Performance of free-standing grids wound from 10-μm-diameter tungsten wire at submillimeter wavelengths: computation and measurement

The power- and phase-transmission spectra of free-standing wire grids at submillimeter wavelengths have been calculated for the case of normal incidence by a least-squares method. The calculations are compared with measurements made on grids wound from 10-μm-diameter tungsten wire with spacings in the 30–65-μm range. The measurements were made at $\tilde{\nu }$ = 29.7 cm⁻¹ (λ = 337 μm) by using an HCN laser and in the 20–450-cm⁻¹ frequency range by a combination of conventional and dispersive Fourier-transform spectrometry. At frequencies below about 100 cm⁻¹, excellent agreement is obtained between theory and experiment, indicating that this work should provide a suitable basis for the design of spectroscopic components, such as laser-coupling devices for use at submillimeter wavelengths. However, there are marked discrepancies between theory and experiment at frequencies near the Rayleigh wavelengths, where d/λ = 1, 2, etc., where d is the wire spacing. From detailed measurements of the periods of the grids, it is concluded that these discrepancies are primarily due to the effects of irregularities in the wire spacings.