TUNABLE GRATING FILTER The Tunable Grating Filter is a low cost optical instrument that is capable of selecting both the wavelength and bandwidth of a variety of ultraviolet, visible and near infrared sources. Designed for use with collimated radiation, the instrument is compatible with both CW and pulsed lasers.
Applications include the elimination of unwanted radiation due to laser discharges as well as fluorescence from dye lasers. The Tunable Grating Filter can replace a multitude of interference filters. It can also be used as a laser line selector for Argon, Krypton and other multiple line lasers. All optical components are made to withstand the high incident energy from lasers.
OPERATION The Tunable Grating Filter is comprised of two modules, an optical unit with a high efficiency replicated grating, grating drive mechanism and folding mirrors and a separate variable aperture on a base plate. The wavelength is selected by turning a calibrated micrometer drive that rotates the grating. The wavelength is read directly from the micrometer.
Bandwidth is a direct function of grating groove spacing and aperture diameter and is inversely proportional to the distance between the aperture and the grating. Since focusing optics are not used, reducing the aperture smaller than the laser beam diameter will reduce the throughput. The aperture diameter and distance from the grating are both variable, allowing the bandwidth required for a specific application to be easily set. The Tunable Grating Filter is designed for in-line use with collimated light and does not displace the beam. It is easily mounted on an optical bench, rail or table.
where: λ = Selected wavelength d = The grating constant, i.e. peak to peak width of a single groove A = Selected diameter for the aperture D = Distance from the exit slit to the variable aperture Example: With an 1800 g/mm grating, 500 nm selected wavelength, 3.0 mm aperture diameter, 1500 mm from the exit aperture.
