Photoinduced transparency of effective three-photon absorption coefficient for femtosecond laser pulses in Ge₁₆ As₂₉ Se₅₅ thin films

We report a dramatic change in effective three-photon absorption coefficient of amorphous Ge₁₆ As₂₉ Se₅₅ thin films, when its optical band gap decreases by 10 meV with 532 nm light illumination. This large change provides valuable information on the higher excited states, which are otherwise inaccessible via normal optical absorption. The results also indicate that photodarkening in chalcogenide glasses can serve as an effective tool to tune the multiphoton absorption in a rather simple way.