We make a comparison study of linear and nonlinear diffraction by a periodically poled lithium niobate[PPLN]dual linear-nonlinear thin-plate grating with weak surface corrugation against four types of white light sour...We make a comparison study of linear and nonlinear diffraction by a periodically poled lithium niobate[PPLN]dual linear-nonlinear thin-plate grating with weak surface corrugation against four types of white light sources.They are the ordinary halogen lamp thermal radiation source[WL1],the silica photonic crystal fiber supercontinuum nanosecond laser source[WL2],and two femtosecond white lasers made by a Ti:sapphire pump laser beam passing through a fused silica plate with significant spectrum broadening[WL3]and through a cascaded silica plate and a chirped PPLN crystal with ultrabroadband second-harmonic generation[WL4].The experiments show that the coherence,peak power,spectral bandwidth,profile,and flatness of the pump white light all contribute to shaping the characteristics of linear and nonlinear optical diffraction patterns.In particular,for WL1,WL2,and WL4,the peak power is not sufficiently large;thus,only linear diffraction occurs.For incoherent WL1,the interference is absent.Remarkably,when a femtosecond white laser with sufficiently large peak power[WL3]shines upon the PPLN grating,bright and sharp linear Bragg scattering spots,dispersive colored linear diffraction patterns,and nonlinear Cherenkov radiation nonlinear diffraction patterns are observed simultaneously by naked eyes.The experiments would enrich the basic physical and optical understanding of linear and nonlinear optical diffraction characteristics of ultrabroadband white laser sources.展开更多
基金supported by the National Natural Science Foundation of China(No.12434016)the Science and Technology Project of Guangdong(No.2020B010190001)the National Funded Postdoctoral Researcher Program(No.GZB20240785)。
文摘We make a comparison study of linear and nonlinear diffraction by a periodically poled lithium niobate[PPLN]dual linear-nonlinear thin-plate grating with weak surface corrugation against four types of white light sources.They are the ordinary halogen lamp thermal radiation source[WL1],the silica photonic crystal fiber supercontinuum nanosecond laser source[WL2],and two femtosecond white lasers made by a Ti:sapphire pump laser beam passing through a fused silica plate with significant spectrum broadening[WL3]and through a cascaded silica plate and a chirped PPLN crystal with ultrabroadband second-harmonic generation[WL4].The experiments show that the coherence,peak power,spectral bandwidth,profile,and flatness of the pump white light all contribute to shaping the characteristics of linear and nonlinear optical diffraction patterns.In particular,for WL1,WL2,and WL4,the peak power is not sufficiently large;thus,only linear diffraction occurs.For incoherent WL1,the interference is absent.Remarkably,when a femtosecond white laser with sufficiently large peak power[WL3]shines upon the PPLN grating,bright and sharp linear Bragg scattering spots,dispersive colored linear diffraction patterns,and nonlinear Cherenkov radiation nonlinear diffraction patterns are observed simultaneously by naked eyes.The experiments would enrich the basic physical and optical understanding of linear and nonlinear optical diffraction characteristics of ultrabroadband white laser sources.
