We present measurements of the resistivity ρx,x of URu2Si2 high-quality single crystals in pulsed high magnetic fields up to 81 T at a temperature of 1.4 K and up to 60 T at temperatures down to 100 mK. For a field H applied along the magnetic easy-axis c, a strong sample-dependence of the low-temperature resistivity in the hidden-order phase is attributed to a high carrier mobility. The interplay between the magnetic and orbital properties is emphasized by the angle-dependence of the phase diagram, where magnetic transition fields and crossover fields related to the Fermi surface properties follow a 1/cos θ-law, θ being the angle between H and c. For H c, a crossover defined at a kink of ρx,x, as initially reported in [Shishido et al., Phys. Rev. Lett. 102, 156403 (2009)], is found to be strongly sample-dependent: its characteristic field µ0H* varies from ≃ 20 T in our best sample with a residual resistivity ratio RRR = ρx,x(300K)/ρx,x(2K) of 225 to ≃ 25 T in a sample with a RRR of 90. A second crossover is defined at the maximum of ρx,x at the sample-independent characteristic field µ0H LT ρ,max ≃ 30 T. Fourier analyzes of Shubnikov-de Haas oscillations show that H LT ρ,max coincides with a sudden modification of the Fermi surface, while H * lies in a regime where the Fermi surface is smoothly modified. For H a, i) no phase transition is observed at low temperature and the system remains in the hidden-order phase up to 81 T, ii) quantum oscillations surviving up to 7 K are related to a new and almost-spherical orbit -for the first time observed here -at the frequency F λ ≃ 1400 T and associated with a low effective mass m * λ = (1 ± 0.5) · m0, where m0 is the free electron mass, and iii) no Fermi surface modification occurs up to 81 T.

An innovative investigation of optical feedback or self-mixing interference within the cavity of a single-longitudinalmode laser is described as an integral part of a novel interrogation scheme to be employed in a fiber Bragg grating-based sensor for strain measurement. The entire sensor device simply consists of a laser diode with an integrated photodiode which is coupled to a fiber Bragg grating under strain. A small percentage of the injected lightwave resonantly reflected off the grating structure reenters the laser cavity and modifies the emission properties of the laser, resulting in the formation of characteristic sawtooth fringes which contain the embedded strain information. The feasibility of demodulating the induced small wavelength shifts of fiber Bragg gratings under dynamic mechanical loading by self-mixing interferometry is thus presented analytically and experimentally verified. A relatively good corroboration has been achieved.

This Letter describes a dual-amplitude modulation technique incorporated into a double reflection extrinsic-type fiber Fabry-Perot interferometer to measure periodic, nonperiodic as well as quasi-static displacements. The modulation scheme simultaneously maintains the interference signal pair in quadrature and provides a reference signal for displacements inferior to a quarter of the source wavelength. The control and phase demodulation of the interferometer carried out via software enable quasi-real-time measurement and facilitates sensor alignment. The sensor system can be exploited in the low frequency range from 10(-3) to ∼500 Hz and has a resolution better than 2.2 nm, targeting applications in geophysics.