Optical Microscopy Laboratory

Polarized light images of B7 banana liquid crystal growing in from the isotropic phase. Checkerboard and stripe textures are characteristic of the B7. The dark regions are isotropic liquid, while the colors are due to birefringence of the smectic domains.

The optical microscopy laboratory is the principal physical characterization facility for the Centerís new liquid crystal materials, and is used by researchers in the region needing equipment and assistance in carrying out polarized light optical microscopy and electrooptic characterization of liquid crystals.

Polarizing light microscope with reflection and transmission optics, color camera, and computer-controlled hotstage.

Equipment includes:

  • five polarizing light microscopes (Nikon, Olympus, Zeiss) with temperature-controlled hot stages (Instec)
  •  two optical spectrometers, one for the visible and the other for UV-Vis (Ocean Optics)
  • setup for liquid crystal electrooptic characterization (e.g. FLC polarization and switching response time)
  • Kofler hot bench (Reichert-Jung Type WME)
  • Instrumentation for generating fast, high-voltage pulses
  • Video imaging and editing equipment including analog and digital component video color CCD cameras and a PC-based digital video editing station with VHS and DV tapedecks
  • Dielectric relaxation spectroscopy (HP 4192A impedance analyzer - 5 Hz to 13 MHz) and Sigma software (Exicone)

Electrooptic Characterization

The electrooptic response of liquid crystals is characterized by the measuring the optical transmission of thin cells between crossed polarizers and, for chiral/polar materials, by detecting the current response to a periodic applied electric field. A collimated HeNe laser beam is brought up into the microscope so that it passes through the liquid crystal cell and continues to a photo-detector. The photo-current and driving voltage are displayed and recorded using a digital oscilloscope interfaced to a computer. The current response is similarly displayed, with analysis enabled by Exicone software under LabView control.

The electrooptic response is measured by passing a probe laser beam through a liquid crystal sample mounted on the polarizing light microscope.

The switching current response may be analyzed in order to distinguish contributions from ionic impurities, cell capacitance, and spontaneous polarization.

Optical Spectroscopy

The thickness of empty liquid crystal cells may be derived from the transmission of randomly polarized visible light using an Ocean Optics spectrometer. The optical transmission spectrum in polarized light can also be used to determine retardance and hence the director structure of filled nematic and smectic liquid crystal cells.

The visible transmission spectrum of an empty liquid crystal cell depends on its thickness.


For more information about the Optical Microscopy Laboratory, contact Joe Maclennan.

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