Design of long focal-depth optical element for plasma diagnostic system in ICF drivers
For the laser plasma diagnostic system in the inertial confinement fusion(ICF) drivers,the logarithmic axicon was adopted and improved by fifth-order super-Guassian edge smoothing,centre apodization and choosing suitable device parameters.The simulation experiments indicated that,to obtain a long-focal depth,small focused spot,small side lobe and homogeneous intensity focused beams in the on-axis and transverse directions,the focal depth of the logarithmic axicon should be 3~5 mm,the apodization radius should be 15~60 mm,and the edge super-Guassian smoothing order should be 5.The long focal depth device whose focal depth was more than 3 mm,axial intensity distribution was uniform and the maximal relative intensity of the side lobe was less than 2% of the center intensity was designed,which could properly meet the diagnostic requirements of the laser plasma,and the Fresnel diffraction integral simulation experiments verified the feasibility of this method.