Nonlinear optics with full three-dimensional illumination

TL;DR

This paper explores third-harmonic generation when focusing pump light from a full solid angle, revealing that nonparaxial focusing enhances photon conversion efficiency and differs from traditional regimes.

Contribution

It demonstrates the effects of full solid angle focusing on nonlinear optics, showing that Gouy phase limitations are bypassed, which is a novel insight into high-intensity light-matter interactions.

Findings

Focusing from a full solid angle increases third-harmonic photon yield.

Gouy phase does not limit conversion efficiency in this regime.

Good agreement between experiments and numerical models.

Abstract

We investigate the nonlinear optical process of third-harmonic generation in the thus far unexplored regime of focusing the pump light from a full solid angle, where the nonlinear process is dominantly driven by a standing dipole-wave. We elucidate the influence of the focal volume and the pump intensity on the number of frequency-tripled photons by varying the solid angle from which the pump light is focused, finding good agreement between the experiments and numerical calculations. As a consequence of focusing the pump light to volumes much smaller than a wavelength cubed the Gouy phase does not limit the yield of frequency-converted photons. This is in stark contrast to the paraxial regime. We believe that our findings are generic to many other nonlinear optical processes when the pump light is focused from a full solid angle.