Maxwell–Bloch laser with broken circular symmetry. Complex bifurcation sequences involving single-mode solutions, mode locking and mode beating regimes are predicted. These sequences are organised by a Z2-symmetric Takens–Bogdanov bifurcation together with a zero-detuning Hopf bifurcation with 1:1 resonance that leads to an unexpected cyclic spatio-temporal symmetry of order 4. Numerical simulations of the original system show good agreement with theory
State dependent pseudo-resonances and excess noise
Full text linkWe show that strong response to nonresonant modulations and excess noise are state dependent in generic nonlinear systems; i.e., they affect some output states but are absent from others. This is demonstrated in complex Swift-Hohenberg models relevant to optics, where it is caused by the non-normality of the linearized stability operators around selected output states, even though the cavity modes are orthogonal. In particular, we find the effective parameters that control excess noise and the response to modulations and show cases where these phenomena are enhanced by an order of magnitude
Diffraction-induced polarization effects in optical pattern formation
No full textWe show theoretically that patterns with concentric rings of bright or dark spots made up by modes with coprime azimuthal indexes may arise in codimension one bifurcations in optical systems with a metallic diffractor, a polarizer, and a nonlinear medium. These patterns are a consequence of diffraction-induced polarization in systems without polarization dynamics. As an example of this type of system, we investigate numerically the symmetry-breaking bifurcations of a ring laser with a metallic duct and a polarizer inside the optical cavity
Picosecond Laser Pulse Correlation by using a Molecular Dye
No full textWe present a new, simple and cost effective scheme for the measure of the second-order correlation function of Nd-YAG laser second-harmonic (532 nm) pulses. We measure the transmission of a probe beam in a cell containing 6G-Rhodamine solution bleached by a counterpropagating pump beam. Under a convenient choice of experimental parameters, we can measure also the contribution of third-order correlation function
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