THz pulse shaping using broadband spintronic – III/V semiconductor hybrid emitters

Terahertz (THz) radiation exhibits sub-millimeter wavelengths, falling in the gap between the visible and microwave range in the electromagnetic spectrum. THz waves have a wide range of applications in pharmaceutics, non-destructive material characterization, and security applications. While most conventional THz sources including nonlinear crystals and photoconductive antennas (PCAs) emit linearly polarized THz waves, it remains challenging to create THz radiation with tunable pulse shape and chirality without additional optical components.

Here, we report tunable pulse shaping and polarization control of THz radiation by combining a spintronic THz emitter with a III/V semiconductor-based PCA. The presented hybrid emitter combines the advantages of PCAs such as high signal strength with the versatility of spintronic THz sources. The sample structure consists of a lithographically- defined PCA made of the III/V semiconducting material ErAs:GaAs grown by molecular beam epitaxy and a magnetic heterostructure of Ta/CoFeB/Pt deposited by magnetron sputtering on two sides of a GaAs substrate respectively. The hybrid emitter is combined with a hyperhemispherical Si lens for a better collection of the THz radiation. The device is excited by two femtosecond laser beams of distinct wavelengths: a laser beam with a central wavelength of 780 nm is used to excite the PCA, while a second laser beam of 1560 nm wavelength is used to excite the spintronic emitter. Varying the relative delay between the THz pulses from the two sources enables efficient pulse shape control of the combined THz wave. The relative intensity and angle between the two THz electric fields can be tuned by external parameters such as laser power, bias voltage, and applied magnetic field, enabling an extraordinary high-level control of the emitted THz wave.