This chapter discusses the spatiotemporal evolution dynamics of a tightly focused femtosecond laser filament with a carrier wavelength of 1.3 μm in the air using a plasma fluorescence imaging technique. The filament properties such as a function of different external focusing conditions and their associated supercontinuum (SC) spectra have been reported here. Our observation shows that filament generation conditions appreciably influence the temporal and spatial characteristics of filaments. The tightly focused filament shows an average of 6 times higher persistence time than the loosely focused filament. Additionally, the shorter focusing condition significantly broadens the supercontinuum spectra, whereas no SC is observed relatively at a larger focusing geometry. Instead, the spectrum is dominated solely by third-harmonic (TH) signals. Furthermore, we study the impact of input power on the filament properties using the 800 nm laser pulse. The results indicate that filament lifetime and length increase with pump pulse energy, whereas no significant changes are observed in the filament diameter.
