Observation of single high-harmonic enhancement by quasi-resonance with a tellurium ion in a laser-ablation plume at 2944 nm

Abstract

We demonstrate the intensity enhancement of a single high-order harmonic (27th harmonic) at 29.44 nm by using lowly charged tellurium ions in a laser-ablation plume. The enhancement of a single harmonic is due to multiphoton resonance with a Te II transition having strong oscillator strength. By tuning the wavelength of the pump laser, we found that the enhancement factor depends on the difference between the wavelength of the enhanced harmonic and that of the strong radiative transition. For tellurium, we show that intense single harmonic generation can be generated when the wavelength of the 27th harmonic is closer to the wavelength of the strong transition.