Knowledge Bank

Semiconductor lasers in the 1.3 to $1.5\mu m$ region are rapidly developed for the demand of optical communication, and a DFB (Distributed Feedback) laser which operates at a single longitudinal mode is available. It is an excellent light source not only for optical communication but for molecular spectroscopy. It has a lot of advantages over Pb-salt diode lasers widely used for infrared spectroscopy: it operates at room temperature needs no monochromator, and continuously sweeps its frequency over 50 $cm-1$ without any gaps and jumps. The emitted power is large and smoothly varied against change of injection current and frequency. Absorption spectra of $NH3$ and HCN are recorded from $6460cm-1$ to $6570cm-1$ with two DFB lasers and the molecular constants of some excited vibrational states will be reported.