Influence of ambient air pressure on the energy conversion of laser-breakdown induced blast waves

摘要

Influence of ambient pressure on energy conversion efficiency from a Nd: glass laser pulse (λ = 1.053 μm) to a laser-induced blast wave was investigated at reduced pressure. Temporal incident and transmission power histories were measured using sets of energy meters and photodetectors. A half-shadowgraph half-self-emission method was applied to visualize laser absorption waves. Results show that the blast energy conversion efficiency η_(bw) decreased monotonically with the decrease in ambient pressure. The decrease was small, from 40% to 38%, for the pressure change from 101 kPa to 50 kPa, but the decrease was considerable, to 24%, when the pressure was reduced to 30 kPa. Compared with a TEA-CO_2-laser-induced blast wave (λ = 10.6 μm), higher fraction absorption in the laser supported detonation regime η_(LSD) of 90% was observed, which is influenced slightly by the reduction of ambient pressure. The conversion fraction η_(bw)/η_(LSD)≈90% was achieved at pressure >50 kPa, which is significantly higher than that in a CO_2 laser case.