Biomedical subjects

Bernard Ségard

Publications and source records attributed to Bernard Ségard.

3 recordsLinked to original sources

PubMed2006

Weak temporal ratchet effect by asymmetric modulation of a laser.

Subjecting lasers to triangular modulations of the pump produces phenomena that drastically depend on the symmetry of the triangle. For instance, with slow up-rising triangles, a laser below threshold on average may deliver coherent pulses, while it does not deliver coherent pulses with fast up-rising triangles. This effect, which requires the presence of fluctuations in addition to the modulation, is reminiscent of the thermal ratchet with which a directed motion is extracted from a stochastic medium.

Journal Article↗

PubMed2005

Optimal superluminal systems.

We demonstrate that significant effects in the "superluminal propagation" of light pulses cannot be observed without involving systems whose gain explodes outside the pulse spectrum. We explicitly determine the minimum norm of the gain to attain given superluminal effects and the transfer function of the corresponding optimal system. The gain norms, which would be required with the most efficient systems considered up to now (dispersive media, photonic barriers) to attain the same effects, are shown to exceed the minimum by several orders of magnitude. We finally estimate the largest superluminal advances which could be attained in a realistic experiment.

Journal Article↗

PubMed2004

Genetic drive of a laser.

Direct production of laser output pulses with arbitrary shapes can be extended to the high-frequency domain by use of optimal driving of the pump power. Genetic algorithms allow us to design the optimal time evolutions of the pump power to counteract the detrimental effect of relaxation oscillations. The method is demonstrated on a Nd3+:YVO4 laser and allows us to produce, e.g., triangular pulses at rates 20 times faster than for proportional modulation.

Journal Article↗