Reversible dark-center diffraction of metal film in the micromachining

摘要

When we utilized femtosecond laser to micromachine Cr film with glass substrate, we found reversible dark-center diffraction of the transmitted probe beam passing through the chromium film and reversible bright-center diffraction of the reflected probe beam from the chromium film, which are induced by the pump femtosecond laser. The dark-center diffraction of the transmitted probe beam and the bright-center diffraction of the reflected probe beam appear and disappear with and without the pump beam. A view of diffractive optics with binary phase plate is put forward, which explains the reversible dark-center diffractive optical phenomenon. The pre-ablated hole on the metal film can be regarded as a uniform light filed without phase modulation, the surrounding circular part around the pre-ablated hole can be regarded as "phase modulated". Therefore, this diffraction optic view might be helpful for us to understand the phase change of the metal film introduced by the femtosecond laser pulse.