Measurement of thermo-elastic deformation of an optic using a polarization-based shearing interferometer

Abstract

A shearing interferometer is presented which uses polarization control to shear the wavefront and to modulate the interference pattern. The shear is generated by spatial walk-off in a birefringent crystal. By adjusting the orientation of the birefringent crystal, the components of the wavefront gradient can be independently measured to allow determination of the full wavefront vector gradient as well as reconstruction of the wavefront. Further, the monolithic nature of the crystal used for shearing allows the interferometer to be setup without need for precise alignment of any components. An algorithm incorporating homodyne detection is presented whichanalyzes the modulated interferograms to determine the components of the wavefront gradient, from which the wavefront is reconstructed. The thermal deformation of a mirror subject to heating from absorption of a Gaussian pump beam was accurately observed with a sensitivity better than λ/160. We show that this sensitivity is scale invariant, and present a method to account for the nonuniform spatial frequency response of the interferometer.

Laser induced thermoelastic surface displacement in solids detected simultaneously by photothermal mirror and interferometry

“…These methods require reflective surfaces in order to directly detect the perturbation caused by light absorption and have to be capable of detecting probe beam wavefront deformation. Two such methods are the photothermal mirror and the interferometry [2][3][4][5][6][7]. Both are naturally similar in this sense, because they detect wavefront distortion, although employing different optical detection mechanisms.…”