Broadband third harmonic generation via four-wave mixing and induced Raman scattering

There are various visible light sources around us. All devices that emit visible light, such as laser pointers, LED lights, and illuminants, can be considered visible light sources. White fluorescent lamps are a mixture of various colors ranging from blue to red, while lasers are an excellent light source that emits purely one wavelength. By inputting laser light into our micro optical resonator, it is possible to convert invisible light (laser light) with a wavelength of 1550 nm into green visible light with a wavelength of 517 nm. This is called third harmonic generation, a physical phenomenon in which the frequency is converted by a factor of three (1/3 the wavelength). In this study, we have confirmed the conversion to broadband visible light from green (498 nm) to red (611 nm) by inducing third harmonic generation in combination with induced Raman scattering and four-wave mixing. Induced Raman scattering and four-wave mixing are also a type of wavelength conversion, but first, these phenomena generate light of different wavelengths around the laser light, which is near-infrared light (left figures (a), (b), and (c)). These new lights are finally converted into visible light with various wavelengths by third harmonic generation (right figure (a)(b)(c)). (Right figure (a)(b)(c))

Silica glass, the material of the resonator, is prone to induced Raman scattering, which was the key to the broadband visible light generation.