  We evaluate the transient response of an optically tunable meta-atom composed
of an electric inductor-capacitor resonator that is loaded with a piece of
high-resistivity silicon and perform a proof-of-concept experiment to
demonstrate the storage and release of electromagnetic waves using this
meta-atom in the microwave region. The transient time of the meta-atom
immediately after commencing laser light illumination of the silicon in the
meta-atom is found to be inversely proportional to the incident laser power.
The transmittance of the meta-atom at the resonance frequency increases to ten
times that obtained without laser illumination at 5.2 ns after the start of
laser illumination for a laser power of 1600 mW, a laser spot size of 2 mm
$\times$ 1 mm, and a laser wavelength of 447 nm. In contrast, the transient
time after turning the laser light off is dependent on the carrier lifetime of
silicon and is measured to be several tens of microseconds. Based on the
results of evaluation of the transient response of the meta-atom, we propose a
method for the storage and release of electromagnetic waves using a Fabry-Perot
resonator that includes the meta-atom as one of its mirrors. The
electromagnetic wave that is stored in the Fabry-Perot resonator for a few tens
of nanoseconds is then successfully released by illuminating the silicon in the
meta-atom with the laser light. It is also possible to use this method in the
higher frequency region because metamaterials with semiconductor elements can
even be used as active metamaterials in the optical region as long as their
bandgap energy is higher than the signal photon energy.
