Modern medical lasers are used in various clinical applications, including cancer therapy and ophthalmology.
Basic understanding of how a laser operates
Max Planck showed that light is released in specific amounts of energy known as quanta and is related to radiation frequency (f). This discovery led to the equation, E=hf, where h is Planck’s constant (6.6262 x 10 -34 Joule⋅second) and is fundamental to medical lasers.
Electromagnetic radiation is emitted from a charged particle (electron) which irradiates energy when it falls from a higher energy state to a lower energy state. Its frequency or wavelength determines the colour of light. The shorter wavelengths are ultraviolet and the longer wavelengths are infrared.
Quantum mechanics describes the smallest particle of light energy as a photon. The energy (E) of a photon is determined by its frequency (f) and Planck’s constant (h). The difference in energy levels across which an excited electron fall determines the wavelength of the emitted light.
The Planck equation set the foundation of the LASER (Light Amplification Stimulated Emission Radiation) and Albert Einstein in 1916 described it as the theory of stimulated emission. This process involved an incoming photon of a specific frequency interacting with an excited atomic electron, causing it to relax back to a lower energy level. These fundamental discoveries of stimulated emission were the basis of the creation of modern lasers. However, it was not until 1960 that Maiman, a physicist at Bell Laboratories, generated a laser from ruby crystal (λ = 694 nm).
However, its practical capabilities began to emerge from the 1940s in the work of Charles Townes and Arthur Schawlow on the development of microwave spectroscopy.
This research led to the invention of the MASER (Microwave Amplification by Stimulated Emission of Radiation). First, however, Theodore Maiman created the first laser using an electrical source to energise a solid ruby.
More lasers were discovered, including the CO2 (carbon dioxide) laser, emitting a concentrated ray of light and absorbing water to vaporise tissue. In addition, the neodymium-yttrium aluminium garnet (Nd-YAG) laser was able to induce coagulative necrosis within the tissue. Also, visible light lasers were used to produce haemostasis.
Modern medical lasers are used in various clinical applications, including cancer therapy, ophthalmology, nerve stimulation, dermatology, plastic surgery, wound healings and dentistry.
However, the more advanced medical lasers based on the diode are used in cancer therapy. For example, these diode lasers are used in surgical procedures, including soft tissue cutting, coagulation and cancer thermal therapy.
Currently, there are different types of lasers capable of undertaking invasive and non-invasive procedures at different depths. The type of laser depends on the region of the electromagnetic spectrum: UV (200-400) µm, visible (400-700) nm, near-IR (700-2900) nm and mid-IR (3-5) µm.
Since the conception of the lasers, they have been classified according to the following characteristics:
- The laser medium where the amplification takes place can be a solid, liquid, or gas. These types of lasers are referred to as solid-state lasers, liquid lasers, or gas lasers.
- Gas lasers include carbon dioxide, excimer (XeF) and argon are used in medical lasers.
- Dye lasers are examples of liquid lasers and ruby or yttrium aluminium garnet doped with neodymium lasers are solid-state lasers.
- Lasers can emit radiation at different wavelengths in the UV, visible, and IR parts of the electromagnetic spectrum. These are classified as UV lasers, visible lasers, and IR lasers.
- Lasers that emit radiation continuously and are called continuous-wave (CW) lasers.
- Lasers that emit bursts of radiation and are called pulsed lasers.
Lasers produce deeper tissue penetration depths in the near-infrared (750-1200) nm than visible lasers. Therefore, procedures that require deep penetrations such as nano-gold mediated cancer therapy.
The visible lasers (430-680) nm have strong absorption in blood and have been used for oral cancer and retina decreases phototherapy.
Mid-IR lasers (1.9-3.0) µm and (9.3 -10.6) µm have strong absorption in water and tissue. This enables them to be used to remove soft and hard tissue, a procedure known as ablation.
IR lasers (1.3-1.6) µm have been used for minimally invasive procedures such as resurfacing due to their more negligible tissue absorption.
