TY  - JOUR
A1  - Schael, Frank
A1  - Reich, Oliver
T1  - In-situ-Analytik heterogener Medien mit frequenz- und leistungsmodulierten Diodenlasern
N2  - Electronic intensity and frequency modulation of diode lasers enables new perspectives for highly sensitive analytical in-situ techniques. For analyis of "heterogeneous" media, which may consist of coexisting gaseous, liquid, and solid phases and often show multiple light scattering, non-invasive techniques with outstanding performance characteristics can be developed. Analysis of photon density waves launched by intensity-modulated lasers provide an elegant way for the determination of absorption and scattering coefficients of multiple scattering media. The absorption coefficient can be used for qualitative and quantitative analysis of chemical constituents (which absorb in the range of the laser wavelengths). The scattering coefficient allows characterization of physical and morphological properties of the sample. In the current work, applicability of appropriate radiation transport models was investigated with simple light scattering solutions and compared with results obtained from the treatment according to the theory of Kubelka and Munk. Measurements of human blood samples are discussed. A new method for determination of water vapor partial pressure in a polyurethane foam with a frequency-modulated external cavity diode laser is discussed.
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Schael, Frank
A1  - Engelhard, Sonja
A1  - Reich, Oliver
T1  - Optische Sensorik für die in-situ-Analytik von Brauprozessen
Y1  - 2001
ER  - 
TY  - JOUR
A1  - Schael, Frank
A1  - Reich, Oliver
A1  - Löhmannsröben, Hans-Gerd
T1  - Near infrared diode laser spectroscopy of organic compounds in turbid aqueous solutions
N2  - Diffuse reflectance measurements and photon migration studies with near infrared (NIR) diode lasers were employed to elucidate experimental methods for determining absorption and scattering coefficients and species concentrations in highly scattering solutions. Applicability of theoretical approaches were established by investigating model systems with absorbing (e.g. ink, malachite green) and scattering (e.g. milk powder, caolinit) species in aqueous solution. While diffuse reflectance measurements practically requires calibration procedures, photon migration studies allow quantitative determination of absorption and scattering coefficients of turbid solutions consistent with absorptions coefficients obtained from Lambert-Beer's law. Furthermore, NIR absorption spectra of water, chlorinated hydrocarbons (chloroform, 1,2-dichloroethane, trichloroethene) and of various sugars ($alpha$-D-glucose, sucrose, maltose) are discussed. Spectral variations of NIR water absorption with temperature and solvents are exammined. Exemplary, NIR diode laser detection of water in acetone/water mixtures is performed.
Y1  - 2000
SN  - 0-9528666-1-7
ER  - 
TY  - JOUR
A1  - Löhmannsröben, Hans-Gerd
A1  - Schael, Frank
A1  - Reich, Oliver
A1  - Lemke, Matthias
A1  - Schober, Lars
T1  - Untersuchung von organischer Bodensubstanz und Bodengasen mit laser-spektroskopischer in-situ Meßtechnik
Y1  - 2000
ER  -