Refractive index change in photoluminescent patterns based on color centers generated in lithium fluoride by EUV radiation

摘要

Periodic luminescent patterns based on active color centers have been efficiently created in Lithium Fluoride (LiF) crystals and films by Extreme Ultra-Violet (EUV) light and soft x-rays from a laser-plasma source by masking the incoming radiation. Strong visible photoluminescence at room temperature has been measured from colored geometric microstructures, produced with high spatial resolution on large areas in short exposure times. Accurate spectrophotometric measurements allow estimating a significant increase in the real part of the refractive index, locally induced by the formation of high concentrations of stable primary and aggregate electronic defects at the surface of the LiF irradiated crystal, in a very thin layer, whose depth has been evaluated around 50 nm. On the basis of a semi-classical dipole-electromagnetic field interaction model, the contribution of different kinds of point defects to the overall refractive index change has been quantified. Promising opportunities in the fabrication of passive and active devices for integrated optics, such as gratings and distributed lasers, are offered by the use of this kind of radiation.