The effect of population inversion saturation on the transverse mode instability threshold in high power fiber laser oscillators

Ali Roohforouz,Reza Rezaei-Nasirabad,Vahid Vatani,Seyed Hassan Nabavi,Reza Eyni Chenar,Kamran Hejaz,Ali Abedinajafi,Ali Hamedani Golshan,Saeed Azizi

doi:10.1038/s41598-021-00400-9

Ali Roohforouz, Reza Rezaei-Nasirabad + Show 7 more

Open Access

https://doi.org/10.1038/s41598-021-00400-9

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Abstract

To achieve a 3.02 kW Yb-doped fiber laser oscillator, the behavior of transverse mode instability (TMI) is experimentally studied in different pumping configurations; co, hybrid, counter, and bidirectional. A comparative analysis showed that population inversion saturation has a substantial impact on TMI threshold enhancement in high power fiber oscillators. Monitoring the dynamic power exchange of fundamental mode and higher-order mode of laser output beam indicates that in a hybrid pumping scheme, simultaneous pumping with two different wavelengths enhances the TMI threshold to a great stand. Moreover, injecting a few watts of pumping light in the counter direction mitigates the TMI caused by pumping in the co-direction. Calculation of population inversion in different pumping configurations using simulation shows that higher population inversion saturation leads to increasing the TMI threshold.

Highlights

To achieve a 3.02 kW Yb-doped fiber laser oscillator, the behavior of transverse mode instability (TMI) is experimentally studied in different pumping configurations; co, hybrid, counter, and bidirectional
The power scaling of fiber amplifiers and oscillators has been faced with two major problems; transverse mode instability (TMI)[1] and stimulated Raman scattering (SRS)[2,3]
Reported achievements to pave the way for a better understanding of the TMI phenomenon and can lead to an increase of TMI threshold and substantial power scaling of fiber oscillators

Summary

Introduction

To achieve a 3.02 kW Yb-doped fiber laser oscillator, the behavior of transverse mode instability (TMI) is experimentally studied in different pumping configurations; co, hybrid, counter, and bidirectional. A comparative analysis showed that population inversion saturation has a substantial impact on TMI threshold enhancement in high power fiber oscillators. The power scaling of fiber amplifiers and oscillators has been faced with two major problems; transverse mode instability (TMI)[1] and stimulated Raman scattering (SRS)[2,3]. These destructive effects create serious constraints on the efficiency and beam quality of high-power fiber lasers in the last decade. Reported achievements to pave the way for a better understanding of the TMI phenomenon and can lead to an increase of TMI threshold and substantial power scaling of fiber oscillators

Methods

Findings

Conclusion