Fig. 4. a) Images of time dependent Tpp and Δpp spectra of the fiber scaffold at 45° azimuth. (b) The first single transmission and absolute phase spectrum with 65 µs integration time (tint). The spectral resolution is 1.4 cm–1.
These time dependent images prove the high stability and robustness of the method in the shown time range for both transmission and absolute phase measurements. The integration time of a single spectrum (see Fig. 5(b)) is 65 µs, plus a shot-to-shot delay of ca. 210 µs, giving a non-stroboscopic time resolution of ca. 275 µs. The time resolution can be pushed to as low as 1 µs with a zero shot-to-shot delay, with a tradeoff of limiting the maximum measurement duration to 256 ms. The noise of the DCS spectrometer in the second to sub-second time regime scales with the inverse of the square root of integration time43; the signal-to-noise can therefore be improved by averaging multiple spectra.
With its high time resolution for spectral monitoring in broad time windows from the min to µs range (with the potential of sub-microsecond time resolution43), IR-DCP is currently a few orders of magnitude faster than reported for QCL-based IR laser polarimetry (≈ 100 ms / 100 cm–1)33.