XFEL: Day of Light: 60th anniversary of the laser

Sixty years after the first laser was operated on 16 May 1960 by Theodore Maiman at Hughes Research Laboratories in California, lasers have revolutionized everyday life as well as science. Lasers are also fundamental for research at the European XFEL. A public event on the European XFEL campus planned to celebrate this anniversary has been postponed to a later date.

When the world’s biggest X-ray laser and one of the planet’s brightest light sources, the European XFEL, started operation in 2017, it was the culmination of several decades of scientific progress in laser and X-ray laser technology. Lasers operating in the visible wavelength range were invented in the 1960s. In these lasers, radiation is generated from electron transitions in atoms or molecules. The light emitted is then continuously amplified between mirrors. This makes it comparatively easy to produce high-quality laser light, and many applications now shape our everyday lives. Examples range from impressive light installations, to high precision surgical instruments, broadband telecommunication, components in the electrical devices we carry in our pockets, and the laser pointer we use during presentations.

In 1971, several years after the invention of the laser using visible light, the American physicist John Madey created laser like emissions based on accelerated electrons. The radiation produced by so-called free-electron lasers, or FELs, covers a wide range of the electromagnetic spectrum, from microwaves to X-rays.

A decade later the process of “self-amplified spontaneous emission”, or SASE, was described, first by Russian physicists Evgeny Saldin, Anatoli Kondratenko and Yaroslav Derbenev at the Institute of Nuclear Physics in Novosibirsk, and then independently by Italian-American physicist Claudio Pellegrini together with Rodolfo Bonifacio and Lorenzo Narducci. This process, where the X-ray light emitted from accelerated electrons interacts with other accelerated electrons to create an even brighter light signal, is the basis of X-ray free-electron laser (XFEL) technologies.

However, it was not until 2005 that the world’s first XFEL, the “free-electron laser in Hamburg” (FLASH) at Deutsches Elektronen-Synchrotron DESY welcomed its first users.

Over the years, several ideas were proposed by different groups of scientists for optimizing the SASE process to produce even brighter X-ray beams. In 2010 Vitali Kocharyan, Gianluca Geloni, and Evgeny Saldin proposed a relatively simple scheme to spectrally filter and amplify light of hard X-ray wavelength.

Today, in addition to the European XFEL, free-electron lasers in the hard, short-wavelength X-ray range are operational in the USA (LCLS), Japan (SACLA), Switzerland (SwissFEL) and South Korea (PAL-XFEL). Another large X-ray laser (SHINE) is planned in China and is scheduled to start operation in 2025.

XFELs now enable scientists to study the atomic structures of materials in unprecedented detail, but lasers operating with visible light are also crucial for research at large X-ray facilities such as European XFEL. By skillfully aligning powerful lasers producing visible light and X-rays, scientists can now shine light onto the intricate workings of biological and chemical reactions, and far off worlds. In so-called pump-probe experiments, lasers emitting pulses of extremely bright light are used to trigger reactions in, for example, light sensitive proteins. The X-ray laser is then used to capture an image of the structure of the protein after a carefully timed delay. By repeating this with different time delays between optical and X-ray lasers, a molecular movie can be produced – just like many still images can be pasted together to make a film.

Video: A year in three mins – watch the infrared pump-probe-laser being built at European XFEL in this time-lapse video.

In addition, at European XFEL a custom built high-energy laser will generate extreme temperatures and pressures in materials simulating the conditions found in the interior of exoplanets with temperatures of up to 10,000°C, and pressures of up to 10,000 tonnes per square centimeter. The atomic structure and dynamics of these materials can then be probed with the extremely bright and intense X-ray pulses generated by the European XFEL, taking scientists a step closer to being able to understand the behavior, composition and conditions of distant planets. The speed, intensity, precision and indeed size of these extremely bright lasers are a far cry from the instruments developed over half a century ago, and yet those simple beginnings are now enabling scientists to reach for the stars.

Robert Feidenhans’l, European XFEL managing director: “60 years after the invention of the laser we now use powerful lasers to study the smallest details of the nanocosm. Lasers are an example on how a device has altered research and our lives in a way that was impossible to predict when it was invented.”

Further information: photos and video are available for download in the media database.