A story of Invention: the Laser

A story of Invention: the Laser 

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation". The laser was the result of not one individual's efforts, but the combination of many leading optics and photonics scientists and engineer over the course of history.  

The laser’s history can be traced back to 1900, when Max Plank published his work on the law of radiation, which explained the relationship between energy and the frequency of radiation, essentially saying that energy could be emitted or absorbed only in discrete chunks. His theory marked a turning point in physics and inspired Albert Einstein, who in 1905 released a paper on the photoelectric effect- which proposed that light also delivers its energy in chunks, now called photons.  Taking these ideas further, in 1917 Einstein published the paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation). He described the theory of stimulated emission, establishing the underlining principle behind the maser and laser. Einstein theorized that, besides absorbing and emitting light spontaneously, electrons could be stimulated to emit light of a particular wavelength.  It took over 30 years for scientists to prove his theory correct. 

In the 1950’s scientists began work focused on harnessing energy by utilizing the principal of stimulated emission; most notable were scientists Charles Townes at Columbia University, and Alexander Prokhorov and Nikolai Basov at the Lebedev Laboratories in Moscow.  In 1953, Townes produced the first maser (microwave amplification by stimulated emission of radiation), which was the first device developed based on Einstein’s theory and the precursor to the laser.  In 1955, Basov and Prokhorov designed and built oscillators, and proposed a method for the production of negative absorption that was called the pumping method, which later became the main method of laser pumping. 

In 1957, Charles Townes continued his work with the theory of stimulated emission and began to investigate visible light amplification. Townes began working with Arthur Schawlow at Bell Labs where they developed a concept called an “optical maser”, which Townes documented in his lab notebook in September 1957.  In 1958, Bell Labs filed a patent application for the optical maser, and Schawlow and Townes submitted a manuscript of their theoretical calculations to the Physical Review, published later that year.

Now this is where the history of the laser starts to get tricky, and scientists theories and concepts began to overlap. In November 1957, Townes met with graduate student Gordon Gould at Columbia University.  At the time, Gould was working on his doctoral thesis on the energy levels of excited thallium, and Townes was interested in discussing thallium lamps for optical pumping with him.  During their discussion Gould and Townes spoke of radiation emission and afterwards Gould noted his idea for a “laser”, which included using an open resonator, and had his notebook notarized. At about the same time in Russia, Prokhorov independently published the idea of using an open resonator design in his work.  In addition, Schawlow and Townes had agreed to an open resonator design for their optical maser – apparently unaware of Prokhorov’s publication and Gould’s unpublished work. 

In early 1959, while working for Technical Research Group (TRP), Gould and TRP applied for laser patents related to Gould’s ideas. At a conference that year, Gould published his paper The LASER, Light Amplification by Stimulated Emission of Radiation, the first published use of the term “laser”. 

In March 1960, Townes and Schawlow, at Bell Labs, were granted a patent for the optical maser, which today is called a laser.  Gould and TRP’s patents applications were denied, which provoked a 28-year patent dispute over the laser invention. (It wasn’t until late 1977- that Gould was issued his first patent related to lasers and 1988 when he began receiving royalties.) 

After Townes and Schawlow’s optical maser article was published in 1958, scientists throughout the US became intrigued by their concept, and the race to build a working laser began. Hughes Research Labs, RCA Labs, Lincoln Labs, IBM, Bell Labs, Technical Research Group, Westinghouse, and Siemens all were all competing to build the first functional laser. 

At Hughes Research Laboratories, Theodore Maiman discovered that high gain pulsed oscillation could be achieved in synthetic ruby by optically pumping with a solid-state flash lamp; on May 16th 1960, Maiman operated the first functioning laser (capable of pulsed operation*). Maiman promptly submitted a short report on his findings to the Physical Review, but the editors turned it down. Eager to quickly publish his work, Maiman submitted his report to Nature, where it was published in August, 1960.  With Maiman’s publication on the way, Hughes Research Laboratory made the first public announcement of the working laser on July 7, 1960 – the race was over. 

 It should also be noted, that the first successful continuous output ruby laser was built two years later by Willard Boyle at Bell Labs. 

