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The Maxwell-Bloch equations (MBE) describe the interaction between a two-level quantum mechanical system and an electromagnetic wave. They are widely used in nonlinear optics in general and to model quantum cascade lasers (QCLs) in particular [1]. Due to their nonlinearity, numerical methods are usually required to solve the equations. In order to cope with the computational complexity that arises,...
The discovery of intersubband transitions in III-V semiconductor heterostructures [I] had a huge impact on large parts of the condensed matter physics community and ultimately led to the development of quantum well infrared photodetectors [2] and quantum cascade lasers [3]. One of the main constraints, however, are the strict lattice matching conditions of the heterostructures — limiting the available...
Their inherently broadband gain and high value of the third order nonlinearity makes quantum cascade lasers (QCLs) ideal candidates for frequency comb generation in the terahertz (THz) and mid-infrared (midIR) spectral ranges. In recent years, it has been demonstrated that free running QCLs can produce broad comb spectra, even without any special endeavour to induce phase-locking of the lasing modes...
Near-field imaging techniques have great potential in many applications, ranging from the investigation of the optical properties of solid state and 2D materials to the excitation and direct retrieval of plasmonic resonant modes, to the mapping of carrier concentrations in semiconductor devices. Further to this, the capability of performing imaging with non-ionizing terahertz (THz) radiation on a...
Quantum cascade lasers (QCLs) are compact and powerful sources that cover a wide spectral range from infrared to terahertz (THz) radiation. The emission characteristics of QCLs depend on design parameters such as layer thickness, material composition and doping. Therefore, the material system has to be chosen accurately. Most commonly used material systems for THz QCLs are GaAs/AlGaAs and InGaAs/InAlAs...
We investigate the possibility of slowing down terahertz light via intersubband transitions in quantum well heterostructures. The slow-down effect is achieved via tunneling induced transparency [1] in a three level Λ-system by careful engineering of the wave functions [2]. The inherently short coherence times in such solid state media inevitably leads to strong absorption of the signal, which we propose...
Terahertz (THz) and sub-THz frequency emitter-detector technology is receiving increasing attention because of key apphcations in several fields. In particular, ultrafast THz receivers are desired for compact, ultrafast spectroscopy and communication systems. While most of the available THz detectors (thermal, FET …) are currently limited in response time by slow thermal processes and/or by the read-out...
Accurate molecular spectroscopy in the mid-infrared (mid-IR) region allows precision measurements with applications in fundamental physics. We present our on-going work towards measuring absolute vibrational frequencies of various polyatomic species — in particular methanol — around 10 μm, at an unprecedented level of accuracy, using a both ultra-stable and widely tuneable near-infrared frequency...
Laser-induced forward transfer appears to be one of the key players of additive manufacturing at the micrometer scale. The basic concept of LIFT consists in the backside laser irradiation of a thin donor film, in solid[1], paste[2] or liquid[3] state, coated on a transparent substrate to transfer a small volume of the donor material onto a receiver substrate placed nearby. From investigations on different...
High-peak-power longwave OPAs operating above the wavelength of 5μm [1] require high-energy picosecond pump pulses >2 μm. These can be generated directly in laser amplifiers, e.g. Ho-doped [1, 2] or via cascaded OPAs [3]. Burst-mode pump lasers offer great advantages over single-pulse amplifiers because they help overcoming the challenges of chirped-pulse as well as direct picosecond pulse amplifiers...
Quantum cascade lasers (QCLs) are unipolar semiconductor devices emitting in the mid-and far-infrared spectral ranges. Due to their relatively narrow linewidths and short gain recovery times, these lasers have been deemed difficult, if not impossible, to passively mode lock (PML) [1, 2]. However, the successful mode locking of QCLs is of utmost importance as it could allow generation of ultrashort...
For a number of applications, high average power in the mid-infrared (MIR) part of the spectrum is required from a compact laser. The quantum-cascade laser (QCL) emitting in the mid-infrared region of 4 to 8 μm has been refined to the point that its internal quantum efficiency is approaching fundamental limits. QCLs designed for power typically contain 30–40 cascades, are less than two wavelengths...
The continuous development of terahertz (THz) sources has opened up many potential applications in spectroscopy, imaging and communications. One popular THz source is the quantum cascade laser (QCL), which has many desirable properties including compactness and high output power with a narrow emission frequency. For such a source to be successfully integrated into a THz communication system, it is...
New laser applications as air pollutant measurement, free-space communications, range-finding, target illumination, molecular spectroscopy, medicine treatment or biomedical diagnostics, industrial technologies (plastics forming, cutting, welding, marking) require the laser radiation with the wavelength in the mid-infrared region. Meanwhile, the lasers based on gas (CO), semiconductor (lead-salt),...
High harmonic generation (HHG) requires high peak-power laser sources. Most of the well-known high peak power lasers are operating in the near-IR wavelength region. Recently it was demonstrated that HHG can be effectively phase matched in the soft X-ray region by using very high intensity UV lasers and multiply charged ions [1]. High average and high peak power UV sources operating around and below...
The QCL comb was first unveiled in the mid-IR in 2014, proven a true comb by a technique called beatnote spectroscopy[1]. The temporal field profile of such a comb is of great interest, but unfortunately such a technique does not capture phase information. We already know the inherently short upper-state lifetime of QCLs inhibits transform limited pulses[2] as in conventional mode-locked laser combs,...
Optical frequency combs (OFCs) generated by quantum cascade lasers (QCLs) have recently been proven in the mid infrared [1] and they have already been applied to spectroscopy in free-running operation [2]. It is clear however that for more demanding applications such as high-resolution and accuracy spectroscopy and metrology the performance obtained in free-running operation is not enough, since a...
We report on metrological-grade saturated absorption spectroscopy of CHF3 at 8.63 μm based on CW distributed-feedback QCL laser and a mid-IR self-frequency referenced optical comb. The experimental setup for the saturation spectroscopy of CHF3 is shown in Fig. 1. A CW DFB-QCL with a maximum output power of ∼40 mW tunable in the wavelength range from 8.55 to 8.65 μm, in coincidence with the us (asymmetric...
Heralded single-photon sources (HSPS) are widely used in experimental quantum science because they have negligibly small jitter and can therefore achieve high visibility for quantum interference. However, it is necessary to decrease the photon generation rate to suppress multi-photon components. To address this problem, two methods have been proposed and discussed: spatial (or temporal) source multiplexing...
Femtosecond laser waveguide writing is a powerful technique to create photonic devices and is already widely applied in glasses and crystals [1]. In polymers however, relatively little work has been reported so far. Material specific effects during femtosecond laser irradiation such as chain scission or crosslinking and an overall low damage threshold demand for alternative writing schemes to overcome...
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