Objective As devices can change the relative delay time of reference light and detection light in optical detection systems, optical delay line (ODL) is widely employed in terahertz timedomain spectroscopy (THz -TDS), optical coherence tomography, ultrafast time resolution spectroscopy, and pumpprobe technique. In particular, ODL is adopted to scan and detect THz -TDS signals by changing the relative delay of femtosecond and terahertz (THz) pulses in THz -