Abstract
We theoretically explore a scheme for generation of bright circularly and elliptically polarized high-order harmonics by bursts of linearly polarized pulses with a rotating polarization axis. Circularly polarized harmonics are formed if the bursts are comprised of N pulses that uphold an N-fold rotational symmetry, for N > 2. Rotating the polarization axes of the comprising pulses can generate elliptical harmonics with a collectively tunable ellipticity, from circular through elliptic to linear. The method preserves the single-cycle, single-atom and macroscopic physics of ‘standard’ linearly polarized high harmonic generation, with a high yield and cutoff energy. We investigate the method from a time-domain perspective, as well as a photonic perspective, and formulate the energy and spin-angular momentum conservation laws for this scheme. We find that the case of N = 4 is optimal for this method, resulting with the highest conversion efficiency of elliptical photons. The new features of this source offer new applications to helical ultrafast spectroscopy and ellipsometry.
Highlights
High harmonic generation (HHG) is a nonlinear process in which intense laser radiation interacts with matter to emit extreme UV and X-ray coherent light [1,2]
The burst in total contains M repetitions of TN long cycles, and each of the individual linearly-polarized pulses is separated by a time τ from the such that the overall period of the dynamical symmetries (DSs) is given in Equation (5), where T is the cycle of the optical frequency T = 2π/ω0
In Reference [38] we showed this is the case for N = 3, but generally a similar approach can be used for an arbitrary amount of pulses, N
Summary
High harmonic generation (HHG) is a nonlinear process in which intense laser radiation interacts with matter to emit extreme UV and X-ray coherent light [1,2]. Linearly polarized HHG schemes driven by linearly polarized pulses, the conversion efficiency and cutoff energy of circular HHG are smaller Overcoming these limitations could have applications in coherent control, and ultrafast spectroscopy of chiral processes. We theoretically proposed and demonstrated numerically a new scheme for generation of bright circularly and elliptically polarized high harmonics [38]. In this scheme, the HHG process is driven by a burst of linearly polarized quasi-monochromatic pulses with rotating polarization axes. The only small coupling is manifested by the appearance of new ‘previously forbidden’ harmonic peaks, which radiate with a relatively low intensity This scheme allows to fully control the polarization of the harmonics while largely preserving the single-cycle, single-atom and macroscopic physics of ‘standard’.
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