We propose a simple pump-coupling-seed scheme to examine the optical X^2Σg^+–A^2Πu coupling in N2^+ lasing. We produce the N2^+ lasing at 391 nm, corresponding to the B^2Σu^+(v = 0)–X^2Σg+(v = 0) transition, by ...We propose a simple pump-coupling-seed scheme to examine the optical X^2Σg^+–A^2Πu coupling in N2^+ lasing. We produce the N2^+ lasing at 391 nm, corresponding to the B^2Σu^+(v = 0)–X^2Σg+(v = 0) transition, by externally seeding the N^2+ gain medium prepared by irradiation of N2 with an intense pump pulse. We then adopt a weak coupling pulse in between the pump and seed pulses, and show that the intensity of the 391-nm lasing can be efficiently modulated by varying the polarization direction of the coupling pulse with respect to that of the pump pulse. It is found that when the polarization directions of the pump and coupling pulses are perpendicular, the 391-nm lasing intensity is more sensitive to the coupling laser energy, which reflects the inherent nature of the perpendicular X^2+Σg^–A^2Πu transition.展开更多
Laser ignition(LI)allows for precise manipulation of ignition tinning and location and is promising for green combustion of automobile and rocket engines and aero-turbines under lean-fuel conditions with improved emis...Laser ignition(LI)allows for precise manipulation of ignition tinning and location and is promising for green combustion of automobile and rocket engines and aero-turbines under lean-fuel conditions with improved emission efficiency;however,achieving completely effective and reliable ignition is still a challenge.Here,we report the realization of igniting a lean methane/air mixture with a 100%success rate by an ultrashort femtosecond laser,which has long been regarded as an unsuitable fuel ignition source.We demonstrate that the minimum ignition energy can decrease to the sub-mJ level depending on the laser filamentation formation,and reveal that the resultant early OH radical yield significantly increases as the laser energy reaches the ignition threshold,showing a clear boundary for misfire and fire cases.Potential mechanisms for robust ultrashort LI are the filamentation-induced heating effect followed by exothermal chemical reactions,in combination with the line ignition effect along the filament.Our results pave the way toward robust and efficient ignition of lean-fuel engines by ultrashort-pulsed lasers.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61625501,11904121,and 61427816)the Open Fund of the State Key Laboratory of High Field Laser Physics(SIOM),China+1 种基金the Program for JLU Science and Technology Innovative Research Team(JLUSTIRT),China(Grant No.2017TD-21)Fundamental Research Funds for the Central Universities of China
文摘We propose a simple pump-coupling-seed scheme to examine the optical X^2Σg^+–A^2Πu coupling in N2^+ lasing. We produce the N2^+ lasing at 391 nm, corresponding to the B^2Σu^+(v = 0)–X^2Σg+(v = 0) transition, by externally seeding the N^2+ gain medium prepared by irradiation of N2 with an intense pump pulse. We then adopt a weak coupling pulse in between the pump and seed pulses, and show that the intensity of the 391-nm lasing can be efficiently modulated by varying the polarization direction of the coupling pulse with respect to that of the pump pulse. It is found that when the polarization directions of the pump and coupling pulses are perpendicular, the 391-nm lasing intensity is more sensitive to the coupling laser energy, which reflects the inherent nature of the perpendicular X^2+Σg^–A^2Πu transition.
基金The work is supported in part by the National Natural Science Foundation of China(61625501 and 62027822)the Open Fund of the State Key Laboratory of High Field Laser Physics(SIOM).
文摘Laser ignition(LI)allows for precise manipulation of ignition tinning and location and is promising for green combustion of automobile and rocket engines and aero-turbines under lean-fuel conditions with improved emission efficiency;however,achieving completely effective and reliable ignition is still a challenge.Here,we report the realization of igniting a lean methane/air mixture with a 100%success rate by an ultrashort femtosecond laser,which has long been regarded as an unsuitable fuel ignition source.We demonstrate that the minimum ignition energy can decrease to the sub-mJ level depending on the laser filamentation formation,and reveal that the resultant early OH radical yield significantly increases as the laser energy reaches the ignition threshold,showing a clear boundary for misfire and fire cases.Potential mechanisms for robust ultrashort LI are the filamentation-induced heating effect followed by exothermal chemical reactions,in combination with the line ignition effect along the filament.Our results pave the way toward robust and efficient ignition of lean-fuel engines by ultrashort-pulsed lasers.
