THz absorption spectra of bone and synthetic reference calcium phosphate compounds.

a) absorption coefficients of an untreated bone sample and a series of temperature-treated samples up to 800 °C; b) absorption coefficients from a series of high-temperature (from 800 to 900 °C) treated bone samples; c) absorption coefficients of commercial ns-HA powder samples, untreated and treated at different temperatures; d) absorption coefficients from a series of reference calcium phosphate compounds: stoichiometric hydroxyapatite s-HA, TTCP, α and β-TCP, and β-CPP.