Enhanced Terahertz Emission from Spatial Light Modulator-Controlled Air-Plasmas

The generation of terahertz (THz) waves by focusing femtosecond lasers can overcome the strong absorption of air, and becomes a hot research topic for intense THz physics. However, the lack of effective enhancement and modulation means has limited the wide use of this source. Structured light fields have complex spatial amplitudes, phases, polarization, and coherence, resulting in new phenomena and effects during transmission, transformation, and interaction with matter. It has been developed into an independent branch of optics that has attracted much attention. Here, we demonstrate a method to effectively enhance and flexibly modulate THz waves by shaping the spatial distribution of air-plasma. In our research, the spatial light modulator (SLM) provides precise manipulation of the light field structure of the femtosecond laser, which in turn precisely controls the spatial distribution of the air-plasma. Experimental results show that this scheme can effectively enhance the conversion efficiency of THz waves. In addition, different topological charges of the vortex beams demonstrate different THz emissions, implying that there are different modes of light-matter interaction inside the air-plasma. Our research sheds light on the optical field modulation algorithms and has the potential in exploring beam modes with higher energy conversion efficiencies. It can break the intensity clamping and helps to deepen our understanding of the ultrafast dynamics.