Two-Step Tapering-Collapse Method Enables Element-Interdiffused Cladding for Enhanced Laser Amplification in Yb:YAG Single Crystal Fibers

TL;DR

This paper introduces a novel two-step tapering-collapse method to create a high-quality, interdiffused crystalline cladding on Yb:YAG single crystal fibers, significantly improving laser efficiency and beam quality.

Contribution

The study presents the first successful fabrication of a crystalline interdiffused cladding on Yb:YAG SCFs using a two-step tapering-collapse process, enhancing laser performance.

Findings

Cladding reduces numerical aperture from 0.280 to 0.199.

Achieves 46.7% increase in slope efficiency.

Improves near-field beam profile.

Abstract

The development of high-power single crystal fiber (SCF) lasers is critically hindered by the lack of a reliable cladding scheme to confine the optical mode and ensure beam quality. Here, we propose and demonstrate a two-step tapering-collapse method for the first time to fabricate a high-quality cladding on Yb:YAG SCFs based on elemental interdiffusion. This in-situ formed crystalline transition layer with a graded refractive index effectively suppresses lattice mismatch and abruptly mitigates core-cladding interfacial stress. Consequently, the numerical aperture of the SCF is significantly reduced from 0.280 to 0.199. In a master oscillator power amplifier configuration, the clad SCF delivers a remarkable 46.7% enhancement in slope efficiency compared to its bare counterpart, accompanied by a substantially improved near-field beam profile. This work establishes a facile and effective route to high-performance clad SCFs, unlocking their full potential for next-generation extreme-condition lasers.