Mie Simulator GUI Running Application - VirtualPhotonics/MieSimulatorGUI GitHub Wiki

This document describes the inputs, outputs, and execution of the Mie Simulator GUI tool. It features one input panel (input selection panel) and five output panels (µ_s (scattering), µ_s' (reduced scattering), number density, phase function and scattering anisotropy panels) as shown below.

This panel lets users choose between a monodisperse distribution (uniform spherical particles) or a polydisperse distribution (spherical particles of varying sizes). Monodisperse distributions are used for analyzing spheres with similar attributes, like size and refractive index. In contrast, polydisperse distributions allow for simulations with diverse sphere attributes.

• Diameter: The current version supports spheres with diameters ranging from 0.1nm to 300μm. The diameter (2 x Radius) must be entered in micrometers (μm).

• Concentration: Enter the concentration as the number of spheres per cubic millimeter. The tool will display an error if the total volume of all spheres exceeds one cubic millimeter.

• Volume Fraction: This represents the ratio of the total sphere volume to the cubic volume. It's calculated by multiplying the sphere's concentration by its individual volume. An error message will appear if the volume fraction exceeds 1.

• Adjusting Concentration/Volume Fraction After a Simulation: After running a simulation, a user can use the ±5 Margin slider to make minor adjustments to either the concentration or volume fraction to visualize how the results change.

• Refractive index: Users can specify the refractive index for both the sphere and the medium. The tool then calculates the relative refractive index. The sphere's refractive index can be either a real or a complex number. A complex refractive index indicates that the sphere absorbs light, with the negative imaginary component representing the absorption coefficient. The simulations use the sign convention defined by Van de Hulst (1957).

• Wavelength: Specify the wavelength in vacuum/air (λ_vacuum) and the medium refractive index (n_med). The tool converts these values. A user can define a range by setting the start and end wavelengths and a step size. To specify a single wavelength, set the "Start" and "End" values to be the same. This tool supports wavelengths from 50nm to 3000nm (3µm).

• Plot Scale Y-Axis: "Log10" selection will change the scale of the y-axis to log10.

Polydisperse distribution selection offers three distributions; “Log Normal”, “Gaussian” and “Custom”.

Users can set the mean diameter, standard deviation, and number of spheres for the Log-Normal and Gaussian distributions. Clicking "Show Distribution" will display the number density distribution, which represents the number of spheres in a 1mm³ volume. For these distributions, all spheres must have the same refractive index. This Custom option allows users to specify different refractive indexes for different spheres. Starting with Version 2.0, users can also specify the refractive index of the medium, which will override the value displayed in the GUI. For details and sample formats for the custom input file, please refer to the documentation here.

Click the "Run Simulation" button to compute the results. Use the "Display Data" button to show the results in a text window. The "Save Data" button allows users to save selected results. The "Close" button will close the application..

This panel graphically presents the number density of spheres N_s [#/mm³] used in the simulation. To properly visualize the "Log-normal" distribution, select the "Log" radio button for the x-axis below the plot. The subsequent tab displays the 'Size Parameter' defined as 2πR n_med / λ_vacuum , where R [µm] denotes the particle radius, n_med the medium's refractive index, and λ_vacuum [µm] is the wavelength in vacuum.

The Mie calculations provide three important efficiency factors: the scattering efficiency (Q_sca), the extinction efficiency (Q_ext), and the back-scattering efficiency (Q_back) (Mie Scattering Efficiencies). These dimensionless quantities combined with the particle's cross section area (πR²) yield the corresponding scattering cross section C_sca [/mm²], extinction cross section C_ext [/mm²] and back-scattering cross section C_back [/mm²] [Van de Hulst 1957, Bohren and Huffman 1983]. The calculated cross sections are displayed across three separate tabs. For mono-disperse distribution, the scattering coefficient (µ_s) is simply the product of the scattering cross-section C_sca and the number density N_s. For poly-disperse distributions the scattering coefficient is calculated using the discrete particle model (Schmitt, App. Opt., 37(13), 1998) detailed in Schmitt and Kumar.

The phase function represents the angular distribution of scattered light. The calculated results for the phase function are displayed in this panel using polar and linear plots. These plots are derived from the complex amplitude scattering matrix elements, S₁, and S₂ , which describe the transformation of incident electromagnetic field to far-field scattered field [@VandeHulst1957; @Bohren1983]. The wavelength slider enables the user to visualize the phase function or S₁ and S₂ data at a specific wavelength. To find the phase function or S1/S2 data for a particular wavelength, use the "wavelength slider". Users can also adjust the resolution of both the phase function and S1/S2 data by changing the "dtheta(dθ)" selection.

The anisotropy (scattering asymmetry) panel displays the directional properties of the scattering phase function. The first tab presents the average cosine of the phase function (g), which quantifies the average scattering angle which indicates the prevalence of forward (g>0) vs backward scattering (g<0). The second tab provides the integrated forward and backward scattering fractions, offering a detailed analysis of the angular scattering distribution.

This panel shows the reduced scattering coefficient (µ_s'), calculated as the product of the scattering coefficient (µ_s) and (1-g). µ_s' is crucial in various fields, particularly in biomedical optics, because it allows for the non-invasive quantification of tissue properties. Users can use "µs' Power Law Fitting" tab to compute the fitting parameters that provide a simplified functional form for the wavelength dependence of µ_s' as described in Steve L. Jacques's review paper (Jacques, Phys. Med & Bio., 58(14), 2013).

Last edited: August 25, 2025