Zinc Telluride ZnTe Crystal for terahertz

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Featured Research Article| August 13 2024
Rotating spintronic terahertz emitter optimized for microjoule pump-pulse energies and megahertz repetition rates

Spintronic terahertz emitters (STEs) are powerful sources of ultra-broadband single-cycle terahertz (THz) field transients. They work with any pump wavelength, and their polarity and polarization direction are easily adjustable. However, at high pump powers and high repetition rates, STE operation is hampered by a significant increase in the local temperature. Here, we resolve this issue by rotating the STE at a few 100 Hz, thereby distributing the absorbed pump power over a larger area. Our approach permits stable STE operation at a fluence of ∼1 mJ/cm2 with up to 18 W pump power at megahertz repetition rates, corresponding to pump-pulse energies of a few 10 μJ and pump power densities approaching 1 kW/cm2. The rotating STE is of interest for all ultra-broadband high-power terahertz applications requiring high repetition rates. As an example, we show that terahertz pulses with peak fields of 10 kV/cm can be coupled to a terahertz-light wave-driven scanning tunneling microscope at 1 MHz repetition rate, demonstrating that the rotating STE can compete with standard terahertz sources such as LiNbO3.

Spintronic terahertz (THz) emitters (STEs) have emerged as versatile sources of ultra-broadband single-cycle terahertz pulses without spectral gaps,1 delivering peak electric fields up to ∼1 MV/cm.2,3 Among other advantages,4,5 STEs offer easy and versatile polarity and polarization control via external magnetic fields,6–8 wavelength-independent excitation9 without phase matching constraints, excellent beam quality and focusability,2 and Fourier-limited single-cycle transients with ultra-wide bandwidth.1 Therefore, they are of particular interest for terahertz field-driven applications such as terahertz-light wave scanning tunneling microscopy (THz-STM)10–12 and field-resolved terahertz scanning near-field optical microscopy (THz-SNOM).10,13 A crucial aspect for these applications is the generation of measurable terahertz-field-induced currents or scattered terahertz near-field signals, which requires operation at megahertz repetition rates and sufficiently high terahertz field strength, e.g., up to few kilovolts per cm in the case of THz-STM.10,14,15 Modern Yb-based high-power femtosecond laser systems16–18 combined with external pulse compressors19–22 provide pulses with a duration down to a few 10 fs at several 10–100 W of output power and megahertz repetition rates, motivating the optimization of broadband terahertz sources such as the STE at such laser parameters.23–27 This will further pave the way for future technological applications in broadband terahertz imaging,28,29 sensing, and spectroscopy that will greatly benefit from high terahertz powers.

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