Due to their ability to split a single laser beam into multiple beams in combination with well-defined power ratios, diffractive beam splitters are widely used for applications such as laser material processing and optical metrology. But because of the small feature sizes required for non-paraxial or even high-NA splitting or diffraction angles, the design and optimization of this type of device can be challenging. VirtualLab Fusion provides optical engineers with several tools to assist them in this task.

To illustrate the general workflow, we showcase two examples: In the first example, we employ the Iterative Fourier Transform Algorithm (IFTA) alongside a structure design based on the Thin Element Approximation (TEA) to generate a series of initial designs for a beam splitter, which are then rigorously analyzed and further optimized rigorously with the Fourier Modal Method/Rigorous Coupled Wave Analysis (FMM/RCWA). In order to define a suitable and efficient merit function for that last optimization step, the Programmable Grating Analyzer is applied. The second example covers this part of the process in more detail.

Mirau interferometry is a well-known technique that allows the measurement of surfaces with an accuracy of up to one hundredth of the wavelength used. To fully investigate and design such a system, a non-sequential simulation approach is helpful because it automatically incorporates the interference effects that arise from the internal reflections.

Therefore, this week we not only present such a device, but also elaborate on the measurement principle by investigating the interference effects of differently shaped etalons.

In spectroscopy of gases, in order to obtain a sensitive enough measurement of the absorption, it is often required to have long optical path lengths. Multiple-pass cells, where the gas-filled volume is encased between mirrors, are a way of fulfilling this requirement while at the same time controlling beam divergence on the way and preempting the need for extremely large devices. The Herriott cell is one example of this kind of system, characterized by the use of two spherical mirrors with a single off-axis hole drilled into one of them to allow for the entry and exit of the beam. The curvature of the mirrors redirects the beam and controls its divergence.

In today’s newsletter we want to demonstrate the simulation of one such Herriott cell. We have used the Parameter Coupling to link several system parameters together, in order to ensure the correct configuration of the setup while allowing the user to investigate the effect of varying, for instance, the distance between mirrors.