Incoherent Fourier transform spectroscopy with room-temperature coverage from NIR to THz

Abstract

Despite the broadband nature of thermal light sources, optical spectroscopy over multiple spectral bands simultaneously remains challenging. Here, we demonstrate a practical Fourier transform infrared spectrometer (FTIR) that achieves room-temperature spectral coverage from 1 to 50 $μ$m (300--6 THz) in seconds using a single set of optics, with the long wave cutoff extendable to 90 $μ$m (3.3 THz) and the short wave to the ultraviolet (0.39 $μ$m). The interferometer employs a diamond plate beam splitter and windowless lithium tantalate (LTO) detector to probe the spectrum of combined incoherent sources operating at different temperatures. Applications of the instrument in modern chemometry, material science, and medicine are envisioned.

Figures (7)

• Figure 1: Spectral coverage of the instrument in wavelength (a) and wavenumber (b) scales. The spectrum contains absorption features of H2O, CO2, and polyethylene foil windows in the flow cell. It was acquired as a single-shot with 1 cm optical path difference (OPD) and acquisition time of 10 seconds.
• Figure 2: Experimental setup using a combination of incoherent thermal sources operating at different temperatures. Broadband operation is possible thanks to the diamond beamsplitter and windowless LTO thermal detector.
• Figure 3: Simulated diamond refractive index over wavelength range of interest as described by the Sellmeier equation turri_index_2017.
• Figure 4: Spectral regions covered by the halogen lamp and CPC sources plotted on wavelength and wavenumber scales. When powered simultaneously, they yield the spectrum in Fig. \ref{['fig:coverageplot']}.
• Figure 5: Breath absorption features measured at different wavelengths and compared with HITRAN reference data for water vapor. Acquired with 100 averages, 1 cm OPD over a combined integration time of 17 minutes.