Highly efficient Yb^3+-doped channel waveguide laser at 981 nm

D Geskus,E H Bernhardi,S Aravazhi,K Van Dalfsen,M Pollnau

doi:10.1364/oe.21.013773

Abstract

Channel waveguide lasers operating at 981 nm are demonstrated in KY(1-x-y)Gd(x)Lu(y)(WO4)2:Yb3+ waveguides grown by liquid phase epitaxy onto undoped KY(WO4)2 substrates and microstructured by Ar+ beam etching. Under pumping at 934 nm of samples with different waveguide geometry and outcoupling degree, a record-high slope efficiency of 76% versus absorbed pump power and a record-high output power of 650 mW for rare-earth-ion-doped microstructured channel waveguide lasers is achieved. The laser performance is compared to that of the same devices when pumping at 981 nm and lasing near 1025 nm.

Highlights

The central line of absorption and emission between two crystal-field multiplets is the transition involving the lowest Stark level of each multiplet
Due to the large Boltzmann population of this Stark level and the selection rules that apply to the individual crystal-field transitions, the central line is often the transition with the largest effective absorption and emission cross-section
This shift of laser wavelength can be examined by comparing the threshold excitation densities N2 of the upper multiplet for the competing laser transitions from its Stark levels i with Boltzmann factors b2i to the different Stark levels j of the lower multiplet with Boltzmann factors b1j via solving the round-trip equation for the intra-cavity photon number in groundstate lasers under the condition that the gain equals the losses: (1 − 2α )Rout exp{2 Γ[b2i N2 − b1 j (Nd − N2 )]σ 2i↔1 j} = 1

Summary

Introduction

The central line of absorption and emission between two crystal-field multiplets is the transition involving the lowest Stark level of each multiplet. With increasing outcoupling degree, i.e., decreasing total reflectivity Rout provided by the cavity mirrors, the laser shifts to shorter wavelengths and can oscillate on the central line [2]. This shift of laser wavelength can be examined by comparing the threshold excitation densities N2 of the upper multiplet (level 2) for the competing laser transitions from its Stark levels i with Boltzmann factors b2i to the different Stark levels j of the lower multiplet (level 1) with Boltzmann factors b1j via solving the round-trip equation for the intra-cavity photon number in groundstate lasers under the condition that the gain equals the losses:. Γ λ α Rout b21 b14 b13 b12 b11 σ21↔14 × b21 σ21↔13 × b21 σ21↔12 × b21 σ21↔11 × b21

Threshold analysis and resulting laser wavelength

Experimental

Laser results

Summary