Tunable vector-vortex beam optical parametric oscillator

Superposition of vortex beams generated by polarization conversion in uniaxial crystals

An optical system comprising a c-cut uniaxial crystal positioned between two axicons and illuminated by a Gaussian or a Laguerre–Gauss mode was used to demonstrate the generation of various vector vortex beams. We focused the generated beams using a 1 m focal length lens and we investigated their intensity profile and the polarization state in the focal plane of the focusing element. We showed that the achieved intensity profile can be controlled by changing the polarization state of the beam incident on the crystal. We observed that, for a particular configuration of the system, the initial circular symmetry of the beam is no longer preserved. The experiments were performed with Ti:Sapphire lasers that were operated in continuous wave mode, as well as in pulsed regime. The optical system presented here ensures a convenient way to generate a great variety of vector vortex beams and it is expected to be of interest for applications that use low and high-power laser sources, such as STED microscopy, light trapping, or material processing.

Control of transverse mode in a He-Ne laser using an astigmatic resonator

The realization of output of the controllable transverse mode in a laser resonator has always been the key problem in applications of lasers. At present, the theory of optical resonators for passive resonators is relatively mature, but the non-uniformity of gain media greatly affects the output of the laser transverse mode for astigmatic resonators in operation; especially for gas lasers, controllable high-order modes have not been studied. To realize the theory of an astigmatic passive resonator of a gas laser as a good approximation of an active resonator, this paper develops the theory of selecting the laser eigenmode through an astigmatic resonator, and verifies that the two-dimensional tilt of the cavity mirror can break the axial symmetry. Controllable output of the laser mode is realized in real time and conveniently for the first time, to the best of our knowledge. This scheme is not only common to all kinds of lasers, but also has important research significance for the high-order modes required for real-time and rapid regulation of gas lasers under operating conditions.

Cascaded vector vortex mode generation from a solid-state Raman laser

Cascaded vector vortex mode generation from a Ba(NO₃)₂ Raman laser cavity pumped by a vector LG_0,2 green laser was demonstrated for the first time to our knowledge. The generated Stokes outputs exhibited a second-order vector vortex beam as evidenced by linearly polarized flower-shaped spatial forms with four petals. The achieved optical conversion efficiencies of the first, second, and third Stokes outputs were 6.59%, 4.22%, and 0.11%, respectively, at a maximum pump energy of 3.6 mJ (360 mW).

Generation of cylindrical vector vortex beams using a biconical glass rod

This Letter proposes a biconical glass rod for generating a cylindrical vector vortex (CVV) beam. Based on the principle of total internal reflection and the cylindrical symmetry structure of the glass rod, a circularly polarized incident beam with a constant phase distribution can be converted into a CVV beam, which possesses both a spatially inhomogeneous polarization and a helical phase distribution. The polarization azimuth of the CVV beam can be tuned with the aid of a polarization rotator composed of two cascade half-wave plates. The design theory is presented, and the feasibility of the design is demonstrated experimentally.

Multi-structured-beam optical parametric oscillator

Structured beams, conventionally generated through the spatial mode conversion of the Gaussian laser beams, have attracted great interest in recent years. Optical parametric oscillators (OPOs) have demonstrated the potential for the generation of tunable structured beams directly from an input pump source. However, to date, a particular OPO design has been shown to produce such beams only in a specific configuration and different spatial structured beams require different system architectures. Here, we report the generation of multiple-structured beams from a single OPO device. Using a vortex-beam-pumped ultrafast OPO in singly-resonant oscillator design and through the control of the mode structure of the resonant beam using a simple intracavity aperture, we generate vortex, Airy, vortex Airy, and Gaussian signal beams over a tunable wavelength range across 1457-1680 nm, simultaneous with vortex beam in the non-resonant idler across 2902-3945 nm, from different ports of the device. The signal and idler vortices have output power in excess of 1 W and maximum vortex order of l_i=2, while the Airy beam and vortex Airy beam have output power of more than 200 mW. The generic experimental design can be used to provide multi-structured spatial beams with broad tunability across different spectral regions by proper selection of pump laser and nonlinear material and in all times-scales from continuous-wave to ultrafast femtosecond domain.

Dual-mode and two-signal-wavelength femtosecond optical parametric oscillator based on LiB3O5

We demonstrate a tunable femtosecond dual-beam-mode (cylindrical vector beam [CVB] and Gaussian beam [GB]), dual-signal-wavelength optical parametric oscillator based on a temperature-tuned lithium triborate crystal, synchronously pumped by a frequency-doubled mode-locked Yb-doped fiber laser. When fixing the CVB wavelength at 780 nm, the central wavelength of the GB signal could be continuously tuned from 664 to 722 nm. The maximum total signal output power is 515 mW at a 4 W pump with dual-wavelength operation (664 and 780 nm). All the measured signal pulse durations are around 150 fs. Moreover, sum-frequency-generation with Gaussian mode tuning from 548 to 588 nm is obtained, with the maximum power of 52 mW at 548 nm. Thanks to the dual-channel configuration, the wavelengths of a CVB and GB can be tuned independently. Such a flexible and versatile configuration makes it a practical tool for many applications such as high-resolution microscopy and high-capacity optical communication.