Femtosecond pulse spectral synthesis in coherently-spectrally combined multi-channel fiber chirped pulse amplifiers

Abstract

We demonstrate coherent spectral beam combining and femtosecond pulse spectral synthesis using three parallel fiber chirped pulse amplifiers, each amplifying different ultrashort-pulse spectra. This proof-of-concept experiment opens a path to simultaneously overcome individual-amplifier energy and power limitations, as well as limitations on amplified pulse spectra due to the gain narrowing in a single fiber amplifier.

Stretching and compressing of short laser pulses by chirped volume Bragg gratings: analytic and numerical modeling

“…The conventional way for doing this is the use of a pair of diffracting gratings for both stretching and compression (Treacy stretchers and compressors 1 ). An especially elegant idea was suggested and implemented by Galvanauskas et al 2,3 with the use of chirped fiber Bragg gratings, which are gratings with a gradually varied period along the fiber. It is possible to use the same grating for compression, and stretching stage, but to illuminate it from the opposite end.…”

Two-channel pulse synthesis to overcome gain narrowing in femtosecond fiber amplifiers

“…It is slightly lower than in the case of previously demonstrated femtosecond coherent combining systems that do not perform spectral separation [12,13]. This is related to differences between the splitting and recombining dichroic mirrors that lead to efficiency drop and to spectral modifications during amplification that change the relative amplitude of spectral components compared to the incident spectrum, thereby affecting the combining efficiency [9]. These effects could be reduced by using steeper spectral-edge filters.…”

“…This idea was recently implemented in Yb fiber amplifiers to increase the available gain bandwidth while allowing power scaling through the coherent combination of several amplifiers. Recent results report on the development of femtosecond spectral combining and pulse synthesis with an actively stabilized feedback loop in a multichannel configuration [9] or in a multicore fiber experiment [10]. Although these results demonstrate the feasibility of spectral combining in the context of fiber amplifiers, they do not show an improvement over a single amplifier setup in terms of optical bandwidth.…”

Extracting cavity and pulse phases from limited data for coherent pulse stacking

“…Coherent pulse stacking (CPS) is capable of conveniently adding large numbers of pulses, enabling the extraction of all available stored energy from a fiber amplifier while maintaining low intensity to minimize nonlinear effects [5][6][7][8] . Integrating CPS with spatial and spectral combining has the potential to provide joule level pulse energy at a kilohertz (kHz) repetition rate to bridge the technical gap [9][10][11] .…”

“…where arg is a function giving the argument of a complex number. Equations (9) and (10) are basic formulas that extract the cavity and pulse phases from limited data. More concretely, we calculate every output pulse phase out ψ k iteratively from the first to the last equation in Eq.…”