Multiple filamentation of supercritical UV laser beam in atmospheric air

Kerr self-defocusing of multiple filaments in TW peak power UV laser beam

“…This effect clearly manifests itself when we used a four-pass amplification scheme in the preamplifier BERDYSH and the USP beam arriving to the main amplifier entrance had been already multiply filamented [15]. Finally formed filaments have a typical diameter in the range 240 ÷ 340 µm (FWHM) and transport high peak intensity of I f ~ 0.2 TW cm −2 and energy fluence ε f ~ 0.2 J cm −2 , which are higher than in the background radiation by a factor of 200 [12][13][14]. A limiting fluence of the USP being amplified in KrF medium is rather low…”

“…In contrast to [3][4][5][6][7][8], in our previous experiments at the sub-TW peak power UV GARPUN-MTW Ti:sapphire/KrF laser facility [9], laser beam was substantially unstable. Multiple filamentation arose [10][11][12][13] being managed by a coherent stimulated Raman scattering (SRS) at rotational transitions of atmospheric nitrogen [14]. Beam filamentation saturated the attained USP energy and was responsible for optics degradation [15].…”

HV discharge acceleration by sequences of UV laser filaments with visible and near-infrared pulses

“…The multiphoton ionization is therefore more efficient at shorter wavelengths, which results in much higher plasma densities in the case of an ultraviolet laser [17,18]. Furthermore, they produce a more homogeneous plasma channel than their near-infrared counterpart [19], and can give rise to similar multiple filamentation patterns [20] that provide numerous filaments in parallel, adding up their conductivities. Indeed, the first proposal to guide lightning using ultrashort lasers focused on ultraviolet lasers [21].…”