Filters

2017 - 201912020 - 20212

More filters

2019 - 201912020 - 20222
Reset filters

Settings

Subject: Blue shift ×

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Continuous tuning of two-section, single-mode terahertz quantum-cascade lasers by fiber-coupled, near-infrared illumination
    (New York : American Institute of Physics, 2017) Hempel, Martin; Röben, Benjamin; Niehle, Michael; Schrottke, Lutz; Trampert, Achim; Grahn, Holger T.
    The dynamical tuning due to rear facet illumination of single-mode, terahertz (THz) quantum-cascade lasers (QCLs) which employ distributed feedback gratings are compared to the tuning of single-mode QCLs based on two-section cavities. The THz QCLs under investigation emit in the range of 3 to 4.7 THz. The tuning is achieved by illuminating the rear facet of the QCL with a fiber-coupled light source emitting at 777 nm. Tuning ranges of 5.0 and 11.9 GHz under continuous-wave and pulsed operation, respectively, are demonstrated for a single-mode, two-section cavity QCL emitting at about 3.1 THz, which exhibits a side-mode suppression ratio better than -25 dB.
  • Thumbnail Image
    Item
    Polarization-dependent vibrational shifts on dielectric substrates
    (Cambridge : RSC Publ., 2020) Yang, C.; Wang, W.; Nefedov, A.; Wang, Y.; Mayerhöfer, T.G.; Wo¨ll, C.
    The interaction of light with matter at surfaces of dielectrics strongly depends on polarization. Here, we present the first infrared spectroscopic evidence for significant polarization effects in the spectroscopic detection of adsorbate vibrational frequencies. In addition to much larger peak intensities for p-polarized light relative to s-polarization, a small but distinct blue shift was identified for CO adsorbed at the surfaces of two prototype dielectric substrates, CeO2(111) and CaCO3(10.4). A simulation using a layer model yields very good agreement with experiment.
  • Thumbnail Image
    Item
    Space-time focusing and coherence properties of supercontinua in multipass cells
    (College Park, MD : APS, 2021) Mei, Chao; Steinmeyer, Günter
    The situation of self-compression and concomitant supercontinuum generation in a multipass cell is analyzed in numerical simulations. This study focuses on multipass cells that contain a dielectric slab as nonlinear medium and overcompensate the dispersion of the slab with intracavity dispersive coatings. A 2D+1 unidirectional pulse propagation equation is utilized to simulate the pulse evolution through successive passes. We observe a previously unreported effect of space-time focusing, leading to a pronounced blue shift, similar to what had been observed in filament compression experiments before. This effect competes with detrimental pulse breakup, which can nevertheless be mitigated under suitable choice of cavity parameters. We further analyze resulting coherence properties, in both the time and frequency domains. Our analysis shows highly favorable properties of multipass cell compression schemes when nonlinearity and dispersion are distributed over as many cavity passes as possible. This quasicontinuous approach is particularly promising for spectral broadening schemes that allow for stabilization of the carrier-envelope phase.