Femtosecond pulse generation beyond photon lifetime limit in gain-switched semiconductor lasers

Takashi Ito,Hidefumi Akiyama,Hidekazu Nakamae,Changsu Kim,Masahiro Yoshita,Shaoqiang Chen,Yohei Kobayashi,Yuji Hazama,Takahiro Nakamura

doi:10.1038/s42005-018-0045-0

Abstract

Femtosecond semiconductor lasers are ideal devices to provide the ultrashort pulses for industrial and biomedical use because of their robustness, stability, compactness and potential low cost. In particular, gain-switched semiconductor lasers have significant advantages of flexible pulse shaping and repetition rate with the robustness. Here we first demonstrate our laser, which is initiated by very strong pumping of 100 times the lasing threshold density, can surpass the photon lifetime limit that has restricted the pulse width to picoseconds for the past four decades and produce an unprecedented ultrashort pulse of 670 fs with a peak power of 7.5 W on autocorrelation measurement. The measured phenomena are reproduced effectively by our numerical calculation based on rate equations including the non-equilibrium intraband carrier distribution, which reveal that the pulse width is limited by the carrier–carrier scattering time, instead of the photon lifetime.

Highlights

Femtosecond semiconductor lasers are ideal devices to provide the ultrashort pulses for industrial and biomedical use because of their robustness, stability, compactness and potential low cost
Mode-locked semiconductor lasers in monolithic and externalcavity architectures have been developed since 1980s and demonstrated stable femtosecond pulse generation with high repetition rates corresponding to the cavity length
Gainswitched semiconductor lasers combined with rare-earth-doped fibre linear amplifiers in a master-oscillator-power-amplifier configuration have significant advantages because of the highly controllable optical pulses, such as variable repetition rate, arbitrary timing operation, flexible pulse duration, waveform spectral control and synchronization to electrical triggers, in addition to the robustness and stability[16,17,18,19,20]

Summary

Introduction

Femtosecond semiconductor lasers are ideal devices to provide the ultrashort pulses for industrial and biomedical use because of their robustness, stability, compactness and potential low cost. Gain-switched semiconductor lasers have significant advantages of flexible pulse shaping and repetition rate with the robustness. Mode-locked semiconductor lasers in monolithic and externalcavity architectures have been developed since 1980s and demonstrated stable femtosecond pulse generation with high repetition rates corresponding to the cavity length. Gainswitched semiconductor lasers combined with rare-earth-doped fibre linear amplifiers in a master-oscillator-power-amplifier configuration have significant advantages because of the highly controllable optical pulses, such as variable repetition rate, arbitrary timing operation, flexible pulse duration, waveform spectral control and synchronization to electrical triggers, in addition to the robustness and stability[16,17,18,19,20]. It was recently reported that additional non-linear pulse shaping in optical fibres can generate femtosecond pulses[21,22]

Methods

Results

Conclusion