Intrinsic frequency tuning of terahertz quantum-cascade lasers

Schrottke, L.; Lü, Xiang; Röben, Benjamin; Biermann, K.; Wienold, Martin; Richter, Heiko; Hübers, Heinz‐Wilhelm; Grahn, H. T.

doi:10.1063/1.5024480

Cited by 7 publications

(6 citation statements)

References 43 publications

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“…Since our model is based on approximations for the carrier transport, the simulation results for complex structures are expected to be of limited quantitative accuracy. Similarly, a reduced predictability for complex structures has been observed in the analysis of the currentinduced tuning based on the same model [35].…”

Section: Intersubband Transitionsmentioning

confidence: 61%

“…The onset of the optical gain in a laser leads to a modification of the refractive index and hence to a difference between the frequency of the laser mode and the resonator mode without pumping and lasing. In contrast to the case of most other lasers, frequency pulling in THz QCLs can substantially contribute to the dynamic tuning induced by the injection current [35]. The influence of the gain on the refractive index is further discussed in subsection 3.3.…”

Section: Figure 3(a)mentioning

confidence: 99%

“…Intersubband transitions have recently been found to substantially contribute to the dynamic tuning of THz QCLs by means of the injection current [35]. These transitions affect the refractive index through optical gain or loss, which can be explained with the Lorentz oscillator model.…”

Section: Intersubband Transitionsmentioning

confidence: 99%

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Effective group dispersion of terahertz quantum-cascade lasers

Röben

Lü

Biermann

et al. 2020

J. Phys. D: Appl. Phys.

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Terahertz (THz) quantum-cascade lasers (QCLs) are based on complex semiconductor heterostructures, in which the optical gain is generated by intersubband transitions. Using the spacing of the laser modes in the emission spectra, we have determined the effective group refractive index n g , e f f for more than one hundred THz QCLs of the hybrid design with Fabry–Pérot resonators based on single-plasmon waveguides. The experimentally obtained values of n g , e f f for emission frequencies between 2.5 and 5.6 THz generally follow the trend of n g , e f f derived from electromagnetic simulations. However, for a certain number of QCLs, the experimental values of n g , e f f exhibit a rather large deviation from the general trend and the simulation results. From a thorough analysis, we conclude that differences in the optical gain/loss spectra are responsible for this deviation, which lead to a modification of the dispersion in the active region and consequently to altered values of n g , e f f . The analysis also provides evidence that these differences in the gain/loss spectra originate from both, the details of the design and the gain broadening due to interface roughness.

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Section: Intersubband Transitionsmentioning

confidence: 61%

Section: Figure 3(a)mentioning

confidence: 99%

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Effective group dispersion of terahertz quantum-cascade lasers

Röben

Lü

Biermann

et al. 2020

J. Phys. D: Appl. Phys.

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“…While the former process leads to a lowering of the energy of the injector state, it compensates for the latter one, resulting in an extended dynamic range. This allows for a reasonable intrinsic tuning range of the laser modes even for designs with a vertical laser transition as shown recently [16].…”

Section: Designsmentioning

confidence: 87%

High-Performance GaAs/AlAs Terahertz Quantum-Cascade Lasers For Spectroscopic Applications

Schrottke

Röpcke

Grahn

et al. 2020

IEEE Trans. THz Sci. Technol.

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We have developed terahertz (THz) quantumcascade lasers (QCLs) based on GaAs/AlAs heterostructures for application-defined emission frequencies between 3.4 and 5.0 THz. Due to their narrow line width and rather large intrinsic tuning range, these THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy, which is expected to allow for a quantitative determination of the density of atoms and ions in plasma processes. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature cryocoolers due to the comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm 2. These lasers emit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications. Index Terms-Quantum-cascade laser (QCLs), terahertz (THz) spectroscopy. I. INTRODUCTION T HE invention of quantum-cascade lasers (QCLs) about 25 years ago [1] opened the path to a variety of spectroscopic approaches in the mid-to far-infrared spectral region. In particular, QCLs for the terahertz (THz) spectral region [2] allow for high-resolution spectroscopy of molecules, atoms, and ions utilizing rotational or fine-structure transitions. During the

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“…For the development of more efficient laser schemes for THz QCLs, as well as a low loss waveguide design, the information is needed on the loss in THz QCLs over a wide range of temperatures and frequencies. It is shown that the loss in THz QCLs plays an important role in the internal tuning of the radiation frequency [3]. In this work, we propose to use a double metal waveguide based on silver (Ag), for reducing the losses of the waveguide.…”

mentioning

confidence: 99%