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.