Two-photon absorption and lasing due to biexciton in CuCl quantum dots

We have demonstrated laser emission in CuCl quantum dots embedded in NaCl matrix by direct creation of biexcitons through two-photon absorption process. Mode distance and emitting direction of laser emission show that cavity is composed of cleaved surfaces of the matrix. In addition, we confirmed that the lasing originated from the biexciton state by taking account of the polarization selection rule of the lowest biexciton state. It is suggested that two-photon excitation of the biexcitons is very useful for high-efficient lasing in quantum dots.