Micro- and Nanoscopy Systems

Measurement setup with scanning laser-Doppler vibrometer microscope. Photo: Kowarsch

Superresolution reflection microscopy via absorbance modulation

Dipl.-Ing. (FH) Robert Kowarsch

State of the Art/Motivation

  • In far-field optical nanoscopy, on- and off-switching of molecular fluorescence overcomes Abbe’s diffraction limit. Though the underlying concept of using optically driven molecular transitions is not limited to switch between fluorescent and non-fluorescent states, the hitherto realized superresolution-imaging modalities almost exclusively rely on fluorescence contrast. Overcoming the diffraction limit in more general imaging contrasts (without relying on fluorescence) is usually enabled by near-field optical microscopy, which employs probes such as subwavelength apertures or sharp tips at close proximity to the sample surface in order to generate highly localized light fields or collect near-field information.
  • Dynamic subwavelength apertures in direct contact with the sample surface have been realized via optically saturable transitions in photochromic compounds for resolution enhancement in optical data storage and optical lithography.
  • Our field of research focuses on absorbance-modulation imaging (AMI) in reflection mode for technical surface.We assess the feasibility and the choice of system- design parameters.

Methods

  • Simulation with a modell of a AMI nanoscope in reflection mode. We employed the nonlinear photokinetics, the diffraction at the sub-wavelength aperture, Fresnel reflections and the imaging properties of a confocal mikroscope.
  • Derivation of analytical estimative equations for a simplified system design.

Results

  • With our analytical equation the resolution-enhancement capability can be evaluated in a first predesign step (in analogy to STED). The decisive parameter ist the power ratio between the beams of different wavelength. We show in our publications that this estimation fit well with our simulation results.
  • Our extensive simulations show the potential to achieve superresolution of λ/5 compared to diffraction limit.
  • Granted DFG project for the proof-of-principle in cooperation with Laser-Laboratorium Göttingen e.V. and other institues of TU Clausthal

Publications

Example of an photochromic layer under complex (rotation-symmetric) illumation at two wavelengths in photo-stationary state. Figure: Kowarsch

Confocal Laser-Doppler-vibrometer miscrosope with variable carrier frequency in GHz range

Dipl.-Ing. (FH) Robert Kowarsch

State of the Art/Motivation

  • Conventional frequency shifters (e.g. Bragg cells) are inefficient for generation of carrier frequencies in the GHz regime and allow usually no variation of the shift frequency.
  • Search of an efficient methode for the generation of a heterodyne carrier which allows a variation to use spectral regions with low noise and disturbances
  • Vibration analysis of micro- or nanoelectromechanical systems vibrating at frequencies of several GHz

Methods

  • Variable carrier frequency generation from MHz to several GHz with two diode lasers in the visible spectrum via frequency-offset-lock in an optical phase-lock loop (OPLL)
  • Setup of a scanning, confocal Laser-Doppler-vibrometer microscope for vibration analysis of tiny structures with high lateral resolution for the reconstruction of operating deflection shapes at high frequencies.

Results

  • Capability of generation of a variable carrier frequency up to 1.4 GHz for the contactless vibration analysis.
  • Noise-equivalent vibration amplitudesin the picometer range (at 1 Hz bandwidth) despite the strong intensity noise of the diode lasers.

Publications

Scanning vibrometer microscope for vibration analysis of microsystems

Dipl.-Ing. (FH) Robert Kowarsch

State of the Art/Motivation

  • Wearables require flexible power supplies. Energy harvesting by exploiting the energy of the human voice with piezoelectric MEMS (microelectromechanical systems) enables energy autarky.
  • In Cooperation with The Choo Labs of Caltech.
  • Scanning laser-Doppler-vibrometer microscopes have proven in the field of MEMS testing.

Results

  • Setup of a scanning confocal vibrometer microscope for out-of-plane vibration analysis of MEMS with a self-developed software.
  • System verification with simulated operating deflection shapes of the energy-harvesting MEMS, which exploits the human vocal energy (maximum energy in the spectral range of 100-300 Hz for adults).
  • Choice of several excitation signals for efficient vibration analysis.

Publications

 

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