High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for femtosecond laser-induced subwavelength periodic surface structures on silicon.Femtosecond laser micromach...High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for femtosecond laser-induced subwavelength periodic surface structures on silicon.Femtosecond laser micromachining is no longer a nonthermal process,as long as the repetition rate reaches up to 100 kHz due to heat accumulation.Moreover,a higher repetition rate generates much better defined ripple structures on the silicon surface,based on the fact that accumulated heat raises lattice temperature to the melting point of silicon(1687 K),with more intense surface plasmons excited simultaneously.Comparison of the surface morphology on repetition rate and on the overlapping rate confirms that repetition rate and pulse overlapping rate are two competing factors that are responsible for the period of ripple structures.Ripple period drifts longer because of a higher repetition rate due to increasing electron density;however,the period of laser structured surface is significantly reduced with the pulse overlapping rate.The Maxwell–Garnett effect is confirmed to account for the ripple period-decreasing trend with the pulse overlapping rate.展开更多
Issue on illegal logging and related trade is a hot topic for the international community. It has brought the negative effects to the sustainable development on global society, economy and ecology, which is also one o...Issue on illegal logging and related trade is a hot topic for the international community. It has brought the negative effects to the sustainable development on global society, economy and ecology, which is also one of the main objectives of international cooperation to combat with. At present, subjects of international law play a decisive role in combating illegal logging and related trade. The subjects of international law generally refer to states, intergovernmental organizations (IGOs) and part of non-governmental organizations (NGOs), which can have an independent international legal personality, enjoy rights and assume obligations of international law. As a responsible big country of the international community and state member of intergovernmental organizations and international treaties of forest resources protection, China ought to fully perform the obligations of international law. In face of illegal logging and related trade around the world, China should rationally tackle with it, resolutely crack down on it, and finally choose the sustainable development strategy based on rule of law.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52175377 and 12174411)。
文摘High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for femtosecond laser-induced subwavelength periodic surface structures on silicon.Femtosecond laser micromachining is no longer a nonthermal process,as long as the repetition rate reaches up to 100 kHz due to heat accumulation.Moreover,a higher repetition rate generates much better defined ripple structures on the silicon surface,based on the fact that accumulated heat raises lattice temperature to the melting point of silicon(1687 K),with more intense surface plasmons excited simultaneously.Comparison of the surface morphology on repetition rate and on the overlapping rate confirms that repetition rate and pulse overlapping rate are two competing factors that are responsible for the period of ripple structures.Ripple period drifts longer because of a higher repetition rate due to increasing electron density;however,the period of laser structured surface is significantly reduced with the pulse overlapping rate.The Maxwell–Garnett effect is confirmed to account for the ripple period-decreasing trend with the pulse overlapping rate.
文摘Issue on illegal logging and related trade is a hot topic for the international community. It has brought the negative effects to the sustainable development on global society, economy and ecology, which is also one of the main objectives of international cooperation to combat with. At present, subjects of international law play a decisive role in combating illegal logging and related trade. The subjects of international law generally refer to states, intergovernmental organizations (IGOs) and part of non-governmental organizations (NGOs), which can have an independent international legal personality, enjoy rights and assume obligations of international law. As a responsible big country of the international community and state member of intergovernmental organizations and international treaties of forest resources protection, China ought to fully perform the obligations of international law. In face of illegal logging and related trade around the world, China should rationally tackle with it, resolutely crack down on it, and finally choose the sustainable development strategy based on rule of law.