Broadband spintronic detection of the absolute field strength of terahertz electromagnetic pulses

TL;DR

This paper introduces Zeeman-torque sampling (ZTS), a broadband, linear, and calibration-friendly method for detecting intense terahertz pulses, offering advantages over traditional electro-optic sampling.

Contribution

The authors demonstrate a novel magneto-optic ZTS technique for absolute, broadband terahertz field measurement with improved linearity and calibration simplicity compared to existing methods.

Findings

Detects terahertz pulses from 0.1-11 THz with >0.1 MV/cm peak field

Provides absolute, calibration-ready field strength measurements

Offers linear response even at high field amplitudes

Abstract

We demonstrate detection of broadband intense terahertz electromagnetic pulses by Zeeman-torque sampling (ZTS). Our approach is based on magneto-optic probing of the Zeeman torque the terahertz magnetic field exerts on the magnetization of a ferromagnet. Using an 8 nm thick iron film as sensor, we detect pulses from a silicon-based spintronic terahertz emitter with bandwidth 0.1-11 THz and peak field >0.1 MV/cm. Static calibration provides access to absolute transient THz field strengths. We show relevant added values of ZTS compared to electro-optic sampling (EOS): an absolute and echo-free transfer function with simple frequency dependence, linearity even at high terahertz field amplitudes, the straightforward calibration of EOS response functions and the modulation of the polarization-sensitive direction by an external AC magnetic field. Consequently, ZTS has interesting applications even beyond the accurate characterization of broadband high-field terahertz pulses for nonlinear terahertz spectroscopy.