Chaos in free electron laser oscillators

The chaotic nature of a storage-ring Free Electron Laser (FEL) is investigated. The derivation of a low embedding dimension for the dynamics allows the low-dimensionality of this complex system to be observed, whereas its unpredictability is demonstrated, in some ranges of parameters, by a positive Lyapounov exponent. The route to chaos is then explored by tuning a single control parameter, and a period-doubling cascade is evidenced, as well as intermittence.Comment: Accepted in EPJ

Generation of ultrabright beams in high energy Nd:glass and KrF laser systems

The development of ultrabright lasers is progressing rapidly particularly in the direction of table-top-terawatt systems operating at high pulse repetition rate with relatively low pulse energy. The highest pulse energies and highest absolute powers are being generated by the adaptation of larger-scale high energy laser systems operating in single pulse mode. The maximum focused intensity from either type of laser is determined by the beam brightness B which can be expressed in units of Watts cm where P is the power, lambda the wavelength and S the Strehl ratio, quantifying the ratio of brightness in a beam with less than diffraction limited quality to that in a diffraction limited beam

Refined beam expansion method for unstable resonator modes

A refined and simplified version of the beam expansion method for computing the modes of unstable resonators is presented here.The principle of the beam expansion method is to express the field pattern on a basis of Hermite-Gaussian functions. Propagating each individual component around the resonator enables a transfer matrix to be constructed from which the eigenvalues and eigenvectors of the modes can be determined.Whereas the earlier proof-of-principle approach performed well for low Fresnel numbers, the refined technique gives good results for the challenging test case of magnification M=1.9 and equivalent Fresnel number Neq=49.4. The performance enhancement has been achieved by incorporating a number of adjustments that improve the accuracy of the calculation

Holographic generation and orbital angular momentum of high-order mathieu beams

We report the first experimental generation of high-order Mathieu beams and confirm their propagation invariance over a limited range. In our experiment we use a computer-generated phase hologram. The peculiar behaviour of the vortices in Mathieu beams gives rise to questions about their orbital-angular-momentum content, which we calculate by performing a decomposition in terms of Bessel beams