Hannah D. Foreman

Vertical-external-cavity semiconductor lasers

Surface-emitting semiconductor lasers can make use of external cavities and optical pumping techniques to achieve a combination of high continuous-wave output power and near-diffraction-limited beam quality that is not matched by any other type of semiconductor source. The ready access to the laser mode that the external cavity provides has been exploited for applications such as intra-cavity frequency doubling and passive mode-locking. The purpose of this Topical Review is to outline the operating principles of these versatile lasers and summarize the capabilities of devices that have been demonstrated so far. Particular attention is paid to the generation of near-transform-limited sub-picosecond pulses in passively mode-locked surface-emitting lasers, which are potentially of interest as compact sources of ultrashort pulses at high average power that can be operated readily at repetition rates of many gigahertz.

High-power, high repetition rate picosecond and femtosecond sources based on Yb-doped fiber amplification of VECSELs

Picosecond pulses at gigahertz repetition rates from two different passively mode-locked VECSELs are amplified to high powers in cascaded ytterbium doped fiber amplifiers. Small differences in pulse durations between the two VECSELs led to amplification in different nonlinear regimes. The shorter 0.5 ps pulses could be amplified to 53 W of average power in the parabolic pulse regime. This was confirmed by excellent pulse compression down to 110 fs. The VECSEL producing longer 4.6 ps pulses was amplified in an SPM dominated regime up to 200 W of average power but with poor recompressed pulse quality.

The lightwave roadshow

Many primary school children perceive science as boring and inaccessible. These misconceptions mould the paths these children will choose for their future education and careers, mirrored in reducing numbers of applicants for physics courses in higher education. We describe our experiences running a photonics outreach project, The Lightwave Roadshow, an interactive collection of photonics demonstrations and experiments aimed at children aged 5 to 11. We discuss how this programme can be instrumental in improving the profile of scientific education and careers for children of a young age.

Pulsed high power fiber laser systems

The master-oscillator power-amplifier approach, cladding pumping technology and large mode area fibers provide a route to compact and efficient pulsed fiber laser systems with high beam quality and high output powers

GaN diode-pumping of a red semiconductor disk laser

We report a 672 nm semiconductor-disk-laser pumped directly by gallium nitride laser diodes. Continuous wave output in a single transverse mode, tuneable over 16 nm and with maximum power of 17 mW, was achieved around room temperature.

Actively stabilised single-frequency red VECSEL

We report an actively stabilised single-frequency vertical external cavity surface emitting laser operating at 678nm with a 200kHz laser linewidth. More than 10mW of output power was achieved in single-frequency operation.

High-power, single-mode picosecond fiber laser based on amplification of a passively mode-locked 1055-nm VECSEL

4.6 ps pulses at 910 MHz produced by a passively mode-locked VECSEL were amplified by ytterbium doped fiber amplifiers to average powers greater than 200 W and subsequently compressed to 430 fs duration.

Passively mode-locked 832-nm vertical-external-cavity surface-emitting semiconductor laser producing 15.3-ps pulses at 1.9-GHz repetition rate

The authors report the first passively mode-locked 830- nm vertical-external-cavity surface-emitting laser. A semiconductor saturable absorber mirror with carrier recovery time governed by surface recombination was used to demonstrate pulses of 15.3 ps duration.

High Power Femtosecond Source Based on Passively Mode-Locked 1055-nm VECSEL and Yb-Fibre Power Amplifier

We report 5-ps pulses at 160 W average power and 910 MHz repetition rate from a passively mode-locked VECSEL source seeding an Yb-doped fibre power amplifier. The amplified pulses were compressed to 291 fs duration.

Science with coffee and Hobnobs

Many parents or guardians of primary school pupils have little knowledge of science, and many lack confidence in their ability to help their children, though most welcome the chance to do so. We describe our experiences running a series of meetings in the form of coffee sessions at local primary schools, where parents can increase their knowledge and confidence in the science their children study, and engage in simple experiments with their children to apply the knowledge they gain. We discuss how this programme can be instrumental in improving the profile of scientific education and scientific careers for children of a young age.