Application of Sinusoidal Phase Modulation Technique for Infrared Spectrum Measurement by Fourier Transform Method
Main Article Content
Abstract
The Fourier Transform Infrared (FTIR) spectrometer is widely utilized for the detection and identification of gas in laboratories and open environments. The measurement sensitivity and range of the spectrometry are limited due to the strength of the absorption or emission signals. This study proposes the use of the sinusoidal phase modulation technique to improve the signal to noise ratio (SNR) of the detected signal of an FTIR spectrometer. In this technique, a sinusoidal signal is applied to a voice coil to create movement of a mirror. Hence, the intensity of the interference signal is a series of harmonics. A synchronous detection (lock-in amplifier) is then utilized to detect and amplify only one suitable harmonic and removed all other harmonics and noise. Therefore, the SNR of the harmonic is improved significantly. In this paper, a weak infrared emission from a commercial heat-lamp is detected successfully using the proposed system.
Keywords
FT-TR spectroscopy, Frequency modulation, Phase modulation, Michelson interferometer
Article Details
References
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[2] R. Harig, and G. Matz, Toxic cloud imaging by infrared spectrometry: A scanning FTIR system for identification and visualization, Field Analytical Chemistry & Technology, Vol. 5, (2001), 75-90.
[3] L. Genzel and J. Kuhl, A new version of a Michelson interferometer for Fourier transform infrared spectroscopy. Infrared Physics. Vol. 18, (1978), 113-120.
[4] Lee, Feiwen, et al. "A MEMS-based resonant-scanning lamellar grating Fourier transform micro-spectrometer with laser reference system, Sensors and Actuators A: Physical Vol. 149, (2009), 221-228.
[5] Lucey, Paul G., and Jason Akagi. "A Fabry-Perot interferometer with a spatially variable resonance gap employed as a Fourier transform spectrometer." SPIE Defense, Security, and Sensing, International Society for Optics and Photonics, (2011).
[6] Bhattacharyya, et al., Wavelength modulation spectroscopy using novel mechanical light chopper blade designs. Review of scientific instruments, Vol. 76, (2005), 083903.
[7] Lindsay, I. D., et al. "Mid-infrared wavelength-and frequency-modulation spectroscopy with a pump-modulated singly-resonant optical parametric oscillator." Optics Express, Vol. 14, (2006), 12341-12346.
[8] Thanh-Tung Vu, et al., Accurate displacement-measuring interferometer with wide range using an 12 frequency-stabilized laser diode based on sinusoidal frequency modulation, Measurement Science and Technology, Vol. 27, (2016), 105201.
[9] Thanh-Tung Vu, et al., Sinusoidal frequency modulation on laser diode for frequency stabilization and displacement measurement, Measurement, Vol. 94, (2016), 927-933,
[10] Hariharan P. Optical Interferometry 2nd Edition, Academic Press. Elsevier, 2003.