VECSEL basics

Group research

People

Papers

Ultrashort pulse generation

A core focus of our work is pushing the limits of ultrashort pulse generation from semiconductor lasers. Recently we produced pulse trains with pulses of duration 60-fs using quantum well gain and absorber material. This is pulse duration sets a new record for semiconductor lasers as a whole as well as VECSELs. We exploit the optical Stark effect in surface recombination SESAMs to modelock our VECSELs and carefully design our gain and absorber samples to achieve the required gain bandwidth and dispersion properties to generate transform limited pulses.

Modelling of absorber dynamics

Closely linked to our experimental work on ultrashort pulse generation we are modelling the fundamental processes which occur in our saturable absorbers to better understand the physical mechanisms and limits of the modelocking techniques we currently use. We have unambiguously shown that the optical Stark effect is capable of shortening pulses in the absence of any other competing processes and we have developed more complete models of our absorbers, to include bleaching and spectral hole burning.

Quantum dot VECSELs

Our research on quantum dot VECSELs has started as a result of our work on ultrashort pulse generation. Quantum dots have 3D quantum confinement, instead of the 1D found in the quantum wells that we typically use. This different confinement offers different dynamical and spectral properties, which we hope to exploit to further push the limits of ultrashort pulse generation in semiconductor lasers.

VECSEL MOPAs

Modelocked VECSELs can be used to great effect as high repetition rate, ultrashort pulse seed sources for ytterbium doped fibre amplifiers. We have explored the potential of these VECSEL MOPA systems in collaboration with the optoelectronics research centre, here at the University of Southampton. We have demonstrated the applicability of this technique, amplifying our pulse train to an average power of 300W. We are currently exploring research and commercial applications of these high power high repetition rate sources.

High repetition rates

VECSELs are unique laser sources due to their class A nature and are therefore ideal for high repetition rate pulse trains with no Q switching instabilities. We have demonstrated 10 GHz repetition rate VECSELs with sub-picosecond pulse durations and are currently working on several methods of increasing this repetition rate up to the 100's of GHz. Such high repetition rate sources could be of interest for applications like optical clock distribution or optical analogue to digital conversion.

Jitter reduction and characterisation

Applications such as optical clock distribution require low jitter sources. VECSELs have very low fundamental limits to their noise due to their class A nature. We have therefore characterised the noise of both picosecond and femtosecond pulse duration VECSELs as well as undertaken active stabilisation, using a variety of phase lock loop feedback schemes.

Terahertz generation using VECSELs

Terahertz time domain spectroscopy is now a large research field, with many potential applications from homeland security, where THz can be used to identify explosives, drugs and even biological agents, through to fundamental research in plasmonics and metamaterials. VECSELs have pulse characteristics which make them potential compact and low cost laser sources which can be used to drive THz spectrometers. We are developing these all semiconductor THz-TDS systems here with the aim of exploring their future commercial potential as ultra compact broadband THz sources.