Research on high-order tunable Hermite-Gaussian and Laguerre-Gaussian lasers based on off-axis pumping and external cavity mode conversion

Background Hermite-Gaussian (HG) beams are fundamental orthogonal solutions of stable optical resonators, and their efficient conversion to Laguerre-Gaussian (LG) vortex beams provides an effective way to generate high-order vortex light. However, the direct intracavity generation of LG beams commonly suffers from chiral superposition and poor controllability, which limits its practical applications.

Purpose This paper aims to propose a scheme to achieve high-order tunable HG and LG laser output with stable chiral control, so as to solve the chiral superposition problem of directly generated LG beams.

Methods An 808 nm fiber-coupled laser diode was used to pump the Nd:YVO₄ crystal in a plano-concave resonator. The pitch and tilt angles of the input mirror were precisely adjusted to realize off-axis pumping. A π/2 astigmatic mode converter composed of a pair of cylindrical lenses was adopted for external-cavity mode conversion. The orbital angular momentum and chirality of LG beams were verified by a Mach-Zehnder interferometer.

Results Continuously tunable HG_0,n (1–68th order) and HG_1,n (1–46th order) modes were obtained. The HG modes were efficiently converted into LG_0,1 to LG_0,68 vortex beams. The chiral symmetry flipping of LG_0,1/LG_0,-1 and LG_0,68/LG_0,-68 was realized by reversely adjusting the input mirror angles.

Conclusions The proposed scheme combines the high-order tunability of HG modes and the chiral controllability of LG modes without intracavity chiral elements, providing a flexible and reliable technical approach for the practical application of high-order vortex lasers.