Reliable laser ablation ignition of combustible gas mixtures by femtosecond filamentating laser

Abstract

Laser ablation ignition is an efficient approach in igniting lean-fuels with significantly reduced minimum pulse energy (MPE), but it requires a precise position control between the laser focal spot and the target surface, and is hardly for long-term use due to laser-induced surface damage. Here we adopt femtosecond filamentating laser to ablate a tantalum target for igniting a premixed methane-air mixture, and demonstrate the experimental realization of lean-fuel ignition over 1-m distance with 100 % success rate and ultralow MPE at ∼1 mJ. We further show that this technique is insensitive to the ablator position and can operate at a durable time with a little amount (∼80 ng/pulse) of sample removal from the target surface. By characterizing the evolution of flame kernel using time-resolved spectroscopy, we clarify the ultralow MPE ignition mechanism, in which the exothermal chemical reactions occurring inside the plasma filament effectively extends the kernel reaction zone, resulting in a plasma-channel-assisted ablation ignition.