Diode-pumped passively mode-locked lasers with high peak power and short pulse width have been widely applied in laser communication, remote sensing and nonlinear optics. In recent years, single-walled carbon nanotube saturable absorbers (SWCNT-SAs) have been intensively investigated because of their characteristics such as low-cost, broad spectral ranges and so on. SWCNT-SAs have much potential to be applied in the generation of ultrafast mode-locked laser pulses.
In order to achieve high output power of mode-locked laser, we employed polymer-free SWCNT-SA fabricated by vertical evaporation method to mode-locked Nd:YVO4 laser. Nd:YVO4 crystal is a widely used laser medium with high gain and polarized emission. However, its relatively poor thermal and mechanical characteristics strongly limit the pump power. In order to reduce the thermal load of the Nd:YVO4 laser crystal, an 880 nm laser diode (LD) pump source was used in our experiment. At the pump power of 11.8 W, 1.8 W average output power of continuous wave mode-locked laser with optical conversion efficiency of 15.3% was achieved. The repetition rate of passively mode-locked pulse was 90 MHz with 15 ps pulse width. The pulse energy and peak power of mode-locked laser were 20 nJ and 1.3 kW, respectively.
From the experimental results, we can see that SWCNT is a promising saturable absorber.
Fig. 1 Typical mode-locked pulse trains