Abstract
Diffraction-free beams have attracted increasing research interests because of their unique performances and broad applications in various fields. Although many methods have been developed to produce such beams, it is still challenging to realize a tunable non-diffracting beam. Here, we report the generation of a tunable diffraction-free array through second-harmonic generation in a nonlinear photonic crystal, i.e., a 2D periodically-poled LiTaO3 crystal. In such a crystal, the second-harmonic wave is engineered by properly designing the domain structure based on the Huygens-Fresnel principle. The characteristics of the generated diffraction-free array including its period, propagation length, and wavelength can be tuned by simply changing the input wavelength. Our observation not only enriches the diffraction-free optics, but also has potential applications for photolithography and imaging.
Highlights
The reciprocal vectors Gm,n and Gm,−n can produce two non-collinear SH waves, which can be considered as the decomposed components of the cosine beam
We have presented the generation of a tunable diffraction-free array, i.e. cosine-Gaussian beam, through non-collinear QPM SHG processes in a nonlinear photonic crystal
By utilizing the excellent thermo-optical, electro-optical and acoustic-optical performances of the LiTaO3 crystal, the diffraction-free array can be modulated by changing the operation temperature, and applying an electrical or acoustic field
Summary
The reciprocal vectors Gm,n and Gm,−n can produce two non-collinear SH waves, which can be considered as the decomposed components of the cosine beam. Considering that the two SH components of the cosine beam have an in-between angle of 2θ(decided by Equation (4)), the transverse profile of the SH intensity (Fig. 1b) can be deduced to be Obviously, the period of the obtained SH array is
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