Type of Laser
Surgery, Photodynamic therapy
Surgery, Photodynamic therapy, Ophthalmology, Dermatology
Photodynamic therapy, Dermatology
Photoacoustic imaging is a hybrid imaging technique based on the photoacoustic effect. It delivers non-ionising laser pulses to tissues and produces heat which initiates thermoelastic expansion to generate an ultrasonic wave. These waves can be detected using ultrasound imaging equipment. This technique can be used to show organs and blood vessels to tumours. Also, more advanced photoacoustic imaging can be used to picture 3-D images of internal body parts and differentiate cancerous cells from healthy cells. This technology platform is known as Photoacoustic Topography Through an Ergodic Relay (PATER).
Clinical applications of medical lasers
Laser Lithotripsy Laser lithotripsy is a technique used to break up urinary and biliary stones. The most popular shockwave lasers used in lithotripsy are based on the one-microsecond pulsed-dye laser. They work by the excitation of coumarin dye to produce monochromatic light.
Laser interstitial thermal therapy (LITT) is used on patients who are not ideal surgical candidates. LITT is used to treat several cancer types, such as gliomas and meningiomas. Also, mucosal ablation techniques use lasers to treat gastrointestinal cancers, superficial oesophageal cancer, colorectal adenoma and Barrett's oesophagus. Moreover, photodynamic therapy utilises lasers to treat lung cancer lesions.
The trans-myocardial laser revascularisation (TMLR), laser vascular anastomosis and laser angioplasty in peripheral arterial diseases are used to improve blood flow to the heart. TMLR is the only treatment procedure for severe angina and is used in coronary artery bypass grafting. In TMLR, the CO2 laser or the Ho-YAG laser are delivered directly to the target areas of the heart muscle.
The parameters of the ophthalmic laser are set at a specific wavelength, duration, pulse pattern, energy, repetition rate and spot size. These settings produce a monochromatic laser beam that is capable of hitting the same spot within the eye. Therefore, changing the parameters will produce a different absorption in the type of tissue. For example, when using the argon laser, local thermal effects such as photocoagulation can result. Other lasers such as excimer lasers, for instance, Nd-YAG, can be applied in refractive surgery.
Endoscopic Gastrointestinal Surgery The Nd-YAG laser is used to produce coagulation of gastrointestinal bleeding. It is also used to treat benign small mucosal lesions. Also, the laser is used as a soothing treatment for malignant gastrointestinal disorders in addition to incision treatment for anatomical lesions such as stenosis or cysts.
The lasers used in oral surgery include CO2, Er-YAG, Diode and Nd-YAG. They are also used in disinfection and healing.
Dermatology and Reconstructive Surgery
The lasers based on the Nd-YAG and diodes are mainly emitted by infra-red light. These systems target the water in the dermis and heat the collagen in the process to initiate regeneration.
Charles Townes, James Gordon, Herbert Zeiger (Columbia University).
The first laser was known as the MASER (microwave amplification by stimulated emission of radiation).
Charles Townes, Herbert Zeiger, James Gordon (Columbia University).
The ammonia MASER obtained the first amplification and generation of electromagnetic waves by stimulated emission.
Nikolai Basov, Alexander Prokhorov (P. N. Lebedev Physical of Institute in Moscow).
They designed and built oscillators and proposed the production of a negative absorption that was called the pumping method.
Nicolaas Bloembergen (Harvard University).
Development of the microwave solid-state MASER.
Coined the acronym LASER.
Charles Townes and Arthur Schawlow (Bell Labs).
The MASERS were able to operate in the optical and infrared regions.
Charles Townes and Arthur Schawlow (Bell Labs).
US patent granted (number 2,929,922) for the optical MASER.
Theodore Maiman (Hughes Research Laboratories).
The first laser was constructed with a cylinder of synthetic ruby.
Peter Sorokin and Mirek Stevenson (IBM Thomas J. Watson Research).
Demonstrated the uranium laser, a four-stage solid-state device.
Ali Javan, William Bennett and Donald Herriott (Bell Labs).
Developed the helium-neon laser.
