The design and fabrication of a micropolarizer array for imaging polarimetry is described for the 3-5-mwavelength region. Each micropolarizer consists of a 475-nm-period Mo wire grid in a 16 m ϫ 16 m aperture. Interference lithography is used to generate the small grating features through an etch mask layer. Arrays of 256 ϫ 256 micropolarizers at three distinct angular orientations have been fabricated that permit the measurement of the first three Stokes vector components in each pixel of an imaging polarimeter. An imaging system composed of a micropolarizer array integrated directly onto a focal plane array has been assembled, and initial testing has been performed.

We discuss the design, fabrication and optical performance of a broadband form-birefringent quarter-wave plate for the 3.5 to 5 aem wave-length region. Rigorous coupled wave analysis (RCWA) was used to design the requisite subwavelength grating for silicon substrates in ambient air. Fabricated samples yield a measured phase retardation of 89ø to 102ø over the desired wavelength range.

We report the use of infrared (IR) scattering-type scanning near-field optical microscopy (s-SNOM) as a nondestructive method to map free-carriers in axially modulation-doped silicon nanowires (SiNWs) with nanoscale spatial resolution. Using this technique, we can detect local changes in the electrically active doping concentration based on the infrared free-carrier response in SiNWs grown using the vapor-liquid-solid (VLS) method. We demonstrate that IR s-SNOM is sensitive to both p-type and n-type free-carriers for carrier densities above ∼1 × 10 cm. We also resolve subtle changes in local conductivity properties, which can be correlated with growth conditions and surface effects. The use of s-SNOM is especially valuable in low mobility materials such as boron-doped p-type SiNWs, where optimization of growth has been difficult to achieve due to the lack of information on dopant distribution and junction properties. s-SNOM can be widely employed for the nondestructive characterization of nanostructured material synthesis and local electronic properties without the need for contacts or inert atmosphere.

We have stacked subwavelength gratings (SWGs) on a single substrate to create a compact, integrated circular polarization filter. The SWGs consist of a wire grid polarizer and a broadband form-birefringent quarter-wave plate (QWP). Rigorous coupled-wave analysis was used to design the QWP for operation over the 3.5-5.0-mum wavelength range. The fabricated silicon broadband QWP exhibited a phase retardance of 82-97 degrees across this wavelength range. Two stacked structures are presented, each with a different wire grid polarizer fabricated on an organic planarization layer (SU-8) that is deposited on a QWP grating. Transmittance measurements of the first structure when illuminated with nominally right- and left-circularly polarized light indicate a circular extinction ratio (CER) limited by the low linear extinction ratio of the polarizer. Use of a wire grid polarizer with a higher extinct ratio led to a stacked SWG structure that demonstrated CERs of 10-45 across the 3.5-5.0-mum wavelength range.

An attractive approach to realizing a real-time imaging polarimeter is to integrate an array of polarizationsensitive filters directly onto the focal plane array. This has the advantage of allowing all of the requisite polarization data to be acquired within each image frame. In this paper we discuss the design, fabrication, and performance of a diffractive optical element (DOE) that fulfills this requirement. The DOE consists of an array of broadband form birefringent quarter-wave plates and wire grid polarizers which are designed to allow the measurement of all four Stokes vector components for each image pixel.