A terahertz spectrometer with a pulsed high magnetic field

Abstract

A terahertz (THz) spectrometer based on backward-wave tubes and combined with a pulsed-magnetic-field generator with a pulse duration of ∼100 μs and an amplitude of up to 50 T is described. This spectrometer is indented for studying magnetic resonances of various magnets in the THz frequency range (30 GHz-1.5 THz) in the Faraday (longitudinal field) and Voigt (transverse field) geometries. Its operating principle is based on measurements of the change in the transmission of polarized THz radiation by studied samples exposed to an applied pulsed magnetic field. Its advantage over the magnetic-resonance technique, in which radiation guides with uncontrolled radiation polarization are used, is the possibility of performing precise polarization measurements necessary for determining the conditions for excitation of resonance magnetic modes and yielding important information on the magnetic structure of materials. The results of polarization measurements of test samples are presented. The degree of radiation polarization is 99.99%; the dynamic measurement range is 25 dB; the measurement accuracy is no worse than 1%; the time resolution of the recording system is 1s; the magnetic-field inhomogeneities at the solenoid’s center at a base of ±2 mm are no worse than 1 (experimental) and 5% (calculated) for the axial and radial components, respectively; and the maximum stored energy is 40.5 kJ.