Summary form only given. A high intensity laser pulse propagates through the H2-gas filled capillary discharge waveguide with parabolic radial electron density profile. The capillary comprises of alumina tube. Laser causes rapid tunnel ionization of aluminium (ionization potential /spl sim/5.986 V) and oxygen (ionization potential /spl sim/13.6 V) introduced into the plasma from the capillary wall. The increasing plasma density leads to a decreasing refractive index, modulating the phase of the laser as it propagates and causing frequency upshift of the laser.