Modeling in Photonics

What is a Model?

Essentially, a model is a mental construction which is supposed to resemble some aspects of reality. Typically, it is used for acquiring a better understanding of reality, which then helps for making good decisions.

A model is always simpler than reality, so that we can better cope with the remaining level of complexity. Of course, it should not be over-simplified, i.e., it must properly describe certain aspects which are of interest in an investigation. The optimum type of model if often one which incorporates everything necessary but nothing more.

In technical areas, modeling starts with some thoughts and ideas, which are then condensed to more formal structures, involving certain quantities, mathematical equations, etc. Computers equipped with suitable software can be used for the corresponding calculations. Computer models simulate the behavior of real objects (e.g., buildings, cars, electronic circuits or lasers) and reveal not only expected outputs, but also the internal workings.

Examples for Models

Models are routinely used in many technical areas; some examples:

Application Area	Type of Model	Aspects to Investigate
Architecture	small-scale artifact or computer model of a building	space for inhabitants and installations distribution of light (sunlight, illumination) energy flows structural stability
Cars	model of a car body	space for passengers structural stability, safety in crashes dynamic driving behavior
Electronics	model of an electronic circuit	validation of functionality influences of imperfections and tolerances of parts operation with over- or under-voltage
Laser Technology	model for a Q-switched laser with laser crystal, modulator and resonator	dynamics of pulse generation power conversion efficiency beam quality effects of gain guiding, limited modulator speed, etc.

The next page gives you more concrete examples for models in laser technology.

General Purposes of Models

Modeling is not a purpose itself, but is done in order to obtain important benefits:

Purpose	Examples in laser technology
Develop a clear understanding of how things work	power conversion in laser crystal or doped fiber beam formation in a laser resonator dynamics of pulse generation or amplification
Plan the construction of prototypes and final products	laser resonators laser heads pulse amplification systems data transmissions systems
Analyze problems of existing or planned devices	poor beam quality poor power conversion efficiency instabilities optical damage
Develop and analyze new ideas	new resonator design concepts new pumping arrangements new gain materials new principles of pulse amplification

But why should you do such investigations on computer models rather than on the real objects?

Making a computer model is often much simpler, quicker and cheaper than fabricating the real object. In particular, making modified versions (copies with some modifications) is by far cheaper with computer models.
So you can easily try out many different versions without ordering a lot of expensive parts, waiting for delivery and spending ages in the lab.

In contrast to real objects, a computer model is fully transparent: you can easily inspect any internal details of its operation, which would often be hard or impossible to observe in a real object. (This aspect is discussed in depth in the presentation "The Transparent Laser".)
Tests on computer models are never destructive – even crash tests for cars or simulations of laser amplifiers at extremely high intensity levels.

Experiments on computer models are often more conclusive than experimental tests, because they are not affected by poorly controlled influences.
For example, two versions of a laser model can be exactly the same except for one detail you have changed; you will clearly see the effect of that change, and you can at any time easily switch between different versions.

Comparisons of real experiments with computer simulations show whether unexpected phenomena occur in your devices. For example, find out whether the performance is as good as it can be for your design.

Building and testing the real objects stays necessary – but is then based on prototype or product designs which result from a clear understanding. Don't build and test what cannot work anyway!

The Benefits

Typical achieved benefits of working with computer models are:

You can develop laser devices more efficiently, i.e., get results more quickly and save resources.
You can deepen your technical competences far beyond the level of textbook knowledge.
When playing with models, you get new ideas e.g. for optimizations or new technical approaches.

Such benefits are of crucial importance for the productivity e.g. of a laser development engineer or a scientist in laser research. Both need to understand exactly how things work and how to effectively optimize them.

For more details, see also our tutorial on modeling.