Oxygen measurements at high pressures with vertical cavity surface-emitting lasers

Measurements of oxygen concentration at high pressures (to 10.9 bar) were m ade using diode-laser absorption of oxygen A-band transitions near 760 nm. The wide current-tuning frequency range (> 30 cm(-1)) of vertical cavity su rface-emitting lasers (VCSELs) was exploited to enable the first scanned-wa velength demonstration of diode-laser absorption at high pressures; this st rategy is more robust than fixed-wavelength strategies, particularly in hos tile environments. The wide tuning range and rapid frequency response of th e current tuning were further exploited to demonstrate wavelength-modulatio n absorption spectroscopy in a high-pressure environment. The minimum detec table absorbance demonstrated, similar to 1 x 10(-4), corresponds to simila r to 800 ppm-m oxygen detectivity at room temperature and is limited by eta lon noise. The rapid- and wide-frequency tunability of VCSELs should signif icantly expand the application domain of absorption-based sensors limited i n the past by the small current-tuning frequency range (typically < 2 cm(-1 )) of conventional edge-emitting diode lasers.