Silk: Optical Properties over 12.6 Octaves THz-IR-Visible-UV Range

Domestic (Bombyx mori) and wild (Antheraea pernyi) silk fibers were characterised over a wide spectral range from THz 8 cm [Formula: see text] ([Formula: see text] 1.25 mm, [Formula: see text] 0.24 THz) to deep-UV [Formula: see text] cm [Formula: see text] ([Formula: see text] 200 nm, [Formula: see text] 1500 THz) wavelengths or over a 12.6 octave frequency range. Spectral features at [Formula: see text]-sheet, [Formula: see text]-coil and amorphous fibroin were analysed at different spectral ranges. Single fiber cross sections at mid-IR were used to determine spatial distribution of different silk constituents and revealed an [Formula: see text]-coil rich core and more broadly spread [Formula: see text]-sheets in natural silk fibers obtained from wild Antheraea pernyi moths. Low energy T-ray bands at 243 and 229 cm [Formula: see text] were observed in crystalline fibers of domestic and wild silk fibers, respectively, and showed no spectral shift down to 78 K temperature. A distinct [Formula: see text] cm [Formula: see text] band was observed in the crystalline Antheraea pernyi silk fibers. Systematic analysis and assignment of the observed spectral bands is presented. Water solubility and biodegradability of silk, required for bio-medical and sensor applications, are directly inferred from specific spectral bands.