Passively mode-locked Yb:CNGG laser
Recently we achieved continuous-wave (cw) and Q-switched laser operation of Yb<sup>3+</sup> in the disordered crystal Ca<inf>3</inf>(NbGa)<inf>2−x</inf>Ga<inf>3</inf>O<inf>12</inf> or shortly CNGG [1] previously studied only with Nd-doping [2] and Tm-doping [3]. It is an isotropic material similar to YAG and exhibits a rather high thermal conductivity of 4.7 Wm<sup>−1</sup>K<sup>−1</sup>, about one third of that of YAG which is much larger than for glasses. The disordered nature of the CNGG crystal provides several different lattice positions for the trivalent dopant ions, resulting in significant inhomogeneous broadening in the absorption and emission spectra. The maximum absorption cross section was measured to 3.3·10<sup>−20</sup> cm<sup>2</sup> at 973.5 nm. Apart from the zero-phonon line the maximum emission cross section is 2.5·10<sup>−20</sup> cm<sup>2</sup> at 1028 nm with a bandwidth of 21 nm (FWHM), roughly twice that of Yb:YAG. The measured fluorescence lifetime amounts to 791 µs. We demonstrated 2.0 W of cw output power with a slope efficiency of 40% for Yb:CNGG and the passively Q-switched operation delivered 1.35 W of average output power at a PRF of 16.7 kHz [1]. Here we demonstrate passive mode-locking of the disordered laser crystal Yb:CNGG using a semiconductor saturable absorber mirror (SESAM).
Polarized laser oscillation of isotropic disordered Yb:Ca3(NbGa)(2-x)Ga3O12 crystal.
Linearly polarized laser oscillation is observed with the isotropic disordered Yb:Ca3(NbGa)(2-x)Ga3O12 crystal, resulting from stress-induced birefringence. At high pump levels, two orthogonal polarization states exist simultaneously. A continuous-wave output power of 2.0 W is obtained with an optical-to-optical efficiency of 32%, the slope efficiency amounts to 40%. In the passively Q-switched regime, the average output power reaches 1.35 W at a pulse repetition frequency of 16.7 kHz, with a slope efficiency of 37%; the laser pulse energy, duration, and peak power amount to 81 microJ, 25 ns, and 3.24 kW, respectively.
5.63 and 5.80 MeV levels of Ne20; de-excitation branching
Abstract The ratio Г γ /Г for the 5.63 and 5.80 MeV levels of Ne 20 has been determined to be 0.077 (±0.008) and −4 , respectively, by using the C 12 (C 12 , α)Ne 20 reaction and determining the fraction of the events in which the alpha-particle and the Ne 20 recoil are present in coincidence at the kinematically correct angles. In both cases these results in themselves are shown to imply radiative E1 transition (5.63→1.63 and 5.80→0, respectively) probabilities ⪡5 × 10 −5 Weisskopf units. When taken together with the life-time for the 5.63 MeV level measured by Evans et al . values of Г( E1 ) ≲ 5 × 10 −6 and Г α ≈ 6% of the particle estimate are obtained for this state.