Tomography of High-order Harmonic Generation for Quasi-phase matching

Yao-Li Liu^1*, Shih-Chi Kao¹, Yi-Yong Ou Yang¹, Zhong-Ming Zhang¹, Jyhpyng Wang^1,2,3, Hsu-hsin Chu^1,3

¹Department of Physics, National Central University, Zhongli 32001, Taiwan
²Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan
³Center for High Energy and High Field Physics, National Central University, Zhongli 32001, Taiwan

* Presenter:Yao-Li Liu, email:nem2050@gmail.com

A tomographic method is demonstrated to analyze the growth and propagation of high-order harmonic generation by integrating 3D phase-matching profile measurement and interaction length control. The method resolves contributions of HHG from different regions of the driving beam as well as different sources of phase mismatch, thus providing an illuminating insight into the HHG process. Phase mismatches due to neutral gas dispersion, plasma dispersion, geometrical phase shift, and intrinsic dipole phase variation are measured in situ, and tomography of the HHG process is done by utilizing a transverse disruptive pulse which suppresses the HHG process in the overlapping area to control the interaction length. Experimental results show that the phase-matching conditions along the longitudinal propagation direction and across the driving pulse transverse profile are both nonuniform, which are reflected in the overall growth of the harmonic yield and the far-field beam profile. Agreement between measurement and calculation verifies the effectiveness of the method and the importance of controlling the 3D phase mismatch profile. We believe this method is a powerful aid for the development of HHG beyond EUV, where highly charged ions will be used to obtain large ionization potential, and programmable periodically disrupted interaction will be beneficial for achieving quasi-phase-matching in high-density plasma

Keywords: High-order Harmonic Generation, EUV, Tomography, Quasi-phase matching