Enhanced deep detection of Raman scattered light by wavefront shaping

Abstract

Light scattering limits the penetration depth of non-invasive Raman spectroscopy in biological media. While safe levels of irradiation may be adequate to analyze superficial tissue, scattering of the pump beam reduces the Raman signal to undetectable levels deeper within the tissue.Here we demonstrate how wavefront shaping techniques can significantly increase the Raman signal at depth, while keeping the total irradiance constant, thus increasing the amount of Raman signal available for detection.

Bessel Beam Beating-Based Spontaneous Raman Tomography Enables High-Contrast Deep Tissue Raman Measurements

“…8,11−14 Although the wavefront shaping technique could help improve the Raman detection depth in a scattering medium to a certain extent, the method still cannot fully reject the backscattered Raman photons arising from other layers of the tissue. 15 Several deep Raman spectroscopy methods (e.g., spatially offset Raman spectroscopy (SORS), and Kerr-gating Raman spectroscopy (KRS)) have been introduced mostly based on the photon migration theory where the Raman signal originating from deeper tissue layers shows differences in the spatial domain due to encountering more scattering processes compared to Raman signal from shallower tissue layers. 8,16,17 Due to the stochastic scattering processes, current deep Raman spectroscopy techniques with solving of the inverse problem can only provide depth-resolved Raman spectra with an axial resolution on approximately millimeter scale.…”

“…Due to the inherent strong scattering nature of tissue, the excitation laser propagation in tissue is largely attenuated, and the out-of-focus Raman photons could be scattered back to the collection pinhole in confocal Raman spectroscopy measurements. Consequently, the axial sectioning and Raman excitation/collection capability of confocal Raman spectroscopy are dramatically deteriorated, particularly in deep tissue Raman measurements. ,− Although the wavefront shaping technique could help improve the Raman detection depth in a scattering medium to a certain extent, the method still cannot fully reject the backscattered Raman photons arising from other layers of the tissue . Several deep Raman spectroscopy methods (e.g., spatially offset Raman spectroscopy (SORS), and Kerr-gating Raman spectroscopy (KRS)) have been introduced mostly based on the photon migration theory where the Raman signal originating from deeper tissue layers shows differences in the spatial domain due to encountering more scattering processes compared to Raman signal from shallower tissue layers. ,, Due to the stochastic scattering processes, current deep Raman spectroscopy techniques with solving of the inverse problem can only provide depth-resolved Raman spectra with an axial resolution on approximately millimeter scale. , Meanwhile, tissue Raman spectra collected using photon migration-based deep Raman spectroscopy techniques are unpreventably contaminated by the Raman signals arising from other tissue layers; Raman spectrum unmixing algorithms (e.g., overconstrained library-based fitting method) are usually utilized for these deep Raman techniques to enhance the quality of deep tissue Raman spectra .…”

Wavefront shaping to improve beam quality: converting a speckle pattern into a Gaussian spot

“…In recent years wavefront shaping techniques have emerged as a method capable of reducing the étendue of a system dominated by elastic multiple scattering, controlling the propagation of light in disordered media [4][5][6] by means of amplitude and/or phase manipulation of the light beam. These techniques were originally proposed to focus light through a scattering material [4], and have since proved very useful in different fields such as imaging [7][8][9][10][11], enhancing energy delivery [12][13][14] or cryptography [15,16]. In principle wavefront shaping techniques should be able to completely control the propagation of light in a disordered medium and even reverse the effect of scattering, thus strongly reducing the étendue.…”

Wavefront shaping to improve beam quality: converting a speckle pattern into a Gaussian spot

“…In recent years wavefront shaping techniques have emerged as a method capable of taking advantage of the properties of multiple elastic scattering, demonstrating the capability of controlling the propagation of light in disordered media [6,7,8] by means of amplitude and/or phase manipulation of the light beam. These techniques were originally proposed to focus light through a scattering material [6], and have since proved very useful in different fields such as imaging [9,10,11,12,13], enhancing energy delivery [14,15,16] or cryptography [17,18]. In principle wavefront shaping techniques should be able to completely control the propagation of light in a disordered medium and even reverse the effect of scattering.…”