Coupling between exiting wavefront error of space gravitational wave telescopes and tilt-to-length (TTL) noise affects the measurement accuracy. Using the LISA Pathfinder signal, we analyzed cancellation and superposition of TTL coupling noise under various optical aberrations. We proposed proportion requirements of any two aberrations amplitude when noise was cancelled and an aberration amplitude control requirement when noise was superposed. Taking them as the aberration control requirements of gravitational wave telescope optical system, the exiting wavefront error requirements was reduced while suppressing the TTL coupling noise. A 40× optical telescope system with detection aperture φ=200 mm was designed. The exiting wavefront error was relaxed from 0.02 λ to 0.0496 λ. The maximum coupling coefficient value did not exceed 6.9448 pm/µrad within a pointing jitter angle of ±300 µrad. The proposed approach should be useful in future telescope design.
In this paper, we propose a novel design of dielectric laser-driven accelerator (DLA) utilizing evanescent electric field of racetrack ring resonator structures. Driven by laser light with the correctly designed optical phase window, sustained acceleration of electrons with controlled deflection is shown. Based on this design, we calculate an acceleration from 30 keV to 148.312 keV in 104.655 μm using a cascaded 11-stage racetrack ring resonators. This new idea poses a solution for on-chip integration of many DLA stages, while maintains high average accelerating gradients, providing a potential practical realization for "accelerator on a chip".
Superposition of two independent orthogonally polarized beams is a conventional principle of creating a new light beam. Here, we intend to achieve the inverse process, namely taking inherent polarization modes out from one single light beam. However, inherent polarization modes within a light beam are always entangled together so that a stable polarization is maintained during propagating in free space. To overcome this limitation, we report an approach that breaks down the modulation symmetry of light beam, thereby disentangling the inherent polarization modes. Using polarization mode competition along with the optical pen, polarization modes are extracted at will in the focal region of an objective lens. This work demonstrates the polarization mode extraction of light beam, which will not only provide an entirely new principle of polarization modulation, but also pave ways for multi-dimensional manipulation of light field, thereby facilitating extensive developments in optics.
Superposition of two independent orthogonally polarized beams is a conventional principle of creating a new light beam. Here, we intend to achieve the inverse process, namely, extracting inherent polarization modes from a single light beam. However, inherent polarization modes within a light beam are always entangled so that a stable polarization is maintained during propagation in free space. To overcome this limitation, we report an approach that breaks the modulation symmetry of a light beam, thereby disentangling the inherent polarization modes. Using polarization mode competition along with an optical pen, polarization modes are extracted at will in the focal region of an objective lens. This work demonstrates polarization mode extraction from a light beam, which will not only provide an entirely new principle of polarization modulation but also pave the way for multidimensional manipulation of light fields, thereby facilitating extensive developments in optics.
As a major component in the air, nitrogen emits fluorescence when it interacts with intensive laser field. The fluorescence comes from the first negative band system (<inline-formula><tex-math id="M7">\begin{document}${{\rm{B}}^{{2}}}\Sigma _{\rm{u}}^{{ + }} \to {{\rm{X}}^{{2}}}\Sigma _{\rm{g}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M7.png"/></alternatives></inline-formula> transition) of <inline-formula><tex-math id="M8">\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M8.png"/></alternatives></inline-formula> and the second positive band system (<inline-formula><tex-math id="M9">\begin{document}${{\rm{C}}^{{3}}}\Pi _{\rm{u}}^{{ + }} \to {{\rm{B}}^{{3}}}\Pi _{\rm{g}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M9.png"/></alternatives></inline-formula> transition) of <inline-formula><tex-math id="M10">\begin{document}${{\rm{N}}_{{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M10.png"/></alternatives></inline-formula>. Under the action of high-intensity femtosecond laser, <inline-formula><tex-math id="M11">\begin{document}${{\rm{N}}_{{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M11.png"/></alternatives></inline-formula> can be directly photo-ionized into <inline-formula><tex-math id="M12">\begin{document}${\rm{N}}_{{2}}^{{ + }}{{(}}{{\rm{B}}^{{2}}}\Sigma _{\rm{u}}^{{ + }})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M12.png"/></alternatives></inline-formula>, which results in fluorescence emission of <inline-formula><tex-math id="M13">\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M13.png"/></alternatives></inline-formula>. In the process of femtosecond laser filament formation, the dynamic processes such as ionization and excitation of nitrogen molecules are affected by the laser intensity distribution and laser polarization direction. The products show different distributions in the propagation direction and radial space, which, in turn, affects its light