In order to increase the laser induced damage threshold of KDP crystal, a well-known solution consists in a laser conditioning process. In our case, the irradiation of the crystal is performed with an excimer laser XeF (λ = 351 nm, 16 ns). The improvements in laser damage thresholds measured at CEA/CESTA laboratory (Lutin, Yag facility 2.5 ns, parallel beam) and at CEA/Ripault laboratory (Excimer facility 16 ns, focused beams) are different. A possible reason to explain this difference is the depth of focus between both facilities. In order to minimize the influence of limited depth of focus, a solution consits in a multi-plane conditioning process. By means of a local study, it is possible to exhibit with a high accuracy the Laser Induced Damage Threshold (LIDT) in different planes along sample irradiation axis (z-axis). The laser damage threshold is measured locally (8 μm) at 355 nm with a Nd:Yag (pulse duration 7 ns) at Fresnel Institute Marseille. Using the local LIDT measurements, the purpose of this paper is to highlight the depth of focus in the excimer conditioning process. We demonstrate that it is possible to exhibit a local increase in the conditioning gain till a maximum value, measured with the excimer laser.