Optical phase conjugation for turbidity suppression in biological samples

Yaqoob, Zahid; Psaltis, Demetri; Feld, Michael S.; Yang, Changhuei

doi:10.1038/nphoton.2007.297

Cited by 690 publications

(441 citation statements)

References 25 publications

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“…By using scattering in the medium behind a lens, light was focused to a spot as small as one tenth of the diffraction limit of that lens. Our results, obtained using spatial wavefront shaping, are valid for all methods for focusing coherent light through scattering matter, including phase conjugation [4] and time-reversal [5]. We anticipate that disorder-assisted focusing will improve the imaging resolution of microscopy in inhomogeneous media.…”

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confidence: 53%

Exploiting disorder for perfect focusing

2010

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We demonstrate experimentally that disordered scattering can be used to improve, rather than deteriorate, the focusing resolution of a lens. By using wavefront shaping to compensate for scattering, light was focused to a spot as small as one tenth of the diffraction limit of the lens. We show both experimentally and theoretically that it is the scattering medium, rather than the lens, that determines the width of the focus. Despite the disordered propagation of the light, the profile of the focus was always exactly equal to the theoretical best focus that we derived.Optical microscopy and manipulation methods rely on the ability to focus light to a small volume. However, in inhomogeneous media, such as biological tissue, light is scattered out of the focusing beam. Disordered scattering is thought to fundamentally limit the resolution and penetration depth of optical methods [1,2,3]. Here we demonstrate in an optical experiment that this very scattering can be exploited to improve, rather than deteriorate, the sharpness of the focus. Surprisingly, the resulting focus is even sharper than in a transparent medium. By using scattering in the medium behind a lens, light was focused to a spot as small as one tenth of the diffraction limit of that lens. Our results, obtained using spatial wavefront shaping, are valid for all methods for focusing coherent light through scattering matter, including phase conjugation [4] and time-reversal [5]. We anticipate that disorder-assisted focusing will improve the imaging resolution of microscopy in inhomogeneous media. The starting situation of the experiment is shown in Fig. 1a: a lens focuses a beam of light onto a CCD camera. In this 'clean' system without disorder, the sharpness of the focus is limited by the numerical aperture and the quality of the lens. We now disturb the light propagation by placing a non-transparent scattering object in the beam path. Although initially the focus disappears, the focus can be restored by shaping the wavefront of the incident light using a spatial light modulator[6] (see Fig. 1b). Here we report and analyze a surprising property of the restored focus: the experimentally obtained focal spot is smaller than the diffraction limit of the clean system. We show both experimentally and theoretically that it is the scattering medium, rather than the lens or the quality of the reconstruction process, that determines the width of the focus. In Fig. 2a we show the measured intensity distribution in the focal plane of the clean system. Ideally, the lens would focus light to an Airy disk with a full width at half maximum (FWHM) of w = 1.03λf 1 /D 1 . In our experiment, λ = 632.8 nm, f 1 = 200 mm, and D 1 = 2.1 mm, FIG. 1: Schematic of the experiment. Light coming from a phase modulator is imaged on the centre plane of a lens, L1 (modulator and imaging telescope not shown). The numerical aperture of the lens is controlled by a pinhole. A CCD camera is positioned in the focal plane of the lens. (a), 'Clean' system without disorder. Light is focused to a...

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confidence: 53%

Exploiting disorder for perfect focusing

2010

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“…Optical phase conjugation has been achieved through holography, nonlinear optics 51 , Brillouin scattering 52 and the use of photorefractive crystals 53 . In 2008, Yaqoob and co-workers provided an implementation of phase conjugation for reversing wavefronts in biological tissue 54 . Using a weak phase-conjugate beam from a photorefractive crystal, the researchers were able to transmit a hologram through a slice of chicken tissue.…”

Section: Using Spatial Degrees Of Freedom To Control Lightmentioning

confidence: 99%

Controlling waves in space and time for imaging and focusing in complex media

et al. 2012

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“…These systems have played an important role in the development of wavefront shaping techniques to manipulate light in complex media. Iterative optimization algorithm [8][9][10] and phase conjugation methods [11,12] have been proposed to focus light at a given output position, an essential ingredient for imaging. An alternative method for light control is the optical transmission matrix (TM).…”

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Spatiotemporal Coherent Control of Light through a Multiple Scattering Medium with the Multispectral Transmission Matrix

et al. 2016

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We report broadband characterization of the propagation of light through a multiply scattering medium by means of its Multi-Spectral Transmission Matrix. Using a single spatial light modulator, our approach enables the full control of both spatial and spectral properties of an ultrashort pulse transmitted through the medium. We demonstrate spatiotemporal focusing of the pulse at any arbitrary position and time with any desired spectral shape. Our approach opens new perspectives for fundamental studies of light-matter interaction in disordered media, and has potential applications in sensing, coherent control and imaging.Propagation of coherent light through a scattering medium produces a speckle pattern at the output [1], due to light scrambling by multiple scattering events [2]. The phase and amplitude information of the light are spatially mixed, thus limiting resolution, depth and contrast of most optical imaging techniques. Ultrashort pulses, generated by broadband modelocked lasers, are very useful for multiphotonic imaging and non-linear physics [3][4][5]. In the temporal domain, an ultrashort pulse is temporally broadened during propagation in a scattering medium, due to the long dwell time within it [6,7], which therefore limits its range of applications.However, this scattering process is linear and deterministic. Therefore, one can control the input wavefront to design the output field. In this respect, spatial light modulators (SLMs) offer more than a million degrees of freedom to control the propagation of coherent light. These systems have played an important role in the development of wavefront shaping techniques to manipulate light in complex media. Iterative optimization algorithm [8][9][10] and phase conjugation methods [11,12] have been proposed to focus light at a given output position, an essential ingredient for imaging. An alternative method for light control is the optical transmission matrix (TM). The TM is a linear operator that links the input field (SLM) to the output field (CCD camera) [1,13]. The measurement of the TM allows imaging through [15] or inside a scattering medium [16], and potentially access mesoscopic properties of the system [17].The possibility of shaping the pulse in time is also essential for coherent control [18]. Temporally, photons exit a scattering medium at different times, giving rise to a broadened pulse at its output [7,19]. Temporal spreading of the original pulse is characterized by a confinement time τ m [20] related to the Thouless time [21]. Equivalently, from a spectral point of view, the scattering medium responds differently for distinct spectral components of an ultrashort pulse, with a spectral correlation bandwidth ∆ω m ∝ 1/τ m , giving rise to a very complex spatio-temporal speckle pattern [22][23][24][25]. With a single SLM, one can manipulate spatial degrees of freedom to adjust the delay between different optical paths. Therefore spatial and temporal distortions can be both compensated using wavefront shaping techniques. This approach allows th...

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Optical phase conjugation for turbidity suppression in biological samples

Cited by 690 publications

References 25 publications

Exploiting disorder for perfect focusing

Exploiting disorder for perfect focusing

Controlling waves in space and time for imaging and focusing in complex media

Spatiotemporal Coherent Control of Light through a Multiple Scattering Medium with the Multispectral Transmission Matrix

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