Did We Forget to Properly Celebrate the 50th Anniversary of the Laser?

In 2010, the ^50th anniversary of the laser celebrated the completion of a scientific race, initiated by A. Schawlow and C. Townes with a famous publication in 1958[1] predicting the laser along with many of its properties in detail. The race was won - mostly unexpected by the large mainstream technical laboratories - by T. Maiman who collected suitable components in his laboratory and succeeded in igniting the world's first (ruby) laser in 1960[2].

Almost immediately after its invention, the laser (Light Amplification by Stimulated Emission of Radiation) was exploited for entertainment. For instance, James Bond was among its earliest clients. To this day, society loves these futuristic aspects, but does it pay sufficient tribute to the laser's deeper relevance?

The laser was clearly initiated and invented in the United States - and 50 years later well recognized for its role in science, technology, and society by an address of President B. Obama to the congress and by numerous other activities[3]. In Europe, the anniversary of the laser seems to have attracted much less attention, in spite of the contribution by European scientists and in spite of the driving force that the laser keeps exerting on science and technology.

The laser is a beautiful result of fundamental research in physics, and it may well keep transforming technology with a potential sisterly rivaling that of semiconductor electronics. Addressing the origin and future of the laser offers interesting insight into the interplay of basic and applied research and asks for the attention of society at an appropriate level.

Let us look back at the history of the laser beginning 125 years ago, with the foundation of the Physikalisch-Technische Reichsanstalt in 1887 in Berlin by farsighted scientists and entrepreneurs: W. von Siemens and H. von Helmholtz. Already in 1888, one of the first laboratories began investigating the properties of black bodies. This work - in plain words - performed technology analyses for the rising industry producing electric lanterns for street lighting. It led directly into the discovery of quantum physics in 1900 by M. Planck, laying no less than the foundations of modern physics. At about the same time, the electron was discovered by J.J. Thomson, triggering the birth of the electronics industry. Moreover, in 1886 H. Hertz proved the transmission of electromagnetic waves predicted by Maxwell's equations, perhaps one of the most significant milestones of modern day technology.

One way to understand the creation of the laser is a continuously evolving process of electromagnetic oscillators with ever increasing frequency - a continued process to this date. Probably at all times during the past 150 years, the evolution of electromagnetic oscillators at higher and higher frequencies had important consequences in history, e.g. it strongly influenced the outcome of the second world war, when compact magnetron cm-wave sources made the use of radar equipment aboard planes efficient.

An extension of the magnetron to ever shorter wavelengths would have called for continued miniaturization, a principle we might straightforwardly follow today but which deemed unrealistic in the early 1950s. This hurdle provoked C. Townes[4] (in parallel with N. Basov and N. Prokhorov in Russia) to invent the maser (micro wave amplification by stimulated emission of radiation) based on the principle of stimulated emission: he left the machined electron tube type devices and resorted to oscillating molecules instead. From there it was a small step only to extend the principles to laser radiation at visible wavelengths.

In fact there was no fundamental obstacle in the 1930s to invent the laser, it might have been conceived when Kopfermann and Ladenburg[5] measured dispersion by neon atoms in a discharge. Extending their observation of what they called "negative dispersion" to e.g. higher discharge currents would have brought inversion! However, the concept of achieving inversion, laid out by Einstein already but corresponding e.g. to negative temperatures, was not yet ready in the minds of physicists.

Following the initial demonstration in 1960, a rapid series of further inventions was observed in less than 4 years: the pulsed ruby laser was followed by the iconic helium-neon laser, the workhorses solid state and_CO2 gas laser; mode locking for generating the shortest pulses ever was demonstrated. Perhaps the most relevant beacon was set in 1962, when the operation of the first semiconductor laser - which had been predicted by J. von Neumann in 1953 already[6] - was shown.

It is interesting to note that, although the concepts for probably all laser sources used today were laid out in an extremely short time, many of them had to wait for 20 to 30 more years until further technological breakthroughs paved their way for widespread applications. Semiconductor lasers are a case in point where samples for room temperature laboratory use became available in the mid-to-late 1980s only. Here, the final breakthrough was owed to the invention of heterostructures in GaAs, a material first used by H. Welker at Siemens laboratories[7]

The semiconductor laser made numerous advances possible: diode lasers replaced exciter lamps bringing the "wall plug efficiency" of high power lasers to 50%; they activated the worldwide optical communication network by offering large bandwidth; tunable diode laser sources opened the way to the simultaneous application of many affordable and narrowband lasers, enabling the complex experiments in today's fundamental quantum optical and other laboratories. It is no surprise that the present world market of lasers is dominated by diode lasers. In conclusion, we may call the laser world we are witnessing today a sister of the semiconductor electronic revolution that will continue to modify the life style of generations to come. The arrival of laser based technologies has been slower but they offer the potential for a similar impact - the^21st century may indeed become a century of the photon.

References

[1] A. Schawlow, C. Townes, Phys. Rev. 112, 1958, 1940.

[2] T. Maiman, Nature, 187, 1960, 493.

[3] Laserfest.

[4] C. Townes, How the laser happened, oxford university press, new york, 1999.

[5] R. Ladenburg, H. Kopfermann Z. Physik, 65, 1930, 167.

[6] J. von Neumann (1953), reprinted in IEEE J. Quant. Electron, QE-23, 1987, 659.

[7] H. Welker and H. Mataré had also realized a European counterpart of the invention of the transistor by Bardeen et al. at the Paris Westinghouse laboratory in 1948.