Energetic, tunable, highly-elliptically polarized higher harmonics generated by intense two-color counter rotating laser fields

Abstract: In this work, we demonstrate experimentally the efficient generation and tunability of energetic highly-elliptical high-harmonics in Ar gas, driven by intense two-color counter rotating laser electric fields. A bi-chromatic beam tailored by a MAZEL-TOV apparatus generates HHG, where the output spectrum of the highly elliptical HHG radiation can be tuned for a energy range of \DeltaE\HF150meV in the spectral range of ~20 eV with energy per pulse EXUV~400 nJ at the source. Furthermore we employ time-dependent density functional simulations to probe in-depth the dependence of the harmonic ellipticity and the strength of the isolated atto pulses on the driving field parameters and demonstrate the robustness of the HHG with the bichromatic field. We show how by properly tuning the central frequency of the second harmonic, the central frequency of the extreme ultraviolet (XUV) high harmonic radiation is continuously tuned. The demonstrated energy values largely exceed the output energy from many other laser driven attosecond sources reported so far and prove to be sufficient for inducing (along with tight XUV focusing geometries) the nonlinear processes in the atomic system. We envisage that such tunable energetic highly-elliptical HHG spectra can remove the facility restrictions from requirements of few-cycle driving pulses for isolated circular attosecond pulse generation.