This invention provides a device for improving laser wavelength conversion efficiency and a laser system configured to provide high-power multi-wavelength femtosecond laser pulses using the device. The device for improving laser wavelength conversion efficiency comprises a wavelength conversion member photonic crystal fiber (PCF), wherein the device for improving laser wavelength conversion efficiency improves wavelength conversion efficiency by shortening the length of the PCF. The device provided in this invention not only reduces the attenuation and dispersion caused by the optical fiber, but also improves the energy conversion efficiency within a specific wavelength range. The use of the technique not only increases the energy of light pulse, but also greatly reduces the amount of fiber used, and can maximize the energy of the desired wavelength according to experimental requirements when using laser input sources of different wavelengths.

This invention provides a device for improving laser wavelength conversion efficiency and a laser system configured to provide high-power multi-wavelength femtosecond laser pulses using the device. The device for improving laser wavelength conversion efficiency comprises a wavelength conversion member photonic crystal fiber (PCF), wherein the device for improving laser wavelength conversion efficiency improves wavelength conversion efficiency by shortening the length of the PCF. The device provided in this invention not only reduces the attenuation and dispersion caused by the optical fiber, but also improves the energy conversion efficiency within a specific wavelength range. The use of the technique not only increases the energy of light pulse, but also greatly reduces the amount of fiber used, and can maximize the energy of the desired wavelength according to experimental requirements when using laser input sources of different wavelengths.

A terahertz-wave generating element includes a waveguide including an electro-optic crystal; an optical coupling member that extracts a terahertz wave, which is generated from the electro-optic crystal as a result of light propagating through the waveguide, to a space; and at least two electrodes that cause a first-order electro-optic effect in the electro-optic crystal by applying an electric field to the waveguide so as to change a propagation state of the light propagating through the waveguide. A crystal axis of the electro-optic crystal of the waveguide is set such that the terahertz wave generated by a second-order nonlinear optical process and the light propagating through the waveguide are phase-matched.

A terahertz wave generating element includes a nonlinear optical crystal generating terahertz waves by propagating light, and a coupling member propagating the generated terahertz waves. The coupling member includes a reflecting face reflecting at least part of the generated terahertz waves. The reflecting face is convex in a propagation direction of the generated terahertz waves. An angle at the coupling member side between the reflecting face and the propagation direction of the light is greater than 90 degreescos.sup.1 (n.sub.g/n.sub.THz) but smaller than 90 degrees at a plane including the light propagation direction. n.sub.g represents a group refractive index of the nonlinear optical crystal at a wavelength of the light, n.sub.THz the refractive index of the coupling member at a wavelength of the generated terahertz waves. A curvature radius of the reflecting face, in a reflection region reflecting the radius terahertz waves, is smaller the farther downstream in the light propagation direction.

A terahertz-wave generating element includes a waveguide including an electro-optic crystal; an optical coupling member that extracts a terahertz wave, which is generated from the electro-optic crystal as a result of light propagating through the waveguide, to a space; and at least two electrodes that cause a first-order electro-optic effect in the electro-optic crystal by applying an electric field to the waveguide so as to change a propagation state of the light propagating through the waveguide. A crystal axis of the electro-optic crystal of the waveguide is set such that the terahertz wave generated by a second-order nonlinear optical process and the light propagating through the waveguide are phase-matched.