ROLE OF THE PLASMA SCALE LENGTH IN THE HARMONIC-GENERATION FROM SOLIDTARGETS

We have investigated the generation of high harmonics from the interac tion of 150 fsec, 790 nm, and 395 nm laser pulses with solid targets. Experiments are presented that demonstrate a strong dependence of the conversion efficiency on the temporal pulse shape and the resulting de nsity scale length (L/lambda) of the preformed plasma. The highest con version efficiencies are achieved for short density scale lengths (L/l ambda less than or equal to 0.4), which result from high contrast rati o pulse interactions. [S1063-651X(98)50211-5].