Tunable diode laser spectroscopy of benzene near 1684 nm with a low-temperature VCSEL

• Published in: Applied physics. B, Lasers and optics Vol. 99; no. 4; pp. 825 - 832
• Main Authors: Lytkine, A., Lim, A., Jäger, W., Tulip, J.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.06.2010; Springer
• Subjects: Atmospheric pressure; Barometric pressure; Benzene; Biological and medical applications; Engineering; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Laser spectroscopy; Lasers; Modulation; Optical Devices; Optics; Photonics; Physical Chemistry; Physics; Physics and Astronomy; Quantum Optics; Semiconductor lasers; laser diodes; Sensors; Tuning; Vertical cavity surface emission lasers; Benzene Vapor; Benzene Concentration; Absorption Path; Wavelength Modulation Spectroscopy; Heat Sink Temperature; Methane; Chemical solution; Atmospheric pressure; Laser diodes; Vertical cavity laser; Concentration measurement; Injection current; Semiconductor lasers; Second harmonic; Ambient temperature; Tunable lasers; Surface emitting lasers; Detection limit; Laser spectroscopy; Heat sinks
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-010-4024-8

We describe the application of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) with extended tuning range to the detection of benzene vapor at atmospheric pressure. A benzene absorption feature centered at 1684.24 nm was accessed by reducing the heat sink temperature of a VCSEL designed for room-temperature operation to −55°C. This allowed us to increase the injection current and thus to extend a single-scan tuning interval up to 46.4 cm −1 or 13.2 nm around a central wavelength of 1687.4 nm. Five absorption lines of methane in the 5903–5950 cm −1 range could be acquired within single laser scans at a repetition rate of 500 Hz. A benzene absorption feature between 5926 and 5948 cm −1 was recorded for concentration measurements at atmospheric pressure using a single-pass 1.2 m absorption cell. A 50 ppmv mixture of CH 4 in N 2 was introduced into the cell along with benzene vapor to calibrate benzene concentration measurements. Benzene mixing ratios down to ∼90 ppmv were measured using a direct absorption technique. The minimum detectable absorbance and detection limit of benzene were estimated to be ∼10 −4 and 30 ppmv, respectively. Using the wavelength modulation technique, we measured a second harmonic sensor response to benzene vapor absorption in air at atmospheric pressure as a function of modulation index. We conclude that a low-temperature monolithic VCSEL operating near 1684 nm can be employed in compact benzene sensors with a detection limit in the sub-ppm range.