Laser light to new regions of the spectrum

Combining concepts from electromagnetic radiation research and fibre optics, researchers have created an extreme-ultraviolet, laser-like beam capable of producing tightly-focused light in a region of the electromagnetic spectrum not previously accessible to scientists.

Between 10-100 times shorter than visible light waves, the extreme-ultraviolet (EUV) wavelengths will allow researchers to "see" tiny features and carve miniature patterns, with applications in such fields as microscopy, lithography and nanotechnology.

The achievement is based on a new structure called a waveguide, a hollow glass tube with internal humps that coax light waves into travelling along at the same speed and help the waves reinforce each other.

The work is part of a continuing project supported by the National Science Foundation (NSF), an independent agency of the US government.

The new beam has peak powers approaching a megawatt and produces nanometer-scale light waves yet the entire apparatus fits on a moderately sized table. Researchers create EUV beams by firing a femtosecond laser through the gas-filled waveguide. A femtosecond is one quadrillionth 1/1,000,000,000,000,000 of a second, and a brief pulse of the laser can be measured in these tiny units. The intense laser light literally rips the gas atoms apart, resulting in charged ions and electrons. The laser beam then accelerates the electrons to high energies and slams them back into the ions, releasing electromagnetic radiation (in this instance, photons at EUV wavelengths). Some of the EUV waves can be out of phase with the laser, cancelling each other and wakening the strength and coherence of the output beam. However, by creating ripples in the diameter of the waveguide, the researchers coaxed the light waves from the laser and EUV beams into travelling at the same speed (a result called Phase matching).

Slowing down the laser allows it to travel at the same speed as the EUV lght and increases the efficiency of the process. The result is a well-synchronised stream of photons firing out of the system - electromagnetic radiation boosted up to a high-energy, extreme ultraviolet, wavelength.

The peak power of the beam is higher than any other light source at the wavelengths is achieves - all the way from the ultraviolet to the EUV region of the spectrum around 6 nanometers.

The group of researchers hopes to extend the beam's range into what scientists call the water-window - the region of the spectrum below 4 nanometers where the light is perfect for imaging biological structures. Producing a beam in this region would allow the researchers to build a small microscope for imaging living tissues on a desktop or for viewing objects at the nanoscale.

The researchers speculate that in 10 years, laser light will span all the way to the x-ray region of the spectrum. The light could be used to produce the most precise microscopes.