Carrier Dynamics of a Bismuth Thin Film Accelerated via Intense Terahertz Field

We observed terahertz transmittances to study carrier dynamics in bismuth (Bi) thin film with optical pump-terahertz probe spectroscopy and terahertz pump-terahertz probe spectroscopy. Under the intense terahertz wave illumination, the transmittance of Bi thin film increases, indicating that the effective mass of the carriers becomes heavier due to the carrier acceleration by the intense field. Then, after the terahertz wave illumination, the transmittance decreases due to the carrier increase. With optical illumination, on the other hand, the transmittance does not increase.