Acousto-optic pulse picking scheme with carrier-frequency-to-pulse-repetition-rate synchronization.

Oliver De Vries,Arno Klenke,Simon Holzberger,Andreas Tünnermann,Armin Hoffmann,Tobias Saule,Fabian Lücking,Thomas Schreiber,Ramona Eberhardt,Tino Eidam,Jens Limpert,Marco Plötner,Steffen Hädrich,Ioachim Pupeza

doi:10.1364/oe.23.019586

Abstract

We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing.

Highlights

Mode-locked laser oscillators used as seeding sources for high-power amplifier systems often emit at tens of MHz pulse repetition frequencies, eventually leading to moderate pulse energies after amplification
We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train
We have introduced and demonstrated a technique utilizing a travelling-wave-type AOM in a high-contrast, high-repetition-rate pulse picking scheme, where pulse peak power fluctuations have to be kept at a minimum

Summary

Introduction

Mode-locked laser oscillators used as seeding sources for high-power amplifier systems often emit at tens of MHz pulse repetition frequencies, eventually leading to moderate pulse energies after amplification. Reducing high pulse repetition rates requires switching methods that periodically pick single pulses out of an input pulse train This can be done optically by selectively amplifying single pulses in nonlinear crystals [11], an approach which even preserves CE phase stability [12]. A travelling-wave-type AOM imposes a Doppler-frequency shift equal to the AOM carrier frequency on the optical comb of the picked pulses and, creating (or contributing to) a new carrier-envelope-offset frequency This very effect can be exploited to provide CE phase stabilization to a free-running mode-locked laser [15], but in this case the AOM is not used as pulse picker. Comparative experiments reveal additional amplitude noise when the AOM carrier signal is not synchronized to the pulse repetition frequency (standard approach) showing that CE phase stable systems benefit from our findings, but rather any pulsed laser system relying on acousto-optic reduction of the pulse repetition frequency

Theory

Experimental setting

CE phase stability

Amplitude stability

Conclusion