Unidirectional ring vortex laser using a wedge-plate shearing interferometer.

In response to growing demand from optical vortex (OV) beam applications, numerous generation techniques have been developed competing in power scalability, purity, and wavelength flexibility. Direct vortex emission from lasers typically grants access to efficient, high power, and pure mode generation. In this work we demonstrate a compact, unidirectional Nd:YVO4 ring laser with an intracavity wedge-plate shearing interferometer (WPSI) as an output coupler, which converted the internal Gaussian mode to LG01 (Laguerre-Gaussian OV) output. It directly generated a watt-level LG01 OV with high mode purity (98%) in a single longitudinal mode. The monolithic WPSI has advantages in stability and simplicity compared to other designs. The system is compact and cheap, using off-the-shelf components, and can be readily adapted to any gain media, widening the scope for OV generation at wavelengths currently unobtainable using competing methods.

Red, orange, and dual wavelength vortex emission from Pr:WPFGF fiber laser using a microscope slide output coupler.

Visible vortex beams have a large array of applications; however, the sources are often large or complex. Here, we present a compact vortex source with red, orange, and dual wavelength emission. This Pr:Waterproof Fluoro-Aluminate Glass fiber laser uses a standard microscope slide as an interferometric output coupler, yielding high quality first order vortex modes in a compact setup. We further demonstrate the broad (∼5 nm) emission bands in the orange (610 nm), red (637 nm) and near-infrared regions (698 nm), with the potential for green (530 nm) and cyan (485 nm) emission. This is a low-cost, compact and accessible device giving high quality modes for visible vortex applications.

Sampling a vortex from a Gaussian beam using a wedge-plate shearing interferometer.

Many vortex-generation techniques have been developed to address a range of potential applications, exploiting their unique amplitude and phase profiles and their possession of orbital angular momentum. In this work, we present what may be the simplest method of vortex beam generation, requiring only a wedged optic: the wedge-plate shearing interferometer (WPSI). We show that the WPSI can reflect a first order Laguerre-Gaussian vortex beam (LG01) with a theoretical purity of >99% from an input fundamental Gaussian beam, with 98% LG01 purity experimentally demonstrated. We demonstrate 1% power conversion with a route to 14%. The monolithic WPSI is a simple, compact, and highly stable device, which can operate at any wavelength that the material is transparent to. We anticipate that it will be useful where sampling a robust, high-purity vortex beam from a Gaussian laser beam is required, including low-cost vortex generation for metrology or education.

Temperature effects on tunable cw Alexandrite lasers under diode end-pumping.

Diode pumped Alexandrite is a promising route to high power, efficient and inexpensive lasers with a broad (701 nm to 858 nm) gain bandwidth; however, there are challenges with its complex laser dynamics. We present an analytical model applied to experimental red diode end-pumped Alexandrite lasers, which enabled a record 54 % slope efficiency with an output power of 1.2 W. A record lowest lasing wavelength (714 nm) and record tuning range (104 nm) was obtained by optimising the crystal temperature between 8 °C and 105 °C in the vibronic mode. The properties of Alexandrite and the analytical model were examined to understand and give general rules in optimising Alexandrite lasers, along with their fundamental efficiency limits. It was found that the lowest threshold laser wavelength was not necessarily the most efficient, and that higher and lower temperatures were optimal for longer and shorter laser wavelengths, respectively. The pump excited to ground state absorption ratio was measured to decrease from 0.8 to 0.7 by changing the crystal temperature from 10 °C to 90 °C.

Vortex laser from anti-resonant ring coupled cavities.

Optical vortex Laguerre-Gaussian (LG0l) modes have wide-ranging applications due to their annular spatial form and orbital angular momentum. Their direct generation from a laser is attractive, due to the pure and high-power modes possible; however, previous demonstrations have had limited ranges of applicability. Here, we propose and implement direct LG0l vortex mode generation with an anti-resonant ring (ARR) coupled laser cavity geometry, where the gain medium inside the ARR is shared between two laser cavities. This generation uses standard wavelength-insensitive optical components, is suitable for high peak and average power levels, and could be applied to any bulk gain medium in pulsed or continuous wave regimes. This work demonstrates the technique with a diode end-pumped Nd:YVO4 gain medium. From 24 W of pump power, 8.9 W LG01 and 4.3 W LG02 modes were generated, all with high mode purity and pure handedness. The LG01 mode handedness was controlled with a new technique.