Acousto-optical spectrometers

Fig. 5 CO J = 1-0 spectrum of Orion. Data were taken with the high resolution acousto-optical spectrometer (2048 channels, resolution 30 kHz/channel) of the Cologne 3-m-radiotelscope at Gornergrat, Switzerland...

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. 

Accelerator mass spectrometry Acousto-optical tuneable filter Acousto-optical tuneable spectrometer/scanning Atom probe... 

Wang, X. Soos, J. Li, Q. 8t Crystal, J., An Acousto-Optical Tunable Filter (AOTF) NIR Spectrometer for On-line Process Control Process Contr. Qual. 1993, 5, 9-16. 

Figure 3.19 Intensity-modulated photocurrent spectroscopy, showing (a) the layout of a typical spectrometer, and (b) the response obtained AOM, acousto-optic modulator RE, reference electrode WE, working electrode CE, counter electrode FRA, frequency response analyzer...

Figure 9.1. Schematic of Raman spectrometer based on an acousto-optic tunable filter (AOTF). BP, bandpass filter BR, band reject filters APD, avalanche photodiode. (Adapted from Reference 9, with permission.)...

In one paper by Kirsch and Drennen [62], three experiments were performed on coated tablets. In the first experiment, intact theophylline tablets coated with an ethylcellulose polymer were analyzed by acousto-optic tunable filter (AOTF) spectrometers. Tablets were coated with increasing levels of ethylcellulose to vary the dissolution profiles. After spectra were collected, the dissolutions were run on a U.S.P. Type II dissolution apparatus. The time required for 50% of the drug to enter solution was used as the measure of dissolution rate. Principal component (PC) regression was used to develop the calibration. This gave a SEE of 2.8 min, a coefficient of variation of 0.977, and a SEP of 6.6 min the time to 50% dissolution ranged from 48 to 93 min. 

DEVELOPMENT OF MINIATURE ACOUSTO OPTIC TUNABLE FILTER (AOTF) SPECTROMETER FOR DETECTION OF TOXIC INDUSTRIAL... 

AOTF (acousto-optical tuneable filter) spectrometers... 

For economic recycling of plastics, various types of polymeric materials have to be separated in a short period of time. The near-infrared spectral range allows the monitoring of structural or molecular properties of the plastic under investigation. The spectrometer system described is based on optical fibres for absorption and reflexion measurements, an acousto-optic tunable filter and a transputer system. It is able to detect 1,000 spectra/ s and to identify 20 pieces/second. 10 refs. 

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. 

AOTF. An acousto-optical tunable filter (AOTF) (53) is a radio frequency (RF)-controlled narrow-band interference filter. Figure 4.1.10 is a schematic of a typical AOTF spectrometer. Most contemporary AOTF crystals are tellurium dioxide (TeOa)... 

Determination of properties of film coated tablets was demonstrated by Kirsch and Drennen [73] in 1995. Here, the thickness of an ethylcellulose coating, T50 (50% dissolution time), and the hardness of the tablet were determined from NIR spectra measured on grating based and acousto-optic tunable filter (AOTF) specfiometers. While the performance of the grating based spectrometer was superior, the AOTF was demonstrated to perform adequately for most pharmaceutical applications and had the advantage of substantially shorter measurement times. This demonstration of the capacity for rapid tablet analysis was a critical step towards the implementation of such systems in an in-line tablet analysis system. 

Besides the speed and efficiency of wavelength selection, the acousto-optical tunable spectrometers (AOTS) are much smaller than grating monochromators with equal resolution. In a properly engineered design the long-term wavelength repeatability also surpasses that of the grating monochromators. 

HR Morris, CC Hoyt, PJ Treado. Imaging spectrometers for fluorescence and Raman microscopy Acousto-optic and liquid crystal tunable filters. Appl Spectrosc 48 857-865, 1994. 

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