What could hologram technology offer us?

More light, more design

Some are feline, others have a piercing look or resemble an eagle's eye. While it used to be the bodywork that distinguished the designs of car brands and models from one another, today it is the headlights. In the so-called vehicle face, they are the eyes - and not just at the front, but also at the rear, even if that may sound like a paradox. For an unmistakable look, vehicle manufacturers rely on increasingly detailed and elaborately designed lights at the front and rear.

A sphere is evenly illuminated to produce the holographic film. The light must hit the film at an angle of 180 degrees so that the hologram can then radiate into the entire half-space. (Image: Thilo Schmülgen / TH Köln)

The technology makes it possible through the use of new LEDs. But no matter how flamboyant the headlights are designed, a separate light is still required for each function such as taillights, indicators and brake lights. Still. Because in the future, a single, multifunctional lamp could push the design language of the car's faces even further. The trick: take a hologram.

Previous design not energy efficient

So far, car lights have consisted of a lamp and lens system. Diffusing lenses are required for the rear lights so that the headlights emit the light evenly into the half-space behind the car. “However, they throw half of the light back into the headlight. That is not exactly energy efficient, ”says Prof. Dr. Stefan Altmeyer from the Institute for Applied Optics and Electronics (AOE).

He and his team have been researching imaging processes and holography for more than ten years. For example, to use them to direct artificial and sunlight. Or to develop holograms with particularly wide radiation characteristics (the research project is currently being funded by the "NRW Patent Validation" program with EUR 200,000). As in so many research fields, the same applies here: What already works on a small scale cannot simply be transferred one-to-one to a larger one.

New process does it in one shot

But Stefan Altmeyer and Roman Bibo, graduates and research assistants at the AOE, are well on their way: by the end of the year they want to have a demonstrator with a hologram film of 100 square centimeters that can be switched on with either red, yellow or green light. And when the light is switched off, the hologram is transparent like a pane of glass. Very special lasers are required for production.

The hologram of an object is created by the fact that the light waves reflected by the object are superimposed on those that were emitted directly by the laser in the film. An interference pattern is created that appears three-dimensional when it is illuminated with the same wavelength as when the picture was taken.

In order to produce a hologram film on a sufficiently large scale for automobile rear headlights, Roman Bibo is currently investigating the optimal beam angles, exposure times, the beam ratio and a few other important parameters. He has also developed a new process to carry out the necessary, complex goniometer measurement "live and in one shot": A complex algorithm calculates distortions, imaging errors and other parameters in order to be able to check whether the lighting conditions are evenly depicted on the hologram become. This is precisely the challenge in developing a process for producing large hologram surfaces. Once the process is in place, the hologram can be created in less than a minute.

Clean designs, flat constructions

With their development, Altmeyer and Bibo hope that automotive suppliers will be very interested in them. Altmeyer also thinks a later spin-off is conceivable. In addition to energy savings of around 50 percent, hologram technology offers other advantages compared to diffusing lenses: automobile manufacturers can visualize their brand logos or images on the film. The new design takes up significantly less space in the body and “you don't see any technology, the headlights are empty and tidy,” says Altmeyer.

The expert in applied optics, however, is critical of using the hologram film for the front headlights: “This is far more difficult to implement, since white light is an additive mixture of the individual colors red, green and blue, each with different wavelengths. And the idea of ​​the hologram foil is to simply switch on a color, i.e. a wavelength. That is why this technology will only be of interest to the rear for the time being. "

October 2017