Abstract
With the development of intense femtosecond laser sources it has become possible to study atomic and molecular processes on their own subfemtosecond time scale. Table-top setups are available that generate intense coherent radiation in the extreme ultraviolet and soft-X-ray regime which have various applications in strong-field physics and attoscience. More recently, the emphasis is moving from the generation of linearly polarized pulses using a linearly polarized driving field to the generation of more complicated elliptically polarized polychromatic ultrashort pulses. The transverse electromagnetic field oscillates in a plane perpendicular to its propagation direction. Therefore, the two dimensions of field polarization plane are available for manipulation and tailoring of these ultrashort pulses. We present a field that allows such a tailoring, the so-called bicircular field. This field is the superposition of two circularly polarized fields with different frequencies that rotate in the same plane in opposite directions. We present results for two processes in a bicircular field: High-order harmonic generation and above-threshold ionization. For a wide range of laser field intensities, we compare high-order harmonic spectra generated by bicircular fields with the spectra generated by a linearly polarized laser field. We also investigate a possibility of introducing spin into attoscience with spin-polarized electrons produced in high-order above-threshold ionization by a bicircular field.
Highlights
Three-Step Model and Bicircular Laser FieldAvailable strong laser fields allow the study of new laser-field-induced atomic and molecular processes such as high-order harmonic generation (HHG) [1] and above-threshold ionization (ATI) [2].These processes are commonly considered for a laser field which is linearly polarized and explained by semiclassical three-step model [3,4,5]
We investigate a possibility of introducing spin into attoscience with spin-polarized electrons produced in high-order above-threshold ionization by a bicircular field
According to this model the electron, liberated in tunnel ionization, moves driven by the laser field and returns to the parent core where it recombines emitting a high-harmonic photon in the HHG process or rescatters and is detected having much larger energy in the high-order ATI (HATI) process
Summary
Available strong laser fields allow the study of new laser-field-induced atomic and molecular processes such as high-order harmonic generation (HHG) [1] and above-threshold ionization (ATI) [2]. These processes are commonly considered for a laser field which is linearly polarized and explained by semiclassical three-step model [3,4,5] According to this model the electron, liberated in tunnel ionization, moves driven by the laser field and returns to the parent core where it recombines emitting a high-harmonic photon in the HHG process or rescatters and is detected having much larger energy in the high-order ATI (HATI) process. Let us explain this three-step model in more detail using Figure 1. +1 are stronger than that of helicity −1 (and vice versa), i.e. if we, by some means, achieve helicity
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