A team of researchers at DTU Photonics Engineering has set the world record in laser efficiency with a green laser diode that is green in more ways than one.
DTU Photonics has taken a quantum leap in laser technology and attracted positive attention in photonics circles. Researchers have successfully produced a green light source with an energy-efficient laser diode that has record-high brightness at 90 per cent of the cost.
Laser diodes are light sources that can emit laser light in a specific colour, and the green lights are particularly important. They are used for laser displays in industry, for processing materials, for gauges and for treating various types of skin diseases.
To make a laser diode produce green light requires a frequency-doubled laser diode. In principle, the frequency doubling occurs when two light particles (photons) in an infrared laser beam are allowed to merge into one more powerful photon, making it possible to change the colour of the light from invisible infrared to visible green.
Until now, this could only be done by sending the beam through a so-called solid-state laser, which is extremely expensive, consumes large amounts of energy and reduces the brightness by 50 per cent in the process.
But now DTU Photonics has discovered how to double the frequency of the infrared beam simply by sending it through a special optical crystal. This allows the researchers to change the colour of the beam to green without reducing the brightness, because the expensive and inefficient solid-state laser is removed from the process. This reduces the costs by up to 90 per cent.
World record
DTU Photonics took another quantum leap in January 2009 when the green laser diode achieved a brightness of 1.58 watts. That is a world record and was covered by the American scientific journal Optics Express in March. The increased brightness is a quadrupling of what laser diodes have otherwise been able to produce.
“We are very proud of our achievement and are working at a high academic level to develop the world’s best laser system. This record opens up some excellent new opportunities for DTU by allowing us to develop new laser technology together with the very best researchers and companies in Europe,” says Paul Michael Petersen.
He is head of research and affiliate professor at DTU Photonics, as well as head of laser cavity development in the international consortium BRIGHTER.EU, which aims to develop a new generation of high-brightness laser diodes. Laser quality is a key aspect of the laser, where light is sent back and forth between two mirrors, making it possible to effectively increase the brightness of the light.
New laser from Germany
The new and more powerful green laser is a combination of German laser technology and DTU know-how. DTU Photonics joined forces with the German research institute for high-frequency technology, Ferdinand-Braun-Institut, to develop a new laser that has turned out to be well-suited for frequency doubling.
“This new laser had the high quality required, and DTU Photonics subsequently developed the method of frequency doubling the beam using an optical crystal,” says Ole Bjarlin Jensen, researcher at DTU Photonics.
What will the future bring?
The new laser technology makes it affordable to produce laser displays for cars so the speedometer, fuel gauge, clock or oil pressure can be displayed in the middle of the windscreen – just like a heads-up display in a fighter plane where the pilot has all the important information right in the middle of his visual field.
“If we can produce colours in the spectrum besides green, this would pave the way for entirely new possibilities, for instance in the development of the new generation of televisions – laser TV – or micro-displays, where it will be possible to project a movie in high quality on your living room wall via a mini-laser in your mobile phone,” says Ole Bjarlin Jensen.