Evaluation of a novel compact shearography system with DOE configuration

• Published in: Optics and lasers in engineering Vol. 104; pp. 90 - 99
• Main Authors: da Silva, Fabio Aparecido Alves, Willemann, Daniel Pedro, Fantin, Analucia Vieira, Benedet, Mauro Eduardo, Gonçalves, Armando Albertazzi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2018
• Subjects: Defect detection; DOE; Non-destructive inspection; Shearography; Non-destructive inspection; Shearography; DOE; Defect detection
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2017.06.021

•A new shearography system with DOE configuration, to operate in unstable environments, is proposed.•DOE is positioned between the image sensor and the objective lens, and it is mounted on a flexible holder.•The phase shifting in the DOE configuration is insensitive to wavelength variations.•The proposed system uses a smaller number of optomechanical elements.•The proposed design resulted in an even more compact, simple, lightweight and rugged system. 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 environment, 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 configuration 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.