Improved transmission method for measuring the optical extinction coefficient of micro/nano particle suspensions

Abstract:We have investigated the transport of light through slabs that both scatter and strongly absorb, a situation that occurs in diverse application fields ranging from biomedical optics, powder technology, to solid-state lighting. In particular, we study the transport of light in the visible wavelength range between 420 and 700 nm through silicone plates filled with YAG:Ce 3+ phosphor particles, that even re-emit absorbed light at different wavelengths. We measure the total transmission, the total reflection, and the ballistic transmission of light through these plates. We obtain average single particle properties namely the scattering cross-section σ s , the absorption cross-section σ a , and the anisotropy factor µ using an analytical approach, namely the P3 approximation to the radiative transfer equation. We verify the extracted transport parameters using Monte-Carlo simulations of the light transport. Our approach fully describes the light propagation in phosphor diffuser plates that are used in white LEDs and that reveal a strong absorption (L/l a > 1) up to L/l a = 4, where L is the slab thickness, l a is the absorption mean free path. In contrast, the widely used diffusion theory fails to describe this parameter range. Our approach is a suitable analytical tool for industry, since it provides a fast yet accurate determination of key transport parameters, and since it introduces predictive power into the design process of white light emitting diodes. 8190-8204 (2014). 30. To be sure, in a scattering system the degree of scattering is given by L/ s rather than L/ t r . Since in the vast majority of scattering systems the transport mean free paths exceeds the scattering mean free path ( t r ≥ s ) due to predominantly forward scattering [34], we consider our characterization to be on the safe side. 31. S. Chandrasekhar, Radiative transfer (Dover, New York NY, 1960). 32. M. Kaveh, Analogies in optics and micro electronics (Springer, Netherlands, 1991) 33.

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“…The contribution of the scattered light in the ballistic signal is estimated following Ref. [46] to be less than 1%.…”

Section: Methodsmentioning

confidence: 99%

Analytical modeling of light transport in scattering materials with strong absorption

Meretska¹,

Uppu²,

Vissenberg³

et al. 2017

Opt. Express

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“…It is studied that even the refractive index of cuvette material influences the measurement accuracy of the optical thickness especially at small values, because of the multiple reflections and refractions at cuvette-suspension and cuvette-air interfaces [47]. However, they can be ignored for the Quartz cuvette used in this work as its refractive index is low.…”

Section: Optimization Of Refractive Indicesmentioning

confidence: 99%

Light extinction spectroscopy applied to polystyrene colloids: Sensitivity to complex refractive index uncertainties and to noise

Eneren

Aksoy

Zhu

et al. 2021

Journal of Quantitative Spectroscopy and Radiative Transfer

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The measurement of particle size distribution (PSD) in nanofluids presents a challenge, especially when it requires to be conducted in-situ and real-time.Our work aims to enhance the capabilities of Light Extinction Spectroscopy (LES) technique for concentration and volumetric PSD (vPSD) determination of nanofluids. To reach this goal, numerical simulations are performed to verify robustness of LES data inversion algorithm and to identify the most relevant uncertainty sources. Via sensitivity analyses, we inspect the LES sensitivity 1) to complex refractive index spectra of the particle, 2) to system noise level.Since inherited noise has adverse effects on inversion stability, we characterize the system noise profile and embed it into numerical simulations. Before processing LES data, we check optical thickness and signal-to-noise ratio (SNR) profiles to adjust sample concentration. Besides, we limit wavelength spectrum to shorter wavelengths (202-484 nm), though it can be extended to UV-NIR.The experiments are carried out on well-dispersed water based nanofluids containing Polystyrene particles with median diameters of 120 and 300 nm. The results are compared with supplier's data, 3D-DLS measurements, and SEM images. After post-processing, we realize that LES results can still be greatly improved with an optimization algorithm on particle complex refractive indices.

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“…However, such effects are usually of second order compared to those here analyzed, so that they become important only for extreme experimental situations. Information for modeling the transmitted light in these situations can be found in [20].…”

Section: Model For Small Optical Thickness: Ballistic Regimementioning

confidence: 99%

Heuristic model for ballistic photon detection in collimated transmittance measurements

Martelli

Binzoni

2018

Opt. Express

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An heuristic model for ballistic photon detection in continuous-wave measurements of collimated transmittance through a slab is presented. The model is based on the small angle approximation and the diffusion equation and covers all the ranges of optical thicknesses of the slab from the ballistic to the diffusive regime. The performances of the model have been studied by means of comparisons with the results of gold standard Monte Carlo simulations for a wide range of optical thicknesses and two types of scattering functions. For a non-absorbing slab and field of view of the receiver less than 3 • the model shows errors less than 15% for any value of the optical thickness. Even for an albedo value of 0.9, and field of view of the receiver less than 3 • the model shows errors less than 20%. These results have been verified for a large set of scattering functions based on the Henyey-Greenstein model and Mie theory for spherical scatterers. The latter has also been used to simulate the scattering function of Intralipid, a diffusive material widely used as reference standard for tissue simulating phantoms. The proposed model represents an effective improvement compared to the existing literature.

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Improved transmission method for measuring the optical extinction coefficient of micro/nano particle suspensions

Cited by 29 publications

References 30 publications

Analytical modeling of light transport in scattering materials with strong absorption

Analytical modeling of light transport in scattering materials with strong absorption

Light extinction spectroscopy applied to polystyrene colloids: Sensitivity to complex refractive index uncertainties and to noise

Heuristic model for ballistic photon detection in collimated transmittance measurements

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