Fig. 1. Schematic diagram of enhanced detection of terahertz absorption spectrum based on dielectric metasurface angle multiplexing. (a) Angle multiplexing principle for all-silicon dielectric metasurface; (b) unit structure of the metasurface

Fig. 2. The reflections of the metasurface with changing of (a) the incident angle, (b) h, (c) w and (d) l

Fig. 3. Qvalues of the reflection curve of the metasurface varying with (a) the incident angle of the terahertz wave, (b) h, (c) w and (d) l

Fig. 4. The dielectric constant of α-lactose at 0.45 THz~0.6 THz and the response curve of a film of lactose coated on a silicon (0.50 THz~0.55 THz). (a) dielectric constant; (b) reflectance; (c) transmittance; (d) absorptivity

Fig. 5. Enhancement of the terahertz absorption spectrum of lactose on the dielectric metasurface based on angle multiplexing. (a) The metasurface unit structure of the medium coated with lactose film; (b) the reflectance of the metasurface without lactose coating; (c) the transmittance of the metasurface without lactose coating; (d) the reflection of metasurface coated with 2 μm lactose; (e) the transmittance of metasurface coated on the 2 μm lactosee; (f) absorption of metasurface with and without lactose coating

Fig. 6. Electric field distributions of the dielectric metasurface coated with lactose film by multiplexing incident angle. (a) α=25° (0.561 THz); (b) α=35° (0.543 THz); (c) α=45° (0.529 THz); (d) α=55° (0.517 THz)

Fig. 7. Enhanced absorption spectra of dielectric metasurface coated with different thicknesses of lactose. (a) 0.5 μm lactose; (b) 1.0 μm lactose; (c) 1.5 μm lactose; (d) 2.0 μm lactose; (e) 2.5 μm lactose; (f) 0.5−2.5 μm lactose enhanced absorption spectra as envelope curves