We have proposed and implemented a scheme for Spiral Phase Plate (SPP) with continuous surface fabrication on fiber tips. By combining Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) system and bitmap (BMP) format processing method, we fabricated a SPP with the topological charge of 1 on the fiber tip, and experimentally analyzed the diffraction and interference properties of the generated vortex beam. The experimental results were in good agreement with the simulation results, which indicated the SPP fabricated by this method had good optical properties and high reliability. This work could be valuable for fiber communication and information encryption.
We report on the continuous-wave (CW) and Kerr-lens mode-locked (KLM) operation of an ytterbium (Yb3+) doped orthorhombic calcium rare-earth borate Yb:Ca3Gd2(BO3)4 (Yb:GdCB) disordered crystal. A high quality 10 at.% Yb:GdCB crystal was grown by the Czochralski method. An X-shaped astigmatically compensated linear cavity was employed for evaluating the CW and KLM laser performance of an a-cut (sp. gr. Pnma) Yb:GdCB crystal. Pumping with a single-transverse mode, fiber-coupled diode laser at 976 nm, a maximum CW output power of 548 mW was obtained at 1049 nm with a slope efficiency of 67.8% and a linear laser polarization (E || b). A broad wavelength tuning range of ~88 nm (1001 – 1089 nm) was achieved in the CW regime. Stable KLM operation was initiated and stabilized by a semiconductor saturable absorber mirror (SESAM). Nearly Fourier-transform-limited pulses as short as 33 fs were generated at a central wavelength of 1055.3 nm with an average output power of 98 mW for a pulse repetition rate of ~67.3 MHz.
We report on the Czochralski growth, polarized optical spectroscopy, thermal lensing and diode-pumped laser operation of a Yb3+-doped monoclinic “mixed” calcium rare-earth oxoborate crystal, Gd0.235Y0.672Yb0.093Ca4O(BO3)3 (Yb:GdYCOB). The absorption, stimulated-emission and gain cross-section spectra are determined for light polarizations E || X, Y, Z. The maximum σSE above the zero-phonon line is 0.61 x 10-20 cm2 at 1022.4 nm (for E || X) and the luminescence lifetime of Yb3+ ions is 2.37 ms. The gain spectra of Yb:GdYCOB extend beyond 1.15 μm. The thermal lens is studied for the three principal cuts, X-cut, Y-cut and Z-cut, and it is found to be positive. A continuous-wave diode-pumped X-cut Yb:GdYCOB laser generates 9.27 W at ~1050 nm with a slope efficiency of 68.2%, linear laser polarization E || X and nearly diffraction-limited beam (M2x,y < 1.16). A continuous wavelength tuning from 1020.9 to 1086.3 nm (a tuning range of ~65 nm) is achieved for the Z-cut crystal and the laser polarization E || X.
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