EXPRESS: Evaluation of the Raman Spectra of LEGO Blocks and Fluorescence Avoidance Using Pulsed Laser Excitation and Time-Resolved Detection

In the first paper in this series, we proposed the use of a set of colored LEGO blocks as “standard” samples for the evaluation of fluorescence avoidance and mitigation schemes in Raman spectroscopy, as well as for use to evaluate the instruments’ performance on dark samples. In the second paper we described the spectra obtained on the same blocks from ten different handheld Raman instruments. We found that the combination of a series of colored blocks (white, yellow, red, and blue), and successively darker tone blocks (white, gray, and black) do challenge these instruments and shed light on the ways that their manufacturers have optimized these instruments in specific areas and for different purposes. In this paper we extend the work using an advanced Raman data collection technique: A fast-repetition-rate, short-pulse, laser with a single-photon avalanche photodiode (SPAD) array detector capable of providing a time-sequence output, commonly known as a “time-gating” or “time-resolved” approach. The results are evaluated and compared to those in the first two papers. In addition, X-ray fluorescence (XRF) spectra were also collected to confirm identifications of some of the blocks’ inorganic pigments, which were detected via their Raman spectra.