Laser projections

Photos and videos can give only a vague idea of the actual effect that the laser projections have on site during a performance. One example is the “Global Rainbow” by the artist Yvette Mattern: sevenbrightly colored very powerful laser beams shine towards the sky from Berlin’s Ernst-Reuter-Platz in the direction of the Victory Column and change the vibe of an entire city center. Or ‘Another Moon’ by the artist duo Kimchi and Chips, where a second moon appears in the sky over the Zeche Zollverein in Essen. Or the fast- paced show at the closing ceremony of the Winter Olympics in Pyeongchang... these are just a handful of many examples.

The often surprising and sometimes breathtaking light effects are based on the unique qualities of the laser beam. In terms of intensity, beam focus, and range, it outperforms light beams from other artificial sources many times over. On the other hand, the laser is subject to optical and technical limitations, as sales manager Richard Schäfer explains: “The beam is usually very small. With our devices, its diameter is usually around 4.0 millimeters. So only a small dot appears on a projection surface.”

In order create a pattern – such as a logo, lettering, or cartoon-like moving images – laser projection relies on the inertia of the human eye. To be precise, it is the image processing in the brain, which also creates a continuous progression in a film made up of 24 individual frames per second. If the laser beam moves fast enough, the person “sees” the projected animation instead of a point of light darting around. To achieve this, the beam in the projector is deflected by means of two mirrors – one each for the x and y axes. Its movement is induced electro-magnetically and reaches a very high speed.

Another limitation is the color. The color of a laser depends on the laser-active material in which the beam is generated. In the case of laser projection, it is the semiconductor, since diode lasers or Coherent OPSL sources are used here. But laser diodes can only produce a few basic colors, mainly red, green, and blue. The high-end devices from LaserAnimation Sollinger also have Coherent OPSL sources for yellow, orange, and cyan. To produce a white beam, beams of multiple colors must be “collinearly superimposed.” The same is the case for other colors: in order to create the different tones of the entire palette, the intensity of the individual rays is modulated.

The trick is to superimpose the different laser sources, each with different wavelengths, as collinearly as possible. The more precisely this is carried out, the sharper and more precise the final beam will appear to the human eye. This is where special optical filters, so-called “dichroic filters,” are used, which deflect certain wavelengths while other wavelengths (colors) beam through the glass filtrate. This is how different laser beams can be “superimposed” to form a single beam. So what looks like a “white” ray to the human eye is ultimately the combination of red, green, and blue sources.  

But that only works if the beams stay together very precisely and, above all, for a long time and at a great distance, because laser installations often have to be visible from hundreds of meters or even several kilometers away. The dichroic filters have to be adjusted with the appropriate precision, as Richard Schäfer explains: “A deviation of one hundredth of a degree results in an offset of 1.7 centimeters per one hundred meters. This means that the individual colors are no longer on top of each other and can be distinguished by the human eye – the color mixing effect is lost.”  

Now, it’s not unheard of that a device from Laser-Animation Sollinger leaves the premises in Berlin to be set up a day later, for example, for a laser show on the Burj Khalifa in Dubai. After minus twenty degrees on the cargo flight, the housing heats up to sixty degrees or more in the desert sun. Despite high-quality materials and sophisticated fastening technology, a certain level of distortion in the optics is inevitable. This means that the position of the dichroic filters may need to be slightly readjusted. This is the reason why the dichroic mirror holders are equipped with a drive: brushless DC-motors from FAULHABER with integrated gears are used for software-controlled fine adjustment to at least a thousandth of a degree.

“For these types of effects, we often use several projectors," explains Richard Schäfer. “They can only unfold their effect if the gratings move completely synchronously, at the highest and lowest speed as well as in start/stop operation with constant changes of direction.” The projectors and the grating modules are full of technology, which means that the installation space is extremely tight. Only very small motors can be accommodated here.

Maximum precision and repeatability are additional minimum requirements. The integrated backlash-free gears play an important role here. When asked about the beginning of the collaboration with FAULHABER, Richard Schäfer replies that it must have been before his time. Looking for the very first order, he finds the year 2003. This means that FAULHABER motors have stood the test of time for this demanding application over the course of twenty years: “We build top of the line devices for laser projections. To do this, we need drives that are on the same level.”