Tunable Doppler shift using a time-varying epsilon-near-zero thin film near 1550 nm

We experimentally investigate the tunable Doppler shift in an 80 nm thick indium-tin-oxide (ITO) film at its epsilon-near-zero (ENZ) region. Under strong and pulsed excitation, ITO exhibits a time-varying change in the refractive index. A maximum frequency redshift of 1.8 THz is observed in the reflected light when the pump light has a peak intensity of similar to 140GW/cm(2) and a pulse duration of similar to 580 fs, at an incident angle of 40 degrees. The frequency shift increases with the increase in pump intensity and saturates at the intensity of similar to 140GW/cm(2). When the pump pulse duration increases from similar to 580 fs to similar to 1380 fs, the maximum attainable frequency shift decreases from 1.8 THz to 0.7 THz. In addition, the pump energy required to saturate the frequency shift decreases with the increase in pump pulse duration for less than or similar to 1 ps and remains unchanged for greater than or similar to 1 ps durations. Tunability exists among the pump pulse energy, duration, and incident angle for the Doppler shift of the ITO-ENZ material, which can be employed to design efficient frequency shifters for telecom applications. (C) 2021 Optical Society of America

Automated summary

In this study, the tunable Doppler shift in ITO film at its ENZ region was experimentally investigated, demonstrating a maximum frequency redshift of 1.8 THz. The frequency redshift increases with pump intensity and decreases with pump duration. The pump energy required to saturate the frequency shift decreases for durations less than or approximately 1 ps.