Terahertz amplifier based on gain switching in a quantum cascade laser

Terahertz time-domain spectroscopy is widely used in a broad range of applications where knowledge of both the amplitude and phase of a terahertz wave can reveal useful information about a sample(1). However, a means of amplifying terahertz pulses, which would be of great benefit in improving the applicability of time-domain spectroscopy, is lacking. Although terahertz quantum cascade lasers(2) are promising devices for terahertz amplification(3), gain clamping(4) limits the attainable amplification(5). Here, we circumvent gain clamping and demonstrate amplification of terahertz pulses by ultrafast gain switching of a quantum cascade laser through the use of an integrated Auston switch(6). This unclamps the gain by placing the laser in a non-equilibrium state that allows large amplification of the electromagnetic field within the cavity. This technique offers the potential to produce high field terahertz pulses that approach the quantum cascade laser saturation field.