Two-Grating Talbot Bands Spectral Domain Interferometer

A configuration for Talbot bands is presented, where two tilted gratings replace the splitter normally used for recombining the signals from the two interferometer arms. The two optical beams from the interferometer are launched by two fiber leads tightly brought together in the front focal plane of a collimating lens. As the tips of the two fibers are slightly off-axis, the emergent beams after the collimating lens are not parallel. In combination with the two tilted gratings, the non parallel launching of the two beams leads to total elimination of mirror terms even when the two beams overlap on either grating. The effects of several geometrical parameters on the visibility performance versus optical path difference between the two arm lengths of the interferometer are evaluated

Scaling Behaviour of the Maximal Growth Rate in the Rosensweig Instability

The dependence of the maximal growth rate of the modes of the Rosensweig instability on the properties of the magnetic fluid and the external magnetic induction is studied. An expansion and a fit procedure are applied in the appropriate ranges of the supercritical induction $\hat B$. With increasing $\hat B$ the scaling of the maximal growth rate changes from linear to a combination of linear and square-root-like scaling. The scaling of the corresponding wave number alternates from quadratic to primarily linear. For very small $\hat B$ the dependence of the maximal growth rate on the viscosity is given. Suggestions are made for experiments to test the predicted scaling behaviours.Comment: 8 pages, 4 figures; to appear in Europhys. Let