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1.
In this paper, the auto-correlation properties of scattering light in random media modulated by ultrasound were studied. The expression of temporal auto-correlation function of scattering light amplitude in the ultrasound-modulated media was presented. The results show that the auto-correlation function is modulated as the ultrasound is introduced into the media and the modulation amplitude decays with correlation time. The influences of ultrasound amplitude, Brownian diffusion coefficient, scattering and absorption coefficients on auto-correlation function were discussed. The auto-correlation imaging of an object hidden in random media was also studied by the use of Monte Carlo simulations. 相似文献
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Murray TW Sui L Maguluri G Roy RA Nieva A Blonigen F DiMarzio CA 《Optics letters》2004,29(21):2509-2511
Ultrasound-modulated optical tomography is a dual-wave sensing technique in which diffusive light in a turbid medium interacts with an imposed acoustic field. A phase-modulated photon field emanates from the interaction region and carries with it information about the optomechanical properties of the medium. We present a technique for detection of ultrasound-induced optical phase modulation using an adaptive, photorefractive-crystal-based interferometry system. Experimental results are presented demonstrating detection of ultrasound-modulated signals in highly scattering media by use of pulsed ultrasound insonation. 相似文献
4.
ZHANG Xiqin XING Da 《Chinese Journal of Lasers》2001,10(5):373-377
1 Introduction Extractingusefulinformationaboutthedynamicalscatterersfromthetemporalfluctuationsofscatteringlightfieldhasbeenstudiedformanyyears.Thedevelopmentofdiffusing wavespectroscopy[1~ 3 ] (DWS)hasextendedthetraditionalapplicationsinsingle scatterin… 相似文献
5.
We present a novel implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast, can image several millimeters deep into soft biological tissues. A long-cavity confocal Fabry-Perot interferometer, which provides a large etendue and a short response time, was used to detect the ultrasound-modulated coherent light that traversed the scattering biological tissue. Using 15-MHz ultrasound, we imaged with high-contrast light-absorbing structures placed >3 mm below the surface of chicken breast tissue. The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120 microm, respectively. The resolution can be scaled down further by use of higher ultrasound frequencies. This technology is complementary to other imaging technologies, such as confocal microscopy and optical-coherence tomography, and has the potential for broad biomedical applications. 相似文献
6.
A novel frequency-swept ultrasound-modulated optical tomography technique was developed to image scattering media. A frequency-swept ultrasonic wave was used to modulate the laser light passing through a scattering medium. The modulated light was received by an optical detector and was heterodyned with a reference frequency sweep. The heterodyned signal was recorded in the time domain and was then analyzed in the frequency domain to yield a one-dimensional image along the ultrasonic axis. Multiple one-dimensional images obtained at various positions perpendicular to the ultrasonic axis were combined to yield a two-dimensional tomographic image of the medium. 相似文献
7.
Acousto-optic imaging is based on light interaction with focused ultrasound in a scattering medium. Thanks to photorefractive holography combined with pulsed ultrasound, we perform a time-resolved detection of ultrasound-modulated photons in the therapeutic window (780 nm). A high-gain SPS:Te crystal is used for this purpose and enables us to image through large optical thickness (500 mean free paths). We are able to generate three-dimensional (3D) acousto-optic images by translating a multielement ultrasound probe in only one direction. A 3D absorbing object is imaged through a 3 cm thick phantom. 相似文献
8.
We show the feasibility of imaging objects having different optical scattering coefficients relative to the surrounding scattering medium using ultrasound-modulated optical tomography (UOT). While the spatial resolution depends on ultrasound parameters, the image contrast depends on the difference in scattering coefficient between the object and the surrounding medium. Experimental measurements obtained with a CCD-based speckle contrast detection scheme are in agreement with Monte Carlo simulations and analytical calculations. This study complements previous UOT experiments that demonstrated optical absorption contrast. 相似文献
9.
