Measurement of the pressure broadening coefficients of the oxygen A-band using a low cost, polarization stabilized, widely tunable vertical-cavity surface-emitting laser

Abstract

Vertical-cavity surface-emitting lasers (VCSELs) are used for oxygen monitoring via tunable diode laser spectroscopy at 760 nm wavelength. For the desired application, novel polarization-stable laser diodes based on AlGaAs were developed. We present measurements of the pressure-broadening coefficients of the electric dipole forbidden oxygen A-band b(exp 1) Sigma+(exp 9) --> X(exp 3) Sigma+(exp 9) transition at 760 nm. The time the pressure-broadening coefficients were determined with a temperature tuned VCSEL. Generally temperature tuning has the disadvantage of frequent mode-hops, but the advantage of a wider tuning range in comparison to current tuning. Because of special techniques of polarization stabilization with a combination of a dielectric surface grating and a surface relief the VCSELs have a mode hop-free tuning range of more than 7 nm and a sidemode suppression of more than 30 dB. This provides a low cost laser diode system with a wide tuning range, which enables the possibility of simultaneous measurement of temperature, pressure and oxygen concentration in air, high pressure measurements and also a higher accuracy of oxygen concentration measurements

Slow-light enhanced light–matter interactions with applications to gas sensing

“…At this wavelength, the O 2 absorption spectrum is minimally sensitive towards temperature changes and it is fairly influenced by the pressure variation [17,11,13]. The lowest oxygen concentration that can be measured is about 20-50 ppm which corresponds to transmission change of about 0.0005 [11]. The smallest experimentally detected absorption is about 3 times larger than the shot noise limit and is about 10 −6 .…”

“…Typically, the absorption of oxygen in ambient air at the 760 nm line is of the order 2.6% with an optical path length of around 1 m [13]. At this wavelength, the O 2 absorption spectrum is minimally sensitive towards temperature changes and it is fairly influenced by the pressure variation [17,11,13]. The lowest oxygen concentration that can be measured is about 20-50 ppm which corresponds to transmission change of about 0.0005 [11].…”

“…These transitions are electric dipole forbidden, so only magnetic transitions are allowed, that require a change in the rotational quantum number of dN = ±1. Therefore the A-band splits in to the R-branch (dN = −1), starting at 759.8 nm with a bandwidth of 2.2 nm and the P-branch (dN = +1) starting at 762.3 nm with a bandwidth of 5.7 nm [17,11]. Though, the A band has a very weak absorption feature, it offers the potential to establish an optical in situ O 2 detection for a variety of applications, ranging from combustion processes [13] and fire research [14] to biomedical and environmental systems [18].…”

VCSEL Fundamentals

“…Owing to their convenient, mode-hop-free tunability via the operating current, high modulation bandwidths, and sufficiently low linewidths, single-mode VCSELs are good candidates for nonlinear spectroscopy [98] (and its use in optical interrogation for atomic sensors like clocks [91,99] or magnetometers [100]) or gas sensing, with oxygen sensors operating in the 760 nm wavelength region as a prominent example [101][102][103]. Gas sensing with long-wavelength VCSELs is discussed in Chap.…”

Compact spectroscopic sensor for air quality monitoring in spacecrafts

“…3 The strength of the broadening effect depends on different properties of the collision partners. The effect of pressure broadening depends therefore on the gas mixture and can only be calculated with the knowledge of the volume mixing ratio of all components contained in the analyzed gas mixture:…”