Acoustic-optic tunable filter

In addition to interference filters, NIR manufacturers use holographic gratings (moving and fixed), interferometers, polarization interferometers, diode arrays, acoustic-optic tunable filters, as well as some specialty types. 

Figure 7.3. Block diagram of a near-lR optical fiber deleclor. A/D = analog-to-digital A OIF = acoustic Optical tunable filter.

C. D. Tran and R. J. Furlan, Spectrofluorometer Based on Acoustic-Optic Tunable Filters for rapid scanning and multicomponent sample Analyses, Anal. Chem. 65, 1675-1681 (1993). 

Mass spectroscopy Remote hyperspectral imaging Acoustically optical tunable filters Multidirectional flow injection sensor technologies... 

Acousto-optic Filters. The newest type of spectrometer to become commercially available is the acousto-optic tunable filter (AOTF). An AOTF is a sohd-state, electronically tunable bandpass filter based on the diffraction of optical waves by acoustic waves in an optically anisotropic crystal. 

A modification of the Debye-Sears effect, i.e., the modulation of the refractive index by acoustical waves functioning as tunable grating, is now applied to fast scanning NIR spectroscopy The Acousto-Optic Tunable Filter (AOTF), (Harris and Wallace, 1969 Chang, 1981). In combination with array detectors, chemical imaging is possible (Treado et ah," 1992). 

Figure 4 An acousto-optic tunable filter [a, tellurium dioxide (Te02) crystal b, incident or input beam c, acoustic transducer d, rf input e, monochromatic light (ordinary beam) f, nonscattered light beam g, monochromatic light (extraordinary beam) h, acoustic wave absorber].

Wavelength scanning in NIR hyperspectral imaging spectrometers has also been accomplished with both a scanning monochromator and an acousto-optic tunable filter (AOTF). AOTFs are electro-optical devices that function as electronically tunable filters. They rely on a birefringent crystal, the optical properties of which vary upon interaction of the crystal with an acoustic wave. The resulting... 

I.C. Chang, Tunable Acousto-Optic Filter Utilizing Acoustic Beam WalkoIF in Crystal Qustrtz, Appl. Phys. Lett., 25, 323-4 (Sept 1974). 

---