ARTICLE IN PRESS JID: OLEN [m5GeSdc;July 6, 2017;20:23] Optics and Lasers in Engineering 000 (2017) 1–10 Contents lists available at ScienceDirect Optics and Lasers in Engineering journal homepage: www.elsevier.com/locate/optlaseng Evaluation of a novel compact shearography system with DOE configuration Fabio Aparecido Alves da Silva a , Daniel Pedro Willemann b , Analucia Vieira Fantin a,∗ , Mauro Eduardo Benedet a , Armando Albertazzi Gonçalves Jr. a a Laboratory of Metrology and Automatization, Federal University of Santa Catarina, UFSC, CEP 88040-970, Florianópolis, Santa Catarina, Brazil b State University of Santa Catarina, UDESC, CEP 88790-000, Laguna, Santa Catarina, Brazil a r t i c l e i n f o Keywords: Shearography DOE Non-destructive inspection Defect detection a b s t r a c t The most common optical configuration used to produce the lateral shifted images, in a Shearography system, is the Modified Michelson interferometer, because of its simple configuration. Tests carried out in recent years have shown that the modified interferometer of Michelson is a device that presents good results in a laboratory environ- ment, but still presents difficulties in the field. These difficulties were the main motivation for the development of a more robust system, able to operate in unstable environments. This paper presents a new shearography config- uration based on Diffractive Optical Element (DOE). Different from the diffractive common-path setups found in literature, in the proposed configuration, the DOE is positioned between the image sensor and the objective lens and mounted on a flexible holder, which has an important function to promote the system’s robustness. Another advantage of the proposed system is in respect to phase shifting, since it is insensitive to wavelength variations. The lateral movement of the DOE produces a phase shifting in the shearography system. Since the pitch of the diffractive grating used is about 60 times greater than the wavelength of a green laser, the DOE configuration becomes much more robust to external influences compared to the Michelson Interferometer configuration. This work also presents an evaluation of the proposed shearography system designed, and some comparative results regarding a classical shearography system. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Shearography [1–3] is a special case of the DSPI (Digital Speckle Pattern Interferometry) techniques [4–6] where the speckled interfering wave fronts come from the sample, which are the reference and the ob- ject simultaneously. Shearography has the advantage of allowing short coherent length illumination and are less sensitive to environmental dis- turbances than other holographic techniques [3]. However, tests carried out in recent years have shown that the Shearography system based on quasi-common path interferometers, like modified Michelson inter- ferometer, presents good results in a laboratory environment, but still presents difficulties in the field due to higher vibration levels induced by industrial equipment in operation . These difficulties were the main mo- tivation for the development of a more robust system able to operate in unstable environments. The proposed configuration presents a common- path interferometer based on Diffractive Optical Element (DOE). The idea of using a DOE as shearing device in shearography applications is not new [7–9]. Different from the DOE common-path setups found in literature, in the proposed configuration, this optical element is placed ∗ Corresponding author. E-mail address: analucia.fantin@labmetro.ufsc.br (A.V. Fantin). between the image sensor and the objective lens, and assembled on a flexible holder, which has an important function to promote the system’s robustness. The design using a DOE to generate the lateral shifted im- ages is an effective alternative regarding classical interferometers, and becomes much more compact and robust to external influences. This work describes the development and the evaluation of a shearography system based on DOE configuration and presents comparative results to another Shearography system based on Michelson interferometer. 2. Shearography A traditional shearography setup requires some basic elements: an illumination module, an optical device to generate the double image, an excitation module and a specific software that drives the image ac- quisition procedure. Fig. 1 shows the basic setup for shearography mea- surements. An expanded laser beam illuminates the specimen under investiga- tion, which generates speckle patterns on the surface [5]. The head sensor is designed to form the laterally sheared image of the surface. After the acquisition and processing of the images, shearography mea- http://dx.doi.org/10.1016/j.optlaseng.2017.06.021 Received 31 March 2017; Received in revised form 20 June 2017; Accepted 26 June 2017 Available online xxx 0143-8166/© 2017 Elsevier Ltd. All rights reserved. Please cite this article as: F.A.A. da Silva et al., Optics and Lasers in Engineering (2017), http://dx.doi.org/10.1016/j.optlaseng.2017.06.021