Arbitrary Sub-THz Pulse Shaping via a Laser-Array-Driven InP-on-Sapphire Switch

We present an amplitude modulator for high-power sub-terahertz radiation based on a laser-driven semiconductor switch capable of arbitrarily shaping pulse sequences with nanosecond time resolution. The core of the device is a photonic switch constructed from a 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m-thick epitaxially grown indium phosphide film bonded to a sapphire substrate. This switch is driven by an array of eight fiber-coupled 905 nm laser diodes, each delivering up to 125 W of peak power with programmable pulse durations ranging from 40 to 250 ns. By optimizing the semiconductor layer and substrate combination, we achieve a two-orders-of-magnitude reduction in the optical excitation fluence required for modulation, a key advancement that enables the use of compact and cost-effective laser diodes rather than high-power pulsed lasers traditionally required for such devices. The modulator was experimentally validated through a 240 GHz pulsed electron spin resonance experiment. The modulator also successfully operated with nearly 1 kW of sub-THz radiation without sustaining damage. Time-resolved reflectance measurements confirmed that the temporal structure of the laser pulses is faithfully imprinted onto the reflected sub-THz signal, demonstrating the system’s capability for flexible and precise pulse shaping at high frequencies.