In this paper, our investigations suggest that the modulation phase of ultrasound-modulated light escaping from the different locations in the ultrasonic field is different. In turbid media, the modulation phase causes the ultrasound-modulated light intensity collected outside the media to fluctuate. However, the ultrasound-modulated optical technology uses the ultrasound-modulated light signals to image. Consequently, the modulation phase affects the quality of ultrasound-modulated optical imaging. 相似文献
10.
Pulse inversion acoustic imaging is useful as it allows second harmonic imaging to be obtained with short acoustic pulses. This allows high axial resolution, but removes any overlap in the frequency spectra of fundamental and harmonic. We demonstrate pulse inversion ultrasound modulated optical tomography using an optical speckle based detection method. Inverted and non-inverted acoustic pulses combined with synchronized strobed illumination are applied to an optically scattering medium. Over the acquisition time of a camera, multiple pulses are summed and at the next frame the phase of the ultrasound is shifted by π/2 and the process repeated. Combining the two frames allows a second harmonic signal to be obtained. A reduction in linewidth is observed (DC=9.26 mm, fundamental=4.02 mm, second harmonic=2.43 mm) in line scans of optically absorbing objects embedded in a scattering medium (thickness=16 mm, scattering coefficient=2.3 mm(-1), anisotropy factor=0.938). 相似文献
11.
Mechanisms of ultrasonic modulation of multiply scattered incoherent light based on diffusion theory 下载免费PDF全文
An analytic equation interpreting the intensity of ultrasound-modulated scattering light is derived,based on diffusion theory and previous explanations of the intensity modulation mechanism.Furthermore,an experiment of ultrasonic modulation of incoherent light in a scattering medium is developed.This analytical model agrees well with experimental results,which confirms the validity of the proposed intensity modulation mechanism.The model supplements the existing research on the ultrasonic modulation mechanism of scattering light. 相似文献
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Brillouin light spectra in water was experimentally investigated by a scanning Fabry-Perot interferometer. The optical properties of the scattering media were modulated by a plane ultrasound wave. An enhancement up to 10 times of the Brillouin signal by modulation with the ultrasound wave has been seen clearly. The dependence of the Brillouin signal amplitude on the ultrasound frequency, amplitude and the position of the ultrasound field based to the light beam was investigated experimentally. Very strong dependence of the enhancement with experimental conditions was obtained. 相似文献
13.
O. Frege 《Czechoslovak Journal of Physics》1998,48(8):933-952
The generalized Bloch equations (GBE) describing the temporal evolution of a single two-level atom interacting with a classical
external field of arbitrary intensity and with a thermodynamic bath are obtained from the time convolutionless generalized
master equation or equivalently from the Tokuyama-Mori identity. These GBE are then used to calculate the absorption spectrum
of a single two-level atom with frequency modulated by dichotomic noise with time-dependent transition probability. 相似文献
14.
The focused ultrasound plays a role in localization and modulating the scattering light in ultrasound- modulated optical tomography (UOT). Both the modulation efficiency of the scattering light and the spatial resolution of UOT are determined by ultrasound. The effects of repetition frequency and pulse energy of impulse ultrasound on the modulated scattering light are derived through experiment in this letter. Purthermore, we compare the imaging sensitivity with 1, 2.25, 5, and 10 MHz center frequencies of impulse ultrasound. Experimental results demonstrate that better signal-to-noise ratios and higher sensitivities can be gained by use of more intense ultrasound and lower ultrasound frequencies. 相似文献
15.
D. Heitmann 《Optics Communications》1977,20(2):292-297
We have investigated the diffraction of light from sinusoidally modulated silver surfaces with grating periods from 4000 to 8000 Å for wavelengths of the visible spectrum. We compare our experiments with theoretical results from a light scattering theory in the first non-vanishing order of the modulation height. This theory includes polarization and the optical constants of the grating material. Good agreement of the theory with the experiments is found for weakly modulated gratings if grating anomalies are avoided. 相似文献
16.
超声调制漫射光子自相关的Monte Carlo模拟 总被引:2,自引:2,他引:0
本文首次用Monte Carlo方法研究了超声调制生物介质中漫射光子的时间自相关性质,讨论了超声参量、运动参量和散射参量对自相关函数的影响.正常生物组织和病变生物组织的自相关函数有明显的差别,超声调制自相关函数为光学医学诊断提供一种新参考. 相似文献
17.
