Time-interval Measurement with Linear Optical Sampling at the Femtosecond Level

High-precision time-interval measurement is a fundamental technique in many advanced applications, including time and distance metrology, particle physics, and ultra-precision machining. However, many of these applications are confined by the imprecise time-interval measurement of electrical signals, restricting the performance of the ultimate system to a few picoseconds, which limits ultra-high-precision applications. Here, we demonstrate an optical means of the time-interval measurement of electrical signals that can successfully achieve femtosecond (fs)-level precision. The setup is established using the optical-frequency-comb (OFC)-based linear optical sampling technique to realize timescale-stretched measurement. We achieve the measurement precision of 82 fs for a single LOS scan measurement and 3.05 fs for the 100-times average with post-processing, which is three orders of magnitude higher than the results of older electrical methods. The high-precision time interval measurement of electrical signals can substantially improve precision measurement technologies.