Experimental characterization of an uniaxial angle cut whispering gallery mode resonator

The usual configuration of uniaxial whispering gallery mode resonators is a disk shaped geometry where the optic axis points along the symmetry axis, a so called z-cut resonator. Recently x-cut resonators, where the optic axis lies in the equatorial plane, became of interest as they enable extremely broadband second harmonic generation. In this paper we report on the properties of a more generalized system, the so called angle-cut resonator, where the optic axis exhibits an arbitrary angle against the symmetry axis. We show experimentally that the modal structure and quality factors are similar to common resonators but that the polarization properties differ quite significantly: due to the asymmetry the polarization depends on the equatorial position and is, in general, elliptical

Safeguarding pollinators and their values to human well-being

Wild and managed pollinators provide a wide range of benefits to society in terms of contributions to food security, farmer and beekeeper livelihoods, social and cultural values, as well as the maintenance of wider biodiversity and ecosystem stability. Pollinators face numerous threats, including changes in land-use and management intensity, climate change, pesticides and genetically modified crops, pollinator management and pathogens, and invasive alien species. There are well-documented declines in some wild and managed pollinators in several regions of the world. However, many effective policy and management responses can be implemented to safeguard pollinators and sustain pollination services

Continuous-wave optical parametric oscillation tunable up to 8 μm wavelength

We demonstrate the first cw OPO emitting mid-infrared light at wavelengths up to 8 μm. This device is based on a 3.5-mm-diameter whispering gallery resonator made of silver gallium selenide (AgGaSe2) pumped by a compact distributed feedback laser diode emitting light at 1.57 μm wavelength. Phase-matching is achieved for a c-cut resonator disk pumped with extraordinarily polarized light at this wavelength. The oscillation thresholds are in the mW region, while the output power ranges from 10 to 800 μW. Wavelength tuning is achieved via changing the radial mode number of the pump wave and by changing the resonator temperature. Simulations predict that whispering gallery OPOs based on AgGaSe2 with diameters around 2 mm can generate idler waves exceeding 10 μm wavelength

Wide-range cyclic phase matching and second harmonic generation in whispering gallery resonators

We report on a wide-range efficient method for optical second harmonic generation based on a whispering gallery mode resonator made from crystalline beta barium borate. In this single resonator, we were able to generate second harmonic fields for four different pump wavelengths ranging from the infrared (1557 nm) to the visible (634 nm) regime. The highest conversion efficiencies achieved in this whispering gallery mode resonator are as high as 4.6% (mW)−1. This conversion process is based on type-I phase matching with continuously varying optical axis orientation in an xy-cut configuration of the resonator. In such a geometry, the second harmonic whispering gallery mode experiences an oscillatory modulation of the refractive index. This enables wide-range cyclic phase matching along the circumference of the disk resonator

Pseudo-type-II tuning behavior and mode identification in whispering gallery optical parametric oscillators

Wavelength tuning of conventional mirror-based optical parametric oscillators (OPOs) exhibits parabolically-shaped tuning curves (type-0 and type-I phase matching) or tuning branches that cross each other with a finite slope (type-II phase matching). We predict and experimentally prove that whispering gallery OPOs based on type-0 phase matching show both tuning behaviors, depending on whether the mode numbers of the generated waves coincide or differ. We investigate the wavelength tuning of optical parametric oscillation in a millimeter-sized radially-poled lithium niobate disk pumped at 1 μm wavelength generating signal and idler waves between 1.7 and 2.6 μm wavelength. Our experimental findings excellently coincide with the theoretical predictions. The investigated whispering gallery optical parametric oscillator combines the employment of the highest nonlinear-optical coefficient of the material with a controlled type-II-like wavelength tuning and with the possibility of self-phase locking