Influence of focal point properties on energy transfer and plasma evolution during laser ignition process with a passively q-switched laser

Abstract

Miniaturized passively q-switched laser ignition systems are a promising alternative to conventional ignition sources to ensure a reliable ignition under difficult conditions. In this study the influences of focal point properties on energy transfer from laser to plasma as well as plasma formation and propagation are investigated as the first steps of the laser induced ignition process. Maximum fluence and fluence volume are introduced to characterize focal point properties for varying laser pulse energies and focusing configurations. The results show that the transferred laser energy increases with increasing maximum fluence. During laser emission plasma propagates along the beam path of the focused laser beam. Rising maximum fluence results in increased plasma volume, but expansion saturates when fluence volume reaches its maximum.

Investigating the Threshold Conditions of Air Breakdown with Mode-Locked Q-Switched Laser Pulses, and the Temporal Dynamics of Induced Plasma with Self-Scattering Phenomenon

“…A few reports also propose that it is adequate to determine the breakdown threshold by the laser power intensity for taking the focused laser beam radius into account [18,22,23]. The thresholds of LIBs under different experimental conditions-such as laser wavelengths [24], pulse durations [25], gas pressures [26], compositions of gas molecules [27], and focal point properties [28,29]-have been widely investigated. Due to the limitation of the response time of photodetectors, the temporal shapes of laser pulses were usually assumed to have Gaussian-like profiles for calculating the breakdown intensities in most works of literature [19,20].…”