Nature and ultimate timescale of ultrafast nonlinearities in indium tin oxide near ENZ

Determine the physical mechanisms and the ultimate response timescale governing the ultrafast nonlinear optical permittivity modulation in transparent conducting oxide semiconductors—specifically indium tin oxide near its epsilon-near-zero frequency—under intense optical pumping.

Background

Transparent conducting oxides such as indium tin oxide exhibit giant optical nonlinearities near their epsilon-near-zero frequency and can sustain very large pumping intensities, enabling ultrafast modulation at optical frequencies.

Despite extensive studies, the literature has not reached consensus on the underlying physical mechanisms and the ultimate temporal limits (fast Kerr-like versus slower photocarrier-mediated contributions) of these nonlinearities, which directly impacts modeling accuracy and device optimization for time-varying photonics.

References

These opportunities arise from the low carrier concentration and high melting temperatures of these semiconductors, which endow them with giant nonlinearities near their epsilon-near-zero frequency and the ability to sustain extremely large pumping intensities, enabling switching timescales of a few femtoseconds, although no agreement has yet been reached on the nature and ultimate timescale of these nonlinearities [38]-[42].

— Optical coherent perfect absorption and amplification in a time-varying medium  (2410.16426 - Galiffi et al., 2024) in Introduction, paragraph discussing ITO nonlinearities near the epsilon-near-zero frequency (preceding the experimental description)