Ultra-broadband THz emission from one- and two-color laser-induced microplasmas at a high repetition rate

The development of terahertz (THz) sources is meeting a widely increasing interest due to their numerous applications across various technological fields and to answer fundamental questions in many scientific areas, e.g., condensed matter physics. For such purposes, plasmas have emerged as promising THz emitters to study phenomena coherently in a large spectral region extending from THz to mid-IR, but their applications have often been restricted by intrinsic limitations of noisy kHz-class systems with mJ pulse energies. Here, we demonstrate the generation of intense and broadband THz radiation from laser-induced micro-plasmas in air, driven by femtosecond fiber lasers operating at a 200 kHz repetition rate and µJ pulse energies. We investigate the tight-focusing regime in which microplasmas are created and study the characteristics of the THz emission in the one- and two-color configurations. In the latter, we report efficient THz generation with a 30 THz bandwidth and high peak amplitudes on par with mJ-systems with a repetition rate 100 times higher. These results offer a promising path toward the practical implementation of plasma-based THz sources at high repetition rates for high signal-to-noise, broadband, and phonon-less THz spectroscopy.