Fourier transform spectrometry with a near-infrared supercontinuum source

Area of Science:

• Spectroscopy
• Optical Engineering
• Light Source Technology

Background:

• Supercontinuum (SC) light sources offer a unique combination of laser brightness and broad bandwidth, making them attractive for spectroscopic applications.
• Near-infrared (NIR) Fourier Transform (FT) spectrometry is a powerful technique for chemical analysis, often limited by the performance of the light source.

Purpose of the Study:

• To investigate the performance of an optical fiber based supercontinuum (SC) light source for near-infrared Fourier transform (FT) spectrometry.
• To compare the SC light source with a conventional tungsten lamp for spectroscopic applications, focusing on spectral stability, noise, and sensitivity.

Main Methods:

• Demonstrated efficient, collimated propagation of broad bandwidth SC light through an 18 m multipass cell.
• Calculated normalized spectral difference for spectral stability assessment.
• Measured root-mean-square (rms) noise on zero absorbance lines at various resolutions (0.125, 2, and 16 cm⁻¹) for both SC and tungsten lamp sources.
• Acquired NIR-FT spectra of methane and methyl salicylate using both light sources.

Main Results:

• The SC light source exhibited excellent spectral stability, with normalized spectral differences less than 0.5%.
• SC sources showed approximately ten times more noise than tungsten lamps under comparable conditions, indicating detector noise is not the limiting factor.
• SC sources provided a sensitivity advantage due to their ability to traverse long path lengths, as demonstrated by spectra of methane and methyl salicylate.
• Increased amplitude noise was observed with the SC source compared to the lamp.

Conclusions:

• Optical fiber based SC light sources are promising for spectroscopic applications requiring high brightness and broad bandwidth, offering significant sensitivity advantages for long path lengths.
• The primary drawback of SC sources in this study was higher amplitude noise compared to conventional tungsten lamps.
• Future research should focus on noise mitigation strategies to fully leverage the potential of SC sources in absorption spectroscopy.