Passively mode-locked radially polarized laser based on ceramic Nd:YAG rod

2 µm cylindrical vector beam generation from a c-cut Tm:CaYAlO4 crystal resonator

Different from the traditional ideal column symmetry cavities, we directly generated the cylindrical vector pulsed beams in the folded six-mirror cavity by employing a c-cut Tm:CaYAlO₄ (Tm:CYA) crystal and SESAM. By adjusting the distance between the curved cavity mirror (M4) and the SESAM, both the radially polarized beam and azimuthally polarized beam are generated around 1962 nm and the two vectorial modes can be freely switched in the resonator. Further increased the pump power to 7 W, the stable radially polarized Q-switched mode-locked (QML) cylindrical vector beams were also obtained with an output power of 55 mW, the sub-pulse repetition rate of 120.42 MHz, pulse duration of ∼0.5 ns and the beam quality factor M² of ∼2.9. To our knowledge, this is the first report of radially and azimuthally polarized beams in the 2 µm wavelength solid-state resonator.

Simple Methods to Synthesize YVO4 Nanocrystals or Microcrystals without Any Templates or Surfactants

YVO4 crystals with different sizes and shapes were produced through hydrothermal treatment and sonication method without any surfactants or templates. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL) were used to characterize the obtained products. YVO4 nanocrystals with spindle-like shape had been produced through the two different treating methods. YVO4 crystals, which are bipyramid-capped and micrometer-sized, had been obtained through a simple hydrothermal treatment. Uniform microsized cuboids had been produced through hydrothermal treatment with the final pH value = 2.5. The effects of different final pH values on the shape and crystallinity of products were studied. To determine photoluminescence performances, Eu3+(5%)-doped YVO4 nanocrystals had been synthesized through different methods in various environments and it had been confirmed that crystallinity would affect photoluminescence intensity.

Novel thin-disk oscillator concept for the generation of radially polarized femtosecond laser pulses

We report on the first demonstration of a radially polarized passively mode-locked thin-disk oscillator. Radial polarization was achieved by the use of a novel circular grating waveguide output coupler. We showed mode-locked operation up to a maximum average output power of 13.3 W with an optical efficiency of 21.8%. The degree of radial polarization of the emitted beam was measured to be 97±1%. The laser system generated pulses with a duration of 907 fs and an energy of 316 nJ corresponding to a peak power of 0.35 MW. To the best of our knowledge, these values exceed the performance of previously reported radially polarized mode-locked oscillator systems.

High-power Yb:YAG single-crystal fiber amplifiers for femtosecond lasers in cylindrical polarization

We demonstrate a three-stage diode-pumped Yb:YAG single-crystal-fiber amplifier to generate femtosecond pulses at high average powers with linear or cylindrical (i.e., radial or azimuthal) polarization. At a repetition rate of 20 MHz, 750-fs pulses were obtained at an average power of 85 W in cylindrical polarization and at 100 W in linear polarization. The report includes investigations on the use of Yb:YAG single-crystal fibers with different length/doping ratio and the zero-phonon pumping at a wavelength of 969 nm in order to optimize the performance.

Mode-locked all-fiber laser producing radially polarized rectangular pulses

We propose and demonstrate a radially polarized mode-locked fiber laser through the use of a figure-8 cavity in combination with cascade fiber Bragg gratings (FBGs). The mode-locked laser emits rectangular pulses with width tunable from 2.8 to 23 ns under an increasing pump power at 1056.3 nm with 0.2-nm 30-dB linewidth. A polarization purity as high as 96% for the output transverse mode has been achieved simultaneously.

Generation of radially polarized Bessel-Gaussian beams from c-cut Nd:YVO₄ laser

We experimentally demonstrate the generation of radially polarized Bessel-Gaussian beams from a c-cut Nd:YVO₄ laser with a hemispherical cavity configuration by proper mode control. The output beam has an annular-shaped intensity distribution with radial polarization. When the beam is focused, the intensity pattern changes to a multi-ring, which is a typical characteristic of the lowest transverse mode of vector Bessel-Gaussian beam. Higher-order modes of vector Bessel-Gaussian beam are also observed from the same cavity by slightly changing the cavity alignment. The experimental results show a good agreement with the simulation results for both focal and far fields. The present method is a simple and direct way for generating vector Bessel-Gaussian beams.