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Waveguide Generates Coherent EUV

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Anne Fischer Lent

Nonlinear optics can convert laser light from one wavelength to another, but the process often requires phase matching to be efficient. Unfortunately, in high-harmonic generation of coherent extreme-ultraviolet radiation, it has not been possible to phase-match above approximately 80 eV, reducing efficiency and limiting its applications. Now researchers from JILA in Boulder, Colo., and Sofia University in Bulgaria have applied concepts from visible light conversion that allow them to extend the range of efficient EUV generation by nearly 100 eV.


A modulated fiber enables researchers to generate coherent extreme-ultraviolet radiation by quasi-phase-matched frequency conversion.

The new method uses a quasi-phase-matched frequency conversion of laser light into the EUV. Firing a femtosecond laser into a gas-filled waveguide creates ions and electrons by ripping apart the gas atoms. Then it accelerates the electrons to very high energies and releases photons at EUV wavelengths when it slams the electrons back into the ions. This conversion process is efficient only if the laser waves and EUV waves travel at the same speed through the gas, which usually happens only at low levels of ionization.

By creating ripples in the diameter of the hollow-core waveguide, the team solved the phase-matching problem. The ripples force the lightwaves from the laser and the EUV beams to travel at effectively the same speed in the tube.

One advantage of this setup is size. Intense EUV sources such as synchrotrons are the size of buildings. The waveguide used in this design, however, fits in one hand, and the laser fits on a desktop.

This method could be used for metrology or for mask inspection in support of advanced lithography. It also may enable high-resolution imaging applications of materials and biological samples.

The next step in the research is to extend the beam's range into the water window: the region of the spectrum below 4 nm. Producing an EUV source at these wavelengths would be useful in designing a compact microscope for imaging biological structures within a wet or frozen cell.
Hamamatsu Corp. - Earth Innovations MR 2/24

Published: February 2003
Glossary
metrology
Metrology is the science and practice of measurement. It encompasses the theoretical and practical aspects of measurement, including the development of measurement standards, techniques, and instruments, as well as the application of measurement principles in various fields. The primary objectives of metrology are to ensure accuracy, reliability, and consistency in measurements and to establish traceability to recognized standards. Metrology plays a crucial role in science, industry,...
nonlinear optics
Nonlinear optics is a branch of optics that studies the optical phenomena that occur when intense light interacts with a material and induces nonlinear responses. In contrast to linear optics, where the response of a material is directly proportional to the intensity of the incident light, nonlinear optics involves optical effects that are not linearly dependent on the input light intensity. These nonlinear effects become significant at high light intensities, such as those produced by...
phase matching
Phase matching is a crucial concept in the field of optics, particularly in nonlinear optics and the generation of coherent light. It refers to the condition where the phases of two or more waves, such as laser beams, are adjusted or aligned in such a way that their combined effect is maximized. In nonlinear optics, various processes involve the interaction of multiple waves within a material. For efficient energy conversion and amplification, it is essential that the phases of these waves...
wavelength
Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.
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