Abstract-Scattering strength dependence of terahertz random lasers

Journal of Applied Physics

S. Schoenhuber, M. Wenclawiak, M. A. Kainz, B. Limbacher, A. M. Andrews,  H. Detz, G. Strasser, J. Darmo, Karl Unterrainer,

(a) and (c) Dielectric environment ϵ(x)$ϵ(\mathrm{x})$ of ordered and random geometries of holes with 20μm$20\mu \mathrm{m}$ diameter which differ from the background in their refractive index. (b) and (d) Fourier space |ϵ(k)|$|ϵ(\mathrm{k})|$ obtained by two-dimensional Fourier transformation of ϵ(x)$ϵ(\mathrm{x})$. Ordered structures exhibit discrete peaks, while the random pattern contains a continuum of k-vectors.

https://aip.scitation.org/doi/abs/10.1063/1.5083699

Random lasing operation requires an active region, a gain medium that supports multiple scattering, and, especially for integrated optoelectronic devices, a nonresonant outcoupling mechanism over a continuous spectrum. For broadband operation, the resonator geometry must provide frequency nonselective, strong feedback over a large bandwidth. The feedback mechanism by multiple scattering in terahertz semiconductor random lasers and the bandwidth of such cavities are presented and discussed. We demonstrate the influence of shape and scattering strength of the scatterers on the lasing process and determine the bandwidth of such resonator structures. We use passive resonator structures to prove that the feedback as well as the outcoupling is frequency independent over a large bandwidth.

Abstract-Spectral gain profile of a multi-stack terahertz quantum cascade laser

D. Bachmann^1,2,a), M. Rösch³, C. Deutsch^1,2, M. Krall^1,2, G. Scalari³, M. Beck³, J. Faist³, K. Unterrainer^1,2 and J. Darmo^1,2

http://scitation.aip.org/content/aip/journal/apl/105/18/10.1063/1.4901316?TRACK=RSS

a) Author to whom correspondence should be addressed. Electronic mail: dominic.bachmann@tuwien.ac.at
Appl. Phys. Lett. 105, 181118 (2014); http://dx.doi.org/10.1063/1.4901316

The spectral gain of a multi-stack terahertz quantum cascade laser, composed of three active regions with emission frequencies centered at 2.3, 2.7, and 3.0 THz, is studied as a function of driving current and temperature using terahertz time-domain spectroscopy. The optical gain associated with the particular quantum cascade stacks clamps at different driving currents and saturates to different values. We attribute these observations to varying pumping efficiencies of the respective upper laser states and to frequency dependent optical losses. The multi-stack active region exhibits a spectral gain full width at half-maximum of 1.1 THz. Bandwidth and spectral position of the measured gain match with the broadband laser emission. As the laser action ceases with increasing operating temperature, the gain at the dominant lasing frequency of 2.65 THz degrades sharply.

Terahertz emission from a two-color plasma filament in a slot waveguide

http://apl.aip.org/resource/1/applab/v100/i9/p091113_s1?bypassSSO=1

Terahertz emission in forward direction from a long two-color filament placed in the center of a slot waveguide is reported. The waveguide improves the collection and imaging of the generated THz radiation. By tuning the plate separation and position of the waveguide along the filament axis, the emitted mode can be matched to the collection optics. We achieved an increase of the detected electric field by 40% and of the THz pulse energy by four times compared to the case without waveguide.

© 2012 American Institute of Physics