Novel method for the angular chirp compensation of passively CEP-stable few-cycle pulses.

Giovanni Cirmi,Benoit Debord,Fetah Benabid,Franz X Kärtner,Yi Hua,Hüseyin Çankaya,Frédéric Gérôme,Peter Krogen,Anne-Laure Calendron

doi:10.1364/oe.384290

Abstract

We demonstrate a novel, energy-efficient, cost-effective simple method for seeding CEP-stable OPCPAs. We couple the CEP-stable idler of a broadband OPCPA into a hollow core Kagome fiber thus compensating for the angular chirp. We obtain either relatively narrow bandwidths with ∼36% coupling efficiency or quarter-octave spanning bandwidths with ∼2.2% coupling efficiency. We demonstrate spectral compressibility, good beam quality and CEP stability. Our source is an ideal seed for high-energy, high-average power, CEP-stable few-cycle OPCPA pulses around 2 µm, which can drive the generation of coherent soft X-ray radiation in the water window spectral region via HHG.

Highlights

The generation of coherent water window (WW) radiation (282-533 eV) is one of the most explored research topics of the ultrafast optics community in the latest years [1,2,3,4,5,6,7,8]
Our source is an ideal seed for high-energy, high-average power, carrier-envelope phase (CEP)-stable few-cycle optical parametric chirped pulse amplifier (OPCPA) pulses around 2 μm, which can drive the generation of coherent soft X-ray radiation in the water window spectral region via high harmonic generation (HHG)
The driver pulses ideally need to have ∼mJ energies to drive enough HHG in the WW to be used in experiments, broad bandwidth and short duration to produce isolated attosecond pulses (IAPs) and carrier-envelope phase (CEP) stability to generate pulse-to-pulse reproducible IAPs

Summary

Introduction

The generation of coherent water window (WW) radiation (282-533 eV) is one of the most explored research topics of the ultrafast optics community in the latest years [1,2,3,4,5,6,7,8]. At the output of the fiber, the CEP-stable broadband idler has a well-defined propagation direction and no detectable angular chirp, and can be directly utilized as a seed for successive DOPA stages. We verified that the fiber did not introduce an oscillatory spectral phase which would not be difficult to compensate To this aim, we measured the temporal profile of the pulses at the output of the fiber via second harmonic generation frequency resolved optical gating (SHG FROG). To measure the angular chirp, we placed a multimode fiber (core size 105 μm) coupled to a spectrometer at ∼81 cm from the OPA output and measured the spectrum at different positions along the idler beam. The setup did not show significant short- or long-term instability in energy and pointing

CEP stability of the broadband OPA and perspectives

Findings

Conclusion