Single IR light pulses induce a membrane depolarization during the light pulses, which is followed by a hyperpolarization that can last up to 100 ms. The depolarization amplitude is dependent on the optical pulse duration, total energy deposition and membrane potential, but is insensitive to tetrodotoxin. 
tetrodotoxin
The hyperpolarization reverses its polarity near the potassium equilibrium potential and is barium-sensitive. 
barium