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We design and experimentally demonstrate a broadband metamaterial absorber in the terahertz (THz) band based on a periodic array of aluminum (Al) squares with two different sizes. A thin silicon dioxide (SiO2) film rather than a conventional polyimide (PI) layer is used as a dielectric spacer to separate Al squares from the platinum (Pt) ground plane in our design, which significantly improves the design precision and the feasibility of the device fabrication. The combination of different sizes of Al squares gives rise to an absorption bandwidth of over 210 GHz with an absorption of over 90%. Our results also show that our device is almost polarization-insensitive. It works very well for all azimuthal angles with an absorption of beyond 80%. [ABSTRACT FROM AUTHOR]

Single-phase VO2 thin films are sputtering deposited on BK7 substrates, and sharp insulator-to-metal phase transition is obtained with a resistivity change of four orders of magnitude. Terahertz (THz) pump-probe measurements reveal that by illuminating the films with a low pumping power of 143 µJ/cm², VO2 films exhibit an ultrafast optical switching to THz transmission within 8 ps. Furthermore, the THz switching ratio reaches over 80% in a wide frequency range from 0.3 to 2.5 THz. All these outstanding features indicate a strong potential of VO2 films for broadband terahertz wave switching and modulation applications. [ABSTRACT FROM AUTHOR]