Simple peak shift analysis of time-of-flight data with a slow instrumental response function

Analysis of time-of-flight (TOF) data is sometimes limited by the instrumental response function, and optical parameters are extracted from the observed response curve by several mathematical methods, such as deconvolution. In contrast to this, we demonstrate that a method using shifts of the peak time of the response curve with different source-detector separations can yield the average path length of the light traveling in a tissue-like sample without deconvolution. In addition, combining the intensity information allows us to separate the scattering and absorption coefficients. This simple method is more robust in signal-to-noise ratio than the moment analysis, which also does not require the deconvolution procedure, because the peak position is not significantly dependent on the baseline fluctuation and the contamination of the scattering. The analysis is demonstrated by TOF measurements of an Intralipid solution at 800 nm, and is applied to the measurements at 1.29 microm, where the temporal response of photomultiplier tubes is not sufficiently good.