Abstract
We experimentally demonstrate continuous-wave ultraviolet emission through forth-harmonic generation in a millimeter-scale lithium niobate whispering-gallery resonator pumped with a telecommunication-compatible infrared source. The whispering-gallery resonator provides four spectral lines at ultraviolet, visible, near-infrared and infrared, which are equally spaced in frequency via the cascaded-harmonic process and span a 2-octave frequency band. Our technique relies on a variable crystal poling and high transverse order of the modes for phase-matching and a resonator quality factor of over 10(7) to allow cascaded-harmonic generation up to the fourth-harmonic at input pump powers as low as 200 mW. The compact size of the whispering gallery resonator pumped at telecommunication-compatible infrared wavelengths and the low pump power requirement make our device a promising ultraviolet light source for information storage, microscopy, and chemical analysis.
Highlights
Basic physics imposes the condition that the required energy for a conventional laser scales as 1/λ5, where λ is the laser wavelength [1]
Instead of using ultra-short pump pulses, whispering-gallery resonators can be used to provide the high field intensities required for various nonlinear phenomena
We experimentally demonstrate continuous-wave harmonic generation up to the fourth-harmonic, enabled by multiple-recirculation intensity enhancement in a lithium niobate whispering-gallery resonator
Summary
Basic physics imposes the condition that the required energy for a conventional laser scales as 1/λ5, where λ is the laser wavelength [1]. “Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators,” Phys. “Low-threshold optical parametric oscillations in a whispering gallery mode resonator,” Phys. K. Chang, “Third-order optical sum-frequency generation in micrometer-sized liquid droplets,” Opt. Lett.
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