Deexcitations of the projectile dominating EUV-photon emission upon transmission of keV ions through solids

We measure the photon emission induced by energetic Ne and He ions transmitted through thin single crystalline Si foils. The emitted photons are detected with a delay line microchannel plate detector. Our measurements show that photon emission detectable from the rear surface of the membranes is multiple times more likely than photon emission from the front surface of the membrane. It can be deduced that photon emission from electronic deexcitation of the sample can only play a minor role, while the vast majority of detected photons are emitted by excited projectiles freely decaying behind the sample. Utilizing shadowing effects, we can show that a large proportion of excited projectiles travels several centimeters before decaying. The photons observed in the present approach are another accessible observable reporting on ultrafast processes during ion-matter interaction.