Absorption spectroscopy using internal second harmonic radiations from diode lasers

Internal second-haraonic (SH) radiations of few picowatts from various diode lasers have been used for absorption spectroscopy. An IR laser spectroaeter with frequency aarker using visible iodine lines at the SH radiation has been constructed. The internal SHG in the double-heterostructure lasers were reported recently. If the available power of internal SH radlntlon at a detector 18 reasonably strong and the spectral width is narrow enough for high resolution spectroscopy, the internal SH radiation froa a laser diode is an excellent light source for spectroscopy because of its single mode tunability. In this paper we would like to report visible absorption spectroscopy by SH radiations from an AlGaAs (750-800 nm) laser and an InGaAsP (1300 na) DFB laser and their application for the frequency calibration.