Laser cleaning of entrance window during ultra-fast pulsed laser deposition

A new mode of ultra-fast pulsed laser deposition has been recently proposed as a solution for deposition of highest quality optical films, such as those required for fabrication of optical waveguides, This mode oflaser ablation employs short ps and sub-ps pulses with rather low energy, of the order of I1J, delivered at MHz repetition rates, as opposed to conventional low-repetition-rate ns pulse deposition. The low energy pulses have to be tightly focused to a focal spot of the order of tens of microns to achieve the ablation conditions on the target surface. This tight focusing together with short time between the pulses, results in much broader expansion of the laser plume when compared to a narrowshaped plume in conventional ns-pulse laser deposition. An advantage of broad plume expansion is a more homogeneous film coating, however this comes at the cost of subsequent deposition of the ablated material on the laser beam entry window. To overcome this problem, a laser cleaning technique was developed for in-situ deposition cleaning, and applied to deposition of chalcogenide glasses comprised of Ge-As-Se and As-S used for creation of nonlinear optical films for photonics applications.