laboratoire pierre aigrain
électronique et photonique quantiques
laboratoire pierre aigrain

THz pulse amplification
dec 9, 2009

The spectral region between 0.1 and 10 THz is known as the “Terahertz (THz) gap”. Compared with other regions of the electromagnetic spectrum, it is underdeveloped and there is a lack of sources, amplificators and detectors. Le development of new devices in this domain is a major goal of modern opto-electronics. The “ultra-fast THz spectroscopy” group at LPA-ENS has recently developed a THz pulse amplificator based on novel scheme of “gain-switching” in quantum cascade lasers.
Ultra-fast THz spectroscopy is a recent technique and is now used for a number of applications ranging from studies of semiconductor nanostructures to bio-systems, where both the amplitude and phase of the THz wave can reveal interesting information. In these experiments, ultra-fast (sub-ps) THz pulses are generated from near-infrared pulses, by optical rectification or using photoconductive antennas. Nevertheless, the resulting THz pulses display a low power and THz techniques would therefore strongly benefit from the development of efficient amplifiers. Even though THz quantum cascade lasers are promising sources, their use as amplifiers is a priori limited. Indeed, in a stationary regime, the laser gain is “clamped” and equal to the losses in the system, as in all lasers.
The solution developed at LPA-ENS consists in placing the laser out of equilibrium using an ultra-fast switch (“Auston switch”), integrated into the device. This allows to switch on the quantum cascade laser on a picosecond timescale, considerably faster than the build-up time of laser action, circumventing gain clamping and amplifying THz pulses up to 26 dB (in our experiment). The device is a gain-switching amplifier.

References :
- N. Jukam et al. Nature Photonics 3, 715 (2009)
- News and Views par A. Tredicucci et A. Di Carlo Nature Photonics 3, 681 (1 Dec 2009)

Contacts : Sukhdeep Dhillon ; Jerome Tignon

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Amplification d’ondes THz
Image by David Darson