2024年4月11日发(作者：)

/cn/fdtd/sp_single_device_on_a_

/cn/fdtd/

进入上面的网页下载仿真程序。

按照下面的仿真方法得到下面的图片。然后改变纳米粒子直径（宽、长），得到不同纳米粒

子参数下的散射截面图。

Simulation setup

The file mie_example_ contains an example of the Mie problem in 3D, using a total-field

scattered-field source(TFSF) that surrounds a gold particle. There are two analysis groups, each of

which consist of a box of power monitors: one in the total field region and one in the scattered

field region. These analysis groups can be used to calculate the absorption and scattering cross

sections, as well as the angular distribution of scattered radiation. In addition, 3 frequency profile

monitors are added in the total field region to calculate the electric field enhancement. The total

scattered field source covers a wavelength range of 300 to 600 nm.

The gold material is a copy of the "Au (Gold) - Johnson and Christy" material that is contained in

the default material database. Since the default number of coefficients is not sufficient to provide a

good fit to the sampled data over the source bandwidth, the maximum coefficients is set to 10. The

theoretical Mie scattering cross sections (absorption and scattering) have been calculated for both

the material fit and the sampled data and are stored in the

files mie_au_jc_ and mie_au_jc_, respectivelty.

With the default settings (simulation span is 1x1x1 um

3

and a mesh accuracy of 3, plus an override

region of 5nm at the sphere) the simulation will require about 234 MB of memory.

Once the simulation is finished, mie_analysis_ will perform the following analysis.

Note: Mesh override region

For simulations with metals, the mesh override region is often used to more accurately resolve the

locations of the metal interface, especially with curved surfaces. In this simulation, the mesh

override region is large enough to encompass not only the gold sphere, but also the entire TFSF

region. This was done intentionally; the TFSF sources work best in uniformly meshed regions.

Also note that the mesh spacing of the override region effects the location of the analysis boxes.

Sources require a certain amount of space to inject the fields. The amount of space required is ~2

mesh cells and is depicted graphically by light white shading that surrounds the source. Within

this region, the fields are not physically meaningful. Hence monitors should not be placed in this

region.

Absorption and Scattering cross sections

The absorption cross section (the rate at which energy is removed from the incident plane wave by

absorption)is calculated by an analysis group located inside the TFSF source. The analysis group

calculates the net power flow into the particle and hence the absorption cross section using the

optical theorem. Similarly, the scattering cross section is calculated by an analysis group located

outside the TFSF source. This group measures the net power scattered from the particle.

The above plots compare the FDTD results with the results from theory which were computed

using the Gold data from the material fit. In the script file, change the name of the file from which

to plot the theoretical results from mie_au_jc_ to mie_au_jc_ to compare the FDTD

results with the results from theory that were computed using the raw Gold data. Running the

script file results in the following two plots for the cross sections.

Note: Power normalization with the TFSF source

Power normalization with the TFSF source can slightly confusing. Rather than normalizing

results to the source power (which is infinite for an ideal plane wave since it has infinite extent), it

is best to normalize by the source intensity. This leads to power measurements being returned in

cross section type units. For more information, see the Power normalization page of the TFSF

sources section.

Higher accuracy results

The default settings for this simulation are designed to give reasonably accurate results while

minimizing the simulation time. If higher accuracy is desired, make the following

modifications. These modifications will increase the memory requirements to around 1.7 GB.