Efficient High-Power Ultrashort Pulse Compression in Self-Defocusing Bulk Media

Marcus Seidel,Jonathan Brons,Kilian Fritsch,Gunnar Arisholm,Oleg Pronin,Vladimir Pervak

doi:10.1038/s41598-017-01504-x

Abstract

Peak and average power scalability is the key feature of advancing femtosecond laser technology. Today, near-infrared light sources are capable of providing hundreds of Watts of average power. These sources, however, scarcely deliver pulses shorter than 100 fs which are, for instance, highly beneficial for frequency conversion to the extreme ultraviolet or to the mid- infrared. Therefore, the development of power scalable pulse compression schemes is still an ongoing quest. This article presents the compression of 90 W average power, 190 fs pulses to 70 W, 30 fs. An increase in peak power from 18 MW to 60 MW is achieved. The compression scheme is based on cascaded phase-mismatched quadratic nonlinearities in BBO crystals. In addition to the experimental results, simulations are presented which compare spatially resolved spectra of pulses spectrally broadened in self-focusing and self-defocusing media, respectively. It is demonstrated that balancing self- defocusing and Gaussian beam convergence results in an efficient, power-scalable spectral broadening mechanism in bulk material.

Highlights

The Ti:Sa technology exhibits only limited power scalability
The pulses entering the compression setup emerged from a commercial-grade Kerr-lens mode-locked (KLM) TD oscillator (UltraFast Innovations GmbH)
The initial experiments on spectral broadening in BBO already pointed out in a brief statement that nonlinear beam distortions became only visible in the self-focusing regime[31]

Summary

Introduction

The Ti:Sa technology exhibits only limited power scalability. This is due to the lack of available high power pump diodes in the green as well as detrimental nonlinear and thermal effects in the rod-type gain materials (cf. e.g. ref. 8). The Ti:Sa technology exhibits only limited power scalability This is due to the lack of available high power pump diodes in the green as well as detrimental nonlinear and thermal effects in the rod-type gain materials The fluorescence linewidth of Yb:YAG is, for instance, only about Δλf = 9 nm full width at half of the maximum (FWHM) at room temperature[17], compared to Δλf = 230 nm for Ti:Sa18 This points out the general difficulty of the Yb-based lasers to directly emit sub-100 fs pulses and highlights the need for power-scalable ultrashort pulse generation schemes. Thin-disk (TD) laser oscillators has been subject to intense research since their first demonstration in the year 200019 Today, these fs laser oscillators deliver average powers of more than 250 W20, 21, pulse energies of up to 80 μJ22 and peak powers of more than 60 MW22, 23. Peak power increase through pulse compression becomes a prerequisite to efficiently drive strong-field effects like high harmonic generation

Methods

Results

Conclusion