Adaptively shaped advanced ultrafast laser sources

The aim of the work presented in this thesis is to investigate adaptively shaped advanced ultrafast laser sources in the near-(NIR) and the mid-infrared (MIR) regimes. The setup involves shaping a NIR pulse using an adaptively controlled liquid crystal spatial light modulator (LC-SLM) in a pulse shaper. The shaped NIR pulse is then transferred to the MIR via a synchronously pumped optical parametric oscillator (SPOPO).<br/><br/>Initially, experiments are conducted to investigate adaptive phase control of the input pulse of a 500 fs fibre-based chirped pulse amplification (CPA) system, which is an attractive pump source for the SPOPO. Results are obtained using both bulk and fibre stretchers in the system. The adaptive process was controlled by a simulated annealing algorithm and three times improvement in the autocorrelation peak intensity was demonstrated, with close to transform-limited pulse durations of 800 fs at pulse energies as high as 65 μJ. Following this, a home-built adaptively shaped fibre CPA system is tested for its average power and energy scalability while maintaining high quality pulses by amplitude and phase pre-shaping. For these results, the LC-SLM is controlled using a differential evolution algorithm and a train of pulses is produced with an average power of 12.6W at a 50MHz repetition rate, which are compressible to high fidelity pulses with duration of 170 fs. High-quality, high-energy pulses are obtained even when the repetition rate of the system is reduced to as low as ~400 kHz.<br/><br/>The second part of the work is to experimentally investigate the effects of various parameters in the transfer of pulse shape from the NIR to the MIR in a SPOPO with a Nd:YLF picosecond pump source and incorporating the factors, high fidelity transfer is achieved. The pulse was characterised using the cross-correlation sonogram technique. Cross-correlation based frequency resolved optical gating is also studied as the method of idler pulse characterisation and the advantages and disadvantages compared to the sonogram technique are discussed.<br/><br/>Finally, the two technologies of an adaptively shaped ultrafast fibre CPA system and the pulse shape transfer in a SPOPO are experimentally combined to form an advanced adaptively shaped ultrafast laser source for various applications.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2011

Author dc:creator

• Daga, Nikita K.

Advisor dc:contributor.advisor

• Shepherd, D.P.