Detection of 660 nm pico-second Laser pulses using NbTiN thin films

Dissipative states created by a supercritical current pulses were investigated at 4 K in superconducting NbTiN sputtered on polished crystalline Al₂O₃. When a current pulse exceeding the critical current (I > I_c) was sent to the sample, a delay time t_d marked the destruction of the superconductivity and followed immediately by a voltage. A bias current pulse excitation was set slight below the critical current (I » I_c), a 50 ps laser pulse (l= 660 nm) with modulated intensity was sent through an optical window to the sample. When the light pulse is absorbed by the film, it leads to the switching from the superconducting state to the normal state. These dissipative states were identified as HSs and a voltage response with a certain delay time was recorded. The delay time t_d was analyzed through a Time-Dependent Ginzburg-Landau (TDGL) theory due to Tinkham and the film cooling times was subsequently deduced.