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How holographic interferometry could influence the future

How holographic interferometry could influence the future

The last two images show the object’s vibration as seen in real time and as a hologram reconstruction. Credit: Karl A. Stetson

Holographic interferometry is the technique of measuring voltage, tension and vibrations with light. It is defined by the wavelength of light, finding defects in structural bonds. It takes full advantage of a hologram’s ability to reproduce the optical field reflected or emitted from an object.

Holographic interferometry takes advantage of two contingencies of a hologram. First, a hologram can record and coherently reconstruct disjointed fields, so they can interfere with the reconstructed field. Second, a hologram can reconstruct an object’s optical field. It can be recreated with such fidelity that it interferes with the object’s original field when moved from its original position.

In a review article published in Light: Advanced Manufacturing, Karl Stetson of Karl Stetson Associates narrated the discovery of holographic interferometry, discussed its development and specified some of its key applications. The article, “The Discovery of Holographic Interferometry, Its Development and Applications,” assessed the original experiments and what might happen in the future.

The author was inspired by Sean Johnston’s “Holographic Visions: A History of New Science” but felt a deep sense of discontent. So he worked on rethinking the approach to many of the experiments described in the book. It allowed him to evaluate everything with fresh eyes and test the theories.

How holographic interferometry could influence the future

Inadvertently, the laser fired a double pulse, the first of which occurred before the bullet was in line of sight. Credit: Karl A. Stetson

An example was the fringes of interference at the edges of specific holographic reconstructions. The author explained how his team worked together to change their methodology, compared to many decades before. They found it essential to properly estimate how these fringes came about. Through their experiments, the team found that it was very useful in measuring real-time vibrations on reflective surfaces.

Measuring real-time vibrations on reflective surfaces is vital for many industries. While the team first used cans and other simple shapes, they struggled to find a sector that could take full advantage of holographic interferometry. However, the aviation industry got on board very quickly, with the support of acoustics professors.

Holographic testing required a significant initial investment, making the products significantly more expensive. Airlines would invest in this because any failure would be greater than the original cost. Jet engines vibrate a lot and fatigue at high cycles is a major cause of blade failure. They are designed to have resonances that are not generated at the rotational speeds of operation. Holography provided a way to visualize the mode shapes and confirm mathematical analysis.

How holographic interferometry could influence the future

Credit: Karl A. Stetson

The high efficiency of a jet engine depends on the narrow gap between the blade tips and the engine housing. An abradable material is adhered to the motor housings. If the rotating blades come into contact with the housing due to deformation, they will only scrape away some material and not break off. If there are areas where the seal is not properly bonded to the housing, they can be knocked out by the scraper blades and result in poor engine efficiency. Ultrasound shows decomposed areas as dark spots during holographic testing of a housing segment.

The move to digital holographic interferometry was inevitable, given the technological developments of the past thirty years. There is no doubt that there will be further developments in this area in the future, but the author is not sure where this will take us.

Linear Polarization Holography

More information:
Karl A. Stetson, The discovery of holographic interferometry, its development and applications, Light: Advanced Manufacturing (2022). DOI: 10.37188/lam.2022.002

Provided by the Chinese Academy of Sciences

Quote: How Holographic Interferometry Could Affect the Future (June 2022, June 17) retrieved June 17, 2022 from https://phys.org/news/2022-06-holographic-interferometry-future.html

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