Laser differential confocal inner-surface profile measurement method for an ICF capsule

To achieve the high-precision measurement of the inner surface profile of a laser inertial confinement fusion (ICF) capsule, a new laser differential confocal ICF target measurement method with high axial resolution and an anti-surface reflectivity capability is proposed for the inner surface profile of an ICF capsule. First, this method uses the laser differential confocal measurement system to radially measure the inner and outer surfaces of an ICF capsule located in the center of the rotary shaft, respectively, and it uses the measured location parameters of the inner and outer surfaces of the ICF capsule and the refractive index of the ICF capsule to obtain the geometrical parameters of the inner surface trigger point by ray tracing. Secondly, it rotates the capsule using a high-precision rotation system, and uses the laser differential confocal measuring system to scan and measure the inner surface profile of the equatorial section of the capsule. Then, it rotates the capsule to the other equatorial section using the auxiliary rotary system, and uses the laser differential confocal measuring system to measure the inner surface profile of other equatorial section of the capsule. Finally, all of the inner surface profile data obtained on each equatorial section are reconstructed to obtain the three-dimensional (3D) profile information of the capsule’s inner surface. For the first time, this proposed method achieves the high-precision nondestructive measurement of the inner surface profile of an ICF capsule. Theoretical analyses and preliminary experiments indicate that the repetitive measurement obtained using the proposed method for the inner surface profile of the capsule can reach 15 nm.