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  • South Africans develop ‘world’s first digital laser’

Photonics Spectra
Dec 2013
PRETORIA, South Africa – The Council for Scientific and Industrial Research (CSIR) announced that it has developed a digital laser, a milestone its creators say represents a paradigm shift for laser resonators.

In a paper published in Nature Communications (doi: 10.1038/ncomms3289), the CSIR researchers showed that beams can be digitally controlled from within a laser. They overcame the limitations of using specialized optical elements to customize the output beam of a laser “comprising an electrically addressed reflective phase-only spatial light modulator as an intracavity digitally addressed holographic mirror.” The phase and amplitude of the holographic mirror can be controlled by writing a computer-generated hologram in the form of a gray-scale image to the device for on-demand laser modes.

Light can be shaped after exiting a laser using a spatial light modulator – an LCD that can be digitally addressed with gray-scale images representing the desired change to the light. The CSIR team is the first to demonstrate that this can all be done inside the laser.

cell optical trapping
Light is delivered through a high-numerical-aperture objective into a sample cell for optical trapping and tweezing. The digital laser could be used as an integral component in a holographic optical trap for control of single cells, delivering the desired beam on demand and in real time. Photo courtesy of Andrew Forbes, CSIR.


“Our digital laser uses the LCD as one of its mirrors that is fitted at one end of the laser cavity. Just as with LCD televisions, the LCD inside the laser can be sent pictures to display. When the pictures change on the LCD inside, the properties of the laser beams that exit the device change accordingly,” said professor Andrew Forbes, leader of CSIR’s mathematical optics research group, where the work was done.

Forbes, who in March became the first South African inducted as an SPIE Fellow, led the team, supported by postdoctoral fellow Dr. Igor Litvin and doctoral students Sandile Ngcobo and Liesl Burger.

“We showed that by sending an appropriate picture to the LCD, any desired laser beam could be created inside the laser device,” Forbes said. “This is a significant advancement from the traditional approach to laser beam control, which requires costly optics and realignment of the laser device for every beam change. Since this is all done with pictures, the digital laser represents a paradigm shift for laser resonators.”

“I believe the digital laser will be a disruptive technology. This is technology which may change the status quo and which could create new markets and value networks within the next few years or decade,” said Ngcobo, who conducted the work as part of his Ph.D. studies at the University of KwaZulu-Natal.

Lasers are a multibillion-dollar industry worldwide, and “the development of the digital laser opens up a whole new world of opportunities,” said Minister of Science and Technology Derek Hanekom at a media event in September announcing the device.

At the press conference, Hanekom read a statement from Dr. Igle Gledhill, president of the South African Institute of Physics, who said, “This is what is often termed a breakthrough – and it is a real breakthrough. The digital laser opens up new visions of laser applications, and there are uses that we haven’t even thought of yet. In that way, it’s very much just like the original invention of the laser over 50 years ago.”

At the CSIR’s laboratories in Pretoria, the team programmed the LCD to play a video of a selection of images representing a variety of desired laser modes. The result was that the laser output changed in real time from one mode shape to another.

“The dynamic control of laser modes could open up many future applications, from communications to medicine. Our device represents a new way of thinking about laser technology, and we see it as a new platform on which future technologies may be built,” Forbes said.


GLOSSARY
hologram
An interference pattern that is recorded on a high-resolution plate, the two interfering beams formed by a coherent beam from a laser and light scattered by an object. If after processing, the plate is viewed correctly by monochromatic light, a three-dimensional image of the object is seen.  
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