In a study published inLight: Science & Applications by Springer Nature, researchers from the Changchun Institute of Optics, Fine Mechanics and Physics and Cardiff University developed a novel spectroscopy platform. This system successfully acquired both Raman and fluorescence lifetime images at the same time, overcoming a long-standing challenge in optical spectroscopy.

Conventional Raman spectroscopy, used widely in materials science and biomedicine, often suffers from strong fluorescence background. This fluorescence can obscure the weaker Raman signals, complicating analysis. Previous attempts to separate them relied on spectral filtering, which could remove useful Raman data and retain fluorescence noise. Time-gated methods using pulsed lasers existed but were limited in spectral range and resolution.

The team designed a time-resolved photon-counting Fourier-transform micro-spectrometer. They combined a Mach-Zehnder interferometer with a high-precision linear motor stage and single-photon avalanche diodes (SPADs). A pulsed 532 nm laser excited the sample. Photons were detected and time-tagged relative to the laser pulses with high precision—80 ps for fine timing and 50 ns for coarse timing—and sorted into a data matrix based on their arrival time and the interferometer's optical delay.

This setup achieved a temporal resolution of 547 ps. It covered a wide Raman shift range from -1000 to 10,000 cm⁻¹ and reached a high spectral resolution of 0.05 cm⁻¹. To validate it, the researchers tested samples including a fluorescently coated silicon wafer and a mixture of fluorescent plastic microspheres.

The results clearly showed that Raman scattering occurred instantaneously with the laser pulse, within the instrument's time resolution. Fluorescence, in contrast, appeared later and decayed over nanoseconds. By analyzing different time windows, the system effectively isolated Raman signals from the dominant fluorescence background. Furthermore, the team demonstrated the technique's imaging capability by distinguishing between polymethyl methacrylate and polystyrene microbeads in a fluorescent environment.

This method provides a powerful tool for analyzing samples where Raman and fluorescence signals coexist. Its high spectral and temporal resolution, combined with simultaneous acquisition, enables clearer material characterization. Potential applications extend to gas-phase spectroscopy, quantum technology, and biomedical imaging. Future improvements could involve faster scanning and detectors for broader spectral ranges.