Researchers at the University of Strathclyde have created the first tunable and continuous diamond-based Raman lasers

World's first 'tunable' diamond-based Raman laser

A new generation of diamond-based lasers could have applications as diverse as treating eye conditions to aeronautical engineering.

A University of Strathclyde team has developed a new type of high-performance, ultra-versatile Raman laser that harnesses diamonds to produce light beams with more power and a wider range of colours than current Raman lasers.

In a Raman laser, a beam of light of one colour is converted to another colour suited to a particular application. Raman lasers are named after Sir Chandrasekhara Venkata Raman, the Indian physicist who played a key role in discovering the ‘Raman effect’ – a change in the wavelength of light that occurs when a light beam is deflected by molecules.

Although researchers in Australia are also working on diamond-based Raman laser technology, the Strathclyde team is the first to develop a ‘tunable’ laser, where the colour of the light can be adjusted to meet specific needs, and the first continuously operating diamond Raman laser.

The research is funded by the Engineering and Physical Sciences Research Council (EPSRC).

“Our new lasers can generate light ranging from the lower end of the ultra-violet part of the electromagnetic spectrum, right through the visible part, up to the middle of the infra-red region. That means they can plug many of the existing gaps in lasers’ capabilities,” said Professor Martin Dawson, who initiated and oversaw the project at the university’s Institute of Photonics.

“We’re now aiming to build on our successes to date, with a view to helping a whole new generation of lasers become available for deployment perhaps within 5 to 10 years.”

The materials, often silicon, conventionally used in Raman lasers to change the colour of light have a relatively limited ability to conduct heat, which restricts the amount of laser output that can be generated, while their particular optical properties limit their ability to generate certain useful colours of light.

By contrast, diamond has unrivalled thermal conductivity which, combined with its unique strength and rigidity make it ideal for use in lasers.

And its optical properties enable it to produce a range of colours that are hard to generate by conventional means – yellow/orange light for example, which can be used in medicine in the treatment of conditions such as vascular lesions or retinal bleeding of blood vessels at the back of the eyes.

Dr Alan Kemp of the University of Strathclyde, who was principal investigator on the project, said: “Exploiting single-crystal diamonds directly in lasers opens up a world of possibilities. A key benefit is that you don’t need a big crystal to generate the power you require, so you can make lasers much smaller.

“Conventional Raman lasers have to incorporate a crystal 3-6cm long. But our new lasers can produce the same amount of power with a diamond crystal just 2-6mm long.

“That means lasers could be deployed in confined spaces where they currently simply can’t go such as in aeronautical applications and medicine where high-power lasers of particular colours are required but space is at a premium.”

The fact the researchers have also created a continuously operating diamond Raman laser is important because lasers that can only provide short pulses of light are unsuited to some medical and other applications, for example where pulses would damage delicate structures in the eye.

Dr Jennifer Hastie of the university’s Institute of Photonics led the project to demonstrate the first tunable diamond Raman lasers, achieved by incorporating the Raman crystals into semiconductor disk lasers.

She said: “Raman lasers work by firing a pump light beam through a crystal, thus creating heat, and as that heat is generated the laser beam is converted to a different colour.  If the initial colour of the pump light is tunable, for example that provided by a semiconductor disk laser, we can achieve tuning of the Raman laser colour.”

The team has worked closely with UK-based firm Element Six, who fabricate artificial diamonds as they are both potentially cheaper than natural diamonds and can be engineered to provide the precise optical properties required.

For an audio slideshow about the new lasers visit the E&T Magazine Facebook page.

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