Measuring local birefringence in photonic materials. (General Developments).

Novel polymer materials with structure on the scale of the wavelength of light, such as high-molecular-weight block co-polymers (BCs), have been noted for their potential use in photonic devices. These materials selfassemble to form spatial patterns that exhibit technologically useful optical properties for optical filters, couplers, and switches.

The promise of photonic BC systems underscores the importance of characterizing their local optical properties, since the optical activity of single microphase domains and defect structures may dictate device function. While traditional spectroscopic techniques and far-field microscopy, being inherently diffraction limited, are successful for measuring the bulk/ensemble optical characteristics of photonic materials, they do not have the spatial resolution required to map out these properties on the mesoscale. However, near-field scanning optical microscopy (NSOM), with its ability to generate optical micrographs with sub-diffraction limit resolution offers a means to accomplish such measurements. Combined with polarimetric techniques, this novel microscopy can be used to directly measure the birefringence and dichroism of thin polymer film samples with lateral resolution of about 50 nm.

Researchers at NIST have constructed a near-field polarimeter and have overcome a variety of measurement challenges to characterize the defect structures and to make quantitative measurement of the local birefringence of thin BC films. These measurements represent the first optical characterization of the domain structure of these novel materials.

This achievement is the result of a collaboration between NIST and researchers in materials science at MIT. The results of this work are published in a paper "Measuring Local Optical Properties: Near-Field Polarimetry of Photonic Block Copolymer Morphology," by M. J. Fasolka, Lori S. Goldner, J. Hwang, A. M. Urbas, P. DeRege, T. Swager, and E. L. Thomas, Phys. Rev. Lett. 90, 016107 (2003).

CONTACTS: Lori Goldner, [phone]; lori. [e-mail] or Michael Fasolka, [phone]; [e-mail].