Sharper and safer diagnostics with light-based 3D imaging

New research at Luleå University of Technology paves the way for faster, more precise, and non-invasive diagnostics by combining two advanced techniques that use laser light to generate detailed images of both structure and chemical content in a sample.

Imagine being able to see inside living tissue without surgery or harmful radiation, and at the same time determine exactly which substances are present. This is the aim of a new research method that combines two optical techniques: one that reveals the chemical composition of a sample, and one that provides a three-dimensional image of its structure.

“The goal is to produce 3D images that not only show the structure, but also identify specific chemical compounds within a sample,” says Ronja Eriksson, doctoral researcher in Experimental Mechanics at Luleå University of Technology.

The first technique is called stimulated Raman scattering (SRS). It involves directing two laser beams at a material, where the difference in their wavelengths makes it possible to select which molecule to visualize. The second technique, digital image correlation of laser speckles, enables detailed imaging of an object’s shape and internal structure by analyzing how the light is affected as it passes through or reflects off the material. By combining these two methods, the researchers aim to develop new ways of studying biological samples, among others, without damaging them.

“So far, we’ve investigated where in the sample the SRS signal is generated, using both experiments and simulations. We’ve also demonstrated that it's possible to control this location with a spatial light modulator,” explains Ronja Eriksson.

Ronja Eriksson, doctoral student in experimental mechanics at Luleå University of Technology.

Initially, the researchers intended to use interferometric imaging – a technique that combines light waves to measure extremely small variations in an object’s shape – together with SRS to create 3D images. However, this method proved highly sensitive to disturbances, which affected image quality. Separating the generated SRS signal from background laser noise also posed a challenge. As a result, the research team developed a new camera system based on speckle correlation. This technique compares light patterns captured by two cameras to create images with high contrast and precision. It allows detection of tiny variations in how light is refracted through a sample, revealing its internal structure. The method is part of a broader research field focused on developing next-generation optical tools for studying sensitive samples quickly, accurately, and without damage – with potential impact in healthcare, materials science, and environmental monitoring.

“Our results show that the method can achieve sensitivity comparable to digital holography, and that it may offer a more stable and flexible alternative,” Ronja Eriksson says.

One application of the technique is the study of bacterial cellulose. In an initial study, the researchers examined potential molecular differences in the chemical bonds of bacterial cellulose produced by bacteria that had used plastic as a carbon source. This type of cellulose has material properties that make it a promising alternative to plastic in, for example, packaging – while the bacteria simultaneously break down plastic and convert it into a biodegradable material.

“We’ve now studied the two techniques separately. The next step is to integrate SRS and speckle correlation into a single camera system,” concludes Ronja Eriksson, who recently presented her findings in the doctoral thesis Speckle Correlation and Stimulated Raman Scattering: towards Species-Specific 3D Imaging.

• Experimental mechanics