Holography is a technique that revolves around reconstructing the whole shape of a 3D object from a 2D image. In traditional holography, surfaces of the investigated objects reflect the laser light. However, when the object is transparent, like clear plastic and water, the light arriving at the detector only comes from the laser's reflection off cracked surfaces or particles. The size of such reflections is relatively small, making their detection impossible with conventional microscopes.
Researchers have created a novel approach to measure 3D (three-dimensional) maps of displacements combined with imaging and scattering processes. The technique is known as DSH (Dynamic Speckle Holography). It would help bring boom within Holography Market as it can identify displacements as tiny as 10 nanometers to several centimeters. Hence, demonstrating its superiority over traditional imaging techniques.
The researchers, in their experiments, aimed a laser at the cracking samples and recorded a video of the scattered light. The optical setup used by them was akin to photon correlation imaging. The results showed a butterfly-like pattern that was surprising as it moved with the cracked tip and moved deep into the material away from the crack.
Through experiments, the team realized that their observed signals were a generalized version of another phenomenon. This helped them develop a novel technique through two lasers and two cameras that can measure the full 3D deformation field of a sample. Through the method, researchers also increased their understanding of fracture propagation.
Further, the team added that illumination from laser light paints an entirely varied picture than regular light. This is due to the laser light's coherence and other minor properties producing bright twinkling spots. The team discovered that such twinkles could be merged with imaging to observe the minute strains and their propagation through research.
Researchers stated that their idea behind DSH essentially consists of a scattering vector (an amalgamation of incoming laser beam + camera/lens/diaphragm) that probes one projection of the displacement area. A whole 3D displacement field was built through a combination of various information obtained by multiple scattering vectors. This is why DSH is being referred to as a holographic technique. As in the ordinary holography approach sense, it doesn't reconstruct any 3D objects; this fails. However, it is indeed a holography approach as it reconstructs 3D displacement fields in a generalized sense.
The technique is impressive and provides a better understanding of fracture propagation. Further, it could also be used by other research teams to advance the investigation of fracture mechanisms within hard and porous materials.