Fig. 1. Traditional terahertz spectroscopy measurement technology. (a) THz-TDS measurement; (b) direct frequency-tuning and heterodyne mixing frequency detection; (c) dispersive optics; (d) narrowband filter array

Fig. 2. Schematic of the spectral encoding and computational reconstruction process

Fig. 3. Structural design and transmission spectra of spectral encoder device. (a) Schematic of array-type metasurface spectral encoder; (b)‒(d) several metasurface units designed in this paper; (e)‒(g) corresponding transmission spectra

Fig. 4. Spectral reconstruction error under different noise levels

Fig. 5. Spectral reconstruction results of proposed dictionary learning algorithm. (a) Reference spectrum measured by THz-TDS; (b) absorption spectrum of lactose; (c) absorption spectrum containing two peaks; (d) absorption spectrum containing three peaks