IOP PUBLISHING REPORTS ON PROGRESS IN PHYSICS Rep. Prog. Phys. 71 (2008) 056701 (28pp) doi:10.1088/0034-4885/71/5/056701 Lasers in medicine Qian Peng 1,2,7 , Asta Juzeniene 3 , Jiyao Chen 2,4 , Lars O Svaasand 5 , Trond Warloe 6 , Karl-Erik Giercksky 6 and Johan Moan 3 1 Department of Pathology, The Norwegian Radium Hospital, University of Oslo, Montebello, 0310 Oslo, Norway 2 State Key Laboratory for Advanced Photonic Materials and Devices, Fudan University, 200433 Shanghai, People’s Republic of China 3 Department of Radiation Biology, The Norwegian Radium Hospital, University of Oslo, Montebello, 0310 Oslo, Norway 4 Department of Physics, Fudan University, 200433 Shanghai, People’s Republic of China 5 Department of Electronics and Telecommunications, Norwegian University of Science and Technology, O.S. Bragstads Plass 2A, 7491 Trondheim, Norway 6 Department of Surgical Oncology, The Norwegian Radium Hospital, University of Oslo, Montebello, 0310 Oslo, Norway E-mail: Qian.Peng@rr-research.no Received 17 January 2008, in final form 5 March 2008 Published 11 April 2008 Online at stacks.iop.org/RoPP/71/056701 Abstract It is hard to imagine that a narrow, one-way, coherent, moving, amplified beam of light fired by excited atoms is powerful enough to slice through steel. In 1917, Albert Einstein speculated that under certain conditions atoms could absorb light and be stimulated to shed their borrowed energy. Charles Townes coined the term laser (light amplification by stimulated emission of radiation) in 1951. Theodore Maiman investigated the glare of a flash lamp in a rod of synthetic ruby, creating the first human-made laser in 1960. The laser involves exciting atoms and passing them through a medium such as crystal, gas or liquid. As the cascade of photon energy sweeps through the medium, bouncing off mirrors, it is reflected back and forth, and gains energy to produce a high wattage beam of light. Although lasers are today used by a large variety of professions, one of the most meaningful applications of laser technology has been through its use in medicine. Being faster and less invasive with a high precision, lasers have penetrated into most medical disciplines during the last half century including dermatology, ophthalmology, dentistry, otolaryngology, gastroenterology, urology, gynaecology, cardiology, neurosurgery and orthopaedics. In many ways the laser has revolutionized the diagnosis and treatment of a disease. As a surgical tool the laser is capable of three basic functions. When focused on a point it can cauterize deeply as it cuts, reducing the surgical trauma caused by a knife. It can vaporize the surface of a tissue. Or, through optical fibres, it can permit a doctor to see inside the body. Lasers have also become an indispensable tool in biological applications from high-resolution microscopy to subcellular nanosurgery. Indeed, medical lasers are a prime example of how the movement of an idea can truly change the medical world. This review will survey various applications of lasers in medicine including four major categories: types of lasers, laser-tissue interactions, therapeutics and diagnostics. (Some figures in this article are in colour only in the electronic version) This article was invited by Professor G Gillies 7 Author to whom any correspondence should be addressed. 0034-4885/08/056701+28$90.00 1 © 2008 IOP Publishing Ltd Printed in the UK