emission. Therefore, it is necessary to further ascertain its generation mechanism through the spatial distribution of nitrogen fluorescence. In this experiment, the spatial distribution of the nitrogen fluorescence emission generated by linearly polarized femtosecond laser pulse filaments in air is measured. By changing the polarization direction of the laser to study the distribution of nitrogen fluorescence in the radial plane, it is found that the fluorescence emission of <inline-formula><tex-math id="M14">\begin{document}${\rm{N}}_2^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M14.png"/></alternatives></inline-formula> is more intense in the direction perpendicular to the laser polarization, while it is weaker in the direction parallel to the laser polarization. The nitrogen fluorescence emission has the same intensity in all directions. The ionization probability of a linear molecule depends on the angle between the laser polarization direction and the molecular axis, which is maximum (minimum) when the angle is <inline-formula><tex-math id="M15">\begin{document}${{{0}}^{\rm{o}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M15.png"/></alternatives></inline-formula>(<inline-formula><tex-math id="M16">\begin{document}${{9}}{{{0}}^{\rm{o}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M16.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M16.png"/></alternatives></inline-formula>). The <inline-formula><tex-math id="M17">\begin{document}${{\rm{N}}_{{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M17.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M17.png"/></alternatives></inline-formula> gas is more likely to be ionized in the laser polarization direction, the nitrogen molecular ions <inline-formula><tex-math id="M18">\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M18.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M18.png"/></alternatives></inline-formula> and electrons are separated in the direction parallel to the laser polarization. Therefore, more ions (<inline-formula><tex-math id="M19">\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M19.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M19.png"/></alternatives></inline-formula>) are generated in the direction parallel to the laser polarization, and the fluorescence emission of <inline-formula><tex-math id="M20">\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M20.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M20.png"/></alternatives></inline-formula> is more intense. Along the propagation direction of the laser, it is found that the fluorescence of <inline-formula><tex-math id="M21">\begin{document}${{\rm{N}}_{{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M21.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M21.png"/></alternatives></inline-formula> appears before the fluorescence of <inline-formula><tex-math id="M22">\begin{document}${\rm{N}}_2^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M22.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M22.png"/></alternatives></inline-formula> and disappears after the fluorescence of <inline-formula><tex-math id="M23">\begin{document}${\rm{N}}_{{2}}^{{ + }}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M23.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M23.png"/></alternatives></inline-formula> has vanished. This is due to the fact that <inline-formula><tex-math id="M24">\begin{document}${{\rm{N}}_{{2}}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M24.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M24.png"/></alternatives></inline-formula> can be ionized into <inline-formula><tex-math id="M25">\begin{document}${\rm{N}}_{{2}}^{{ + }}{{(}}{{\rm{B}}^{{2}}}\Sigma_{\rm{u}}^{{ + }})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M25.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M25.png"/></alternatives></inline-formula> at the position of high enough laser intensity, thus emitting fluorescence of <inline-formula><tex-math id="M26">\begin{document}${\rm{N}}_2^ + $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M26.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M26.png"/></alternatives></inline-formula>. However, the laser energy is not enough to ionize nitrogen at the beginning and end of laser transmission, but it can generate <inline-formula><tex-math id="M27">\begin{document}${\rm{N}}_2^ * $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M27.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M27.png"/></alternatives></inline-formula>, which emits nitrogen fluorescence through the process of intersystem crossing <inline-formula><tex-math id="M28">\begin{document}${\rm{N}}_2^*\xrightarrow{{{\rm{ISC}}}}{{\rm{N}}_2}({{\rm{C}}^3}\Pi _{\rm{u}}^ + )$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M28.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M28.png"/></alternatives></inline-formula>. The spatial distribution of nitrogen fluorescence emission during femtosecond laser filament formation shows that in the case of short focal length, the intersystem crossing scheme can explain the formation of <inline-formula><tex-math id="M29">\begin{document}${{\rm{N}}_{{2}}}{{(}}{{\rm{C}}^{{3}}}\Pi _{\rm{u}}^{{ + }})$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M29.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20201704_M29.png"/></alternatives></inline-formula>. This research is helpful in understanding the mechanism of nitrogen fluorescence emission.
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