Quantum-dot based ultrafast photoconductive antennae for efficient THz radiation

Abstract

Here we overview our work on quantum dot based THz photoconductive antennae, capable of being pumped at very high optical intensities of higher than 1 W optical mean power, i.e. about 50 times higher than the conventional LT-GaAs based antennae. Apart from high thermal tolerance, defect-free GaAs crystal layers in an InAs:GaAs quantum dot structure allow high carrier mobility and ultrashort photocarrier lifetimes simultaneously. Thus, they combine the advantages and lacking the disadvantages of GaAs and LT-GaAs, which are the most popular materials so far, and thus can be used for both CW and pulsed THz generation. By changing quantum dot size, composition, density of dots and number of quantum dot layers, the optoelectronic properties of the overall structure can be set over a reasonable range-compact semiconductor pump lasers that operate at wavelengths in the region of 1.0 µm to 1.3 µm can be used. InAs:GaAs quantum dot-based antennae samples show no saturation in pulsed THz generation for all average pump powers up to 1 W focussed into 30 µm spot. Generated THz power is superlinearly proportional to laser pump power. The generated THz spectrum depends on antenna design and can cover from 150 GHz up to 1.5 THz.

Enhancement of terahertz photoconductive antenna operation by optical nanoantennas

“…With the development of compact ultrafast fiber and semiconductor lasers, followed by the use of new photoconductive materials suitable for the longer‐wavelength, e.g. Yb‐based lasers (1030 nm), Er‐doped fiber lasers (1550 nm) or semiconductor quantum dot lasers (950–1300 nm) pumping, such as GaBiAs , InGaAs , and also containing ErAs , and InAs quantum dots in GaAs substrates, these can lead to the creation of highly effective, miniature THz transmitters, working at room temperatures both in pulsed and CW regimes. Despite the complexity and high cost of hybrid electrodes fabrication, the total setup cost, that will exclude the extremely expensive titanium‐sapphire laser, should significantly decrease.…”

“…As a result, QCLs are geared mostly towards imaging, whereas photonic sources are especially demanded for spectroscopic applications. Development of antenna‐based monolithic THz sources in conjunction with compact semiconductor lasers is also highly feasible .…”

Photoelectric Properties of InAs/GaAs Quantum Dot Photoconductive Antenna Wafers

“…The laser output was monitored using an optical spectral analyzer (OSA Advantest Q8383) with the resolution of 0.1 nm and a broadband thermopile power meter. With this laser, broad tunability of 182 nm (between 1128 nm and 1310 nm), at room temperature (20 • C) and an operation current of 1.7 A giving a maximum output power of 435 mW, was achieved [5].…”

“…An extra spacer layer of GaAs was grown under the active photoconductive region on an AlAs/GaAs Distributed Bragg Reflector (DBR) of 30 layers. The need for the DBR is two-fold: to reflect the pump beam thus reducing the IR power at the antenna output, and to allow the possibility for full optical cavity-type optimization of the structure [20].…”

“…Recently, QD based PCAs have been demonstrated to successfully generate coherent THz radiation in the pulsed [6], [20] and CW [5], [6], [21] regimes. THz generation was achieved both within a Ti:Sapphire (GaAs bandgap) and a compact QD-based laser diode (QD bandgap) pumps.…”