Temporally Resolved Properties of Femtosecond Laser-Induced Plasmas in Air

We present the temporally resolved measurements of electron number density and temperature over timescales on the order of \(1\) ns to \(10\) ns in a femtosecond (fs) laser-induced plasma (LIP). Additionally, we also report on the neutral gas number density and rotational temperature over timescales on the order of $1$ ns to \(1000\) ns. The fs LIP was generated in ambient air and investigated using laser Thomson and rotational Raman scattering. Electron number densities were observed to decrease from \(\sim10^{21}\) m\(^{-3}\) at early times to \(\sim10^{20}\) m$^{-3}$ at later times, while the electron temperature remained within \(0.5-1\) eV throughout the probed range. The neutral gas number density remained nearly constant at \(\sim2\times10^{25}\) m$^{-3}$ for the first \(50\) ns before declining to \(\sim1.1\times10^{25}\) m$^{-3}$ after \(500\) ns. The rotational temperature initially decreased from \(\sim700\) K within the first \(30\) ns to \(\sim500\) K at \(100\) ns, before rising back to $\sim700$ K. Finally, the experimental results were compared with simulations, showing good agreement.