application of medical lasers

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
Wavelength (nm)
Medical Applications
Ruby
694
Dermatology
Nd-YAG
1064
Broad application
Er-YAG
2940
Surgery
Diode
630-980
Surgery, Photodynamic therapy
Argon
350-514
Surgery, Photodynamic therapy, Ophthalmology, Dermatology
Carbon dioxide
10600
Surgery
Pumped-dye
504-690
Photodynamic therapy, Dermatology

Photoacoustic imaging

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

Clinical Application
Medical Procedure
Laser LithotripsyLaser 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.
Oncology
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.
Cardiovascular Surgery
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.
Cataract Surgery
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 SurgeryThe 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.
Oral Surgery
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.

YEAR
INVENTORS/COMPANY
DISCOVERY
1953
Charles Townes, James Gordon, Herbert Zeiger (Columbia University).
The first laser was known as the MASER (microwave amplification by stimulated emission of radiation).
1954
Charles Townes, Herbert Zeiger, James Gordon (Columbia University).
The ammonia MASER obtained the first amplification and generation of electromagnetic waves by stimulated emission.
1955
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.
1956
Nicolaas Bloembergen (Harvard University).
Development of the microwave solid-state MASER.
1957
Gordon Gould.
Coined the acronym LASER.
1958
Charles Townes and Arthur Schawlow (Bell Labs).
The MASERS were able to operate in the optical and infrared regions.
1960
Charles Townes and Arthur Schawlow (Bell Labs).
US patent granted (number 2,929,922) for the optical MASER.
1960
Theodore Maiman (Hughes Research Laboratories).
The first laser was constructed with a cylinder of synthetic ruby.
1960
Peter Sorokin and Mirek Stevenson (IBM Thomas J. Watson Research).
Demonstrated the uranium laser, a four-stage solid-state device.
1960
Ali Javan, William Bennett and Donald Herriott (Bell Labs).
Developed the helium-neon laser.
1961
Trion Instruments, Perkin Elmer and Spectra-Physics.
Lasers began to appear on the commercial market.
1961
Elias Snitzer (American ed Company).
The first operation of a neodymium glass.
1961
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.
1962
Fred McClung
Contributed to the theory of lasers.
1962
Groups at GE and MIT Lincoln Laboratory.
Development of the gallium-arsenide laser.
1962
Nick Holonyak (General Electric).
Gallium arsenide phosphide laser diode.
1963
Logan Hargrove, Richard Fork and M Pollack.
The introduction of the mode-locked laser.
1963
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.
1964
William Bridges (Hughes Research Labs).
The invention of the pulsed argon-ion laser.
1964
Townes, Basov, and Prokhorov.
Nobel Prize in physics for quantum electronics and the construction of oscillators and amplifiers based on the maser-laser principle.
1964
Kumar Patel (Bell Labs).
The invention of the carbon dioxide laser.
1964
Joseph Geusic and Richard Smith (Bell Labs).
The neodymium doped YAG laser.
1965
Bell Laboratories.
Two lasers were phase-locked for the first time.
1965
Jerome Kasper and George Pimentel (University of California, Berkeley).
Development of the first chemical laser based on a 3.7 μm hydrogen chloride instrument.
1966
Mary L. Spaeth (Hughes Research Labs).
The invention of the dye laser pumped by a ruby laser.
1966
Charles K. Kao, George Hockham (Standard Telecommunication Laboratories in Harlow, UK).
A breakthrough in fibre optics.
1966
Alfred Kastler
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.
1967
Bernard Soffer and Bill McFarland (Korad Corp. in Santa Monica, Calif).
The invention of the dye laser.
1970
Basov, Danilychev (Lebedev Physical Institute).
Development of the excimer laser.
1970
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.
1970
Arthur Ashkin (Bell Labs).
The invention of optical trapping.
1971
Hayashi, Morton B Panish (Bell Labs).
The first semiconductor laser operated continuously at ambient temperature.
1972
Charles H. Henry
The invention of the quantum well laser.
1972
Bell Labs.
