MPI	multiphoton ionization
$\mathcal{E}$	electrical field envelop
${\omega }_0$	carrier wave frequency
c	speed of light in air
$w_0$	beam radius
$w_f$	beam waist
$z_f$	Rayleigh length
$t_p$	FWHM pulse duration
k	wavenumber
f	beam curvature
$n_2$	nonlinear refractive index
$P_{cr}$	critical power for self focusing
$\sigma$	cross section for inverse bremsstrahlung process
${\tau }_c$	electron collision time
${\rho }_c$	critical plasma density
$U_i$	band gap
$\gamma$	Keldysh parameter
$W_{PI}$	photon ionization rate
${\sigma }_4$	cross section for multiphoton ionization
$\eta$	avalanche ionization coefficient
${\rho }_{at}$	background atom density
${\tau }_r$	electron recombination time