Progressive power lens measurement by low coherence speckle interferometry

This work proposes a method for dioptric power mapping of progressive lenses through dual wavelength, low-coherence digital speckle pattern interferometry. Lens characterization finds several applications and is extremely useful in the fields of ophthalmology and astronomy, among others. The optical setup employs two red diode lasers which are conveniently aligned and tuned in order to generate a synthetic wavelength. The resulting speckle image formed onto a diffusive glass plate positioned behind the test lens appears covered of contour interference fringes describing the deformation on the light wavefront due to the analyzed lens. By employing phase stepping and phase unwrapping methods the wavefront phase was retrieved and then expressed in terms of a Zernike series. From this series, expressions for the dioptric power and astigmatic power were derived as a function of the x- and y-coordinates of the lens aperture. One spherical and two progressive lenses were measured. The experimental results presented a good agreement with those obtained through a commercial lensometer, showing the potentialities of the method. ► A method for lens analysis by dual wavelength, digital speckle pattern interferometry is proposed. ► A CCD camera captures the contour interferogram formed onto a diffusive glass plate behind the lens. ► The wavefront due to the lens is reconstructed by evaluating the contour interferogram. ► The wavefront is described by a Zernike series, through which the lens dioptric power are obtained. ► The experimental results were compared with measurements performed through a commercial lensometer.