Key insights in materials at extreme temperatures and pressures can be gained by accurate measurements that determine the electrical conductivity. Free-electron laser pulses can ionize and excite matter out of equilibrium on femtosecond time scales, modifying the electronic and ionic structures and enhancing electronic scattering properties. The transient evolution of the conductivity manifests the energy coupling from high temperature electrons to low temperature ions. Here we combine accelerator-based, high-brightness multi-cycle terahertz radiation with a single-shot electro-optic sampling technique to probe the evolution of DC electrical conductivity using terahertz transmission measurements on sub-picosecond time scales with a multi-undulator free electron laser. Our results allow the direct determination of the electron-electron and electron-ion scattering frequencies that are the major contributors of the electrical resistivity.

The THz beamline at FLASH, DESY, provides both tunable (1–300 THz) narrow-bandwidth (∼10%) and broad-bandwidth intense (up to 150 uJ) THz pulses delivered in 1 MHz bursts and naturally synchronized with free-electron laser X-ray pulses. Combination of these pulses, along with the auxiliary NIR and VIS ultrashort lasers, supports a plethora of dynamic investigations in physics, material science and biology. The unique features of the FLASH THz pulses and the accelerator source, however, bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles. Here, these challenges are discussed and the pulse diagnostic tools developed at FLASH are presented. In particular, a radiometric power measurement is presented that enables the derivation of the average pulse energy within a pulse burst across the spectral range, jitter-corrected electro-optical sampling for the full spectro-temporal pulse characterization, spatial beam profiling along the beam transport line and at the sample, and a lamellar grating based Fourier transform infrared spectrometer for the on-line assessment of the average THz pulse spectra. Corresponding measurement results provide a comprehensive insight into the THz beamline capabilities.

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This paper proposes an optical voltage sensor (OVS) with a dual-crystal structure for eliminating the impacts of linear birefringence in sensing crystal, which is induced by thermal gradients and pressure on a crystal surface. First, the configuration and the principle of the linear birefringence-free OVS are introduced. Second, the effectiveness of the dual-crystal structure is analyzed by the theoretical method and eventually verified by experiments. Moreover, the impact of the half-wave plate employed in the dual-crystal structure is investigated. When applied AC voltages exceed 500 V, the OVS achieves accuracy within ±0.1% at indoor temperature and ±0.3% with temperature varying from 0°C to 60°C. On the other hand, the scale factor error of the OVS is within ±0.078% at indoor temperature and ±1.63% when temperature varies from 0°C to 60°C.

Structure and magnetic properties of nanocrystalline PrCo 3 J. Appl. Phys. 107, 083916 (2010); 10.1063/1.3388364 Partitioning behavior and the effect of Co on the Curie temperature of nanocomposite PrFeCoB hard magnetic alloys Appl.