Under extremely intense illumination materials may exhibit so-called nonlinear optical properties such as ceasing to absorb light beyond a certain brightness, or becoming highly ionized.
Yasumasa Hikosaka, Mitsuru Nagasono and colleagues at RIKEN and several other Japanese research institutes have now described the details of this ionization process by using very short bursts of bright laser light1. Their finding is relevant to a broad range of pure and applied research, including x-ray imaging of biological molecules, ultrafast optical switches, fusion and astrophysics.
The researchers focused on the behavior of argon atoms, which is easy to handle and well-characterized, under illumination by laser light about one hundred trillion times brighter than the noonday sun, and containing about seven times more energy per photon than the bluest light visible to the human eye. Previous work by other researchers showed that such intense, energetic light removes multiple electrons from target atoms, resulting in highly charged ions. While the mechanism of the ionization process was partially understood from observations of the yields and momenta of these ions, important details were missing.
Hikosaka, Nagasono and colleagues chose to observe the electrons emitted during the ionization process, instead of the ions themselves. Not only do these electrons carry unique information about the ionization process, but they can be measured after each ultra-short laser pulse. Since the laser spectrum and power are constantly fluctuating, the fine details of the ionization process are averaged or ‘smeared’ during a continuous measurement. A shot-by-shot measurement, however, can account for laser fluctuations.
The experiment showed that the dominant ionization pathway of the argon atoms has two steps: first, a single laser photon is absorbed to create singly-ionized argon, and then two more photons are absorbed to create doubly-ionized argon. The researchers also found that the intermediate argon ion states had energy levels, or energy resonances, that induced this pathway.
The research leverages the recent development of free electron lasers, which are uniquely capable of producing very bright, energetic and short pulses of radiation. The work also illustrates that energy resonances are key to multi-photon, multiple ionization processes, a finding that is likely to be relevant to a variety of research programs. Hikosaka says that the research team will continue to focus on the basic science, as well as applications: “Our goal is to develop and leverage a deep understanding of the mechanism and dynamics of non-linear processes in order to manipulate or control these processes and their final products.”
The corresponding author for this highlight is based at the EUV-FEL Experimental Facility Team, RIKEN XFEL Project Head Office
Hikosaka, Y., Fushitani, M., Matsuda, A., Tseng, C.-M., Hishikawa, A., Shigemasa, E., Nagasono, M., Tono, K., Togashi, T., Ohashi, H. et al. Multiphoton double ionization of Ar in intense extreme ultraviolet laser fields studied by shot-by-shot photoelectron spectroscopy. Physical Reveiw Letters 105, 133001 (2010).
gro-pr | Research asia research news
New technology for ultra-smooth polymer films
28.06.2018 | Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP
Diamond watch components
18.06.2018 | Schweizerischer Nationalfonds SNF
There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.
The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
20.08.2018 | Information Technology
20.08.2018 | Life Sciences
20.08.2018 | Information Technology