Measurement of angular distributions by use of low-coherence interferometry for light-scattering spectroscopy

Abstract

We present a novel interferometer for measuring angular distributions of backscattered light. The new system exploits a low-coherence source in a modified Michelson interferometer to provide depth resolution, as in optical coherence tomography, but includes an imaging system that permits the angle of the reference field to be varied in the detector plane by simple translation of an optical element. We employ this system to examine the angular distribution of light scattered by polystyrene microspheres. The measured data indicate that size information can be recovered from angular-scattering distributions and that the coherence length of the source inf luences the applicability of Mie theory. © 2001 Optical Society of America OCIS codes: 120.3180, 120.5820, 030.1640, 290.4020. Light-scattering spectroscopy is an established technique that uses the spectrum of backscattered light to infer structural characteristics, such as size and refractive index, of spherical scattering objects. 2 that structural information can be recovered from a subsurface layer of a scattering medium by use of interferometric light-scattering spectroscopy. In this approach, multiple wavelengths of low-coherence light are used simultaneously in a Michelson interferometer, where the coherence properties of the source are exploited to yield depth resolution, and the multiple wavelengths probe the spectral variation of the scattering properties. This method has great potential for biological application, as it is compatible with optical coherence tomography, an imaging technique based on using a low-coherence source in a Michelson interferometer to obtain depth-resolved images. 3The structure of a light-scattering object can also be investigated by examination of its angular-scattering characteristics at a given wavelength. Angleresolved scattering distributions are conventionally obtained by use of a goniometer 4 or through exploitation of the antenna properties of a heterodyne receiver. 5Recently an interferometric technique was developed that can measure the optical phase-space distribution of a light field, 6 i.e., its joint position and momentum distribution. This technique has been used to study multiple diffractive scattering by examination of the angular distribution of transmitted coherent light 7 and to study the phase-conjugation properties of enhanced backscattering by measurement of the phase-space distribution of backscattered low-coherence light. However, since this method is based on a Mach-Zehnder interferometer, it cannot be readily adapted as an adjunct to optical coherence tomography, which limits its applicability for biomedical imaging.We present a means of obtaining light-scattering spectroscopy information by use of a low-coherence source in a Michelson interferometer that avoids the need for multiple wavelengths by measurement of the angular distribution of scattered light. The angleresolved scattering information is obtained by simple scanning of an optical element and thus can be easily applied as an adjunct to o...

Optical coherence tomography today: speed, contrast, and multimodality

“…3). OCT contrast enhancement (prerequisite 3) has been accomplished by introducing polarization-sensitive OCT, [24][25][26][27][28] phasesensitive OCT, [29][30][31][32][33] optical coherence elastography, [34][35][36][37][38][39] spectroscopic low coherence interferometry, [40][41][42][43] elastic scattering spectroscopy, 31,[44][45][46] and nonlinear interferometric vibrational imaging (NIVI), as well as employing endogenous or exogenous contrast. [47][48][49][50][51][52] In this paper, a recently developed contrast improvement for OCT, named label-free optical angiography, is reviewed (cf.…”

Rapid, depth-resolved light scattering measurements using Fourier domain, angle-resolved low coherence interferometry

“…The detected signal at pixel (m, n) can be related to the signal and reference fields (E s , E r ) as: (1) where φ is the phase difference between the two fields and 〈...〉 denotes an ensemble average in time. The interference term is extracted by measuring the intensity of the signal and reference beams independently and subtracting them from the total intensity.…”

“…Angle-resolved low coherence interferometry (a/LCI) has been developed as a means to obtain sub-surface structural information by examining the angular distribution of scattered light [1][2][3]. The a/LCI technique combines the ability of low coherence interferometry to detect singly scattered light from sub-surface sites with the capability of light scattering methods to obtain structural information with sub-wavelength precision and accuracy [2,4].…”

“…The initial prototype a/LCI system [1,2] and the faster, second generation system [3] both relied on time domain depth scans, implemented by mechanically adjusting the length of the reference arm of the interferometer and serial scanning of the detected scattering angle. However, it has recently been shown that improvements in signal-to-noise, and commensurate reductions in data acquisition time are possible by recording the depth scan in the Fourier (or spectral) domain [7][8][9].…”

Fourier-domain low-coherence interferometry for light-scattering spectroscopy

“…7 More recently, angle-resolved low-coherence interferometry was used to obtain structural information by examination of the angular distribution of scattered light. 8,9 Angle-resolved LCI has been successfully applied to measuring cellular morphology 3 and to diagnosing intraepithelial neoplasia in an animal model of carcinogenesis. 6 The latter study was significant because it demonstrated the strength of joining LSS and LCI as a biomedical diagnostic technique.…”