Photoinduced Broadband Tunable Terahertz Absorber Based on VO2 Thin Film.

The demand for terahertz (THz) communication and detection fuels continuous research for high-performance of THz absorption materials. In addition to varying the materials and their structure passively, an alternative approach is to modulate THz wave actively by tuning the external stimulus. Correlated oxides are ideal materials for this because the effects of a small external control parameter can be amplified by the inner electronic correlations. Here, by utilizing an unpatterned strongly correlated electron oxide VO2 thin film, a photoinduced broadband tunable THz absorber is realized firstly. The absorption, transmission, reflection and phase of THz waves can all be actively controlled by external pump laser above room temperature. By varying laser fluence, the average broadband absorption can be tuned from 18.9 to 74.7% and the average transmission can be tuned from 9.2 to 69.2%. Meanwhile, a broadband antireflection is obtained at 5.6 mJ/cm2, and a π phase shift of reflected THz wave is achieved when the fluence increases greater than 5.7 mJ/cm2. Apart from other modulators, the photoexcitation assisted dual-phases competition is identified as the origin of this active THz multifunctional modulation. Our work suggests that advantages of controllable phase separation in strongly correlated electron systems could provide viable routes in the creation of active optical component for THz wave.