Filters

2020 - 20213

More filters

2021 - 20233
Reset filters

Settings

End date: 2024 × Start date: 2020 × Start date: 2020 × DDC: 500 × DDC: 530 × WGL Institute: IPHT ×

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Memory effect assisted imaging through multimode optical fibres
    ([London] : Nature Publishing Group UK, 2021) Li, Shuhui; Horsley, Simon A.R.; Tyc, Tomáš; Čižmár, Tomáš; Phillips, David B.
    When light propagates through opaque material, the spatial information it holds becomes scrambled, but not necessarily lost. Two classes of techniques have emerged to recover this information: methods relying on optical memory effects, and transmission matrix (TM) approaches. Here we develop a general framework describing the nature of memory effects in structures of arbitrary geometry. We show how this framework, when combined with wavefront shaping driven by feedback from a guide-star, enables estimation of the TM of any such system. This highlights that guide-star assisted imaging is possible regardless of the type of memory effect a scatterer exhibits. We apply this concept to multimode fibres (MMFs) and identify a ‘quasi-radial’ memory effect. This allows the TM of an MMF to be approximated from only one end - an important step for micro-endoscopy. Our work broadens the applications of memory effects to a range of novel imaging and optical communication scenarios.
  • Thumbnail Image
    Item
    Observation of direction instability in a fiber ring laser
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Arshad, Muhammad Assad; Hartung, Alexander; Pratiwi, Arni Candra; Jäger, Matthias
    We report on the observation of a new phenomenon occurring in a fiber ring laser. This phenomenon is about the transition from an initially bidirectional emission of a reciprocal fiber ring laser to a unidirectional emission at a certain pump power threshold. In addition, the final direction is not predefined but appears to be randomly chosen every time the threshold is exceeded. Therefore, we term this new phenomenon direction instability. Furthermore, we provide a first discussion of how the instability threshold is influenced by the length and the loss of the cavity. We show that the threshold follows a power times length scaling, indicating a nonlinear origin.
  • Thumbnail Image
    Item
    New methodology to process shifted excitation Raman difference spectroscopy data : a case study of pollen classification
    ([London] : Macmillan Publishers Limited, 2020) Korinth, F.; Mondol, A.S.; Stiebing, C.; Schie, I.W.; Krafft, C.; Popp, J.
    Shifted excitation Raman difference spectroscopy (SERDS) is a background correction method for Raman spectroscopy. Here, the difference spectra were directly used as input for SERDS-based classification after an optimization procedure to correct for photobleaching of the autofluorescence. Further processing included a principal component analysis to compensate for the reduced signal to noise ratio of the difference spectra and subsequent classification by linear discriminant analysis. As a case study 6,028 Raman spectra of single pollen originating from plants of eight different genera and four different growth habits were automatically recorded at excitation wavelengths 784 and 786 nm using a high-throughput screening Raman system. Different pollen were distinguished according to their growth habit, i.e. tree versus non-tree with an accuracy of 95.9%. Furthermore, all pollen were separated according to their genus, providing also insight into similarities based on their families. Classification results were compared using spectra reconstructed from the differences and raw spectra after state-of-art baseline correction as input. Similar sensitivities, specificities, accuracies and precisions were found for all spectra with moderately background. Advantages of SERDS are expected in scenarios where Raman spectra are affected by variations due to detector etaloning, ambient light, and high background.