Introduction

Polarization of light can be achieved in a variety of ways. The relative efficiency of the polarization will depend on the method of polarization and the wavelength. The established methods of making polarizers include photo-lithography, holography, ruled grating, free standing wires, bire-fringence, dichroic glasses, dielectric coatings and brewster angle plates.

Specac manufactures polarizing components using a number of these methods and offers polarizers for use from vacuum UV to the far infrared.

Regularly spaced thin strips of parallel conductive wires will behave as a low loss polarizer. They will transmit one component (Ts) of the incident radiation with the electric field perpendicular to the wires, and reflect the other component (Rp) with the electric field parallel to the wires, in the sub-millimeter and millimeter wavelengths.

Theoretically, all types of parallel grids are expected to be efficient polarizers when the ratio of the grid spacing, or period, (d) to the wavelength of interest (λ) is <<1, but in practice agreement is obtained between measured and theoretical values when d/λ <0.5. Polarization efficiency also depends on the conductivity of the wire, higher conductivity wire materials being preferred.

The performance of polarizers can be charcterized by two parameters; K₁ and K₂. These are defined as follows:-

K₁ = Transmission efficiency for normally incident polarized light whose electric field vector is perpendicular to the wire direction.

K₂ = Transmission efficiency for normally incident polarized light whose electric field vector is parallel to the wire direction.

For a 'perfect polarizer' K₁ = 1 and K₂ = 0.

Other Commonly used measures of performance deduced from K₁ and K₂ are:

Degree of polarization = (K₁ - K₂) ÷ (K₁ + K₂)

Extinction Ratio = K₁ ÷ 2K₂

Principal transmittance ratio or contrast = K₁ ÷ K₂

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