High intensity lasers will be the powerful tools to investigate the nature of vacuum.
If the vacuum shows the reaction to electric field, if only slightly, we can observe its reaction in laboratory by focusing the extremely high intensity lasers. 
 The resonant states of low-mass neutral bosons can be produced via the photon-photon scattering in the focusing lasers and the frequency-shifted photons are observed as the signature of the four-wave mixing process in vacuum. For example, the resonant state of “Axion” can be produced by this method. Axion is expected to be one of the most reasonable candidates for cold dark matter and it may couple to two photons via extremely weak interactions.
 In this seminar, I will introduce the previous search for scalar and pseudoscalar particles with tabletop laser system at Kyoto university.  The prospects for the future experiments with higher intensity lasers will be also introduced.