Abstract
A fundamental phenomenon of coherent control is investigated theoretically using the example of neon photoionization by the bichromatic field of a free-electron laser. A system exposed to coherent fields with commensurable frequencies loses some symmetry, which manifests itself in the angular distribution and spin polarization of the electron emission. We predict several such effects, for example, the violation of symmetry with respect to the plane perpendicular to the polarization vector of the second harmonic and the appearance of new components of spin polarization. Furthermore, we predict a very efficient control of spin polarization via manipulation of the phase between the harmonics. Experimental observation of these effects is accessible with modern free-electron lasers operating in the extreme ultraviolet wavelength regime.
Highlights
Spin is a fundamental property of particles and plays a crucial role at any level of matter from elementary particles to macroscopic objects, such as magnets and even white dwarfs
The spin polarization may be controlled by changing relative strength and phase of the two harmonics in the ω + 2ω ionization, taking advantage of the two ionization pathways: single photon ionization by the second harmonic 2ω and two-photon ionization by the first harmonic ω
Iω = 1012 W/cm2, while the intensity of the second harmonic was chosen as 0.1% of the fundamental
Summary
Spin is a fundamental property of particles and plays a crucial role at any level of matter from elementary particles to macroscopic objects, such as magnets and even white dwarfs. Similar symmetries occur for one circularly polarized and another for linearly polarized harmonics, when the direction of the former beam is along the electric field of the latter In this case, the electric field vector points out of the reaction plane. The spin polarization may be controlled by changing relative strength and phase of the two harmonics in the ω + 2ω ionization, taking advantage of the two ionization pathways: single photon ionization by the second harmonic 2ω and two-photon ionization by the first harmonic ω We analyzed these effects in the ω + 2ω process for collinear circularly polarized beams and linearly polarized beams with parallel electric field vectors on the example of the neon atom in the region of the 2p6 –2p5 4s, 4s0 , 3d excitations [22]. The harmonic intensity ratio is chosen differently for different panels for better visualization
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