1060 nm interferometric near-infrared spectroscopy

Recently, interferometric near-infrared spectroscopy (iNIRS) has emerged to measure diffuse light field fluctuations with time-of-flight (TOF) resolution. Yet, current iNIRS implementations suffer from low throughput, achieving marginal brain sensitivity. In diffuse correlation spectroscopy (DCS), longer wavelengths, with lower photon energy, lower reduced scattering, and higher permissible exposures, have been shown to improve throughput. Motivated by these results, in this Letter, we investigate iNIRS at 1060 nm. We experimentally find that the autocorrelation SNR is improved by 6.2±2.3 times compared to 855 nm and 18±11 times compared to 773 nm at TOFs of 800-1000 ps. Physical system parameters alone cannot account for this improvement, implying that the tissue response also plays a role. We conclude that the 1060 nm range has the potential to significantly improve iNIRS measurements of TOF-resolved speckle fluctuations.