A laser beam to form electronic circuit patterns on ceramic.
1974
Wrigley's
A packet of Wrigley's chewing gum was the first product to be read by a barcode scanner.
1975
NJ Metuchen (Laser Diode Labs Inc).
Engineers develop the first commercial continuous-wave semiconductor laser operating at room temperature.
1975
an der Ziel, Dingle, Miller, Wiegman, Nordland.
The first quantum well laser operation.
1976
Bell Labs.
A semiconductor laser operating continuously at ambient temperature with a wavelength greater than 1 μm.
1976
John M.J. Madey (Stanford University).
The first free-electron laser (FEL).
1977
Bell Labs.
The first commercial installation of a fibre optic lightwave communications system is completed under the streets of Chicago.
1977
Gordon Gould.
A patent was granted for optical pumping.
1978
LaserDisc.LaserDisc hits the home video market.
1978
Philips.
The launch of the compact disc project.
1979
Gordon Gould.
A patent was granted to cover a broad range of laser applications.
1981
Nobel Prize in Physics.
Schawlow and Bloembergen received the Nobel Prize in physics for their contributions to the development of laser spectroscopy.
1982
Peter F. Moulton (MIT Lincoln Laboratory).
Development of the titanium-sapphire laser.
1982
Audio CD.
The first audio CD was released.
1985
Steven Chu (Bell Labs).
Laser light is used to manipulate atoms.
1987
David Payne (University of Southampton).
Optical amplifiers are used to boost light signals.
1994
Faist, Capasso, Sivco, Sirtori, Hutchinson, Cho (Bell Labs).The first semiconductor laser was able to emit light, known as the quantum cascade laser, simultaneously.
1994
Nikolai Ledentsov (A.F. Ioffe Physico-Technical Institute).
The first quantum dot laser.
1996
Wolfgang Ketterle (MIT).
The first pulsed atom laser, which used matter instead of light.
1997
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.
1997
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.
2003
NASA.
Successfully flies the first laser-powered aircraft.
2004
Ozdal Boyraz, Bahram Jalali (University of California, Los Angeles).
Electronic switching in a Raman laser.
2006
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.
2007
John Bowers, Brian Koch (University of California, Santa Barbara).The first mode-locked silicon evanescent laser.
2009
Chunlei Guo (University of Rochester in NY).
A new process that used femtosecond laser pulses to generate regular incandescent light bulbs.
2009
National Ignition Facility (Lawrence Livermore National Laboratory in Livermore).Built the largest and highest-energy laser in the world.
2009
NASA.
NASA launched the Lunar Reconnaissance Orbiter.
2009
Intel.
Lasers enter household PCs with Intel's announcement of its Light Peak optical fibre technology.
2009
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.
2009
Global laser market.
In 2010 the global laser market will grow about 11% and generate total revenue of $5.9 billion.
2010
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.
2011
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.
2012
Yale University.

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.
2013
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.
2014
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.
2015
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.

2016
ASML.


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.

2017
Jet Propulsion Laboratory.

Lockheed Martin.

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.

2018
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.
2019
MIT.
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.

Conclusion

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.

LASER TYPE
WAVELENGTH (nm)
Argon fluoride
193
Xenon chloride
308 and 459
Xenon fluoride
353 and 459
Helium cadmium
325 - 442
Rhodamine 6G
450 - 650
Copper vapour
511 and 578
Argon
457 - 528
Nd:YAG
532
Helium-neon
543, 594, 612, and 632.8
Krypton
337.5 - 799.3 (647.1 - 676.4 most used)
Ruby
694.3
Laser diodes
630 - 950
Ti-Sapphire
690 - 960
Alexandrite
720 - 780
Nd-YAG
1064
Hydrogen fluoride
2600 - 3000
Erbium: Glass
1540
Carbon monoxide
5000 - 6000
Carbon dioxide
10600

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