NIU Department of
Chemistry & Biochemistry
Where the study of matter...matters!
Chair, Department of Chemistry and Biochemistry
Office: FR 320, FW 411
Phone: (815) 753-1181
Ph.D., University of Cincinnati, 1983
M.S., Southern Illinois University at Carbondale, 1980
B.S., Southern Illinois University at Carbondale, 1978
Analytical spectrometry; instrument development; acousto-optic tunable filters and deflectors; hyperspectral imaging; atomic spectrometry.
Determination of active pharmaceutical ingredients by heteroatom selective detection using inductively coupled plasma mass spectrometry with ultrasonic nebulization and membrane desolvation sample introduction. Kwok, K.; Carr, J. E.; Webster, G. K.; Carnahan, J. W. (2006) Appl. Spectrosc., 60: 80–85.
Inductively coupled plasma chemistry examinations with visible acousto-optic tunable filter hyperspectral imaging. Bei, L.; Duffin, K. L.; Carnahan, J. W. (2004) J. Anal. At. Spectrom., 19: 1151–1157.
Acousto-optic tunable filters: Fundamentals and applications as applied to chemical analysis. Bei, L.; Dennis, G. I.; Miller, H. M.; Spaine, T. W.; Carnahan, J. W. (2004) Prog. Quant. Electron., 28: 67–87.
Development and application of acousto-optic background correction for inductively coupled plasma atomic emission spectroscopy. Miller, H. M.; Spudich, T. M.; Carnahan, J. W. (2003) Appl. Spectrosc., 57: 703-710.
Ultraviolet quartz acousto-optic tunable filter wavelength selection for inductively coupled plasma atomic emissions spectroscopy. Gillespie, S. R.; Carnahan, J. W. (2001) Appl. Spectrosc., 55: 730-738.
Moderate volatility analyte transport behavior with membrane desolvation reversed-phase liquid chromatography-helium microwave-induced plasma atomic emission spectroscopy. Das, D.; Carnahan, J. W. (2001) Anal. Chim. Acta, 444: 229-240.
Optical enhancements and applications of rapid atomic emission spectrometry acousto-optic deflector background correction. Spudich, T. M.; Carnahan, J. W. (2001) J. Anal. At. Spectrom., 16: 55-61.
Characterization of an acousto-optic tunable filter and use in visible spectrometry. Bucher, E. G.; Carnahan, J. W. (1999) Appl. Spectrosc., 53: 603-611.
Research in our group centers on the development of novel spectroscopic instrumentation. Our experimental efforts involve a variety of topics which revolve around two major goals. The first of these goals is the development and application of acousto-optical devices for hyperspectral imaging and other spectroscopic applications. The second major effort involves the development of atomic and mass spectrometric techniques to determine nonmetals.
Acousto-optic tunable filters (AOTFs) consist of optically transparent crystals (glass, paratellurite, etc.) to which a piezoelectric transducer is attached. Applying a high frequency AC signal to the transducer forces it to vibrate and send "compression" waves (more formally, shear waves) through the optical material at acoustic velocities (approximately 600 to 6000 m/s). Light traveling through the optical material interacts with these "phonon" waves to produce what is known as the "acousto-optical" effect.
The AOTF radiation output consists of a single wavelength of light, dependent on the transducer frequency. AOTF devices may be used as solid-state monochromators or for wavelength-selective imaging. Possessing qualities inherent in many solid-state devices, AOTFs are small and permit wavelength "switching" on a microsecond time scale. Current investigations include the development of AOTF-based inductively coupled plasma (ICP) spectrometers, spectrophotometers, spectrofluorimeters, Raman spectrometers, and obtaining wavelength-specific images of surfaces. This latter technique is termed "hyperspectral imaging."
This research has also generated applications to various types of spectrometry, with a particular focus on ICP atomic emission spectrometry (AES). A UV quartz AOTF has been used as a compact and efficient spectrometer for ICP-AES. The figure at right shows a multielement atomic emission spectrum obtained with the AOTF. In a different configuration for plasma diagnostic purposes, images of the ICP may be obtained. The picture of the inductively coupled plasma below is a wavelength-specific hyperspectral image.