Characterization and validation of the frequency-modulated continuous-wave technique for assessment of photon migration in solid scattering media

In English The frequency-modulated continuous-wave (FMCW)
technique, based on the beat signal of a Mach–
Zehnder interferometer employing a frequency-ramped light
source, is studied for solid scattering media applications.
The method is used to evaluate the mean time-of-flight
(MTOF) of light traveling in scattering media, specifically
polystyrene foams. We assume that each the time-of-flight
(TOF) time corresponds to different light scattering paths
resulting in a different phase shift. The phase shift variations
produce a speckle pattern, which together with the frequency leakage induced by the discrete Fourier transform
(DFT) cause “spikes” in the power spectrum of the beat signal,
thus decreasing the accuracy of the measured MTOF
values in solid scattering media. For comparison, time-offlight
spectroscopy (TOFS) is also employed to evaluate the
MTOF for the same samples, while the geometrical difference
between these two techniques is compensated for
by using diffusion theory. The MTOFs measured by the
FMCW and TOFS techniques agree well, which demonstrates
a great potential to develop a robust FMCW setup for
simplified MTOF assessment.