Third and fifth harmonics generation by tightly focused femtosecond pulses at 2.2 {\mu}m wavelength in air

摘要

We report experiments on the generation of third and fifth harmonics ofmillijoule-level, tightly focused, femtosecond laser pulses at 2.2 {\mu}mwavelength in air. The measured ratio of yields of the third and fifthharmonics in our setup is about 2 \cdot 10-4. This result contradicts therecent suggestion that the Kerr effect in air saturates and changes sign inultra-intense optical fields.