Broad frequency shift of parametric processes in Epsilon-Near-Zero time-varying media

TL;DR

This paper demonstrates a significant frequency shift in nonlinear optical processes within epsilon-near-zero materials, showing potential for advanced frequency conversion applications.

Contribution

It provides experimental evidence of large frequency shifts in AZO films near epsilon-near-zero wavelengths during four-wave mixing, highlighting new opportunities in nonlinear optics.

Findings

Frequency shift of over 60 nm observed in AZO films.

Enhanced frequency shift near epsilon-near-zero spectral regions.

Potential applications in nonlinear optics and frequency conversion.

Abstract

The ultrafast changes of material properties induced by short laser pulses can lead to frequency shift of reflected and transmitted radiation. Recent reports highlight how such a frequency shift is enhanced in the spectral regions where the material features a near-zero real part of the permittivity. Here we investigate the frequency shift for fields generated by four-wave mixing with a nonlinear polarisation oscillating at twice the pump frequency. In our experiment we observe a frequency shift of more than 60 nm (compared to the pulse width of ~40 nm) for the phase conjugated radiation generated by a 500 nm Aluminium-doped Zinc Oxide (AZO) film pumped close to the epsilon-near-zero wavelength. Our results indicate applications of time-varying media for nonlinear optics and frequency conversion.