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

**Authors:** A. L. Chekhov, Y. Behovits, U. Martens, B. R. Serrano, M. Wolf, T. S. Seifert, M. Muenzenberg, T. Kampfrath  
**arXiv:** [2306.09734](https://arxiv.org/abs/2306.09734)  
**Date:** 2023-06-16  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.09734v1/

## Key points

- Study titled "Broadband spintronic detection of the absolute field strength of terahertz electromagnetic pulses"
- Demonstrates successful detection of intense terahertz electromagnetic pulses using Zeeman-torque sampling (ZTS)
- Approach based on magneto-optic probing of Zeeman torque exerted by terahertz magnetic field on 8 nm thick iron film
- Detection of pulses from silicon-based spintronic emitter with bandwidth ranging from 0.1 to 11 THz and peak field exceeding 0.1 MV/cm
- Use of static calibration method for accurate measurement of absolute transient terahertz field strengths
- Comparison between ZTS and electro-optic sampling (EOS) highlighting advantages such as absolute and echo-free transfer function, linearity at high terahertz field amplitudes, straightforward calibration of EOS response functions, and modulation of polarization-sensitive direction by external AC magnetic field
- Potential applications beyond characterizing broadband high-field terahertz pulses for nonlinear terahertz spectroscopy
- Thickness-dependent nature of 𝑄 and 𝑛2(𝜔pr) in thin iron films, recommendations for obtaining more accurate results by determining refractive index values separately or using epitaxially grown films to minimize thickness dependence
- Acknowledgment of funding sources including DFG collaborative research center SFB TRR 227 "Ultrafast spin dynamics," DFG priority program SPP2314 INTEREST, and financial support from Horizon 2020 Framework Program under FET Open Grant No. 863155 (s-Nebula)
- Disclosure that T.S.S. and T.K. are shareholders of TeraSpinTec GmbH, with T.S.S. also being an employee of the company

## Summary

In the study titled "Broadband spintronic detection of the absolute field strength of terahertz electromagnetic pulses," Chekhov et al. demonstrate the successful detection of intense terahertz electromagnetic pulses using Zeeman-torque sampling (ZTS). The approach is based on magneto-optic probing of the Zeeman torque exerted by the terahertz magnetic field on an 8 nm thick iron film. The researchers were able to detect pulses from a silicon-based spintronic emitter with a bandwidth ranging from 0.1 to 11 THz and a peak field exceeding 0.1 MV/cm. One key aspect highlighted in their findings is the use of a static calibration method, which allows for accurate measurement of absolute transient terahertz field strengths. The authors also compare ZTS to electro-optic sampling (EOS) and identify several advantages, including an absolute and echo-free transfer function with simple frequency dependence, linearity even at high terahertz field amplitudes, straightforward calibration of EOS response functions, and modulation of polarization-sensitive direction by an external AC magnetic field. This study suggests that ZTS has potential applications beyond just characterizing broadband high-field terahertz pulses for nonlinear terahertz spectroscopy. It is noted that both 𝑄 and 𝑛2(𝜔pr) are thickness-dependent in thin iron films, and recommendations are provided for obtaining more accurate results by determining refractive index values separately or using epitaxially grown films to minimize thickness dependence. The authors acknowledge funding from various sources such as the DFG collaborative research center SFB TRR 227 "Ultrafast spin dynamics," DFG priority program SPP2314 INTEREST, and financial support from Horizon 2020 Framework Program under FET Open Grant No. 863155 (s-Nebula). Additionally, it is disclosed that T.S.S. and T.K. are shareholders of TeraSpinTec GmbH, with T.S.S. also being an employee of the company. Overall, this study provides valuable insights into utilizing ZTS for detecting broadband intense terahertz electromagnetic pulses and highlights its potential applications in advanced spectroscopic techniques beyond traditional methods like EOS.