A 1.8 µmwavelength single frequency InGaAlAs–InP vertical-cavity surface-emittinglaser (VCSEL) was used successfully for the first time for highresolution absorption spectroscopic measurements. As a demonstrationof the multi-species measurement capability, spectra of HCl, CH4 andH2Ogases were measured at pressures ranging from 0.07 to 1.5 bar andcompared with calculations based on the HITRAN2000 database. Ingeneral, good agreement was observed. The laser threshold was 0.9 mA,the temperature tuning rate was 0.125 nm K−1(0.38 cm−1 K−1)and the current tuning rate was 0.9 nm mA−1(2.75 cm−1 mA−1). Acontinuous mode-hop-free single frequency current tuning range of 8.4 cm−1(2.8 nm) was achieved using a 0–4.1 mA driving current. Single frequencyVCSELs show a variety of advantages compared to edge emitting semiconductorlasers, such as wide current tuning range, very high tuning speeds (MHz)and therefore very good time resolution, little susceptibility to opticalfeedback and low manufacturing costs. The availability of long wavelengthsingle frequency VCSELs (1.3–2 µm)should make VCSEL the preferred choice for diode-laser gas sensing and processcontrol applications and help to significantly expand the application fields forinfrared diode-laser gas sensors.