Trion Instruments, Perkin Elmer and Spectra-Physics.
Lasers began to appear on the commercial market.
Elias Snitzer (American ed Company).
The first operation of a neodymium glass.
Charles Campbell (Institute of Ophthalmology at ed Medical), Charles Koester (American Optical Co. at Columbia-Presbyterian Hospital in Manhattan).
The first medical treatment was used to destroy a retinal tumour using the ruby laser.
Contributed to the theory of lasers.
Groups at GE and MIT Lincoln Laboratory.
Development of the gallium-arsenide laser.
Nick Holonyak (General Electric).
Gallium arsenide phosphide laser diode.
Logan Hargrove, Richard Fork and M Pollack.
The introduction of the mode-locked laser.
Herbert Kroemer (University of California), Rudolf Kazarinov and Zhores Alferov (A.F. Ioffe Physico-Technical Institute in St. Petersburg, Russia).
The idea of semiconductor lasers was introduced.
William Bridges (Hughes Research Labs).
The invention of the pulsed argon-ion laser.
Townes, Basov, and Prokhorov.
Nobel Prize in physics for quantum electronics and the construction of oscillators and amplifiers based on the maser-laser principle.
Kumar Patel (Bell Labs).
The invention of the carbon dioxide laser.
Joseph Geusic and Richard Smith (Bell Labs).
The neodymium doped YAG laser.
Two lasers were phase-locked for the first time.
Jerome Kasper and George Pimentel (University of California, Berkeley).
Development of the first chemical laser based on a 3.7 μm hydrogen chloride instrument.
Mary L. Spaeth (Hughes Research Labs).
The invention of the dye laser pumped by a ruby laser.
Charles K. Kao, George Hockham (Standard Telecommunication Laboratories in Harlow, UK).
A breakthrough in fibre optics.
Nobel Prize in physics for the method of stimulating atoms to higher energy states. This technique was known as optical pumping and was influential in developing the MASER and the laser.
Bernard Soffer and Bill McFarland (Korad Corp. in Santa Monica, Calif).
The invention of the dye laser.
Basov, Danilychev (Lebedev Physical Institute).
Development of the excimer laser.
Alferov's group (Ioffe Physico-Technical Institute), Mort Panish, Izuo Hayashi (Bell Labs).
Produced the first continuous-wave room-temperature semiconductor lasers, which led to fibre optic communications.
Arthur Ashkin (Bell Labs).
The invention of optical trapping.
Hayashi, Morton B Panish (Bell Labs).
The first semiconductor laser operated continuously at ambient temperature.
Charles H. Henry
The invention of the quantum well laser.
A laser beam to form electronic circuit patterns on ceramic.
A packet of Wrigley's chewing gum was the first product to be read by a barcode scanner.
NJ Metuchen (Laser Diode Labs Inc).
Engineers develop the first commercial continuous-wave semiconductor laser operating at room temperature.
an der Ziel, Dingle, Miller, Wiegman, Nordland.
The first quantum well laser operation.
A semiconductor laser operating continuously at ambient temperature with a wavelength greater than 1 μm.
John M.J. Madey (Stanford University).
The first free-electron laser (FEL).
The first commercial installation of a fibre optic lightwave communications system is completed under the streets of Chicago.
A patent was granted for optical pumping.
LaserDisc. LaserDisc hits the home video market.
The launch of the compact disc project.
A patent was granted to cover a broad range of laser applications.
Nobel Prize in Physics.
Schawlow and Bloembergen received the Nobel Prize in physics for their contributions to the development of laser spectroscopy.
Peter F. Moulton (MIT Lincoln Laboratory).
Development of the titanium-sapphire laser.
The first audio CD was released.
Steven Chu (Bell Labs).
Laser light is used to manipulate atoms.
David Payne (University of Southampton).
Optical amplifiers are used to boost light signals.
Faist, Capasso, Sivco, Sirtori, Hutchinson, Cho (Bell Labs). The first semiconductor laser was able to emit light, known as the quantum cascade laser, simultaneously.
