Light diffusion model for determination of optical properties of rectangular parallelepiped highly scattering media

Method for Measuring Absolute Optical Properties of Turbid Samples in a Standard Cuvette

Many applications seek to measure a sample's absorption coefficient spectrum to retrieve the chemical makeup. Many real-world samples are optically turbid, causing scattering confounds which many commercial spectrometers cannot address. Using diffusion theory and considering absorption and reduced scattering coefficients on the order of 0.01 mm-1 and 1 mm-1, respectively, we develop a method which utilizes frequency-domain to measure absolute optical properties of turbid samples in a standard cuvette (45 mm × 10 mm × 10 mm). Inspired by the self-calibrating method, which removes instrumental confounds, the method uses measurements of the diffuse complex transmittance at two sets of two different source-detector distances. We find: this works best for highly scattering samples (reduced scattering coefficient above 1 mm-1); higher relative error in the absorption coefficient compared to the reduced scattering coefficient; accuracy is tied to knowledge of the sample's index of refraction. Noise simulations with 0.1 % amplitude and 0.1° = 1.7 mrad phase uncertainty find errors in absorption and reduced scattering coefficients of 4 % and 1 %, respectively. We expect that higher error in the absorption coefficient can be alleviated with highly scattering samples and that boundary condition confounds may be suppressed by designing a cuvette with high index of refraction. Further work will investigate implementation and reproducibility.

Controllable coherent backscattering of light in disordered media filled with liquid crystal

We have investigated multiple scattering of light in a disordered system based on liquid crystals for a temperature-controllable random laser. Coherent backscattering measurements at several temperatures have been well fitted by the theoretical model deduced for a random collection of spherical point scatters based on a diffusion approximation. The transport mean free path exclusively depends on the diffusivity of the liquid crystalline phase of the hybrid scattering system. It is shown how the laser threshold excitation intensity is strongly correlated with the transport mean free path.

Measurement of transport mean-free path of light in thin systems

We extensively investigate in-plane light diffusion in systems with thicknesses larger than but comparable with the transport mean free path. By exploiting amplified spontaneous emission from dye molecules placed in the same holder of the sample, we obtain a directional probe beam precisely aligned to the sample plane. By comparing spatial intensity distribution of laterally leaking photons with predictions from random walk simulations, we extract accurate values of transport mean free path, opening the way to the investigation of a previously inaccessible kind of sample.

Analysis of aggregation and dispersion states of small particles in concentrated suspension by using diffused photon density wave spectroscopy

Recently, inspection of chemical components like melamine plays an important role in food industry for the food safety. However, conventional analyzing methods require a lot of preparations and much of time. We propose a real-time method for investing the mean particle size and number density of concentrated suspensions without any preparations. There are several techniques of analyzing concentrated suspensions. Laser light scattering (LLS) and dynamic light scattering (DLS) are used to measure the particle size. Fourier transform infrared spectroscopy (FT-IR) is used to measure the number density. They have been successfully describing the physical and dynamics characteristics near single light scattering regions. On the other hand, they require samples to be highly diluted. This is a major disadvantage in studying real concentrated suspensions, or phenomena such as gelation. Our proposed method diffused photon density wave spectroscopy (DPDWS) is based on the multiple light scattering theory. Thus, DPDWS measures the particle size and number density of the concentrated suspensions without dilution in real time. Diffused photon density wave (DPDW) is a spherical energy wave generated from the intensity-modulated point light source in the concentrated suspensions. The absorption and scattering coefficients can be simultaneously obtained from the amplitude and phase of DPDW propagated through the concentrated suspensions. Furthermore, the particle size and number density of nanoparticles can be estimated from the obtained optical properties using the absorption and the scattering theory. In this study, we qualitatively estimated the gelation of milk from the measured particle size and number density by use of DPDWS.

Full characterization of anisotropic diffuse light

We demonstrate a method for fully characterizing diffuse transport of light in a statistically anisotropic opaque material. Our technique provides a simple means of determining all parameters governing anisotropic diffusion. Anisotropy in the diffusion constant, the mean free path, and the extrapolation length are, for the first time, determined independently. These results show that the anisotropic diffusion model is effective for modeling transport in anisotropic samples, providing that the light is allowed to travel several times the transport mean free path from the source.