Wavelength modulation of semiconductor lasers for absorption spectroscopy employing harmonic detection

Audra Michelle Bullock; James M. Barrington; Colleen M. Fitzgerald; Brian Seavey; Amin N. Dharamsi

doi:10.1117/12.380529

29 March 2000 Wavelength modulation of semiconductor lasers for absorption spectroscopy employing harmonic detection

Audra Michelle Bullock, James M. Barrington, Colleen M. Fitzgerald, Brian Seavey, Amin N. Dharamsi

Proceedings Volume 3945, Laser Diodes and LEDs in Industrial, Measurement, Imaging, and Sensors Applications II; Testing, Packaging, and Reliability of Semiconductor Lasers V; (2000) https://doi.org/10.1117/12.380529
Event: Symposium on Integrated Optoelectronics, 2000, San Jose, CA, United States

Abstract

Wavelength modulation spectroscopy using semiconductor lasers is a sensitive tool for identifying species and measuring concentrations, velocities, and temperature in gaseous media. One advantage of modulation spectroscopy is that detection is carried out at frequencies far from the base-band noise, improving the signal-to-noise ratio. An additional benefit of performing wavelength modulation spectroscopy is that it allows for detection at harmonics of the modulation frequency. When a sinusoidal modulation is imposed, the harmonic detection signals resemble the frequency derivatives of the absorption profile, where the derivative order corresponds to the harmonic detection order. For this reason, the higher harmonic signals can be exploited to obtain more sensitive measurements of spectroscopic parameters, such as lineshape profile, absorption cross-section, temperature, and concentration. Wavelength modulation of semiconductor lasers, such as Fabry-Perot, vertical cavity, and external-cavity lasers, is discussed along with the advantages and disadvantages associated with each laser source. Applications of wavelength modulation spectroscopy are explored and it is shown that the higher harmonic detection signals exhibit structure and magnitude variations that are extremely useful in many spectroscopic applications.

Citation Download Citation

Audra Michelle Bullock, James M. Barrington, Colleen M. Fitzgerald, Brian Seavey, and Amin N. Dharamsi "Wavelength modulation of semiconductor lasers for absorption spectroscopy employing harmonic detection", Proc. SPIE 3945, Laser Diodes and LEDs in Industrial, Measurement, Imaging, and Sensors Applications II; Testing, Packaging, and Reliability of Semiconductor Lasers V, (29 March 2000); https://doi.org/10.1117/12.380529

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KEYWORDS

Modulation

Signal detection

Spectroscopy

Semiconductor lasers

Amplitude modulation

Absorption

Frequency modulation

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