Differential Optical Reflectivity (DOR) setup measures the differential and total reflectivity of a linearly polarized light after it reflects from a free standing smectic liquid crystals film. DOR is extremely sensitive to the biaxiality of the film.

With the applied in plane electric field and continuous data acquisition mode, we are able to obtain information about the symmetry, optical thickness and biaxiality of the films.

Figure to the left shows Mr. Shun Wang preparing a smectic liquid crystal film on DOR.

Null Transmission Ellipsometer (NTE) measures the change of polarization state of a linearly polarized light after transmitted through the sample. NTE has been a powerful tool in studying the structure and properties of smectic liquid crystals.

With the application of a rotatable in-plane dc field, we are able to obtain information about the symmetry, optical biaxiality, azimuthal stack profile and tilt angle of the film.
             
Picture to the right shows the NTE in our lab.

Depolarized Reflected Light Microscopy (DRLM) enables us to study the director field of free standing films. When defects are present, the optical image from DRLM can be used to understand how the liquid crystal molecules are arranged in the film, especially around the defects.

Also as explained, different tilted smectic phases have very different, but characteristic defect patterns. With the sample being prepared inside a temperature controlled oven, proper optical arrangements, and the CCD camera, we are able to perform preliminary phase identification from DRLM.

A function generator is used to apply an ac electric field onto the smectic film to study the field response. The results allow us to obtain information whether a net polarization exists in the film of different phases.

Picture to the left shows the DRLM system in our lab.

Resonant X-Ray Diffraction (RXRD) is a very powerful probe to study the orientational periodicity of smectic liquid crystal samples. Unlike conventional x-ray diffraction, in which the structure factor is a scalar; in RXRD, the structure factor becomes a tensor when the probing photon energy is tuned to the peak position of the fluorescent spectra near the K absorption edge of the heavy element in the molecule.

In RXRD, we are able to obtain the resonant satellite peaks corresponding to the size of the azimuth repeating units, thus allowing us to determine unambiguously the phase of the smectic liquid crystal sample.    
 
Figure to the right shows the schematic setup of our RXRD experiments in beamline X19A, NSLS, BNL.                                                                                                                                                                                                                                                                                                                                    [more]