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).
Kerr-Lens Mode-Locked Diode-Pumped Yb:YAG Laser with the Transverse Mode Passively Stabilized
We have developed a Kerr-lens mode-locked diode-pumped Yb:YAG laser in which the transverse mode is passively stabilized. The mode-locking scheme can be used for various diode-pumped Yb-doped bulk lasers. The pulse duration is as short as 100 fs, which is to our knowledge the shortest pulse ever produced from an Yb:YAG laser. The center wavelength and laser output power are 1051 nm and 151 mW, respectively.
Experimental Study for a Double-Glazed Forced-Flow Solar Collector/Regenerator
Experimental study of a double-glazed forced-convection solar collector/regenerator for absorption solar cooling is presented. The south facing experimental solar collector/regenerator with 10 deg slope is located at Kaohsiung, Taiwan at 120{degree}19minutesE longitude and 22{degree}34minutesN latitude. The size of the collector is 1 m wide and 7 m long with an effective regeneration area of 0.9 m by 6 m. Previous study for single-glazed forced-convection solar collector/regenerator operated at the same location has shown to have a best day-average efficiency of 17%. In order to raise the system performance, a double-glazed collector/regenerator is constructed such that air can be preheated in the upper channel flow. The preheated air is then conducted into the lower channel where it contacts with the film flow of solar heated lithium-chloride solution and regenerates the solution by carrying out the evaporated water vapor. The preheated air has lower relative humidity but the same humidity ratio since it is sensibly heated. Therefore, the regeneration driving potential is increased. The present study shows that the best day-average efficiency can reach 20% which increases the feasibility of the open-cycle absorption solar cooling system. Effects of controlling parameters on the collector/regenerator performance are studied, and heat and mass transfer correlationsmore » are also presented for design purposes.« less