Even with the controversy over who invented the laser, the work of these laser pioneers sparked a technological revolution. Townes, Basov, and Prokhorov shared the 1964 Nobel Prize in Physics for their fundamental work in the field of quantum electronics, which led to the construction of oscillators and amplifiers based on the maser-laser principle. Schawlow shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Kai Siegbahn for their contributions to the development of laser spectroscopy. And, there are already at least ten other Nobel Prize winners whose work was made possible by lasers! 

The first medical treatment using a laser on a human patient is performed by Dr. Charles J. Campbell of the Institute of Ophthalmology at Columbia-Presbyterian Medical Center and Charles J. Koester of the American Optical Co. at Columbia-Presbyterian Hospital in Manhattan. An American Optical ruby laser is used to destroy a retinal tumor. 

In 1963, Dr. Leon Goldman pioneered the use of lasers for cutaneous applications by promoting ruby laser for various cutaneous pathologies. The development of the argon & CW carbon dioxide (CO₂) lasers soon followed and served as the focus of cutaneous laser research during the next two decades .  

Cutaneous laser surgery was revolutionized in the 1980s with the introduction of the theory of selective photothermolysis by Anderson and Parrish. During the past decade extensive advances in laser technology have refined cutaneous laser surgery to the point that it is now considered a first line treatment for many congenital and acquired cutaneous conditions. 

Advances in laser technology have progressed so rapidly during the past decade that successful treatment of many cutaneous concerns and congenital defects, including vascular and pigmented lesions, tattoos, scars and unwanted hair- can be achieved. The demand for laser surgery has increased as a result of the relative ease with low incidence of adverse postoperative sequelae. In this review, the currently available laser systems with cutaneous applications are outlined to identify the various types of dermatologic lasers available, to list their clinical indications and to understand the possible side effects.

Abbreviatons used 

· APTD: Argon-pumped                tunable dye  · CO2 : Carbondioxide  · CW : Continuouswave  · FDA : Foodand Drug                Administration  · IPL : Intensepulsed light

· KTP : Potassiumtitanyl phosphate  · LP : Long-pulsed  · Nd : Neodymium  · PDL : Pulseddye laser  · PDT : Photodynamictherapy  · QS : Quality-switched  · YAG : Yttrium-aluminum-garnet

Laser Principles  

The therapeutic action of laser energy is based on the unique properties of laser light itself and complex laser-tissue interactions^13-15. At certain wavelengths of light, specific absorption of laser energy can be achieved by distinct cutaneous targets. Laser light can be focused into small spot sizes allowing precise tissue destruction. When a laser is used on the skin, the light may be absorbed, reflected, transmitted or scattered. Once laser energy is absorbed in the skin 3 basic effects are possible: photothermal, photochemical or photomechanical effects. The depth of penetration of laser energy into the skin is dependent upon absorption and scattering. Scattering is minimal in the epidermis and greater in the dermis. In general, the depth of penetration of laser energy increases with wavelength. Therefore, on the basis of these principles, laser parameters (wavelength, pulse duration, and fluence) can be tailored for specific cutaneous applications to effect maximal target destruction with minimal collateral thermal damage. Because cutaneous lasers have different clinical applications related to their specific wavelengths and pulse duration, the choice of laser should be on the basis of the individual absorption characteristics of the target chromophore.

Vascular-specific laser

Vascular-specific laser systems target intravascular oxyhemoglobin to effect destruction of various congenital and acquired vascular lesions. Lasers that have been used to treat vascular lesions include: Argon (488-514 nm), APTD (577 and 585 nm), KTP (532 nm), Krypton (568 nm), Copper vapor/bromide (578 nm), PDL (585-595 nm), Nd:YAG (532 and 1064 nm).

The flashlamp-pumped PDL was the first laser specifically developed for treatment of vascular lesions based on the principles of selective photothermolysis. The PDL has revolutionized the treatment of many vascular lesions and is considered the laser of choice for most benign congenital and acquired vascular lesions because of its superior clinical efficacy and low risk profile. This laser has been used to successfully treat a variety of vascular lesions such as port-wine stains, facial telangiectases, hemangiomas, pyogenic granulomas, Kaposi's sarcoma and poikiloderma of Civatte.