Ultrashort pulse lasers are widely used in various application areas including NT, BT, and IT, and demand for them is continually increasing. Therefore, the development and application of such lasers are still considered very important. For simple femtosecond laser development, semiconductor saturable absorbers (SESAMs) have been widely used, but their applications are also limited due to their complex manufacturing process and high production costs.
In this thesis, ultrafast single-walled carbon-nanotube-based saturable absorbers (SWCNT-SAs), which can replace the conventional SESAMs, are developed as new ultrafast optical switches and applied to the development of passively-mode-locked solid-state lasers operating between 1.0 and 2.0 ？？m. The linear and nonlinear optical properties of SWCNT-SAs are then characterized using spectrophotometry, pump-probe spectroscopy, and nonlinear transmission/reflection measurement, and their superior optical characteristics are verified as comparable with those of SESAMs.
Various near-IR solid-state lasers, such as Cr:forsterite (1.25 ？gm), Cr:YAG (1.5 ？gm), Tm:KLuW (1.9 ？gm), and Yb:KYW (1.0 ？gm) lasers, are developed in this thesis for application of passive-mode-lockers, SWCNT-SAs. The first experimental results on the passively mode-locked Cr:fosterite laser, which delivered a sub-100 fs near 1.25 ？？m, were achieved using reflective SWCNT-SAs, fabricated from SWCNTs synthesized via the high-pressure CO conversion (HiPCO) technique. In the femtosecond regime, the Cr:forsterite laser delivered an average power of up to 300 mW. These SWCNT-SAs exhibited an ultra-broadband nonlinear absorption properties between ~1.0 and 1.7 ？？m, such that these saturable absorbers were also applied to the Cr:YAG laser that operated near 1.5 ？？m. The passive mode-locking of the Cr:YAG laser using the transmitting SWCNT-SA was also successfully demonstrated for the first time, and stable sub-100 fs pulses with average powers of as high as 110 mW were generated. In the case of the SWCNTs that were synthesized using the Arc-discharge method, they showed nonlinear absorption properties of near 2.0 and 1.0 ？？m, which means that Arc-made SWCNT-based saturable absorbers are applicable for passive mode-locking of other bulk lasers, such as Tm:KLuW and Yb:KYW lasers. Using transmission-type SWCNT-SAs, transform-limited pulses of ~10 ps at 1.94 ？？m were stably generated from the Tm:KLuW laser that delivered a maximum output power of 240 mW, and the passively mode-locked operation of the solid-state Tm laser was the first demonstration, to the best of the authors… knowledge. The Yb:KYW laser was also passively mode-locked via reflective SWCNT-SA and produced transform-limited 83 fs pulses, assuming sech2-shaped pulses, and delivered an average output power of up to 170 mW.
Different solid-state lasers that operated between 1.0 and 2.0 ？？m were successfully mode-locked using novel SWCNT-based passive devices. These SWCNT-SAs, with their various attractive properties, can be considered real alternatives to the currently widely used SESAMs. Simultaneously, this new optical switching device can contribute to the improvement of the technical standards of saturable absorbers.