Knowledge Bank

“Polyethylene transmission filter gratings of different grating constants and various groove shapes have been studied in the wavelength region from 30 $\mu$ to 300 $\mu$. The dependence of the cutoff frequency has been obtained for different groove shapes as well as for different groove spacings. The relationship between the cutoff wavelength $\lambda e$ and the grating constant d for a specific groove shape in shown. Using this relationship it is possible to design a filter grating for any arbitrary cutoff wavelength $\lambda e$ by the proper selection of d. In the far infrared where there are no transmission cutoff filters available this is especially convenient, since the groove spacing increases with $\lambda e$, and as a result, the filters are very coarse. The efficiency of transmission filter gratings is compared with other transmission filters which are used in the far infrared.”