Space-time adaptive control of femtosecond pulses amplified in a multimode fiber

TL;DR

This paper demonstrates space-time adaptive control of femtosecond pulses in a multimode fiber, achieving focused amplification in space and time despite modal dispersion, using wavefront shaping based on output intensity patterns.

Contribution

It introduces a method for adaptive wavefront shaping based on output intensity to control femtosecond pulse amplification in multimode fibers.

Findings

Achieved spatial focusing of amplified pulses by 1/32.

Achieved temporal focusing of amplified pulses by 1/10.

Optimized input to excite the principal mode, limiting pulse duration by group velocity dispersion.

Abstract

Ultrashort light pulse transport and amplification in a 1.3 m long step-index multimode fiber with gain and with weak coupling has been investigated. An adaptive shaping of the input wavefront, only based on the output intensity pattern, has led to an amplified pulse focused both in space (1/32) and in time (1/10) despite a strong modal group delay dispersion. Optimization of the input owing to the two-photon detection of the amplified signal permitted to excite the fastest and more intense principal mode of the fiber and to get an output pulse duration limited by group velocity dispersion.