ABSTRACT
Ultrashort pulse technology is an important means for such disciplines as physics, chemistry, biology, optoelectronics, and laser spectroscopy to study the microscopic world and reveal new ultrafast processes. The development of ultrashort pulse technology has experienced the stages of active mode-locking, passive mode-locking, synchronously pumped mode-locking, collision pulse mode locking (CPM), as well as additive pulse mode-locking (APM) that emerged in the 1990s or the coupled cavity mode-locking (CCM) and self-modelocking. Since the realization of laser mode-locking in the 1960s, the mode-locked optical pulse width had reached nanosecond and subnanoseond 10−9 ∼10−10 s order of magnitude by the mid-and late 1960s. By the mid-and late 1970s, the pulse width had reached the subpicosecond (10−13 s) order of magnitude and by the 1980s, there had appeared an upsurge, that is, definite breakthroughs had been made in both theory and practice, with the width of the ultrashort pulse entering the femtosecond (10−15 s) stage. In 1981, R.L. Fork and others with Bell Laboratories of the U.S. proposed the theory of collision mode-locking and realized collision mode-locking in a 6-mirror ring-shaped cavity by obtaining a stable optical pulse sequence of 90 fs. Following the adoption of the optical pulse compressing technique, 6 fs optical pulses were obtained. The emergence of the self-mode-locking technology in the 1990s made it possible to obtain the ultrashort typical pulse sequence of 8.5 fs in the titanium-doped sapphire self-mode-locked laser.
