Spheric long-focal-depth lens

Spheric lens designed by nonlinear phase fitting method is proposed to duplicate the performance of logarithmic axicon, which can obtain a beam with long-focal-depth, small focal spot and side lobe. Moreover, the spheric lens is easier and less expensive for manufacture than logarithmic or aspherical elements. Based on this method, a simple lens is designed for the plasma diagnostic system in inertial confinement fusion. It is verified through Fresnel diffraction integral and an initial experiment that the performance of the lens can satisfy the requirements of the plasma measurements.