Nikolai Ledentsov (A.F. Ioffe Physico-Technical Institute).
The first quantum dot laser.
Wolfgang Ketterle (MIT).
The first pulsed atom laser, which used matter instead of light.
Shuji Nakamura, Steven P. DenBaars, James S. Speck (University of California, Santa Barbara).
The development of a gallium-nitride laser was able to emit pulses of bright blue-violet light.
Wind Tunnel Facility (Marshall Space Flight Center).
The application of lasers to measure the velocity and gradient of distortion during a cold-flow propulsion research test.
Successfully flies the first laser-powered aircraft.
Ozdal Boyraz, Bahram Jalali (University of California, Los Angeles).
Electronic switching in a Raman laser.
John Bowers (University of California, Santa Barbara), Mario Paniccia (Intel Corp's Photonics Technology Lab in Santa Clara).
The first electrical powered hybrid silicon laser used in the silicon manufacturing process.
John Bowers, Brian Koch (University of California, Santa Barbara). The first mode-locked silicon evanescent laser.
Chunlei Guo (University of Rochester in NY).
A new process that used femtosecond laser pulses to generate regular incandescent light bulbs.
National Ignition Facility (Lawrence Livermore National Laboratory in Livermore). Built the largest and highest-energy laser in the world.
NASA launched the Lunar Reconnaissance Orbiter.
Lasers enter household PCs with Intel's announcement of its Light Peak optical fibre technology.
Nanfang Yu, Federico Capasso (Harvard School of Engineering and Applied Sciences), Hirofumi Kan (Laser Group at Hamamatsu Photonics), Jérôme Faist (ETH Zürich).
Demonstrated the compact, multibeam and multiwavelength lasers emitting in the IR.
Global laser market.
In 2010 the global laser market will grow about 11% and generate total revenue of $5.9 billion.
University of Konstanz.
National Nuclear Security Administration.
Manijeh Razeghi (Northwestern University).
Rainer Blatt, Piet O. Schmidt (University of Innsbruck in Austria).
Lawrence Livermore National Laboratory.
Generation of a 4.3-fs single-cycle pulse of light at 1.5-µm wavelength from an erbium-doped fibre laser.
NIF was able to deliver 1 MJ of laser energy to a target.
Quantum cascade laser efficiency increased to 53%.
Demonstrated using a single-atom laser with and without threshold behaviour by tuning the strength of atom-light field coupling.
The use of ultrafast laser pulses to probe basic material properties.
Hans Zogg (ETH Zürich).
Malte Gather, Seok Hyun Yun (Harvard University).
Jianlin Liu (University of California, Riverside).
Developed a vertical external-cavity surface-emitting laser (VECSEL) that operated in the mid-IR at about 5 μm.
Demonstrated a laser was able to genetically engineer cells to produce a novel material called green fluorescent protein (GFP)
Produced zinc oxide nanowire waveguide lasers.
Lawrence Livermore National Laboratory.
NASA's Curiosity Rover.
Development of the random laser.
192 UV laser beams produced a peak power above 500 trillion watts.
A rock on mars was zapped with a laser.
Stefan Rotter (Vienna University of Technology).
Camille Brès, Luc Thévenaz (Ecole Polytechnique Fédérale de Lausanne).
Benedikt Mayer (Technical University of Munich).
A laser control layout was developed using granular material to determine the emission direction.
Laser pulses travelling down fibre optic cables carry the world's information
Demonstrated the use of room temperature laser nanowires that emitted in the near-IR.
Yuri Rezunkov and Alexander Schmidt.
European Space Agency.
European Space Agency.
Lawrence Berkeley National Laboratory.
Berkeley Lab Laser Accelerator.
Reported a boost from lasers. This laser ablation has long been proposed for rocket propulsion.
Lasers are used to generate a gigabit transmission between a satellite in low Earth orbit and one in geosynchronous orbit (about 45,000 km).
A laser from Tenerife connects with a satellite in orbit, providing an optical data path.
A new world record for a tabletop particle accelerator (4.25 GeV).
