A novel CPA (Chirped Pulse Amplification) technology has made it possible to generate a laser pulse, which has a pulse duration of 10s of femtosecond. Its impact to science appears in two directions. One is the usage of such an ultrashort nature. As a probing pulse in either direct or indirect way, ultrafast phenomena can be observed. An UED (Ultrafast Electron Diffraction) system, an electron diffraction facility which utilizes an ultrashort electron beam generated by an ultrashort laser pulse, aims to reveal underlying fundamental mechanisms of materials by observing ultrafast structural dynamics of atoms or molecules. The other is the usage of an ultra-intense nature. The very high intensity of the laser pulse with much smaller energy has been possible in the laboratory scale due to the short pulse width. This leads to a relativistic plasma – a plasma with relativistic electrons. One of exciting applications of the relativistic plasma is a plasma accelerator, which generates high energy charged particles on a table-top due to much higher accelerating field strength compared with a conventional RF accelerator.

The research activities related to such fields at KAERI will presented.