Optical conductivity of an electron gas driven by a pulsed terahertz radiation field

We present a theoretical study to examine the optical conductivity of an electron gas in the presence of a pulsed terahertz (THz) radiation field. Applying a very simple Drude like approach, we calculate the transit current for an electron gas driven by a pulsed light field. By taking three types of the pulsed radiation fields with different analytical forms, we prove analytically or numerically that although the corresponding transit current depends on the shape of the radiation field in time-domain, the optical conductivity in frequency-domain is independent upon the profile of the pulsed light field when optical conductivity in frequency-domain is obtained by Fourier transformation of both the pulsed radiation field and the transit current. Thus, the optical conductivity in frequency-domain can be described by the well known Drude formula even in the presence of the pulsed THz field. This finding can be applied for experimental measurement of the real and imaginary parts of optical conductivity in electronic and optoelectronic materials by using, e.g., the THz time-domain spectroscopy (TDS). Graphical abstract