Simultaneous reference and differential waveform acquisition in time-resolved terahertz spectroscopy.

We present a new method for data acquisition in time-resolved terahertz spectroscopy experiments. Our approach is based on simultaneous collection of reference and differential THz scans. Both the optical THz generation beam and the pump beam are modulated at two different frequencies that are not harmonic with respect to each other. Our method allows not only twice as fast data acquisition but also minimization of noise connected to slowly varying laser power fluctuations and timing instabilities. Our use of the nonlinear crystal N-benzyl-2-methyl-4-nitroaniline (BNA) enables time-resolved THz spectroscopy to beyond 5 THz, thereby highlighting that the presented method is especially valuable at higher frequencies where phase errors in the data acquisition become increasingly important.