Search for multiphoton-induced inner-shell excitations

Photon-counting experiments have been conducted to test the conjecture that at sufficiently high laser irradiance, atomic inner-shell excitations can be induced by laser-driven outer-shell oscillations. Using KrF light at an irradiance ≊3×${10}^{17}$ W/${\mathrm{cm}}^2$ on low-density noble-gas targets, we detect no prompt photons which are characteristic of inner-shell processes.