Scientists from the Korea Advanced Institute of Science and Technology in South Korea, the Max Planck Institute of Quantum Optics in Germany and the Georgia State University in USA has managed to concentrate the energy of infrared light pulses with a nano funnel and used the concentrated energy to generate extreme ultraviolet light flashes. These flashes, which repeated 75 million times per second, lasted only a few femto seconds.
Extreme ultraviolet light
Light composing different wavelengths can change frequency by interactions with matter, depending on type and shape of material. Light in the infrared (IR) can be converted to the extreme ultraviolet light by a process known as high-harmonic generation, whereby the atoms are exposed to a strong electric field from the IR laser pulses. These fields have to be as strong as the fields holding the atom together. With these fields electrons can be extracted from the atoms and accelerated with full force back onto the atoms. Upon impact highly energetic radiation in the extreme ultraviolet light is generated. .Due to their short wavelength and potentially short pulse duration reaching into the atto second domain, extreme ultraviolet light pulses are an important tool for the exploration of electron dynamics in atoms, molecules and solids. In order to capture a moving electron, light flashes are needed, which are shorter than the timescale of the motion.
Nano funnel
The researchers have modified light waves with a nano funnel made out of silver and filled with xenon gas to convert femto second laser pulses in the infrared spectral range to femto second light flashes in the extreme ultraviolet.
Process
Light in the infrared (IR) can be converted to the extreme ultraviolet by a process known as high-harmonic generation, by exposing the atoms to a very strong electric field generated by concentrating using a nano funnel. The infrared light pulses were sent into the funnel entrance where they travel through towards the small exit. The electromagnetic forces of the light result in density fluctuations of the electrons on the inside of the funnel. Here, a small patch of the metal surface was positively charged, the next one negative and so on, resulting in new electromagnetic fields on the inside of the funnel, which are called surface plasmon polaritons. The surface plasmon polaritons travel towards the tip of the funnel, where the conical shape of the funnel results in a concentration of their fields.
The funnel acts as an efficient wavelength filter at the small opening only extreme ultraviolet light comes out. With these fields electrons can be extracted from the atoms and accelerated with full force back onto the atoms. Upon impact highly energetic radiation in the extreme ultraviolet is generated. The researchers have created a powerful extreme ultraviolet light source with wavelengths down to 20 nanometers with high repetition rate.
Applications
The new technology can help in the future to measure the movement of electrons with the highest spatial and temporal resolution., and in laser physics to explore the inside of atoms and molecules.