Abstract
Time-reversal symmetry is important to optics. Optical processes can run in a forward or backward direction through time when such symmetry is preserved. In linear optics, a time-reversed process of laser emission can enable total absorption of coherent light fields inside an optical cavity of loss by time-reversing the original gain medium. Nonlinearity, however, can often destroy such symmetry in nonlinear optics, making it difficult to study time-reversal symmetry with nonlinear optical wave mixings. Here we demonstrate time-reversed wave mixings for optical second harmonic generation (SHG) and optical parametric amplification (OPA) by exploring this well-known but underappreciated symmetry in nonlinear optics. This allows us to observe the annihilation of coherent beams. Our study offers new avenues for flexible control in nonlinear optics and has potential applications in efficient wavelength conversion, all-optical computing.
Highlights
A novel concept named ‘‘coherent perfect absorber’’ (CPA)[11,12,13] that explores time-reversed process of laser emission has shown that incident coherent optical fields can be perfectly absorbed by a time-reversed optical cavity, where the gain is replaced with an equal amount of loss
For spontaneously-grown second harmonic generation (SHG) in BBO1, the time-reversed process points in exactly the opposite direction: second harmonic (SH) signals with the appropriate relative amplitude and phase to the pumping beam can be totally annihilated when they incident onto a nonlinear crystal
In an undepleted-pump scheme, we consider the quasimonochromatic waves with carrier frequencies of fundamental wave at v1, and second harmonic wave at v2 5 2v1
Summary
A nonlinear version of CPA has been theoretically proposed to investigate signal and idler beams’ phase-varying dynamics in the presence of a pumping beam under a time-reversed optical parametric oscillation (OPO) scheme[14] These studies of time symmetry have been attracting increasing attention, since they provide alternative and substantial ways to manipulate light in the nonlinear regime. Unlike the case of CPA in the linear regime where incident fields are totally absorbed and converted into heat[11,14], annihilation of incident fields can lead to the generation of new fields Such backward-parametric interactions may have a future application in efficient wavelength conversion for better long-wavelength detection, e.g. mid-IR, THz. More interestingly, a flexible phase control can be utilized to probe nonlinear dynamics during wave mixing, and redirect wave mixing forward or backward in time. This offers new techniques for flexible control in nonlinear optics and has potential applications in all-optical computing
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