Time-resolved infrared spectroscopy of superconducting NbTiN film near H$_{c2}$*

We use subnanoseconds time-resolved, pump-probe infrared spectroscopy to study vortex dynamics of a conventional superconductor, Nb$_{0.5}$Ti$_{0.5}$N near H$_{c2}$. The measurements were performed at the National Synchrotron Light Source, Brookhaven National Laboratory; Picosecond pulses from a near-infrared Ti:sapphire laser were used as a pump and, subnanosecond pulses of infrared synchrotron radiation as a probe. We report detailed magnetic field dependences of the amplitude of photoinduced quasiparticles and the effective lifetime of the quasiparticles and also discuss vortex dynamics in the system near H$_{c2}$. Near H$_{c2}$, we observe an interesting deviation from the field-independent behavior of the effective lifetime at lower fields.