Signal Stitching Algorithm for Faster Acquisition of Long Traces in Terahertz Time Domain Spectroscopy

In this paper, an iterative algorithm is developed to combine time shifted traces in pulsed terahertz time domain spectroscopy (THz-TDS). This method intends to correct errors due to mechanical sampling in the trailing ends of the traces in systems that utilize a combination of a fast voice coil optical delay line and a slow long delay range one. The algorithm works by iteratively combining three basic modifications on the trace shape to match the overlapping areas of consecutive time windows. In order to validate the method, both simulated and experimental traces affected by ODL distortions are stitched. Proper stitching is shown to mitigate the increase of noise floor and the frequency shift of spectral resonances that arises with direct stitching, i.e. just compensating for the offset between traces. An enhancement in acquisition speed by a factor 7 in comparison to conventional lock-in detection based on a long range optical delay line is shown in tests with the experimental setup available.