Selective amplification effect on the diffraction efficiency of a phase grating generated by femtosecond laser pulses.

A phase grating that selectively amplifies diffraction orders that are multiples of a determined integer is designed. For the proposed grating, multiples of the fourth order are enhanced. These results are supported by experiments. The structure is inscribed in the volume of a lithium niobate crystal by employing the femtosecond laser pulse micro-machining technique. A model based on the Raman-Nath behavior of the grating predicts a diffraction efficiency enhancement for those selected orders. Moreover, it is observed that by changing the incidence angle allows transferring energy from multiples of fourth orders to multiples of three. These findings have potential applications in optical spectroscopy and optical communications as well as for photonic devices in which a controlled energy exchange between orders is necessary. The basic wave nature of the mentioned effect allows finding a counterpart in different wavelength ranges of the electromagnetic spectrum.