Fig. 1: Design overview and technical evaluations of label-free IR-LSM.

a Schematic is based on a galvanometer scanning confocal design with refractive optical assemblies custom-built for broadband performance and coupled to an EC-QCL array spanning the mid-IR spectral range. b Cross-sections of the interchangeable 10× and 20× objectives with design specifications are presented in the Supplementary Information (Supplementary Figs. S3 and 4) in conjunction with the tube and scan lens (Supplementary Figs. S5 and 6). Technical comparisons between FT-IR and IR-LSM configurations including: (c) system noise and SNR calculations (detail in Supplementary Table S3) with evaluations per (i) single pixel 100% lines in absorbance, (ii) spatial noise per wavenumber, (iii–iv) spectral and spatial noise obtained over time (IR-LSM: 100 bands, FT-IR: 4 cm⁻¹ spectral resolution) presented as mean values ± s.d. (n = 1000); d spatial resolution demonstrated with (i) subjective images of a Siemens star target, and with (iv–vi) objective MTF curves evaluated respectively at discrete wavenumbers using a slant-edge target; e applied field of view; and f single pixel measurements of absorbance and derivative spectra of SU-8 photoresist deposition. A comprehensive glossary of terms is in the Supplementary Information.