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Low-temperature-grown GaAs (LT-GaAs)-based Fabry-Pérot cavity photoconductors, designed for RF and THz optoelectronics applications using1550 nm lasers, are studied. The sub-sampling of continuous waves at frequencies up to 300 GHz is presented. The duty-cycle-limited conversion losses measured up to 67 GHz show that this GaAs-based photoconductor behaves as a nearly perfect photoswitch controlled...
We study low-temperature-grown GaAs (LT-GaAs) based ultrafast Fabry-Pérot cavity photoconductors, designed for THz optoelectronics applications using 1550 nm pulsed lasers. We present here, as a proof of concept, the under-sampling of continuous RF waves up to 67 GHz.
Dual-comb sampling of an actively mode-locked phase-stabilized THz quantum cascade laser with 10 GHz Ti:sapphire frequency combs provides a method to directly determine the absolute frequency of the QCL with Hz-level precision.
Plasmonic THz photodetectors have been realized in this work, by implementing the active region of a 5 THz quantum well detector with an antenna-coupled microcavity array. Our results demonstrate a clear improvement in responsivity, polarization insensitivity and background limited performance.
We present a mid-infrared quantum cascade laser embedded into a micro-strip line for high frequency modulation. Modulating with less than 10mW at the round trip frequency, we observe beat-note injection locking within a range in the order of 1 MHz.
CEA-Leti has developed a real-time reflection imaging system: it combines illumination by QCL sources and a telescope that focuses the reflected radiation onto a camera that houses an uncooled 320×240 antenna-coupled micro-bolometer array driven by a FPGA card. We present first high resolution images of illuminated surfaces acquired in real-time.
A new scheme for coherent detection of a laser electric field has been demonstrated by stabilizing the emission frequency of a THz quantum cascade laser (QCL) on a harmonic of the repetition rate of a fs-fiber laser. This scheme has permitted to measure the pulses (10ps long) of a QCL that operates mode-locking, while the injected current is modulated close to its round trip frequency.
Ultrafast gain switching of THz quantum cascade lasers is demonstrated and applied to amplify sub-ps THz pulses as well as to initiate THz laser emission with a controlled phase. Impact on THz time domain spectroscopy and on future development for mode-locking will be discussed.
Laser action normally is initiated by the amplification of spontaneous emission. As spontaneous emission is a random process, the carrier phase of a laser is different each time a laser is turned on. As a consequence, it is not possible to measure the time-resolved field of a free-running laser using coherent detection techniques [1, 2]. Here we show [3] that it is possible to fix the carrier phase...
Mode-locked femtosecond (fs) lasers have become established as a means to probe fast transient phenomena, with pump-probe experiments using two mode-locked fs-lasers with slightly different repetition rates becoming widespread [1,2]. In these experiments, the time delay between the pump and the probe laser pulses is automatically scanned at the difference frequency between the repetition rates. Such...
We demonstrate coherent detection of the emission from a terahertz frequency quantum cascade laser which is actively mode-locked by modulating its bias-current with a microwave synthesizer. Coherent sampling of the terahertz pulse train is achieved by phase-locking the repetition rate and the carrier frequency of the terahertz quantum cascade laser to the repetition rate of the of a commercial erbium-doped...
Manual delineations by experts are often used as reference standards for validating segmentation algorithms, although it is well known that they always show some degree of variability. Our goal is to estimate the effects of using a limited number of expert segmentations. Given ten manual delineations of 13 liver tumors, we analyzed the volume error made by randomly selecting subsets of the ten segmentations...
The QCL carrier phase is set by coherent injection seeding with a THz pulse. This enables the phase-resolved laser emission to be measured in the time-domain and the QCL to be used directly for time-domain-spectroscopy.
Electro-optic sampling in ZnTe is used to phase-lock the line of a 2.5 THz quantum cascade laser to the repetition rate of a femtosecond fibre laser and to perform an absolute measurement of the laser emission frequency.
Integrated THz pulse generation and amplification in THz QCLs is demonstrated. Intracavity narrowband THz pulses are generated at 2.1THz by exciting the facet of a THz quantum cascade laser with a resonant interband-intersubband transition and detected using electro-optic sampling.
We demonstrate that the cavity resonance frequency - the round-trip frequency - of terahertz quantum cascade lasers can be injection-locked by direct modulation of the bias current using an RF source. Metal-metal and single-plasmon waveguide devices with roundtrip frequencies up to 35GHz have been studied, and show locking ranges above 200MHz. Inside this locking range the laser round-trip frequency...
This paper presents a CW raster-scanning THz imaging setup used to perform Non-Destructive Testing of Kevlar™ and carbon fibre samples. The setup uses a 2.5 THz Quantum Cascade Laser as a source. Delamination defect in a Kevlar sample was detected showing a sensitivity to laser polarization orientation. Detection of a break in a carbon/epoxy sample was also performed.
The population inversion of a terahertz quantum cascade laser is placed out of equilibrium using an integrated Auston switch. As a result, the dynamic gain of the laser is no longer clamped at threshold by the mirror losses, and large amplification of input terahertz probe pulses is observed.
We demonstrate the phase-locking of Quantum Cascade Lasers emitting at 2.4 and 2.7Terahertz, to the repetition rate of a commercial Er-doped fiber-fs-laser. We observe a linewidth of the beat-note signal with a signal-to-noise of 80dB in 1Hz bandwidth.
In this paper, a fast and robust graph-based approach for boundary estimation of fiber bundles derived from Diffusion Tensor Imaging (DTI) is presented. DTI is a non-invasive imaging technique that allows the estimation of the location of white matter tracts based on measurements of water diffusion properties. Depending on DTI data, the fiber bundle boundary can be determined to gain information about...
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