Mid-infrared or Raman spectroscopy together with multivariate data analysis provides a novel approach to clinical laboratory analysis, offering benefits due to its reagent-free nature, the speed of the analysis and the possibility of obtaining a variety of information from one single measurement. We compared mid-infrared and Raman spectra of the sera obtained from 247 blood donors. Partial least squares analysis of the vibrational spectra allowed for the quantification of total protein, cholesterol, high and low density lipoproteins, triglycerides, glucose, urea and uric acid. Glucose (mean concentration: 154 mg/dl) is frequently used as a benchmark for spectroscopic analysis and we achieved a root mean square error of prediction of 14.7 and 17.1 mg/dl for mid-infrared and Raman spectroscopy, respectively. Using the same sample set, comparable sample throughput, and identical mathematical quantification procedures Raman and mid-infrared spectroscopy of serum deliver similar accuracies for the quantification of the analytes under investigation. In our experiments vibrational spectroscopy-based quantification appears to be limited to accuracies in the 0.1 mmol/l range.

The quantum kinetics of optically excited crystal electrons coupled to a bath of dispersionless phonons is studied in the regime of strong electron-phonon coupling. Four wave-mixing experiments on a thin film of bulk ZnSe using 13 fs blue pulses give evidence for corresponding effects that are distinctly different from those found for GaAs which has proven to be a model system for the weak-coupling regime. The experimental results on ZnSe are compared with solutions of a simple model Hamiltonian of electron-phonon interaction suitable for both GaAs and ZnSe. Exact analytic solutions of this model for arbitrary electron-phonon coupling strengths are compared with numerical solutions of the same model following the usual approach in terms of an infinite hierarchy of correlation functions. Virtues and limitations of the simple model Hamiltonian with respect to the experiment are discussed. ͓S0163-1829͑99͒10441-7͔

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