Abstract

We have recently described a new type of acoustooptic device called the acoustooptic dispersive light filter (AODLF), which is functionally a tunable diffraction grating for analyzing light. It is based on anisotropic diffraction in biréfringent crystals but operates in a regime different from the well-known AOTF. Like the anisotropic scanner, bandcenter is chosen at the minimum of the Bragg angle of incidence, in this case with respect to wavelength at fixed rf. This allows the device to operate with a wide optical bandwidth. The output of the device resembles that of a blazed grating in that all the diffracted light is concentrated in a single diffraction order, but in this device the grating constant and blaze angle are tunable. This allows the optical bandcenter to be varied by changing the rf, and also makes it simple to implement modulation or derivative spectroscopy. We fabricated a TAS AODLF to measure the properties of the device in the IR; its optical bandcenter was 10 µm, with a rf drive at 100 MHz. Measurements were done using lines of the CO₂ laser from 9 to 11 µm. The optical aperture was 2 cm and the measured resolution was consistent with the theoretical value of 1:2000. Perfect agreement was also measured for the dispersion, 10°/µm. A TeO₂ AODLF was built for operation over the visible and again results in excellent agreement with theory were obtained.

© 1986 Optical Society of America