Micro- and Nanoscopy Systems

Photo: Kreutzmann

Superresolution reflection microscopy via absorbance modulation

Dipl.-Ing. (FH) Robert Kowarsch and Dennis Leitz, B.Sc.

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

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.
  • Modeling of generated mutual coherence (coherence collape) and the resulting vibration amplitude resolution for the laser-Dopplerinterferometry.

Results

  • Capability of generation of a variable carrier frequency up to 1.4 GHz for the contactless vibration analysis.
  • Noise-equivalent vibration amplitudes below 1 pm (at 1 Hz bandwidth) for vibration frequencies > 50 MHz despite the strong intensity noise of the semiconductor lasers.

Publications

Scanning vibrometer microscope for vibration analysis of microsystems

Dipl.-Ing. (FH) Robert Kowarsch

  • Setup of a scanning confocal vibrometer microscope for out-of-plane vibration analysis of MEMS with a self-developed software up to vibration frequency of 25 MHz.
  • Choice of several excitation signals for efficient vibration analysis.
  • Implementation of a vector network analyzer for electrical characterization in parallel to vibration mesurement and monitoring purposes.

Cooperations

Publications

 

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