Simulation of metallic nanostructures for emission of THz radiation using the lateral photo-Dember effect

A 2D simulation for the lateral photo-Dember effect is used to calculate the THz emission of metallic nanostructures due to ultrafast diffusion of carriers in order to realize a series of THz emitters.Comment: Corrected version of a paper given at 2011 36th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz

Mode-locked surface emitting semiconductor lasers

Optically-Pumped Vertical External Cavity Surface Emitting Lasers (OP-VECSELs) arc novel semiconductor-based lasers that have many advantages over other lasers in terms of the power scalability, good beam quality, compactness and low cost they can offer. They can be passively mode-locked with a Semiconductor Saturable Absorber Mirror (SESAM) to produce transform-limited sub-300 fs pulses directly from the laser cavity with high repetition rates.This thesis describes an experimental and theoretical investigation of OP-VECSELs. A full characterization is done on a VECSEL sample to understand time physics behind its operation iii the Continuous Wave (CW) mode and in the mode—locked mode. Then. a numerical model that, for the first time, shows the role of the Optical Stark Effect (OSE) in shaping the mode-locked pulses in the approach to steady state is introduced. TIme model results are broadly consistent with observed behavior of our diode-locked VECSELs.Here, I also report the first coherent generation and detection of terahertz radiation using all-semiconductor components. Radiation with a bandwidth of 0.8 THz has been generated using sub-500 fs pulses with an average power of 20 mW from a mode-locked VECSEL which contains InGaAs quantum wells and an LT-GaAs/InGaAs emitter/receiver antenna in a Terahertz Time Domain Spectrometer (THz-TDS) setup. The first mode locked OP-VECSEL at 830 rim is reported here. The combination of a GaAs quantum well-based gain sample and SESAI\I yielded an output with an average power of 5 mW and 15 ps-long pulses at a repetition rate of 1.9 GHz. A pumping module used to drive the laser was built for this purpose by combining the output of two commercial 665 nm diode lasers

Spectrotemporal gain bandwidth measurement in an InGaAs/GaAsP quantum well vertical-external-cavity surface-emitting semiconductor laser

Analysis of spectral condensation in a VECSEL with a near-antiresonant gain structure incorporating InGaAs/GaAsP quantum wells emitting around 1030 nm shows the effective FWHM gain bandwidth of this laser to be 32 nm

Mode-locking build-up measurements:probing the mode-locking mechanisms in Vertical-External-Cavity Surface-Emitting Lasers

The pulse evolution from onset to steady state in a mode-locked vertical-external-cavity surface-emitting laser producing femtosecond and picosecond pulses was studied. A 40-times reduction in pulse shortening rate from picosecond to femtosecond regime was observed

Ultrafast optical Stark mode-locked semiconductor laser

We report on 260 fs transform-limited pulses generated directly by an optical Stark passively mode-locked semiconductor disk laser at a 1 GHz repetition rate. A surface recombination semiconductor saturable absorber mirror and a step-index gain structure are used. Numerical propagation modeling of the optical Stark effect confirms that this mechanism is able to form the pulses that we observe

Gain Saturation in 60-fs Mode-Locked Semiconductor Laser

A passively mode-locked optically-pumped InGaAs/GaAs quantum well laser with an intracavity semiconductor saturable absorber mirror emits sub-100-fs pulses. Pulse energy declines steeply as pulse duration is reduced below 100 fs due to gain saturation

Numerical modelling of optical Stark effect saturable absorbers in mode-locked femtosecond VECSELs

Quasi-soliton modelocking has been identified as the mechanism responsible for the formation of picosecond pulses in passively mode-locked VECSELs, but neither this mechanism nor Kerr lens modelocking can account for the formation of sub-picosecond pulses from these lasers. Numerical simulations have shown that the optical Stark effect is capable of shortening pulses in the absence of bleaching, but to date no studies have been performed under realistic operating conditions. We model the interaction of an optical pulse with an absorbing quantum well using a semi-classical two level atom approximation. As the bandwidth of a VECSEL pulse is small compared to the spread of energies within a semiconductor band the population of two level atoms is divided into "live" atoms which interact with the optical field, and "dead" atoms which do not. Live and dead states are coupled by carrier-carrier scattering. Results from this model show an increase in pulse shortening above that due to saturable absorber bleaching at pulse durations below one picosecond, implying that an additional effect is responsible for the formation of femtosecond pulses. At these pulse durations the model predicts that the absorbing resonance broadens and decreases in amplitude. This is recognisable as a result of the optical Stark effect. The predictions of this model are compared to experimental results from several femtosecond VECSELs. For some modelocked VECSELs an excellent match between simulation and experiment is found, but in other cases the model cannot reproduce experimental results. We conclude that while the optical Stark effect may be the dominant pulse shaping mechanism in some modelocked VECSELs, others appear to be dominated by other effects

High peak power femtosecond pulse VECSELs for terahertz time domain spectroscopy

We report on a high peak power femtosecond modelocked VECSEL and its application as a drive laser for an all semiconductor terahertz time domain spectrometer. The VECSEL produced near-transform-limited 335 fs sech2 pulses at a fundamental repetition rate of 1 GHz, a centre wavelength of 999 nm and an average output power of 120 mW. We report on the effect that this high peak power and short pulse duration has on our generated THz signal