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  • The Laser’s European Family Tree

Apr 2010
Jörg Schwartz, European Correspondent,

As we celebrate the 50th anniversary of the date when the first man-made laser saw the light of day, it is important to look back at its birth. And although that beginning took place in the hills of sunny Malibu, Calif., on May 16, 1960, this groundbreaking invention has quite a few European forebears and descendants.
Although it seems that, for this particular baby, a bit of disagreement exists as to who the parents were, there is good certainty about the grandfather: Albert Einstein. He came up with the concept of stimulated emission in 1916-17 in his paper “Zur Quantentheorie der Strahlung” (“On the Quantum Theory of Radiation”). Much later – but still 10 years before Maiman’s first demonstration of a working ruby laser – another European, Frenchman Alfred Kastler, proposed a method of optical pumping of paramagnetic atoms or nuclei in the ground state. This was considered an important step toward lasers and earned Kastler the 1966 Nobel Prize in physics.

Albert Einstein is generally considered the grandfather of the laser, thanks to his 1916-17 paper “On the Quantum Theory of Radiation,” in which he presented the concept of stimulated emission.

Stanford professor Anthony Siegman, author of well-known laser textbooks and reviews, sees the development of the laser as having been facilitated by the postwar situation, in which many very capable scientists “returned to their home laboratories, carrying with them … new skills and … pieces of their wartime apparatus – waveguides, cavities, signal generators and receivers, sensitive detection methods – which they were eager to apply to more basic scientific pursuits. At the same time, the wartime experience … led to unprecedented funding.” Because of the Cold War situation, financial backing was significant in the US and the Soviet Union, leading to major, speedy steps on both sides.

Europe was in the middle of this competition and, interestingly, the first lasers built in Berlin were constructed around the time the Wall was built in 1961 – “and on both sides of the Iron Curtain,” remembers Hans Joachim Eichler, professor at the Technical University of Berlin, one of the first places in Germany where lasers were (and still are) developed. The two researchers who did the first experiments there, Horst Weber and Gerd Herziger, became landmark figures on Germany’s laser scene. During their careers, they left a trail of laser research centers that they established in Germany and Switzerland, including the Fraunhofer Institute for Laser Technology in Aachen and Laser Medicine Technology Berlin.

Ten years before Theodore Maiman first demonstrated a working ruby laser, Alfred Kastler of France proposed a method of optical pumping of paramagnetic atoms or nuclei in the ground state. This was an important step toward lasers and earned Kastler the 1966 Nobel Prize in physics.

Mastering applications

“Many other of [the] top research centers for laser technology were set up by Europeans returning from the US, such as Wolfgang Kaiser from TU Munich, or Herbert Welling, who made Hanover a center of laser research,” says Eichler, who made himself a name in nonlinear optics, one of the first offshoot fields of research, which was practicably not possible without the laser. Promoting this investigation were many European research centers, such as the Polytechnic School of Milan, where Orazio Svelto worked on ultrashort laser pulses and solid-state lasers, including the recent invention of the hollow-fiber compressor used in extreme nonlinear optics and attosecond science.

Technical University of Berlin’s laser labs host a demonstration event during the annual Long Night of Sciences.Courtesy of the Technical University of Berlin.

After the birth of the ruby laser, many Europeans were involved in bringing its brothers and sisters to life. For example, groups in the UK – such as Royal Signals and Radar Establishment under Cyril Hilsum – and in France – Maurice Bernard and Guillaume Duraffourg, working at CNET, for example – were strongly involved in developing the first semiconductor laser, launched on Sept. 16, 1962, at General Electric Research Development Center in Schenectady, N.Y. In fact, there are reports that Pierre Aigrain from École Normale Supérieure in Paris was planning to visit the US with a working semiconductor laser in his pocket ... in 1961.

Another sibling that was conceived almost in parallel, but independently, in Europe and the US is the dye laser introduced in 1966 by both Fritz Peter Schäfer at Marburg University and P.P. Sorokin at IBM. A little later, Theodor Hänsch added frequency-selective elements to pulsed dye lasers, extending their use in spectroscopy and atomic physics applications. Incidentally, Hänsch received the Nobel Prize in physics for his contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique he developed.

In the late 1960s, Theodor Hänsch added frequency-selective elements to pulsed dye lasers, extending their use in spectroscopy and atomic physics applications. He was awarded the 2005 Nobel Prize in physics for his contributions to the development of laser-based precision spectroscopy.

Schäfer, however, moved to Göttigen to become director of the Max Planck Institute for Biophysical Chemistry, from which the commercial laser manufacturer Lambda Physik was spun off in 1971. Lambda Physik became a very successful player in the fieof excimer and dye lasers and is now part of Coherent Inc. Another example of an early – and yet still successful – commercial player is French Quantel, started in 1970. Quantel remains a big player in the field of solid-state lasers.

A drilling application using a solid-state laser is shown. Materials processing was one of the first applications identified for the laser, and today lasers have replaced classical tools in many fields. One of them is mechanical engineering, in which European companies are historically strong and have maintained their position, thanks to early investments in laser development. Courtesy of the Technical University of Berlin.

In general, Europeans have been doing very well in commercializing lasers and developing their applications. “In the early days, industrial giants such as Siemens or Telefunken took a strong interest in developing lasers,” Eichler said.

Take Rofin-Sinar, for example, which is a former Siemens subsidiary and today a leading industrial laser supplier. Trumpf, an international heavyweight in the field of metal cutting and welding, has its roots as a “classical” machinery supplier. Berthold Leibinger saw the trend and acquired a lot of the engineering talent in the field, recently by purchasing Southampton Photonics of the UK, a leader in fiber lasers. The company sees great potential in fiber lasers and also in direct applications of semiconductor lasers for materials processing.

Europe has also contributed to general laser applications in telecommunications and consumer electronics. The extremely popular compact disc was developed by Dutch Philips Electronics NV and subsequently commercialized in cooperation with Sony of Japan.

Charles Kao, 2009 Nobel Prize winner, suggested glass fibers for communications in the early 1960s while working at Standard Telecommunications Labs in the UK. Eichler predicts further growth and progress in everyday laser use in medicine and optical sensing. He foresees a bright future for the integration of optics and electronics through the use of silicon photonics and polymer materials. So there is a lot to come for the laser and its offspring, and let’s wish them many happy returns – and many more happy children and grandchildren – that is, technologies that would not exist without the laser.

dye laser
A laser using a dye solution as its active medium. Its output is a short pulse of broad spectral content and its achievable gain is high. Dye lasers function at room temperature. Synchronous pumping can be used to produce a continuous train of tunable picosecond pulses for sustained periods.
optical pumping
The process whereby the number of atoms or atomic systems in a set of energy levels is changed by the absorption of light that falls on the material. This process raises the atoms to specific higher energy levels and may result in a population inversion between certain intermediate levels. The optical pumping of an optical medium within a laser cavity is one of the fundamental processes involved in the generation of a beam.
semiconductor laser
A semiconductor material which is designed and grown for the efficient production of short wavelength stimulated emission through high gain as well as low internal losses. Materials with band gap energies which emit radiation efficiently within the desired wavelength region are used. Diodes may emit vertically in relation to the laser material junction in a VCSEL configuration or horizontally in an edge emitting configuration. Synonymous with laser diode.  Sometimes used...
stimulated emission
Radiation similar in origin to spontaneous emission but determined by the presence of other radiation having the same frequency. Because the phase and amplitude of the stimulated wave depend on the stimulating wave, this radiation is coherent with the stimulating wave. The rate of stimulated emission is proportional to the intensity of the stimulating radiation.
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