Programmable, Transform-Limited Pulses from a Terahertz Quantum Cascade Laser

We report programmable control of pulses from a quantum cascade laser. A programmable arbitrary waveform generator is used to control the emission of the lasers by gain-switching. Quantum cascade lasers with both multi-mode and single-mode emission are studied. Laser emission is coherently detected using a phase resolved injection seeding technique based on time domain spectroscopy. For the single mode laser, pulse widths of 500–4000 ps are demonstrated, with time-bandwidth products remaining close to, or below, unity for all pulse widths. Additionally, sequences of two pulses are demonstrated, where the pulse widths, delay, and amplitude of each of the pulses are programmed electronically. A range of pulse parameters are explored. This approach allows for the generation of arbitrary terahertz pulse sequences, which will enable coherent multidimensional spec-troscopy and applications requiring optimized pulse shapes.