Yoshihiro NISHIGATA
Cheng-Yeh LEE
Katsuhiko MIYAMOTO
Yung-Fu CHEN
Takashige OMATSU
The optical vortex carries a donut-shaped spatial profile and an orbital angular momentum (OAM) associated with its helical wavefront with an on-axis phase singularity, and it has been widely studied in many fields, such as super-resolution microscopes, optical communications, quantum information, optical manipulation, and laser microfabrication. The aforementioned applications desire strong wavelength-versatile optical vortex sources. To date, the nonlinear frequency extension of optical vortex sources has been intensely investigated by employing second-order or third-order nonlinear optical phenomena, such as second harmonic generation, sum frequency generation, optical parametric oscillation, and stimulated Raman scattering.
The OAM conservation between the pump and frequency-converted photons in second-order nonlinear processes is well established. Stimulated Raman Scattering (SRS), a well-known third-order nonlinear frequency conversion process, is inelastic scattering by the vibration of molecules, termed optical phonon. Thus, SRS provides a dilemma, i.e., how does the OAM of the pump photon transfer to the Stokes photon.
In this paper, the authors discover that the OAM of the Stokes photon is determined by the spatial overlap between the pump and Stokes optical fields: this manifests that the OAM conservation among the pump and Stokes photons, and an optical phonon should be established.
This discovery should enable the development of wavelength-versatile optical vortex sources to fill up the frequency gap of conventional solid-state lasers, and it will also offer novel fundamental and advanced material sciences, based on the interaction between the OAM of optical fields and matter. Going beyond conventional nonlinear frequency extension techniques, this paper with outstanding achievements will certainly contribute to significant advances in singular optics, nonlinear optics, and fundamental materials science. Thus, this paper deserves the IEICE best paper award.
