  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.
