Frequency dependence of tunnel ionization of deep impurities in terahertz field

Abstract

The nonlinear process of ionization of deep impurities in high-frequency electromagnetic fields show different types of frequency dependencies in two limit cases: tunnel ionization at low frequencies and multiphoton ionization at high frequencies. In terahertz range, depending upon temperature, and radiation frequency and intensity, both processes may take place. Here we report on investigations of frequency dependence of ionization of Au in Ge by terahertz electromagnetic field. The dependence of ionization probability on the intensity and radiation frequency has been investigated for wavelengths between 35 and 280 mm and temperatures between 20 and 90 K. Excitation has been produced by pulsed powerful molecular FIR laser optically pumped by TEA CO2 laser. The results have been analysed in terms of tunnel and multiphoton ionization.