Coherently Controlled Terahertz Magnetic Impulses in GaAs

Wire-based magnetic field sources limit magnetic field metrology. Using ultrashort laser pulses to drive ultrafast currents in solids and gases paves a novel route towards generating spatially isolated, intense, THz magnetic impulses [1]. In semiconductors, ultrafast currents can be injected and controlled by exploiting quantum interference between different pathways linking the same initial and final states, popularly known as coherent control. We apply cylindrical vector beams to excite the ring currents and their accompanying magnetic fields [1,2].

 

As coherent control is sensitive to the relative phase between two laser pulses, modulating the phase of one pulse enables us to structure the generated currents. We used two femtosecond pulses, one circularly polarized fundamental (1480 nm) and the other a linearly polarized second harmonic (740 nm) that has been reflected from a spatial light modulator, to excite programmable current patterns [3,4] in the GaAs. These reconfigurable transient current structures serve as a source of spatially tailored ultrafast THz magnetic fields.

 

We have measured electric fields of the THz radiation emitted by ring currents using electro-optic sampling. We calculate the corresponding magnetic field using Maxwell’s equations. These all-optically driven magnetic fields find potential applications in magnetic materials, imaging and spintronics.

 

1.S. Sederberg et al. Phys. Rev. X 34, 011063 (2020).

2.S. Sederberg et al. Nat. Photonics 14,680(2020).

3. K. Jana et al. Nat. Photonics 15, 622(2021).

4. K. Jana et al. Nanophotonics (2021).