Abstract
Large topological charge optical vortex beams carrying orbital angular momentum have potential applications on optical trapping, optical communication with high capacity, quantum information processing. However, the beam quality is degraded in vortex beams generated with spiral phase plates or resonator mirrors with defect spots and optical conversion efficiency in solid-state lasers is sacrificed by controlling the loss of resonator. It is a big challenge for generating high beam quality, high-order cylindrical vector beams with large topological charge in compact solid-state lasers. Here, high-order cylindrical vector beams [Laguerre-Gaussian (LG) modes with zero degree and order of l, LG0,l] with tunable topological charges up to 14 have been generated in an annular beam pumped Yb:YAG microchip laser by manipulating the pump power-dependent population inversion distribution. Efficient performance with optical efficiency of 17.5% has been achieved. The output power is 1.36 W for a vector-vortex laser with 14 topological charges. The pump power dependent wavelength tunable and dual-wavelength laser oscillation in vector-vortex beams has been observed by controlling the reabsorption loss at 1030 nm. Wavelength tunable, dual-wavelength (1030 and 1050 nm) laser oscillation has been achieved for vector-vortex beams with topological charges of 8, 9, and 10. The laser beam quality factor M2 close to the theoretical value (l + 1) has been achieved for LG0,l vector-vortex beams with tunable topological charges up to 14. This work provides a new effective method for generating large topological charge high-order cylindrical vector beams in solid-state microchip lasers with high efficiency and high beam quality.
Highlights
Large topological charge vector-vortex laser beams have been demonstrated for potential applications on high capacity storage,1 information processing,2 quantum entanglement,3 high resolution imaging,4 and optical manipulation
The spatial light modulator (SLM),3 spiral phase plate (SPP),10 and hologram formed with liquid crystal11 have been used to generate specially designed vortex beams in the extra-cavity laser scheme
Oscillation of LG0,l modes in the annular beam pumped Yb:YAG microchip laser is attributed to the pump power-dependent population inversion distribution inside the Yb:YAG crystal
Summary
Large topological charge vector-vortex laser beams have been demonstrated for potential applications on high capacity storage, information processing, quantum entanglement, high resolution imaging, and optical manipulation. Laguerre-Gaussian (LG) modes with zero degree and order of l (LG0,l) are ideal vortices and possess unique properties of intensity zero along the beam axis and helical phase, especially carrying orbital angular momentum (OAM). Besides unique properties of amplitude and phase, the inhomogeneous polarization states of LG0,l vector-vortex beams (one class of the high-order cylindrical vector beams) provide more flexibilities for various potential applications such as tightly focusing, imaging, and optical communications. Various methods have been proposed to generate vector-vortex beams. Compared to Nd3+-doped laser materials, ytterbium ions (Yb3+) doped laser materials especially Yb:YAG crystals are ideal candidates of solid-state lasers for achieving large topological charge vector-vortex lasers with high power and high efficiency because they have remarkable properties such as low quantum defects, broad absorption and emission spectra, and high doping concentration.26,27 It is worth investigating annular beam pumped Yb:YAG microchip lasers for generating high beam quality, large topological charge LG0,l vector-vortex beams with spatial polarization distribution in a form of E0,l(φ) = Ex cos(lφ) + Ey sin(lφ), where l is the topological charge and Ex and Ey are the unit vectors in the Cartesian coordinate system. The output power was measured to be 1.36 W for the vector-vortex laser with a topological charge of 14 and optical efficiency was as high as 17.5%
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