Production and characterization of a fully ionized He plasma channel

We report guiding of intense (I=1.3 +/-0.7x10(17) W/cm(2)) 80 fs laser puls es with negligible spectral distortion through 1.5-cm-long preformed helium plasma channels. Channels were formed by axicon-focused laser pulses of ei ther 0.3 J energy, 100 ps duration, after preionizing a 200-700 Torr backfi ll of He gas to n(e)similar to 10(16) cm(-3) with a pulsed electrical disch arge; or 0.6-1.1 J energy, 400 ps duration, which required neither preioniz ation nor intentional impurities for seeding. Transverse interferometry sho wed that He was fully ionized on the channel axis in both cases. Identical femtosecond pulses suffered substantial ionization-induced blueshifts after propagating through Ar and Ne channels of similar dimensions. (C) 2000 Ame rican Institute of Physics. [S0003-6951(00)04648-9].