Speckle holographic imaging of a sound field using Fresnel lenses.

In this Letter, we propose to use Fresnel lenses for holographic sound-field imaging. Although a Fresnel lens has never been used for sound-field imaging mainly due to its low imaging quality, it has several desired properties, including thinness, lightweight, low cost, and ease of making a large aperture. We constructed an optical holographic imaging system composed of two Fresnel lenses used for magnification and demagnification of the illuminating beam. A proof-of-concept experiment verified that the sound-field imaging with Fresnel lenses is possible by using the spatiotemporally harmonic nature of sound.