Possibility of high power THz radiation via electromagnetically induced transparency at ion acoustic frequency region in laser-produced dense plasmas

Electromagnetically induced transparency (EIT) is a well-known quantum phenomena that electromagnetic wave controls the refractive index of medium. It enables us to create a passband for low frequency electromagnetic wave in a dense plasma even if the plasma is opaque for the electromagnetic wave. This technique can be used to prove the ion acoustic wave because the ion acoustic frequency is lower than the plasma frequency. We have investigated a feasibility of electromagnetic radiation at THz region corresponding to the ion acoustic frequency from a dense plasma. We confirmed that the passband is created at about 7.5 THz corresponding to the ion acoustic frequency in the plasma (1021 cm-3) with a Ti:Sapphire laser (800 nm, 1017 W/cm2). The estimated radiation power is around 1 MW, which is expected to be useful for nonlinear THz science and applications.