Adjustment-Free Long-Distributed-Cavity Laser Using Small Glass Ball Cat-Eye Retroreflector

We report an adjustment-free long-distributed-cavity laser using a small high-index glass ball cat-eye retroreflector as the receiver. When the glass ball cat-eye was rotated or off-axis moved, its working characteristics were studied via the single cat-eye structure and the double cat-eyes structure. With the single cat-eye structure and an incident pump power of 4.22 W, the end-pumped Nd: YVO $_{\mathbf {4}}$ laser delivered 985 mW continuous-wave output at a working distance of 2.85 m, whose full rotation angle at half power was ±27°. In addition, with the double cat-eyes structure and the same incident pump power, the laser delivered 385 mW output at a working distance of 1.20 m, which had a full rotation angle of ±19° and a transverse displacement tolerance of ±21 mm. As far as we know, this is the first time that a ball-shaped cat-eye retroreflector is used to establish an adjustment-free long-distributed-cavity laser.

I. Introduction

The adjustment-free laser using corner prism or cat-eye retroreflector (CER) can maintain stable working when its output coupler is tilted or off-axis moved [1], [2]. Due to their excellent mechanical and thermal stability, adjustment-free lasers have been a research hotspot in aerospace and military laser applications [1], [3]. As a retroreflector, the corner prism has the disadvantage of reflected beam’s transverse drift and unavoidable ridgeline/vertex loss, so it is not suitable for long-cavity continuous-wave (CW) laser. In contrast, the CER does not have such problems and has been widely used to stabilize the output power or improve the beam quality of long-cavity lasers with various gain media such as carbon dioxide lasers, helium-neon lasers, copper vapor lasers, semiconductor lasers and solid-state lasers, etc. [2], [4], [5], [6], [7], [8], [9], [10]. In 2021, researchers of Shanghai Institute of Optics Fine Mechanics reported an adjustment-free Nd: YVO₄ thin disk laser using double CERs structure, which had a rotation tolerance of ±11° and a transverse displacement (the displacement perpendicular to the laser optical axis) tolerance of ±20 mm at a relatively short working distance of 150 mm [8].