60 years of laser technology

Since their introduction to the market in the 1960s, lasers have become omnipresent, indispensable devices with areas of application that are as diverse as the types available. For example, lasers are used for reading CDs, DVDs and barcodes at supermarket checkouts.

They can measure the exact distance from earth to the moon; they can take ultra-high-resolution images of living tissue; and they are able to perform surgeries without a scalpel. Lasers even entertain people with light shows. The list goes on.

The word ‘laser’ stands for ‘light amplification by stimulated emission of radiation’. It is a technical device that consists of a medium which is excited through the effect of electrical energy to emit radiation of a specific wavelength. The word was introduced in 1957 by the American physicist Gordon Gold, even before the first laser was constructed.^1-3

Also relevant to the development of lasers was the atom model postulated by Niels Bohr in 1913. His ‘planetary model’ demonstrated that electrons can only move in specific orbits around the atomic nucleus.

When energy is supplied, an electron can absorb this energy in order to leave its original orbit and reach an energetically higher one. Conversely, if the electron returns to its actual orbit, it must release the corresponding energy difference, for example, by emitting light.

A short while later, in 1917, the theoretical basis for stimulated amplification of light was postulated by Albert Einstein, in which he described it as the inverse of the absorption by forced radiation. The physicists Rudolf Ladenburg and Hans Kopfermann were able to prove this theory experimentally in 1928.^1,2,5,7

Microwave predecessor

In the 1950s, research focused on the analogue amplification of microwaves which was perceived to be more promising than the use of light. The American physicists Charles Townes and Arthur Schawlow from Columbia University in New York, United States, were the first to successfully implement Einstein’s hypothesis on stimulated emission. In 1958 they presented their ‘maser’, which stands for ‘microwave amplification by stimulated emission of radiation’.

For his maser, Townes used a beam of ammonia molecules, which was led through a defined cavity. If a molecule randomly emitted a microwave, it could stimulate other ammonia molecules in the container to also emit microwaves of the same frequency.

This led to the intensification of the microwave radiation and the emission of a continuous microwave with a uniform frequency – Einstein’s idea of stimulated emission had thus been realised. The maser can be understood as the predecessor of the laser.^1-5

Enter Theodore Maiman

The American physicist Theodore Harold Maiman (1927-2007) received his doctorate in physics in 1955. He was not interested in an academic career but decided to work at Hughes Research Laboratories, owned by eccentric billionaire Howard Hughes and considered as a first-class research company.

With the support of Cold War military funds, Hughes had assembled a team of highly talented researchers. Maiman’s research initially focused on microwaves and maser technology.

He was asked to build a more practical version of the maser by using the chromium atoms in synthetic rubies. The older version of the maser weighed over 2 tons compared with Maiman’s maser, which weighed only 2kg.

He soon became preoccupied with the idea of stimulated emission on the frequency domain of light. His fascination with this concept was so deep that he conducted private research on it.

However, his interest was not in line with the general opinion, which saw no practical application and use for the laser, and so his supervisors banned him from further research on laser technology. After he threatened to resign, the supervisors decided to appease the scientist by providing him with a limited budget of $50,000 and a research assistant for 9 months.^1-7,9,10

Other international research groups were also exploring laser development. However, progress on the search for a suitable material that could temporarily store energy and then, after being stimulated, emit the energy as a beam of light, stalled. Contemporary research focused on the use of various gases as the active medium and researchers had ruled out rubies as being unsuitable. ^1,2,9,10

Maiman found promise in rubies; he carefully studied the unsuccessful research results on the substance and found the previous measurements/ calculations by the other researchers to be incorrect. Along with his assistant Charles Asawa, the scientist presented the first ruby laser on 16 May, 1960.

It comprised a finger-sized ruby rod mirrored at both ends (one end with a semi-transparent mirror, because this is where the laser beam should be emitted), surrounded by a commercially available, spiral-shaped flash lamp (which was supposed to stimulate the chrome atoms of the ruby to emit light). This was contained within an aluminum cylinder. The laser emitted a sharply focused red laser light beam (see Figure 1).^1-7,9,10

The special properties of this new radiation were that it emitted light which was almost parallel and interference-capable (collimation and coherence) of only one specific frequency (monochromatism), which had a very high energy density and which could be focused very accurately.

