Affordable free-electron laser design shows potential for biological imaging

Researchers at the RIKEN SPring-8 Center have designed an electron laser that delivers x-rays with unprecedented short wavelengths, with utility in biological imaging.

The SACLA laser design consists of various electron acceleration stages (C-TWA) and focusing elements. The key to achieving short wavelength operation is, however, the design of the undulator (UND)
The SACLA laser design consists of various electron acceleration stages (C-TWA) and focusing elements. The key to achieving short wavelength operation is, however, the design of the undulator (UND)

Researchers at the RIKEN SPring-8 Center (Harima, Japan) have designed an electron laser that delivers x-rays with unprecedented short wavelengths. What's more, the laser is compact and affordable to build, giving research institutes and universities the ability to build it at low cost and utilize powerful laser light in biological imaging.

User operation of the electron laser, known as the SPring-8 Angstrom Compact free-electron Laser (SACLA), began in March 2012. Applications for the laser design—in addition to biological imaging—include nonlinear interactions of light and matter and ultrafast phase-transition in materials, says Makina Yabashi, who led the work.

Construction of a high-energy laser is based on the concept that electrons accelerate by going very fast around a curve and also emit radiation. The energy of this radiation, and therefore its wavelength, depends on the acceleration. The tighter the curved path, the shorter the wavelength of the light emitted. This is the operating principle of free electron lasers.

The SACLA laser design consists of various electron acceleration stages (C-TWA) and focusing elements. The key to achieving short wavelength operation is, however, the design of the undulator (UND)The SACLA laser design consists of various electron acceleration stages (C-TWA) and focusing elements. The key to achieving short wavelength operation is, however, the design of the undulator (UND)
The SACLA laser design consists of various electron acceleration stages (C-TWA) and focusing elements. The key to achieving short wavelength operation is, however, the design of the undulator (UND). (Image courtesy of the RIKEN SPring-8 Center)

The group's goal with the work was to push free-electron lasers to new limits by producing shorter wavelengths. To accomplish this, they sent electrons on a very tight twisting path in a section of the laser known as the undulator. Normally, the period of the curved electron beam measures several centimeters, but the group achieved a period of only 1.8 cm by directly placing the magnets that deflect the electron beams into the vacuum chamber of the beam. Doing so reduced the laser wavelength down to 0.6 Å, which is about the radius of a hydrogen atom.

The research team plans to increase the laser beam's energy density, which would, for example, make biological imaging easier. Scientists are interesting in using the laser and other institutions are planning similar machines.

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