[Dynamic double modulation with step scan FTIR spectroscopy on polyurethane film].

The principle of step scan FTIR spectroscopy and the relationship between phase modulation and sample modulation were described in detail. Demodulation of the frequency domain detector signal was discussed and illustrated using double digital signal processing (DSP2) algorithm. In-phase and quadrature dynamic spectra of polyurethane with 5 Hz stretching under 100 Hz phase modulation as compared to the normal spectrum were presented. The spectral resolution of the overlapped features had greatly been enhanced.