Fabien Destic

Dynamic Modeling of Terahertz Quantum Cascade Lasers

In this paper, the influence of the simplifications made in the four-equation-based set of rate equations describing the dynamic behavior of a quantum cascade laser (QCL) is studied. Numerical simulations based on the set of four rate equations has been developed, enabling the theoretical study of the influence of different parameters on the direct modulation response of the laser. These equations have been then linearized in order to deduce a set of state system equations, which was written in a matrix formalism. Finally, an approximate second-order transfer function has been derived with the linearized dependence of its times constant.

THz QCL-based active imaging dedicated to non-destructive testing of composite materials used in aeronautics

This paper presents a CW raster-scanning THz imaging setup, used to perform Non-Destructive Testing of KevlarTMand 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.

Direct modulation and bandwitdh measurement of terahertz quantum cascade laser

The authors present a home made cryogenic electro-optical probe station allowing the direct modulation of quantum cascade lasers up to 40GHz. Based on a QMC cryostat, it should make the QCL bandwidth measure possible and then help answering questions about the modulation possibilities of such a kind of laser. The experimental results will be compared to simulation bandwidth prediction based on a complete set of rate equations describing the dynamic behavior of the laser. Bandwidth will be then linked to the different intrinsic and structural parameters.

THz QCL-based active imaging applied to composite materials diagnostic

This paper is a presentation of the on going research at OLIMPES laboratory in the field of active imaging using THz Quantum Cascade Lasers applied to composite materials diagnostic. We have performed transmission measurements on various types of materials, most of them used in aeronautical engineering. We present some transmission mode images realized to investigate the possibilty to use THz imaging in nondestructive material diagnostic.

Bandwidth simulation and measurement of terahertz quantum cascade laser

We present a new modeling of the direct modulation response of a Quantum Cascade Laser (QCL), using the complete set of rate equations describing its behavior. We show in the first part that the bandwidth could not be as high as it has been proposed in previous work. The second part describes the experimental setup to access the dynamic behavior of the QCL thanks to a non linear transfer onto a telecom optical carrier.

Non destructive observation of defects in composite materials using time domain THz imaging

Terahertz waves can penetrate opaque materials and fingerprint spectra appear as those in infrared bands. The technique is expected to be used as a new non-invasive analysis method for various materials. The authors have applied terahertz time domain spectroscopy (THz-TDS) to observe cracks of two types of fibre-reinforced polymers (FRPs) which were Kevlar-and Carbon - FRPs in reflection mode. Internal defects, cracks or a void of Kevlar - FRP were clearly observed, which cannot be detected non-invasively by existing methods, such as ultrasound imaging. Although CFRP is highly reflective and the internal structure was hardly recognised observed, surface defects under the paint can be easily observed.

Modeling of static and dynamic behaviour of 2.9THz Quantum Cascade Lasers

Based on simplified rate equations, both static and dynamic behaviour have been studied in order to characterize 2.9THz QCLs that will be used in detection or transmission systems. Comparison of expected static behaviour and experimental one shows good correspondence. We have been able to extract a semi-empirical law of evolution of the threshold current with temperature and link it with the optical gain. About the dynamic behaviour, theoretical simulations show that bandwidth of more than 150 GHz is attainable during direct intensity modulation (IM), with a response without any peak of resonance (due to the different estimated lifetimes of the tested QCL).