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.