Quantum dot photoconductive antenna-based compact setups for terahertz spectroscopy and imaging (original) (raw)

Quantum-dot based ultrafast photoconductive antennae for efficient THz radiation

SPIE Proceedings, 2016

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.

Characterisation of InAs:GaAs quantum dot-based photoconductive THz antennas

2013 IEEE Photonics Conference, 2013

• Background, THz research and devices -Ultrafast semiconductors and photonics -The quantum-dot solution • QD photoconductive THz devices and test setups • Performance of QD-based THz sources -Pulsed operation, "traditional" Ti:Sapphire-driven -Characteristic output signals and efficiency -Long-wavelength options

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

Applied Physics Letters

Photoconductive antennas deposited onto GaAs substrates that incorporate InAs quantum dots have been recently shown to efficiently generate both pulsed and CW terahertz radiation. In this Letter, we determine the operational limits of these antennas and demonstrate their extreme thermal breakdown tolerance. Implanted quantum dots serve as free carrier capture sites, thus acting as lifetime shorteners, similar to defects in low-temperature grown substrates. However, unlike the latter, defect-free quantum-dot structures possess perfect lattice quality, thus not compromising high carrier mobility and pump intensity stealth. Single gap design quantum dot based photoconductive antennas are shown to operate under up to 1 W of average pump power ($1:6 mJ cm À2 energy density), which is more than 20 times higher than the pumping limit of low-temperature grown GaAs based substrates. Conversion efficiency of the quantum dot based photoconductive antennas does not saturate up to 0.75 W of pump power ($1:1 mJ cm À2 energy density). Such a thermal tolerance suggests a glowy prospect for the proposed antennas as a perspective candidate for intracavity optical-to-terahertz converters.

Quantum dot materials for terahertz generation applications

Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well-established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual-wavelength continuous wave laser systems, though some limitations , such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot-based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical-to-terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy-dependent optical and electronic characteristics of quantum-dot-based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot-based semiconductor lasers as pump sources. Proof-of-concept experiments are demonstrated here that show quantum dot-based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power.

THz Superradiance from a GaAs: ErAs Quantum Dot Array at Room Temperature

Applied Sciences

We report that an ErAs quantum-dot array in a GaAs matrix under 1550 nm pulsed excitation produces cooperative spontaneous emission—Dicke superradiance—in the terahertz frequency region at room temperature. Two key points pertain to the experimental evidence: (i) the pulsed THz emission power is much greater than the continuous wave (CW) photomixing power; and (ii) the ultrafast time-domain waveform displays ringing cycles. A record of ~117 μW pulsed THz power was obtained, with a 1550 nm-to-THz power conversion efficiency of ~0.2%.

THz generation using 800 to 1550 nm excitation of photoconductors

2009

We demonstrate the efficient generation of terahertz (THz) radiation from Fe-doped InGaAs-based photoconductive antennas. We present time-domain data showing generation of pulsed THz radiation from antennas fabricated on two different wafers, optimized to maximize the near-infrared-to-THz conversion efficiency. Detection was performed using both (110) ZnTe and GaP crystals, with pump and probe wavelengths being adjusted from 800 nm to 1550 nm using a cavity-tuned OPO pumped by a pulsed near-infrared Ti:Sapphire laser.

Quantum dot-based semiconductor Terahertz transceiver systems

2014

Terahertz (THz) technology is still currently a rapidly developing area of research with applications already demonstrated in the fields of biology [1, 2], medicine [2-4], security [5-7], chemical/materials inspection [8-11] and astrophysics [12] to name a few. The diversity of applications which require the generation and measurement of THz or sub-millimeter (sub-mm) electromagnetic (EM) signals is the result of the vast number of chemical elements and compounds which exhibit molecular transitions and vibrational behavior that occur at frequency ranges corresponding to the so-called "THz gap", roughly defined as 0.05-10 THz. The THz gap was named as such because of the relative difficulty in