An enhancement of the He2+ yield near the appearance intensity was not
observed by linearly polarized KrF laser light (248 nm), whereas a si
gnificant enhancement was observed by linearly polarized Ti:sapphire l
aser light (745 nm). These results are consistent with the quasistatic
model proposed by Corkum [Technical Digest of Short Wavelength V: Phy
sics with Intense Laser Pulses (Optical Society of America, Washington
, DC, 1993), p. 25].