09:15 〜 09:30
▼ [8a-Z19-2] Q-switched Tb:LiYF4 laser at 544 nm
キーワード：Visible laser, Terbium
Tb3+-lasers can emit directly in the visible spectral region via blue-emitting semiconductor pumping. Compared to the conventional frequency-converted visible lasers, the cavity design is simple and the energy losses during the frequency-conversion operation are circumvented. Moreover, the upper laser level of Tb3+ usually shows a long lifetime, which is, e.g., 5 ms in LiYF4, and negligible non-radiative losses. This makes Tb3+ favorable for Q-switched operation.
We succeeded in the first Q-switched laser operation using Tb3+ as active ion. The gain medium was a 30-mm 15%Tb:LiYF4 crystal and the Q-switcher was single-layer graphene deposited on a silica substrate. Graphene is considered to be a suitable candidate for this preliminary investigation due to its broadband spectral response and low non-saturable losses as saturable absorber.First, the cw laser performance was tested without saturable absorber. A maximum output power of 1.25 W and a slope efficiency of 63% was obtained. After inserting the graphene, we were able to achieve stable Q-switched operation. The maximum average output power was recorded to be 0.74 W and the slope efficiency was 41%. As is shown in Fig.1, the pulse repetition rate increased linearly with the increase of incident power. However, the pulse width (FWHM) remained almost constantly at around 3 µs at Pout>400 mW. The pulse energy and peak power at the maximum output power were found to be 19 µJ and 6.6 W, respectively. The optical-to-optical efficiency of this Q-switched Tb:LiYF4 laser was 26.7%, which is much higher than the value of 4.9% obtained from a conventional frequency converted Nd:YVO4/KTP green laser using single-layer graphene as Q-switcher as well [Opt. Eng 54, 076103 (2015)].
We succeeded in the first Q-switched laser operation using Tb3+ as active ion. The gain medium was a 30-mm 15%Tb:LiYF4 crystal and the Q-switcher was single-layer graphene deposited on a silica substrate. Graphene is considered to be a suitable candidate for this preliminary investigation due to its broadband spectral response and low non-saturable losses as saturable absorber.First, the cw laser performance was tested without saturable absorber. A maximum output power of 1.25 W and a slope efficiency of 63% was obtained. After inserting the graphene, we were able to achieve stable Q-switched operation. The maximum average output power was recorded to be 0.74 W and the slope efficiency was 41%. As is shown in Fig.1, the pulse repetition rate increased linearly with the increase of incident power. However, the pulse width (FWHM) remained almost constantly at around 3 µs at Pout>400 mW. The pulse energy and peak power at the maximum output power were found to be 19 µJ and 6.6 W, respectively. The optical-to-optical efficiency of this Q-switched Tb:LiYF4 laser was 26.7%, which is much higher than the value of 4.9% obtained from a conventional frequency converted Nd:YVO4/KTP green laser using single-layer graphene as Q-switcher as well [Opt. Eng 54, 076103 (2015)].