A 9 cm long capillary discharge waveguide to generate multi-GeV electron beams.
Brett Hokr (Texas A&M University).
Anders Kristensen (Technical University of Denmark).
University of St Andrews and Harvard Medical School.
Report on a random Raman laser capable of producing a wide-field, speckle-free image with a strobe time of about a nanosecond.
Created a 50 µm wide reproduction of the Mona Lisa.
Research involving cells swallowing microresonators.
Cardiff University, University College London, University of Sheffield.
EUV (extreme ultraviolet) lithography technology resultant in wavelength, much shorter than the 193 nm deep UV lasers used in semiconductor production.
Produced quantum dot lasers on silicon.
Jet Propulsion Laboratory.
The University of St Andrews, University of Wurzburg, Technical University of Dresden.
Lasers could give space communications broadband.
A system produced a single laser beam of 58 kW.
Created a fluorescent protein polariton laser.
Lawrence Livermore National Laboratory.
National Institute of Standards and Technology.
Shanghai Super intense Ultrafast Laser Facility.
The National Ignition Facility laser system set a new record of 2.15 MJ.
Showed that a commercial laser could produce 3D images of objects as they melted in a fire.
The generation of a 10-petawatt laser burst.
Scientists used a 1.9 µm wavelength thulium laser to excite water molecules near a microphone, which transmit an audible signal.
World’s most powerful laser
The Thales and ELI-NP (Extreme Light Infrastructure for Nuclear Physics) project have developed the world’s most powerful laser. The ultra-high intensity laser system can produce a pulse at a peak power level of 10 petawatts (1015 W). This laser system is designed to generate twin laser beams of 10 PW and is used in nuclear physics. For example, this type of laser can be used to study key nuclear reactions relevant to nucleosynthesis. In particular, the fusion of α particles and carbon nuclei to produce oxygen (4He + 12C → 16O), which is central to life on Earth.
The main features of the laser system are:
- The high-power laser system (HPLS) consists of two 10 PW beams that can deliver a laser pulse of up to 225 J in each of the arms during a laser pulse duration of 15–22.5 fs. The wavelength region is 814 – 825 nm.
- The maximum focal spot intensity is I0 ∼ 1023 W cm−2.
- The laser system is capable of delivering lower powers at 100 TW and 1 PW.
- The Variable-Energy Gamma Ray (VEGA) system at ELI-NP can deliver monoenergetic gamma rays with up to 19.5 MeV.
- The primary performance parameters are a photon density of ∼104 s−1 eV−1, with a high degree of linear polarisation of >95%.
- The laser will be able to study the extreme states in gases, solids and plasma.
- The configuration of the laser can be altered to investigate systems that involve non-linear quantum electrodynamics (QED). In addition to vacuum birefringence, relativistic induced transparency (RIT) and nuclear resonance fluorescence (NRF). Including photoactivation, photonuclear reactions and photofission.
The next generation of lasers will generate powerful beam sources at precisely the right wavelength for all medical and industrial applications. Since the laser conception, they are becoming smaller devices due to the advancement of semiconductor and direct diode lasers. This technology platform led to the Extreme Light Infrastructure for Nuclear Physics (ELI-NP) project, which uses the ultra-high intensity laser system to generate pulses at a peak power level of 10 petawatts. However, laser weapons based on electro-optical systems can increase the lethal power. For example, a high-energy laser system mounted on a US Army Boeing AH-64 Apache attack helicopter. Furthermore, the US Navy has developed solid-state lasers, including the Solid-State Laser Technology Maturation (SSL-TM) effort and High Energy Laser Counter-ASCM Program (HELCAP). However, continued research into LLLT on how to relate the dose to treat a range of clinical conditions in patients in a safe manner.
308 and 459
353 and 459
325 - 442
450 - 650
511 and 578
457 - 528
543, 594, 612, and 632.8
337.5 - 799.3 (647.1 - 676.4 most used)
630 - 950
690 - 960
720 - 780
2600 - 3000
5000 - 6000