Enhancing the performance of THz quasi time-domain spectroscopy systems by low duty cycle laser operation.

We investigate the performance of terahertz (THz) quasi time-domain systems (QTDS) driven by electrically pulsed multi-mode laser diodes operating at 659 nm. We show that at the same average output power, a reduced duty cycle considerably increases the obtained bandwidth. In the presented experiment, the high frequency performance is improved by 50 dB/THz. We identify the broadening of the optical spectrum caused by pulsing the laser source to be responsible for the increased THz bandwidth.