The main streamline of research in our group was high resolution laser spectroscopy of small molecules and clusters. Through the combination of collimated supersonic cold molecular beams and Doppler-free techniques of laser spectroscopy the rotational spectra of the investigated molecules and small alkali clusters and even the hyperfine structure of electronic transitions could be resolved. Also Doppler-free spectroscopy of molecules in cells or heat-pipes was performed using saturation- and polarization spectroscopy, combined with optical double resonance methods for analyzing complex spectra.
The detection efficiency could be greatly enhanced by resonant two-colour two-photon ionization spectroscopy with pulsed and with continuous single mode lasers in molecular beams. The ions were mass selected and allowed the isotope selective Doppler-free spectroscopy.
With such high resolution techniques in combination with time resolved spectroscopy the dynamics of molecules in excited electronic states, such as predissociation or couplings between rotational-vibration levels in different electronic states could be inferred.
Part of our work concentrated on sensitive absorption techniques in the visible and near infrared, in order to learn about interactions between high vibrational levels in the electronic ground state. Here photo-acoustic- and opto-thermal spectroscopy proved to be useful techniques. Absorption spectroscopy with frequency modulation of well stabilized single mode diode lasers, multipass absorption cells and difference detection with matched photodetectors gave high absorption sensitivities with a minimum absorption coefficient of α > 10-10cm-1.
After my retirement I work for several weeks per year in other laboratories, such as LENS in Florence, the Molecular Spectroscopy Institute at the Kobe University, Japan. In 2006 I was appointed as Fellow of the Photon Science Institute of the University of Manchester, England. In these institutes larger molecules are attacked by advanced high resolution spectroscopic techniquesv or by the ZEKE technique (Photo-ionization of molecules at the ionization threshold and collection of zero kinetic energy electrons).