Intensity noise as a driver for transverse mode instability in fiber amplifiers

Abstract

The effect of transverse mode instability (TMI) is currently the main limitation for the further average-power scaling of fiber laser systems with diffraction-limited beam quality. In this work a main driving force for TMI in fiber amplifiers is identified. Our experiments and simulations illustrate that the performance of fiber laser systems in terms of their diffraction-limited output power can be significantly reduced when the pump or seed radiation exhibit intensity noise. This finding emphasizes the fact that the TMI threshold is not only determined by the active fiber but, rather, by the whole system. In the experiment an artificially applied pump intensity-noise of 2.9% led to a reduction of the TMI threshold of 63%, whereas a similar seed intensitynoise decreased it by just 13%. Thus, even though both noise sources have an impact on the TMI threshold, the pump intensity-noise can be considered as the main driver for TMI in saturated fiber amplifiers. Additionally, the work unveils that the physical origin of this behavior is linked to the noise transfer function in saturated fiber amplifiers. With the gained knowledge and the experimental and theoretical results, it can be concluded that a suppression of pump-noise frequencies below 20 kHz could strongly increase the TMI threshold in high-power fiber laser systems.

Experimental investigations of seeding mechanisms of TMI in rod fiber amplifier using spatially and temporally resolved imaging

“…We obviously still record a strong correlation between the resulting significant frequencies in the ST measurement and the intensity noise of the pump diode. This correlation can be explained by the intensity noise stimulating the TMI gain for these frequencies which was also concluded by Stihler et al [14].…”

“…The seeding mechanism of TMI has been discussed extensively. Recent studies by Stihler et al [14,24] have shown large impact of pump intensity noise on the TMI threshold of fiber amplifiers. In these studies, the TMI threshold was investigated when adding a controlled homogeneous white noise in some frequency range on the pump intensity.…”

“…The physics of TMI has been widely accepted but many models of TMI are still used which have some differences with respect to describing the inner workings of the instabilities [8][9][10][11]. Besides numerical models to improve the understanding and mitigation of this limitation, comprehensive experimental work has been performed to describe TMI [12][13][14][15]. Some early work utilized high-speed cameras to show transfer of power between different transverse modes [16,17] and since then the simpler photodiode (PD) method proposed by Otto et.…”

Reconfigurable Parametric Amplifications of Spoof Surface Plasmons

“…It can also be exploited as the candidate for replacing the existing fiber amplifiers. [ 28 , 29 , 45 ] Optical fiber parametric amplifiers can offer broadband amplification in a spectrum not accessible by other optical amplification technologies, boosting the ability of optical communication systems beyond their current limits. [ 30 , 31 , 32 , 33 , 34 , 35 ] However, as the third‐order Kerr nonlinearity of the optical fiber is weak, it normally requires a substantial number of transmission wavelengths (at the order of 10 8 wavelengths) to achieve sufficient gain at the normal incident pump power.…”

Study of seeding mechanisms of TMI with spatially and temporally resolved imaging

“…Recent work by Stihler et al 11,12 has shown the large impact of pump intensity noise on the TMI threshold. In the cited work, a controlled white noise in different frequency ranges is applied on the pump intensity and the TMI threshold is measured.…”