Very High Order Harmonic Conversion of an Intense Yag Laser Radiation in Rare Gases

Abstract

An atom exposed to a strong laser field can absorb a large number of photons through high-order nonlinear processes. This leads to the production of multiply charged ions and electrons with energies much larger than the energy expected for a N₀-photon absorption (ATI processes)¹But the energy absorbed by the atomic system may be also transfered back to the photon field under the form of energetic photons with energy Nhv, hv being the laser photon energy, and N the number of photons absorbed. Due to the poor collection efficiency of the photon detection, photon experiments require to be performed at relatively high atomic densities, typically 10¹⁷ to 10¹⁸ atoms/cm³, about 10 to 20 Torr. At such high pressures, the laser light interacts with a collective assembly of atoms. Provided the medium has the required pressure and geometrical properties for proper phase matching of the generated radiation, one may expect production of high-order harmonics of the laser field^2,3 The purpose of the present paper is to describe experimental measurements of VUV light emission (355 – 30 nm) and in particular harmonic generation in a rare gas medium irradiated by an intense 1064 nm laser field.