2.1. Focusing

Run Simulation

The SIMULATE module with focusing mode is shown in the image below. In focusing simulation, a plane wave is used to simulate the lens for focusing. You can see details about the unit cells and parameters on the left side of the module that were used to build the lens in BUILD module. On the right side is the area for user inputs to run simulation. Enter values in all entry fields as shown in the image. To simulate with a circular aperture, make sure "Use Circular Lens Aperture Diameter" is checked in GENERAL section. The default diameter is the lens size; 50 µm in this tutorial. Click RUN SIMULATION on the bottom right.

  • Inc. Med. Ref. Index: Incident medium's refractive index.

  • Intensity Profile: Intensity distribution across the incident beam's cross-section. Options of Uniform and Gaussian are available. The intensity profile of the incident beam is saved as an image file (.png) in the directory: your_SMDPRO_project_folder/results/sim/foc

  • Gaussian beam:

    • SMD PRO assumes that the beam is collimated (or is at the beam waist) and the beam width is constant over a distance.

    • Beam diameter refers to the diameter where the beam's normalized intensity drops to 1/e2.

    • Beam center is at the lens center at all incidence angles.

Analyze Results

Once the simulation completes, the ANALYZE button in the left sidebar will be activated. Click that button to see simulation results in ANALYZE module.

  • Simulation results:

    • Intensity on focal plane (Ixy): This is required to calculate the lens' focusing efficiency.

    • Intensity on yz-plane (Iyz)

    • Intensity along y-axis on focal plane (Iy): The FWHM is automatically evaluated from this result.

[Focusing Simulation] If you simulate the lens at off-normal incidence, then FWHMs in the x- and y-directions may differ. Thus, in such cases, users should use caution when calculating the focusing efficiency since the software uses FWHM in the y-direction for the calculation. See the section Focusing Efficiency for the definition of focusing efficiency.

To export simulated images or data, click the figure(s) you need to export and click SAVE FIGURE(S) or EXPORT DATA on top right corner of the module. You can also click SELECT ALL to export all figures or data at once. If you need to display the intensities in a log scale, click 'Log' in the toolbar at the bottom of the module.

Focusing simulation results in linear scale: Ixy (left) and Iyz (right). The z-position of focal plane is z = - f, where f is focal length.
Focusing simulation results in log scale: Ixy (left) and Iyz (right). The z-position of focal plane is z = - f, where f is focal length.

You can use the toolbar (see image below) to calculate the focusing efficiency from the results of Ixy. In the toolbar, enter the x- and y-coordinates of the lens' focal point; (0,0) in this tutorial. Since we simulated the lens with a circular aperture, select 'Circle' under Focal Area and click the calculator button (). The focusing efficiency will be automatically calculated and displayed above this button.

See Focusing Efficiency for the definition of focal area.

Toolbar in ANALYZE module (focusing).

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