Maiman’s research results were initially rejected for publication in the journal Physical Review Letters. However, his manuscript went on to be published in Nature in August 1960. Other research groups quickly replicated lasers in countless variations – the triumphal march of the laser was unstoppable.^1,2,9,10

Hughes still did not believe in the benefits of the laser, so he did not support the research. Maiman subsequently left Hughes Laboratories and founded his own successful company, Korad Cooperation, in 1962, receiving a US patent for his work five years later. ^1-3,9-11

Many things then happened in quick succession. Obviously, the time was right for the laser: the technological race for the laser had begun. Of the nearly500 research institutes and companies worldwide, 20 to 30 of these developed marketable products. In the following years, solid-state devices such as the ruby laser, various gas, semi-conductor, CO2 and dye lasers came onto the market.^1-3,5-7

Maiman’s invention was honoured with many awards and accolades. Sadly, while he was also nominated twice for the Nobel Prize several eminent, he never received it. It was particularly appropriate that he himself would benefit from his invention when he was successfully treated with laser surgery for prostate problems at Ludwigs-Maximilian University in Munich, Germany, in 2000.¹¹

Lasers in ophthalmology

Thanks to its transparent media, the eye is the ideal part of the body for laser light to be applied. It is therefore not surprising that ophthalmology was the first medical discipline in which a laser was used: the ruby laser was applied to retinal surgery in 1961.

This first attempt turned out not to be overly successful in comparison with Meyer-Schwickerath’s already very sophisticated technology, which had been further developed from its original sunlight coagulator to using a high-pressure xenon lamp.^1,2,12,13

In the years that followed, the understanding of the effect of laser treatment of the retina improved and its use became optimised. Initially, only the retina was treated.

Later, other lasers were introduced which offered a wide variety of therapeutic options in ophthalmology. Today, lasers are widely used in the therapy of various retinal alterations; for vitreous opacities and various visual disorders; and in cataract and glaucoma surgeries.

In fact, lasers are indispensable devices in treatment and diagnostics in modern ophthalmology. However, it is important to note that one size does not fit all. There is no laser that can be used for ‘everything’.

The active mediums of today’s lasers can be solid-state, liquid or gas, which determine the wavelength emitted by the respective laser, and thus the depth of penetration of the laser beam into the tissue. Lasers on the market include CO2-lasers for cutting tissues; Erbium-YAG lasers for ablative removal of tissue; EXCIMER and femtosecond lasers for correcting refractive errors and in femtosecond laser-assisted cataract surgery; Nd-YAG lasers for posterior capsulotomy and iridotomy; and argon and diode lasers for retinal therapies.

Conclusion

Hughes’ reluctance to use the laser seems quite difficult to understand today. Perhaps he simply could not foresee any practical use of such a device; Maiman did himself reflect on the laser as being “a solution that seeks a problem”.

Despite the shaky start of the development of the first laser, however, the amazing device continues to march ahead. We are living in an era in which a constant stream of new technologies, devices and applications enable doctors and patients to perform increasingly precise diagnostics, and gentle therapies for countless diseases. And so we can be thankful for Maiman’s knowledge, perseverance and dedication in producing that first laser.

Dr Sibylle Scholtz

E:sibylle.scholtz@gmx.de

Dr Scholtz, Ms MacMorris and Prof. Langenbucher are based at the Institute of Experimental Ophthalmology, Saarland University, Germany. They have no financial disclosures.

References

(1) Dittmann F. Hagmann J-G. Eine internationale Erfindung, Zur Geschichte des Lasers. Kultur und Technik, Das Magazin aus dem Deutschen Museum München. 1/2011, 4-9

(2) Grötker R. Wie der Laser ansLicht kam. Max Planck Forschung 4/09, 84-90 and https://www.mpg.de/800422/W006_Kultur-Gesellschaft_084-090.pdf

(3) Saleh B. The Laser. In: Al-Amri MD, El-Gomati M, Zubairy MS (ed). Optics in Our Time. Springer, Cham, 2016, 71-85

(4) Kastler A. Birth of the maser and laser. Nature.1985;316:307–309

(5) Bertolotti M. The history of the laser. IoP, Bristol (UK) 2005

(6) Hecht J. Beam: The race to make the laser. Oxford University Press, Oxford (UK), 2005

(7) Lemmerich J. Zur Geschichte der Entwicklung des Lasers. DAVID-Verl.-Ges., Berlin, 1987

(8) https://www.nytimes.com/2007/05/13/world/americas/13iht-obits.1.5685872.html?searchResultPosition=1

(9) Maiman TH. The laser odyssey. Laser Press, Blaine (USA), 2000

(10) Maiman TH. The Laser Inventor: Memoirs of Theodore H. Maiman, Springer, Cham (CH), 2018

(11) Stirn A. 50 Jahre Laser: Das erste Laserlicht der Geschichte. Süddeutsche Zeitung, 20. Mai 2010 and https://www.sueddeutsche.de/wissen/50-jahre-laser-der-tanz-des-roten-lichtpunkts-1.937997

(12) Pasta J. Laser therapy in ophthalmology, chapter 13 in: Jelinkova H. (ed). Lasers for medical applications, Diagnostics, therapy and surgery, Woodhead Publishing Limited, Cambridge, 2013, 395-458

(13) Wiegand W. Lasertherapie in der Augenheilkunde, Dt. Ärztebl. 85, Heft 39, 29. September 1988 (37), A-2661 - A-2666