Fig. 2

Illustration of the experimental arrangement used for injection seeding of the coupled-cavity laser. A Ti:Sapphire laser was used to generate femtosecond pulses, a fraction of the power was used to trigger a radio frequency source to generate gain switching pulses. The remaining power was split to form a pump beam and a probe beam. The pump beam was focused onto a photoconductive antenna to generate broadband terahertz pulses. These terahertz pulses were used to injection seed the lasing section of the coupled-cavity laser. The terahertz field emitted from the facet of the tuning section was sampled using an electro-optic crystal with the time-delayed probe beam. The gain switching pulses were combined with quasi-direct current pulses using a bias tee to drive the lasing cavity above threshold. A second quasi-direct current pulse generator was synchronised with the first pulse generator and was used to drive the tuning cavity