Saved by the light

 作者:雍门俞     |      日期:2019-03-08 09:15:00
By Paul Marks SUNLIGHT might one day offer developing countries a cheap alternative to expensive medical lasers, say researchers in Israel. By collecting sunlight in a parabolic dish and feeding the light energy down an optical fibre into an operating theatre, they say it should be possible to carry out many of the techniques normally done by laser—as long as the Sun keeps shining. Physicists Jeffrey Gordon and Daniel Feuermann of Ben-Gurion University in Beersheva say that many medical laser treatments do not require the power of lasers. If tissue does not have to be cut, they say, all that is needed is for the tissue to absorb high levels of radiation. So the pair propose that intense sunlight could be harnessed to provide energy for therapies as diverse as treating skin tumours and diseases, tissue welding and angioplasty, in which powerful light destroys plaque in arteries (Optical Engineering, vol 37, p 2760). The lasers used in medical applications typically deliver light flux densities of up to 100 watts per square millimetre, whereas the solar surgery unit proposed by Gordon and Feuermann could deliver between 30 and 70 watts per square millimetre. They say that this is enough to destroy some tumours: “The key issue in most conventional treatments in killing malignant cells is simply heating it up to approximately 60 °C—and to do it quickly and with great precision,” says Gordon. The heart of their system is a parabolic mirror 20 centimetres in diameter (see Diagram). A commercially available sun-tracker, such as those used for solar panels, keeps it facing the Sun. “We’ve been very careful to ensure that the whole system could be made with existing technology,” says Gordon. Just below the focal point of the dish, a flat mirror reflects the concentrated light onto the tip of an optical fibre. The fibre, which can be up to 100 metres long, links the dish to the operating room. If surgeons need more power, the light can be concentrated further. This can be done either at the roof-top end, by adding a funnel-shaped extension to the tip of the fibre to gather more light rays from the flat mirror, or in the operating room. Here, the light intensity is increased using a specially shaped optical-fibre tip that ensures that all rays converge on a small area and are not scattered back into the fibre. The Ben-Gurion team believe their system can be put together for a few thousand dollars, compared with more than $120 000 for a laser. Gordon says that the system would be used mainly in developing nations and field hospitals. He calculates that solar surgery would be feasible “in clear climates” on half the days of the year, for about 7 to 10 hours a day. “This sounds like a great idea for places where you can’t guarantee electricity,” says Gordon McVie of the Cancer Research Campaign. “We’re great at inventing machines that need dependable power sources,