Once just a James Bond Fantasy, diamond-based lasers are now becoming a reality. Scientists at the University of Strathclyde are using the unique properties of diamonds to develop a new generation of Raman lasers. Raman lasers work by firing a pump light at a crystal to create heat and then that heat generates a laser beam.
The materials conventionally used in Raman lasers, such as silicon, are limited in the range of colours they can produce. Diamond, however has unrivalled thermal conductivity along with tremendous rigidity, strength and optical properties. So Raman lasers that use diamonds produce light beams with more power and a wider range of colours. Dr Alan Kemp is a research team leader at the Institute of Photonics at the University of Strathclyde.
Dr Alan Kemp - Institute of Photonics, University of Strathclyde [AK]
Diamond lasers work in the same way as conventional lasers. There are three important components in any laser. We have to have an energy source, called a pump, to provide energy to a laser material, in this case diamond that excites the material. We then use that material as an amplifier for light and we pass the light beam repeatedly through the amplifying material to generate an oscillating beam, and that’s our laser output. So diamond works in the same way as a conventional laser material would, our interest is that we should be able to make that laser work in more extreme ways by exploiting the extreme properties of diamond.
Martin Dawson is Professor of Photonics at the University of Strathclyde.
Professor Martin Dawson - University of Strathclyde
Quite simply diamond lasers are lasers made from diamond as you might imagine. They differ from established and more conventional lasers in the potential wavelength coverage, the colour coverage that they have and the specific way in which they operate. All lasers involve an optical resonator, an optical cavity, involving mirrors with some kind of an active fluorescent luminescent material inside that can be excited to produce amplification. In diamond, the process by which amplification is produced is a process called stimulated Ramon scattering. That sounds like a scary thing but it’s basically related to the heating of diamond crystals and lattice vibrations, the shaking of the diamond lattice. When heat is generated, light interacts with diamond, or can interact with diamond, in a very specific way where it essentially scatters from these vibrations in the lattice or produces them and this process can take place in a stimulated way. The acronym laser stands for light amplification by stimulated emission of radiation and this scattering, this Ramon scattering process, can be stimulated in a way which allows light signals to be amplified and that is the basis of any laser.
This research makes use of the very latest advances in the manufacture of high quality synthetic diamond and, in fact, diamond based lasers have been around for a while, but this work has led to two major new developments because they are the first ever ‘tuneable’ diamond Raman lasers where the colour of light can be adjusted to suit specific needs and they are the first ever continuously operating lasers of this kind.
Regarding the tuneable aspect, diamond’s optical properties mean that these lasers can produce a range of colours that are much more difficult to generate using conventional methods. For example, yellow/orange light, 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 Jennifer Hastie is a research team leader at Strathclyde’s Institute of Photonics.
Dr Jennifer Hastie - Institute of Photonics, University of Strathclyde
All materials have a wavelength dependent response to light, so for example human tissue transmits red wavelengths very well, but absorbs blue wavelengths so if your particular application requires you to look through skin you need to use red wavelengths to enable optimum light transmission. If on the other hand you need the light to be absorbed, for example for cauterisation of the skin, then you would need to use a wavelength that is strongly absorbed rather than red wavelengths. Red wavelengths in that case would be a poor wavelength to use, so if you have a tuneable source then you are able to tune the laser to the optimum wavelength for your particular application.
Dr Alan Kemp elaborates on the possible uses of this tuneable aspect such as the ability to produce yellow / orange light.
One of the potential applications of Ramon lasers and one of the things that has been driving this research both in diamond and in more conventional Ramon laser materials, is the generation of yellow and orange wavelengths. These are wavelengths that are rather hard to demonstrate or to generate by conventional laser means; they just aren’t the right laser sources to get into that area. What we do in a Ramon laser is to take a conventional laser, shift the wavelength slightly and then double that wavelength back into the visible region and that takes us into this yellow / orange area of interest and why that is interesting to a lot of people, particularly in the medical area, is that our constituents of blood absorb those wavelength changes and if you can tune the wavelength of the output, you can tune exactly which components within the skin for example or within the retina are absorbing light and at what depth. You can then control the interaction of the laser beam with the retina or with the skin and that is often used to treat problems with vascular conditions in the skin or with retinal bleeding of blood vessels at the back of the eye. You can cauterise the bleeding at the back of the eye and by changing the colour you can change exactly where the beam is absorbed and have much more control over exactly what it is that you are cauterising and actually damage the right components and not damage the things that you would like to leave behind.
Regarding the continuously operating aspect of these lasers Alan explains more about the advantages this offers. For instance, in medical treatment for sensitive areas, there are situations where using a pulsed laser would create more acoustic disturbance.
[Dr Alan Kemp]
It’s not to say that pulse lasers are not important, of course they are, but continuously operating lasers can do some things that pulse lasers can’t and one example of that is when medics wish to treat the retina for example and it turns out that pulse lasers are just too damaging to the retina that they tend to cause to much collateral damage around the retina, so the medics would prefer to work with continuously operating light sources where they can specifically target deliberately make damage and cauterise blood vessels, for example, very locally without doing damage to surrounding tissue.
One of the real attractions of this technology is that it could be used as an add-on to other lasers, as a way of making other laser systems more versatile. This world leading research is funded by the Engineering and Physical Sciences Research Council. In the long term a wide variety of areas could benefit ranging from pollution monitoring to the treatment of diabetes related eye conditions and cancerous tumours.