High-order harmonic generation in an x-ray range from laser-induced multivalent ions of noble gas
Jixing Gao, Jiaqi Wu, Zhiyuan Lou, Fan Yang, Junyu Qian, Yujie Peng, Yuxin Leng, Yinghui Zheng, Zhinan Zeng, Ruxin Li
Abstract
Tabletop coherent x-ray sources extending to multi-keV or higher photon energies have versatile applications, including in 4D imaging and semiconductor detectors. However, these sources can be realized only via high-order harmonic generation (HHG) with an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>10</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mtext>µ</mml:mtext> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:mrow> </mml:math> laser interacting with neutral atoms. As shown in previous work by Popmintchev et al. [ Science 350 , 1225 ( 2015 ) 10.1126/science.aac9755 SCIEAS00 36-8075 ], multiply ionized plasmas can efficiently produce hundred-eV harmonics with an ultraviolet laser. Here, we experimentally investigate multi-keV x-ray sources up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>5.2</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">k</mml:mi> <mml:mi mathvariant="normal">e</mml:mi> <mml:mi mathvariant="normal">V</mml:mi> </mml:mrow> </mml:math> , the highest photon energy generated via HHG to date, to our knowledge, using a 1.45-µm driving laser that interacts with multivalent ions. Both the angular distribution and the ellipticity dependence of the signal are strong evidence of the HHG mechanism.