AMPLIFICATION OF HARMONICS GENERATED BY WAVE MIXING

We present the results dealing with the harmonic generation in N-2 and Ar produced by wave mixing of parallel-polarized fundamental and seco nd harmonics of a Nd-YAG picosecond laser. The wave-mixing scheme enha nces the conversion efficiency and is barely affected by phase mismatc h of pump fields in a large range of gas density. Particularly, in thi s work, we compare the dependence of conversion efficiency on the focu sing conditions of pump fields. We show that an enhancement up to abou t two orders of magnitude can be achieved when the foci of pump fields are kept coincident by an achromatic lens.