Laser-induced Energy Deposition for Active Flow Control

Abstract

Proved by numerous studies, the laser-induced energy deposition is applied for wave drag reduction in supersonic flow. Due to the optical air breakdown threshold of about 10ˆ9W/cm² (for CO2-laser radiation in atmospheric conditions), the experimental realisation nowadays is still restricted to the pulsed regime of solid-state and gas laser systems (ns- to µs time domains). A reasonable use of this flow control principle requires the increase of deposited energy in air. In a laser breakdown application, the phase shift determines the energy absorption. The measured phase shift, realized by a Nomarski interferometer setup, indicates the electron density of the laser induced air breakdown. Numerical, 3-dimensional spatial and temporal simulations of focused pulse propagation in air are compared with the experimental measurements of the electron density in the breakdown region. Furthermore, scaling ideas for prospective laser breakdown experiments to reduce the wave drag will be presented. In the near future, a laboratory experiment is planned to align a pulsed (ns-regime) and a continuous wave (kW-regime) laser system in order to initialize and extend the laser-induced plasma.