D. Comelli

Time-Resolved Optical Spectroscopy of Wood

We have proposed and experimentally demonstrated that picosecond time-resolved optical spectroscopy in the visible/near-infrared (NIR) region (700–1040 nm) is a useful technique for noninvasive characterization of wood. This technique has been demonstrated on both softwood and hardwood samples treated in different ways simulating the aging process suffered by waterlogged woods. In all the cases, alterations of absorption and scattering spectra were observed, revealing changes of chemical and structural composition.

Effects of a finite spectral bandwidth light source in time-resolved diffuse spectroscopy

We discuss the spectral distortions occurring when time-resolved diffuse spectroscopy is performed illuminating with a spectrally wide source. We show that the spectral region within the source bandwidth that exhibits the lowest absorption will dominate the resulting time-resolved curve, leading to significant distortions on the retrieved absorption spectrum (including shifts in peak positions). Due to the nonlinear behavior of the light attenuation due to absorption, this effect becomes more pronounced when including longer and longer photon path lengths. First, a theoretical treatment of the problem is given and then the distortion is described by timeresolved reflectance simulations and experimental measurements of lipid and water samples. Finally, a spectrally constrained data analysis is proposed to overcome the distortion and improve the accuracy of the estimation of chromophore concentrations from absorption spectra. Measurements on a lipid sample show a reduction of the error from 30% to 6%.

In vivo time-resolved multi-distance spectroscopy of human forehead: a step towards optical characterization of brain tissue

Multi-distance time-resolved spectroscopy of in-vivo human forehead was performed on five volunteers in the range 700-1000 nm. A Monte Carlo simulation based on a four-layer model was employed and compared with in vivo data.

Analysis of ICCD time-gated images through turbid media using a perturbative model

Optical imaging through turbid media has gathered a great interest as a non-invasive method to localize tumors inside the body. A step forward in this direction could be provided by a parallel detector that allows one to acquire a huge amount of data in a short time. This could result in a more stable reconstruction of the optical properties of the sample and in a more reliable diagnosis. We used a system based on a fast gated intensified CCD camera capable of a gate width <200 ps to acquire time sliced images of the light transmitted though a phantom simulating the optical properties of the human breast. Light pulses emitted by a laser diode (633 nm) were delivered to the central position of the phantom, while the output plane was imaged by the ICCD (fan geometry). Experimental data were analyzed using an analytical expression for homogeneous medium and a perturbative model, both derived from the Random Walk Theory (RWT). By using the perturbative approach we evaluated the depth (along Z axis) of scattering inclusions and their scattering coefficient.