RESUMO
To practically predict the design criteria of diode-end-pumped passively Q-switched (PQS) lasers with energy scaling to millijoule region, an analytical model with longitudinally spatial dependence is derived to investigate the influence of pump beam quality. In comparison with PQS theory that considers transverse spatial dependence only, it is found that the threshold pump power can be up to 5 times larger when the beam quality factor was 80. This result indicates the importance of considering pump beam quality when designing PQS lasers especially for operation at high pump power level. The theoretical results are verified by a series of PQS experiments. The influence of thermal lensing effect on cavity design is further discussed to obtain good laser quality. Finally, an end-pumped millijoule PQS laser is successfully realized based on the theoretical analysis and the resonator design.
RESUMO
Controlling the chemo- and regioselectivity of transition-metal-catalyzed C-C activation remains a great challenge. The transformations of benzocyclobutenones (BCBs) usually involve the cleavage of C1-C2 bond. In this work, an unprecedented highly selective cleavage of C1-C8 bond with the insertion of alkynes is achieved by using blocking strategy via Ni catalysis, providing an efficient method for synthesis of 1,8-disubstituted naphthalenes. Notably, the blocking group could be readily removed after the transformation.
RESUMO
Di- and multinuclear hafnium complexes bridged by ligands have been rarely reported. In this article, a novel 3,5-disubstituted pyrazolate-bridged ligand LH5 with two [N2 N]2- -type chelating side arms was designed and synthesized, which supported a series of dinuclear hafnium complexes. Dinuclear hafnium azides [LHf2 (µ-1,1-N3 )2 (N3 )2 ][Na(THF)4 ] 3 and [LHf2 (µ-1,1-N3 )2 (N3 )2 ][Na(2,2,2-Kryptofix)] 4 were further synthesized and structurally characterized, featuring two sets of terminal and bridging azido ligands like jellyfishes. The reactivity of 3 under reduction conditions was conducted, leading to a formation of a tetranuclear hafnium imido complex [L1 Hf2 (µ1 -NH)(N3 ){µ2 -K}]2 5. DFT calculations revealed that the mixed imido azide 5 was generated via an intramolecular C-H insertion from a putative dinuclear HfIV -nitridyl intermediate.