Abstract
This work presents density, spectroscopic temperature, and shockwave measurements of laser induced breakdown plasma in atmospheric air by subthreshold intensity (5.5×109 W/cm2) 193 nm laser radiation. Using molecular spectroscopy and two-wavelength interferometry, it is shown that substantial ionization (>1016 cm−3) occurs that is not predicted by collisional cascade (CC) breakdown theory. While the focused laser irradiance is three orders of magnitude below the theoretical collisional breakdown threshold, the substantial photon energy at 193 nm (6.42 eV/photon) compared with the ionization potential of air (15.6 eV) significantly increases the probability of multiphoton ionization effects. By spectroscopically monitoring the intensity of the N2+ first negative system (B Σu+2−X Σg+2) vibrational bandhead (v′=0,v″=0) at low pressure (20 Torr) where multiphoton effects are dominant, it is shown that two photon excitation, resonant enhanced multiphoton ionization is the primary mechanism for quantized ionization of N2 to the N2+(B Σu+2) state. This multiphoton effect then serves to amplify the collisional breakdown process at higher pressures by electron seeding, thereby reducing the threshold intensity from that required via CC processes for breakdown and producing high density laser formed plasmas.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
