Phase-controlled Fourier-transform Infrared Spectroscopy with Cantilever-enhanced Photoacoustic Detection

Cantilever-enhanced photoacoustic spectroscopy (CEPAS) is an extremely sensitive spectroscopic technique and capable of broadband measurements [1]. For example, it has been combined with Fourier-transform infrared spectroscopy (FTIR), where the power of each frequency component in the optical spectrum is modulated at a unique radio or acoustic frequency [2]. The power modulations are transformed into pressure waves by absorption inside the sample cell and detected by the sensitive silicon-cantilever microphone of the CEPAS detector. Due to the sensitivity of CEPAS, the detection bandwidth is limited to low acoustic frequencies $(< 1\ \text{kHz})$ leading to the necessity of slow interferometer scans and long measurement times.