What limitations?

© Photo | Fotolia © Steve Mann

Prof. Ulrich Wittrock, head of the Photonics Laboratory at the Münster University of Applied Sciences, seeks out the ultimate boundaries of laser technology

Ask an engineer responsible for developing internal combustion engines what they’d like more than anything. They’ll tell you it would be to shrink the 300 kW V8 engine used in luxury sedans down to the size and weight of a motorbike engine and then multiply its efficiency to drastically cut fuel consumption.

There is more

Disk laser:


Disk lasers are solid-state lasers where the active laser medium is in the shape of a disk. With every pass, the pump beam strikes the disk from the front and is reflected by the silvered reverse side. Because the surface area of the reverse side is huge in relation to the volume, the small thin disk cools down extremely well. As a result, disk lasers combine high laser power and outstanding beam quality.


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We know that this is impossible. Sadly, internal combustion engines come up against the physical limitations set by the uncompromising second law of thermodynamics. It implies that achieving this goal would call for much higher combustion temperatures than any known material can withstand.


Prof. Ulrich Wittrock is head of the Photonics Laboratory and speaker for the Institute for Optical Technologies at the Münster University of Applied Sciences.

The laser technology makes it possible

We’d therefore suggest the engineer switch specialties. Because in the field of laser technology, results like that are very much within reach. Modern disk lasers capable of delivering 4 kW of power are much smaller than comparable rod lasers were 20 years ago. And yet these disk lasers are five times more efficient, meaning they can deliver the same 4 kW of power while drawing a fifth of the energy previously required.

So are there any physical limitations at all in this field? Unfortunately, it seems there are. Interestingly, it would appear that the same second law of thermodynamics limits the size and efficiency of lasers, too. With both internal combustion engines and lasers, energy is transformed from a state with lesser energetic value into a higher-energy form. Thermal energy from burning gasoline is used to carry out mechanical work. Pump light from lamps or laser diodes is turned into a sharply focused working beam.

Research focus disk laser

The following rule applies: the higher the value of the input energy, the more successfully this transformation takes place. Disk lasers benefit directly from advances in laser diode technology, which are constantly increasing the quality of the pump light produced. Unlike internal combustion engines, though, we’re still a long way from reaching the theoretical limitations of this process.

We laser scientists can well imagine new materials and concepts that will keep thermal problems manageable in the future.

Strictly speaking, we don’t really know where these limits are. We have yet to discover the fundamental technical barrier that might set them. For internal combustion engines it turned out to be the maximum combustion temperature. But what is it for the laser?

This far and further

It’s true that laser engineers have always had to contend with thermal problems, so our newly recruited engine-technology specialist would certainly be able to offer some creative insights straight away.

Nonetheless, the fundamental factor determining the basic limits of the process must be something else. Unlike engineers working on internal combustion engines, we laser scientists can well imagine new materials and concepts that will keep thermal problems manageable in the future.

Engineers dreams come true

While physicists attempt to explore the basic limitations of the technology, engineers take a more pragmatic approach, trying things out and making step-by-step improvements as they go. Again and again, this strategy has allowed them to push back the practical limits of what’s possible.

From a physics standpoint, there’s still no reason you couldn’t make a disk laser the size of a V8 engine, delivering 300 kW of power. This would make it just as powerful as the combustion engine mentioned earlier. It shouldn’t differ too much in terms of efficiency, either. This is a fascinating field that looks set to make a few more dreams come true for engineers. Limitations? None in sight.

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