Laser spectroscopy of gas confined in nanoporous materials

Svensson, Tomas; Shen, Zhijian

doi:10.1063/1.3292210

Cited by 65 publications

(31 citation statements)

References 39 publications

(60 reference statements)

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“…Accordingly, the turbid material between holes, is found to exhibit t ranging from 0.7 µm at 600 nm to 2.2 µm at 900 nm and low absorption (0.026 cm −1 at 660 nm down to 0.005 cm −1 at 900 nm). The small size of the nanopores makes scattering strongly wavelength-dependent, and the transport scattering coefficient µ s decays as ∼ λ −2.7 (in good agreement with previous reports on scattering of nanoporous ceramics [48,51]). Figure 5a shows the diffusivity spectra for the holey (bimodal) system and for the nanoporous reference, and compares it to MC and the proposed analytical model.…”

Section: Diffusion Equation In Spherical Shells (Derivation Given Insupporting

confidence: 70%

Light diffusion in quenched disorder: Role of step correlations

Svensson

Vynck

Adolfsson³

et al. 2014

Phys. Rev. E

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We present a theoretical and experimental study of light transport in disordered media with strongly heterogeneous distribution of scatterers formed via non-scattering regions.Step correlations induced by quenched disorder are found to prevent diffusivity from diverging with increasing heterogeneity scale, contrary to expectations from annealed models. Spectral diffusivity is measured for a porous ceramic where nanopores act as scatterers and macropores render their distribution heterogeneous. Results agree well with Monte Carlo simulations and a proposed analytical model.Series of incremental random changes govern the evolution of countless systems around us, from the movement of particles and molecules [1][2][3][4] and wave propagation in disordered media [5,6], to the foraging of animals [7] and spread of disease [8]. By virtue of the central limit theorem, macroscopic evolution of such random walk processes can often be explained in terms of classical diffusion. Although therefore ubiquitous, diffusion is in each particular case determined by unique microscopic mechanisms. These mechanisms are often complex and understanding the onset and speed of diffusion is generally a challenge [9][10][11][12][13][14]. The matter is particularly relevant to research in optics of disordered media, including the study of radiative transfer through planetary atmospheres [15][16][17], optical imaging and spectroscopy in biomedical [18] and material science [19] and, more recently, anomalous diffusion in engineered disordered materials [20][21][22][23][24].Multiple scattering of light is typically viewed as a Poissonian random walk of independent and exponentially-distributed steps. This viewpoint inherently assumes a uniform random distribution of scatterers throughout the medium and results in a well-known expression for the diffusion constant [25], D = v t /3, where v is the average transport velocity for light in the medium and t the transport mean free path. This diffusivity relation, however, breaks down in systems with an heterogeneous distribution of scatterers, such as clouds, biological tissues, porous materials and foams. The reason is two-fold. First, the presence of non-scattering regions in the scattering medium leads to a broader (nonexponential) distribution of step lengths, which, in turn, induces an increase of the diffusivity [26]. Second, the quenched (i.e. spatially frozen) heterogeneity induces step correlations that tend to counteract the increase in diffusivity caused by long steps [21,26]. Due to the complexity of these aspects, understanding of light transport in systems with heterogeneous distribution of scatterers remains rather limited. Important insight has, nonetheless, been reached with the development of generalized transport equations and homogenization theory [27][28][29][30][31][32][33][34][35] as well as probabilistic analysis of random walks [26,36,37]. When it comes to quenched disorder, most works are theoretical and fall within the context of anomalous diffusion [21,23,24,[38][39][40]....

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Section: Diffusion Equation In Spherical Shells (Derivation Given Insupporting

confidence: 70%

Light diffusion in quenched disorder: Role of step correlations

Svensson

Vynck

Adolfsson³

et al. 2014

Phys. Rev. E

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“…1 a mean free path of 60 nm for molecules in air at atmospheric pressure, a broadening is certainly expected [12]. The data presented in Fig.…”

Section: Resultsmentioning

confidence: 68%

“…Under confinement, however, the molecules will collide with the walls and become perturbed, resulting in further broadening of the absorption lines. The geometry of the confinement will determine the wall-collision rate, and it has been experimentally shown that the broadening exhibits a pore-size dependence [12,13,18,19]. Prediction of the total collision broadening of absorption lines is, on the other hand, highly nontrivial.…”

Section: Resultsmentioning

confidence: 99%

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Wall-collision line broadening of molecular oxygen within nanoporous materials

Lewander

Andersson‐Engels

et al. 2011

Phys. Rev. A

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“…Understanding of the interaction of light and turbid porous materials is of fundamental importance in many areas-from fundamental studies of photon localization in porous semiconductor materials [1,2] to analysis of chemistry, pore structure and optics of powders and pharmaceutical materials [3][4][5], porous ceramics [6][7][8], and porous silicon [9,10]. Throughout the years, massive efforts have been put into developing models for the macroscopic aspects of photon migration in turbid materials.…”

Section: And Stefan Andersson-engelsmentioning

confidence: 99%