Computation of tightly-focused laser beams in the FDTD method

Capoglu, Ilker; Taflove, Allen; Backman, Vadim

doi:10.1364/oe.21.000087

Cited by 32 publications

(20 citation statements)

References 22 publications

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“…Although this assumption is commonly made for optical Monte Carlo simulations in both the ballistic and diffuse regime, beam steering due to inhomogeneous scatterers (e.g. organelles, glands, and vascular structures) is a known phenomenon that is difficult to model in a traditional ray-tracing Monte Carlo simulation, but has been investigated using various alternative methods [27, [44][45][46][47][48]. In addition, note that our results assume that the imaging is limited by SBR (contrast) and not limited by SNR (a photon-limited situation).…”

Section: Discussionmentioning

confidence: 99%

Assessing the imaging performance of light sheet microscopies in highly scattering tissues

Glaser

Wang

Liu

2016

Biomed. Opt. Express

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Light sheet microscopy (LSM) has emerged as an opticalimaging method for high spatiotemporal volumetric imaging of relatively transparent samples. While this capability has allowed the technique to be highly impactful in fields such as developmental biology, applications involving highly scattering thick tissues have been largely unexplored. Herein, we employ Monte Carlo simulations to explore the use of LSM for imaging turbid media. In particular, due to its similarity to dual-axis confocal (DAC) microscopy, we compare LSM performance to pointscanned (PS-DAC) and line-scanned (LS-DAC) dual-axis confocal microscopy techniques that have been previously shown to produce highquality images at round-trip optical lengths of ~9 -10 and ~3 -4 respectively. The results of this study indicate that LSM using widefield collection (WF-LSM) provides comparable performance to LS-DAC in thick tissues, due to the fact that they both utilize an illumination beam focused in one dimension (i.e. a line or sheet). On the other hand, LSM using confocal line detection (CL-LSM) is more analogous to PS-DAC microscopy, in which the illumination beam is focused in two dimensions to a point. The imaging depth of LSM is only slightly inferior to DAC (~2 -3 and ~6 -7 optical lengths for WF-LSM and CL-LSM respectively) due to the use of a lower numerical aperture (NA) illumination beam for extended imaging along the illumination axis. Therefore, we conclude that the ability to image deeply is dictated most by the confocality of the microscope technique. In addition, we find that imaging resolution is mostly dependent on the collection NA, and is relatively invariant to imaging depth in a homogeneous scattering medium. Our results indicate that superficial imaging of highly scattering tissues using light sheet microscopy is possible.

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Section: Discussionmentioning

confidence: 99%

Assessing the imaging performance of light sheet microscopies in highly scattering tissues

Glaser

Wang

Liu

2016

Biomed. Opt. Express

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“…While more advanced numerical models of light propagation exist, (e.g., the FDTD method), the BPM utilizes an approximation (discussed in the following paragraphs) to the Helmholtz equation that places less-restrictive constraints on the numerical step-size and spatial grid resolution (e.g., the FDTD method requires a fine spatial sampling of λ /20) [23–25]. While there are many variations of the BPM, here we employ the split-step spectral-domain method, a common numerical technique for solving non-linear partial differential equations.…”

Section: The Fractal Propagation Methodsmentioning

confidence: 99%

Fractal propagation method enables realistic optical microscopy simulations in biological tissues

Glaser

Chen

Liu

2016

Optica

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Current simulation methods for light transport in biological media have limited efficiency and realism when applied to three-dimensional microscopic light transport in biological tissues with refractive heterogeneities. We describe here a technique which combines a beam propagation method valid for modeling light transport in media with weak variations in refractive index, with a fractal model of refractive index turbulence. In contrast to standard simulation methods, this fractal propagation method (FPM) is able to accurately and efficiently simulate the diffraction effects of focused beams, as well as the microscopic heterogeneities present in tissue that result in scattering, refractive beam steering, and the aberration of beam foci. We validate the technique and the relationship between the FPM model parameters and conventional optical parameters used to describe tissues, and also demonstrate the method’s flexibility and robustness by examining the steering and distortion of Gaussian and Bessel beams in tissue with comparison to experimental data. We show that the FPM has utility for the accurate investigation and optimization of optical microscopy methods such as light-sheet, confocal, and nonlinear microscopy.

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“…1). 14 The TF/SF method also offers the possibility to inject a plane wave at an oblique angle, which is important for the modeling of focused beams in the FDTD method, since it facilitates the modeling of any desired beam as long as we have its ASPW description, 8,9 as will be seen in the next section. In the second region, the scattered-field region, which surrounds the total-field region, only the scattered fields exist.…”

Section: Finite Difference Time Domain Methodsmentioning

confidence: 99%

“…9 In a similar approach, the minimum number of plane waves ðM min Þ needed to get a focus with no numerical artifacts due to sampling in the spatial range of size ðy m Þ, and for a maximum incident angle θ max (which is the definition for the maximum divergence angle for a focused beam) is found to be This sampling problem has been addressed before in general terms.…”

Section: Angular Spectrum Of Plane Wavesmentioning

confidence: 97%

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Simulating the scanning of a focused beam through scattering media using a numerical solution of Maxwell’s equations

2014

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A highly efficient method based on Maxwell's theory was developed, which enables the calculation of the scanning of a focused beam through scattering media. Maxwell's equations were numerically solved in two dimensions using finite difference time domain simulations. The modeling of the focused beam was achieved by applying the angular spectrum of plane waves method. The scanning of the focused beam through the scattering medium was accomplished by saving the results of the near field obtained from one simulation set of plane waves incident at different angles and by an appropriate post processing of these data. Thus, an arbitrary number of focus positions could be simulated without the need to further solve Maxwell's equations. The presented method can be used to efficiently study the light propagation of focused beam through scattering media which is important, for example, for different kinds of scanning microscopes.

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Computation of tightly-focused laser beams in the FDTD method

Cited by 32 publications

References 22 publications

Assessing the imaging performance of light sheet microscopies in highly scattering tissues

Assessing the imaging performance of light sheet microscopies in highly scattering tissues

Fractal propagation method enables realistic optical microscopy simulations in biological tissues

Simulating the scanning of a focused beam through scattering media using a numerical solution of Maxwell’s equations

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