Acousto-optic tunable filter instruments

In general, AOTF-based instruments are rugged and fast, capable of numerous readings per second. As long as there is no radio frequency interference, the wavelength accuracy and reproducibility are excellent. While individual instruments vary, the nominal spectral resolution is around 10 nm. This is sufficient for process purposes, but if greater resolution is needed, a FT-NIR is required. 

The in-the-field history of these instruments is relatively short, and the service record that is available for grating and FT instruments is still to come. However, the durability of these devices with no moving parts appears to be excellent. Additionally, original concerns over crystal uniqueness causing calibration transfer problems appear to be insignificant. 

Pharmaceutical and medical applications of near-infrared spectroscopy 

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There are several measurement techniques that can be considered for use in IR-based instrumentation in the NIR and the mid-IR spectral regions, and these are summarized in Table 4.1. Some of these techniques are classical, as in the case of optical filter-based instruments and scanning monochromators. Others, such as acousto-optically tunable filter (AOTF), have been considered for 15+ years, but are mainly applied to NIR... 

Acousto-optic tunable filters (AOTF) are solid-state, rapidscanning instruments. The heart of the instrument is an anisotropic crystal (Fig. 4) capable of splitting a particular wavelength of light into its ordinary and extraordinary (clockwise and counter-clockwise rotated) rays. One face (orthogonal to the light beam) has a transducer bonded to it. 

Numerous styles and brands of instruments and sample cells have been used for the analysis of tablets. The authors currently use several brands of instrumentation for tablet analysis, including filter-, diffraction grating-, and acousto-optic tunable filter-based instrumentation. Detector configurations are evolving slowly toward an optimal design however, the designs of most manufacturers are suitable for many applica-... 

Sweat, J.A. and Wetzel, D.L. (2001) Near infrared acousto-optic tunable filter based instrumentation for the measurement of dynamic spectra of polymers. Rev. Sci. Instrum., 72 (4), 2153-8. 

FT-instruments grating, filter. FT and acousto-optical tunable scanning instruments... 

An acousto-optical tunable filter is a specialized optic whose bandpass is determined by the radio frequency applied across the optic. AOTF spectrometers are full-spectrum instruments. 

C. Chang, Tunable acousto-optic filters an overview, in Acousto-Optics Device Development/Instrumentation/Applications, J. B. Houston, ed., Proc. SPIE 90, p. 12-22 (1976). 

A standard error of calibration (SEC) of 0.18 MON and an SEP of 0.22 MON was obtained using a tunable acousto optic filter based instrument [7]. The spectral range measured was 900 to 1700 nm. Multiple linear regression (MLR) analysis was used to correlate the motor value with the NIR value. The paper did not specify how many samples were used in the analysis or verification set or if any preprocessing steps were used. 

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