Large Terahertz Phase Shift Induced by Photothermal Effect of Gold Nanoparticles Incorporated with Toluene

Phase and amplitude modulation of propagating terahertz (THz) waves in free space is essential for many rapidly developing THz technologies. Herein, an all-optical, high-performance, and ultra-broadband THz phase shifter is demonstrated. Tunable phase shift is achieved by the photothermal effect of plasmonic gold nanoparticles in toluene, which can induce variations in the THz refractive index of toluene as the temperature increases. A phase shift of 270 degrees at 1 THz can be achieved under a laser irradiation of 2.5 W (3.9 W cm(-2)) on the mixture solution. Constructive and destructive interference of THz waves can be achieved by tuning the relative phase of two split THz waves, which can be controlled by the power of the irradiation laser. This is the first broadband THz phase modulator in free space driven by optical stimuli, and it provides a new solution for tuning the phase shift of THz waves.