Abstract
We report on a new experimental method for enhanced backscattering spectroscopy (EBS) of strongly scattering media over a bandwidth from 530-1000 nm. The instrument consists of a supercontinuum light source and an angle-dependent detection system using a fiber-coupled grating spectrometer. Using a combination of two setups, the backscattered intensity is obtained over a large angular range and using circularly polarized light. We present broadband EBS of a TiO(2) powder and of a strongly scattering porous GaP layer. In combination with theoretical model fits, the EBS system yields the optical transport mean free path over the available spectral window.
Highlights
Transport of light in random photonic media is governed by an interplay of diffusion and interference
enhanced backscattering spectroscopy (EBS) is traditionally performed at a fixed optical frequency using a coherent light source such as a laser
Since EBS involves interference of reciprocal light paths of equal length, temporal coherence of the impinging light does not affect the shape of the EBS-cone in time-independent measurements
Summary
Transport of light in random photonic media is governed by an interplay of diffusion and interference. We present a new technique employing a supercontinuum light source for spectrallyresolved enhanced backscattering over a large optical bandwidth from 530 nm to 1000 nm This novel approach has been enabled by the very high spectral stability of modern integrated supercontinuum fiber sources, allowing for long acquisition times with low drift. The technique is especially suited for very strongly scattering media near k = 1, k = 2π/λ and being the optical wavevector and the transport mean free path, respectively, where the EBS-cone spans a large angular range. To cover the important angular range around the exact backscattering direction, the setup is converted to configuration (ii) [c.f. Fig. 1(b)], in which the prism is replaced by a beamsplitter while maintaining the same optical beam path. As the response of the beamsplitter in configuration (ii) is strongly polarization dependent, in this configuration a single λ /4 waveplate is placed directly in front of the sample
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