Diode laser absorption sensor for detecting oxygen in head space of vials

Tunable Diode Laser Absorption Spectroscopy (TDLAS) has been employed in the development of a sensor designed to measure oxygen concentration in the head space of vials during inspection on an assembly line. The beam from a 760-nm Vertical Cavity Surface Emitting Laser (VCSEL) was passed through room air and detected by a pair of photodiodes in a noise-canceling detection scheme that enables near shot-noise-limited performance. Wavelength scans of the laser produced O₂ lineshapes, from which oxygen concentrations were measured with a detection limit of 5.7 ppm*m/(Hz)^0.5 when all optics were fixed, and 21 ppm*m/(Hz)^0.5 when the positions of some optics were varied in order to vary the effective oxygen concentrations. Measurements were also made through a curved surface that showed the potential to apply the technique to the inspection of pharmaceutical vials.