Quantum dot photoconductive antenna-based compact setups for terahertz spectroscopy and imaging

Abstract

We present the overview of the results on the development of compact THz setups based on the quantum dot photoconductive antennas obtained during the past five years. We demonstrate the potential of the InAs/GaAs Quantum-Dot based setups to become an efficient approach to compact, room-temperature operating CW and pulsed terahertz setups for spectroscopy and imaging. We describe the photoelectronic processes in quantum dot substrates and reveal the role of quantum dots in free carrier lifetimes and the formation of the ultrafast photocurrent. We demonstrate the operation mode of the proposed antennas in pulsed and CW regimes under resonant (carriers are excited only inside the quantum dots) and off-resonant (carriers are excited in the bulk volume of the substrate) pumps with compact quantum dot semiconductor lasers. The results allow suggesting the quantum dot based setups as a new approach to field condition compact THz sources for imaging and spectroscopy.

Photoconductive emitters for pulsed terahertz generation

“…Until recently there has been little interest in photoexciting in this wavelength range. Unlike at other wavelengths, where the use and development of a PC material is driven by laser technology, here the discovery of PC emission from materials such as GaAs incorporating InAs quantum dots (QDs) has prompted a shift in excitation to longer wavelengths [55,56,[130][131][132][133]. The reason for this is to enable resonant excitation within the InAs QD structures.…”

“…Firstly, an increase in optical pump power results in a rise in saturation bias field, this is typically not observed in bulk devices [134]. Secondly, the shorter carrier lifetime results in both increased signal at higher frequencies and the ability to sustain greater optical intensities prior to breakdown, compared with LT-GaAs devices [133]. The optical-to-THz conversion efficiency of the material can be improved by optimising the uniformity of QD sizes and the inter-QD spacing.…”

Operation of quantum dot based terahertz photoconductive antennas under extreme pumping conditions

“…Recently, we proposed more compact setups that use quantum dot (QD) based compact semiconductor lasers in conjuction QD based PCAs for generation of both pulsed and CW THz radiation [7][8][9][10] . Indeed, semiconductor materials incorporating InAs QDs in bulk GaAs possess all the properties required for efficient optical-to-THz conversion, such as short carrier lifetimes enabled by carrier capture into the dots 11 , while maintaining high carrier mobility 8 , unlike low temperature grown materials 2 .…”

Enhanced THz Generation From Interdigitated Quantum Dot Based Photoconductive Antenna Operating in a Quasi-Ballistic Regime

“…The QD based photoconductive substrate provides an inherent compatibility [10] with the QD ultrafast lasers [11]. Since introduction, QDPCA have proven to be an efficient THz emitters capable of generating tunable CW [12] and pulsed [9], [13] THz radiation. Due to high-quality, defect-less QD substrates, such PCAs demonstrate exceptional thermal and electrical breakdown tolerance, allowing for up to 1 W of pump power into a single gap antenna [14].…”