Robust high-order petal-mode laser with tunable topological charge pumped by an axicon-based annular beam

Abstract

In this work, we demonstrate a watt-level laser producing high-order, petal-shaped output modes with tunable topological charge, by using an axicon-based divergent annular pump beam. The topological charge of the output beam could be varied in the range of 34–72 by adjusting the position of the Nd:YVO4 crystal relative to the focal plane of the pump beam. The highest order petal-mode beam generated from the system had a topological charge of 72 and a power of 1.3 W. The highest output power up to 2.1 W with a topological charge of 34 was achieved at an absorbed pump power of 5.8 W. The generated output modes were observed to be robust under power scaling and on propagation, with the same spatial profiles being maintained in the near- and far-fields. We anticipate that this system design may find use as a laser source in applications such as 3D optical trapping, fabrication of optical vortex arrays, optical communications, and high-sensitivity spatial measurement.

Excitation of Laguerre-Gaussian and geometric modes in a dye laser

“…To improve the homogeneity of the pump spot, in the second series of experiments the Nd:YAG laser beam was passed through a fiber, at the output of which an axicon/lens pair was used [5] to obtain a hollow pump beam profile. In this case, the simultaneous lasing of high order LG modes and non-planar geometric modes was recorded at the resonator frequency degenerate configurations.…”

“…Taking into account the cylindrical symmetry of the resonator, structureless annular beams should be classified as Laguerre-Gaussian LG 0,l vortex modes. The structured beams were similar to LG 0,l petal modes, which are known to be a result of coherent addition of 2 vortex modes with opposite helicities [1][2][3][4][5][6]. The diameters of the laser beams were 5-9 times larger than the diameter of the fundamental mode and, therefore, corresponded to higher-order modes, such as the LG 0,10 and LG 0,16 modes shown in Fig.…”

“…Structured beams at the laser output arise due to variety of resonator transverse modes. Several comprehensive reviews and original studies on methods of transverse modes selection in lasers, both "classical" like Hermite-Gaussian, Laguerre-Gaussian, Ince-Gaussian and so-called geometric modes were published recently, see for example [1][2][3][4][5]. The "toolkit" for controlling the mode composition inside a resonator includes various techniques that affect the amplitude, phase, polarization of laser radiation, its gain and losses [1][2][3][4][5][6].…”

“…Several comprehensive reviews and original studies on methods of transverse modes selection in lasers, both "classical" like Hermite-Gaussian, Laguerre-Gaussian, Ince-Gaussian and so-called geometric modes were published recently, see for example [1][2][3][4][5]. The "toolkit" for controlling the mode composition inside a resonator includes various techniques that affect the amplitude, phase, polarization of laser radiation, its gain and losses [1][2][3][4][5][6]. The recent impressive achievement here was the "digital laser" based on an intra-cavity spatial light modulator (SLM), with which one can set almost any required beam profile on the SLM matrix and obtain it at the laser output [7].…”

“…To obtain more uniform pumping, the beam of the multimode Nd:YAG laser was passed through a fiber with a core diameter of 550 µm and a length of 10 m (a cuvette-diffuser with a ball was not used). After collimating the beam at the output of the fiber, an axicon/lens pair was used to obtain hollow pump beams [5]. Pump radiation at the fiber output was non-polarized.…”