Abstract
We have developed a mode-locked ultra-short pulse C $r^{4+}$:YAG laser, as well as a continuous wave C $r^{4+}$:YAG laser. The laser was pumped by a Nd:YAG laser and its characteristics were investigated. In continuous wave mode, we obtained as much as 600 mW at 1.436 ${\mu}{\textrm}{m}$ with pumping power of 6 W, by using an output coupler with a reflectivity of 98%. The power slope efficiency was 10%, when the gain medium was cooled to 19$^{\circ}C$. The tuning range was varied from 1.39 ${\mu}{\textrm}{m}$ to 1.55 ${\mu}{\textrm}{m}$ and the maximum power was 400 mW at 1.492 ${\mu}{\textrm}{m}$ with a 3-plate birefringent filter. The C $r^{4+}$:YAG laser was mode-locked by a Kerr lens mode locking method. Mode locking at 1.436 ${\mu}{\textrm}{m}$was initiated by slightly rocking a mirror mount. But the pulses were very unstable because of the strong water absorption at this region. So we shifted the lasing wavelength to 1.492 ${\mu}{\textrm}{m}$ by using a 3-plate birefringent filter. Then we obtained stable state mode-locking with the maximum average power of 280 mW for a pumping power of 6 W. The pulse width of 43 fs was measured using an autocorrelator and the repetition rate was 104.5 MHz.
1.064 $\mu\textrm{m}$ 파장의 연속발진 Nd:YAG 레이저를 펌핑 광원으로 하여 적외선 영역에서 광대역으로 파장 가변되는 연속발진 및 극초단펄스 C $r^{4+}$ :YAG 레이저를 자체 제작하였다. C $r^{4+}$ :YAG 레이저의 연속발진 및 펄스의 출력특성과 파장 가변 영역은 다음과 같다. 연속발진일 경우 1.436 $\mu\textrm{m}$에서 600 mW의 평균출력을 보였으나, 복굴절 필터를 삽입했을 경우는 1.492 $\mu\textrm{m}$근처에서 400 mW의 평균출력을 보였다. 펄스발진일 경우 1.436 $\mu\textrm{m}$에서 최초로 평균출력 320 mW의 모드록킹된 펄스가 발생하였지만 물 흡수대의 영향으로 불안정함을 피할 수 없었다. 따라서, 복굴절 필터를 사용하여 중심파장을 1.492 $\mu\textrm{m}$로 이동시켰으며 이 영역에서 안정한 상태의 모드록킹된 43 fs의 극초단 펄스를 생성하였다. 이 때의 평균출력은 280 mW이고, 반치폭(FWHM)은 45 nm이었다.
