Novel systems via nonlinear frequency conversion of fibre-amplified ultrafast semiconductor lasers

Abstract

This thesis presents the development of novel, high-power and high-energy ultrashort-pulse sources by exploiting nonlinear frequency conversion of Yb³⁺-doped-fibre (YDF)-amplified compact semiconductor lasers. Being highly efficient, compact and flexible, such topology offers tremendous opportunities across various industries and scientific communities such as electronics, photonics, manufacturing, healthcare, defence and fundamental physics. Here, tunable near- and mid-infrared (NIR and MIR) as well as supercontinuum sources with record-breaking and novel attributes are demonstrated.

Microjoule picosecond MIR pulse sources running at MHz repetition rates, particularly ones that are compact and economical, are highly sought after for resonant-infrared pulsed-laser deposition and ablation (RIR-PLD and RIR-PLA) in commercial facilities. A compact, stable, gain-switched-diode (GSD)-seeded picosecond master-oscillator power amplifier (MOPA), employing simple direct amplification via conventional YDFs in a nearly all-fiberised configuration, was developed to generate 18µJ pulse energies and an average power up to 100W at MHz repetition rates, with narrow spectral linewidth in a diffraction-limited and single-polarisation output beam. This flexible 1µm source demonstrated the highest reported pulse energies from a GSD-seeded picosecond MOPA and enabled successful generation of microjoule MIR (and multi-microjoule NIR) picosecond pulses at 1MHz via various periodically-poled-MgO:LiNbO₃-based optical parametric devices in the regime of 2.5-4µm, covering such vibrational resonances as the CH-stretch and OH-stretch. Moreover, the presented optical parametric oscillators (OPOs) showed the highest reported MIR and NIR pulse energies from a picosecond OPO.

GHz repetition rates are desirable for metrological applications of frequency combs. The first reported use of a fibre-amplified, mode-locked vertical-external-cavity surface-emitting laser as a pump source for supercontinuum generation is presented. The system consisted of a 1040nm femtosecond MOPA generating average power up to 40W at 3GHz repetition frequency, a high-throughput transmission-grating compressor and a photonic crystal fibre (PCF). Firstly, supercontinuum with a 10dB spectral bandwidth of 200nm and a flatness of better than ±1.5dB over a span of 150nm was generated via an all-normal-dispersion PCF. Secondly, a PCF with zero-dispersion wavelength at 1040nm was used to generate spectral components covering 750-1300nm but with much higher spectral intensity variations. Finally, an improved power amplifier was designed and built to boost the slope efficiency by more than two-fold to 90%. Potential applications include power-scaling femtosecond oscillators to average power of > 100W, as well as high-power self-referencing frequency-comb
generation.

More information

Identifiers

ORCID for David Shepherd: orcid.org/0000-0002-4561-8184

Catalogue record

Export record