Monolithically integrated selectable repetition-rate laser diode source of picosecond optical pulses.

We describe the characterization of a monolithically integrated photonic device for short pulse generation featuring a mode-locked laser diode, a Mach-Zehnder modulator (MZM), and a semiconductor optical amplifier (SOA). The integrated device is designed for fabrication by a generic foundry scheme with a view to ease of design, testing, and manufacture. Trains of 6.8 ps pulses are generated at repetition rates that are electronically switchable from 14 GHz to 109 MHz. The SOA boosts the peak power by 7.4 dB, and the pulses are compressible to 2.4 ps by dispersion compensation using single-mode telecommunications fiber.This research leading to these results has received support from the UK EPSRC COPOS award EP/H022384/1 and from the European Commission’s Seventh Framework Programme FP7/2007-2013 under grant agreement NMP 228839 EuroPIC.This is the author accepted manuscript. The final published version can be found on the publisher's website at: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-14-414

175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser

We report a harmonically mode-locked vertical external cavity surface emitting laser (VECSEL) producing 400 fs pulses at a repetition frequency of 175 GHz with an average output power of 300 mW. Harmonic mode-locking was established using a 300 µm thick intracavity single crystal diamond heat spreader in thermal contact with the front surface of the gain sample using liquid capillary bonding. The repetition frequency was set by the diamond microcavity and stable harmonic mode locking was achieved when the laser cavity length was tuned so that the laser operated on the 117th harmonic of the fundamental cavity. When an etalon placed intracavity next to the gain sample, but not in thermal contact was used pulse groups were observed. These contained 300 fs pulses with a spacing of 5.9 ps. We conclude that to achieve stable harmonic mode locking at repetition frequencies in the 100s of GHz range in a VECSEL there is a threshold pulse energy above which harmonic mode locking is achieved and below which groups of pulses are observed

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

Femtosecond pulse generation in surface-emitting semiconductor lasers

In this thesis I report significant advances towards the goal of stable ultrashort pulse generation in mode-locked optically pumped vertical external-cavity surface-emitting lasers (VECSELs). Continuous wave VECSELs were first designed as a type of semiconductor laser capable of producing high output power in near transform-limited beams. Optical pumping allows the output power of the device to be increased simply by increasing the pumped area of the sample, and an external cavity forces the laser into single transverse mode operation. VECSELs’ external cavities also allow for the insertion of semiconductor saturable absorber mirrors (SESAMs) for modelocking. Mode-locked VECSELs have surpassed the performance of other types of mode-locked semiconductor laser, with modelocking via the optical Stark effect allowing VECSELs to produce sub-picosecond pulses in transform-limited beams, at power levels up to 100 mW and at GHz repetition rates.The work presented in this thesis describes recent progress in reducing the durations of VECSEL pulses to below 100 fs. At these pulse durations, gain saturation forces the laser oscillator to enter a dynamic regime never before seen in semiconductor lasers, which is also investigated here. In addition, the timing jitter of a VECSELmode-locked using the optical Stark effect is characterised for the first time, and a versatile frequency-divider-based active stabilisation technique is demonstrated. Finally, the fabrication of carbon nanotube based saturable absorbers for VECSEL modelocking via solution processing is investigated