The influence of laser clipped by the laser entrance hole on hohlraum radiation measurement on Shenguang-III prototype

Measuring the x-ray flux exiting the target's laser entrance hole (LEH) is the most common diagnostic that quantifies the x-ray intensity inside the laser-driven hohlraum. However, this signal accounts for only a small portion of the incident laser power and thus is likely to be affected by unwanted x-ray background from non-target area, leading to an overestimation of the hohlraum drive. Unwanted emission might be produced when the laser light is clipped by the LEH (LEH clipping) because of a lack of clearance for laser spot, or with a laser spot comprising of discrete structure, or even with a poor pointing accuracy. Its influence on the hohlraum radiation diagnostic is investigated on Shenguang-III prototype laser facility with the typical 1 ns square pulse. The experiment employed three types of targets to excite the unwanted x-ray background from LEH clipping, unconverted light, and both effects, respectively. This work gives an absolute evaluation of x-ray produced by the LEH clipping, which is meas...