Near-infrared broad-band cavity enhanced absorption spectroscopy using a superluminescent light emitting diode

Abstract

A fibre coupled near-infrared superluminescent light emitting diode that emits $10 mW of radiation between 1.62 and 1.7 mm is employed in combination with a broad-band cavity enhanced spectrometer consisting of a linear optical cavity with mirrors of reflectivity $99.98% and either a dispersive near-infrared spectrometer or a Fourier transform interferometer. Results are presented on the absorption of 1,3-butadiene, and sensitivities are achieved of 6.1 Â 10 À8 cm À1 using the dispersive spectrometer in combination with phase-sensitive detection, and 1.5 Â 10 À8 cm À1 using the Fourier transform interferometer (expressed as a minimum detectable absorption coefficient) over several minutes of acquisition time.

Trace species detection in the near infrared using Fourier transform broadband cavity enhanced absorption spectroscopy: initial studies on potential breath analytes

“…In principle this method leads to a more realistic value for the minimum detectable absorption, than for example just determining the noise level on a particular dataset from a broadband absorber, as it also reflects to a certain extent the stability of the system. For the SLED measurements, sensitivities expressed as a minimum detectable absorption coefficient of α min ~ 2 × 10 -8 cm -1 are obtained, in keeping with our previous results using the same cell and mirror set [25]. However, for the SC source experiments we see an improvement in sensitivity, such that α min is reduced to ~5 × 10 -9 cm -1 .…”

“…The experimental arrangement is similar to that used in our previous study [25] and differs essentially in only two aspects: firstly, only a Fourier transform interferometer is used for detection; and secondly, a supercontinuum source is demonstrated as well as SLED sources. An experimental schematic is illustrated in figure 1 showing both SC source and SLED source beam paths, which are not used simultaneously.…”

“…An earlier study from this laboratory [25] demonstrated the principles of near infrared BB-CEAS using a superluminescent light emitting diode (SLED), a source with a relatively high spectral power density and spatial coherence. Preliminary data were shown using butadiene as a test molecule absorbing SLED radiation between ~1.6 and ~1.7 µm, a spectral region where many hydrocarbons exhibit overtone and combination band absorptions.…”

Understanding the sensitivity of cavity-enhanced absorption spectroscopy: pathlength enhancement versus noise suppression

“…[5]). Since its advent, CEAS has found numerous applications in detecting trace species [5][6][7][8][9][10][11][12][13][14][15], studies of gas phase kinetics [16][17][18][19][20][21], capturing weak molecular transitions [22][23][24][25][26] and probing interfacial interactions [27][28][29] and molecular dynamics [30].…”

Broadband Cavity-Enhanced Absorption Spectroscopy with Incoherent Light

“…Typical resolutions reported in the context of broadband cavity experiments are between 0.02 41 cm -1 and 4 cm -1 [35,67]. With the option of a much higher spectral resolution than dispersive 42 methods, FTS in conjunction with broadband CEAS has been mainly applied in the (near) IR 43 region, where narrow band ro-vibrational absorption features of molecular species can be ex-44 ploited to achieve good selectivity.…”