Wavelength Modulation Atomic Absorption Spectrometry With Semiconductor Diode Lasers

Abstract

Commercial semiconductor laser diodes of the AlGaAs and AlGaInP types are small, long-lived devices with excellent spectroscopic properties [1]. They are easy to operate and have low power consumption. These are the requirements for the arrangement of many independently operating laser diodes in compact instruments for simultaneous multielement analysis [2]. The main drawback of atomic diode laser spectroscopy is the limited wavelength range of commercially available laser diodes (625-950 nm). It will be extended to shorter wavelengths in the short and medium run. However, if low radiation powers can be used in experiment, it can be overcome by second harmonic generation (SHG) in non-linear crystals. Depending on the fundamental power of the laser diodes and on the efficiency of the crystal used, extracavity SHG-powers in the nW and μW can be generated easily in the range 315-500 nm. Such powers are sufficiently high for laser atomic absorption spectroscopy (LA AS). A list including more than 50 elements which can be measured by LA AS with fundamental and SHG radiation is given in a recent review paper [3].