We propose an analytical model of the spatio-temporal structure of a short laser pulse transmitted through a layer of an optically
inhomogeneous medium with high anisotropy of scattering. The light-field brightness in the medium is represented as a finite
series in terms of multiplicities of the small-angle scattering, while the contribution from the higher-order scattering is
allowed for as a quasi-diffuse component. The scattered-pulse structure is calculated on the basis of solving the radiative-transfer
equation in the small-angle approximation with allowance for the effect of multipath light propagation. Compared with the
first approximation of the multiple-scattering theory (attenuated nonscattered light plus the diffuse component), this approach
makes it possible to describe more correctly the transformation of the spatio-angular distribution of light in the medium
when passing from the single-scattering to multiple-scattering regime, as well as specify the temporal profile of the scattered
pulse. The temporal profile of the femtosecond pulse transmitted through a layer of model scattering medium with various concentrations
of scatterers is studied experimentally. The blurred-pulse structure is studied with the help of nonlinear optical gating
in the case of noncollinear generation of the second harmonic. Good agreement between the theoretical and experimental time
profiles of the scattered pulse is shown for the optical-thickness intervals corresponding to both the predominantly low multiplicity
scattering and multiple small-angle scattering, which allows us to use the proposed analytical model for solving the inverse
problem of the pulse sounding of a homogeneous turbid medium.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 4, pp. 333–348, April 2008. 相似文献
18.
V.L. Kuzmin 《Optics Communications》2007,273(2):307-310
Based on an expansion of the Bethe-Salpeter equation in scattering orders a semi-analytic approach for simulation of coherent phenomena of multiple scattering in random media has been developed. We found that for scalar field the manifestation of these phenomena, observed as temporal field correlation function and coherent backscattering, are universal and well agreed with the results predicted by diffusion approximation. For the electromagnetic field the temporal correlation function and coherent backscattering are noticeably differ from those found for the scalar field, depending strongly on the scattering anisotropy. The obtained numerical results, for the first time to our knowledge, are compared directly with the known generalizations of the Milne solution. 相似文献
19.
The scattering properties of a metallic nano-spheroid under the illumination of different polarized light waves are investigated using 3D boundary element method. The influences of different geometrical sizes of the nano-spheroid and incident directions of the illuminating light wave on the scattering spectrum are studied for different incident polarized light waves. The results show that the metallic nano-spheroid has two intrinsic resonant modes, corresponding to different polarization states and resonant wavelengths. The scattering enhancement, the resonant wavelength, and the location of the enhanced optical field are strongly dependent on the polarization properties of the illuminating light waves, and they can be modulated by appropriately choosing the polarization directions of the incident light wave. 相似文献
20.
L. M. Kovachev L. I. Pavlov L. M. Ivanov D. Y. Dakova 《Journal of Russian Laser Research》2006,27(3):185-203
We have investigated the evolution of picosecond and femtosecond optical pulses governed by the amplitude vector equation
in the optical and UV domains. We have written this equation in different coordinate frames, namely, in the laboratory frame,
the Galilean frame, and the moving-in-time frame and have normalized it for the cases of different and equal transverse and
longitudinal sizes of optical pulses or modulated optical waves. For optical pulses with a small transverse size and a large
longitudinal size (optical filaments), we obtain the well-known paraxial approximation in all the coordinate frames, while
for optical pulses with relatively equal transverse and longitudinal sizes (so-called light bullets), we obtain new non-paraxial
nonlinear amplitude equations. In the case of optical fields with low intensity, we have reduced the nonlinear amplitude vector
equations governing the light-bullet evolution to the linear amplitude equations. We have solved the linear equations using
the method of Fourier transform. An unexpected new result is the relative stability of light bullets and the significant decrease
in the diffraction enlargement of light bullets with respect to the case of long pulses in the linear propagation regime. 相似文献