Abstract

Time resolved optical experiments, as useful tools, give scientists a chance to research the dynamic processes ‘frame by frame’ of a series of ultrafast phenomena, including high resolution terahertz spectroscopy [1], transient absorption spectroscopy [2] and so on. In the beginning, ‘Mechanical Delay Line’ is employed to scan the time differences between the pump and the signal, but this method is inherently limited by either its low scan rate or its small scan range. Then, ‘Asynchronous Optical Sampling’ (ASOPS) [3] is invented in 1987. This method requires two synchronized femtosecond laser with slightly different repetition rates, which can overcome the drawbacks of mechanical method. However, system cost, which is mainly determined by the laser, increases significantly. Subsequently, ‘Optical Sampling by Cavity Tuning’ (OSCAT) method [4] is firstly employed in 2009. It utilizes time division multiplexing concept to make one laser act as two lasers at different time. Nevertheless, the signal to noise ratio reduces severely and it does require complicated electronic control loops.

© 2017 IEEE