by Researchers from the University of Warsaw’s Faculty of Physics, in collaboration with colleagues from Stanford University and Oklahoma State University, have developed a quantum-inspired phase-imaging method that can reveal hidden images in noise. This novel imaging technique is robust to phase noise and can operate even with extremely dim illumination. The method holds great potential for applications in areas such as infrared and X-ray interferometric imaging, as well as quantum and matter-wave interferometry. The findings of the research study have been published in Science Advances.
When capturing images, whether with a smartphone or an advanced microscope, the intensity (brightness) of light is measured pixel by pixel. However, light is not only characterized by its intensity, but also by its phase. By being able to measure the phase delay of light introduced by transparent objects, it is possible to make them visible.
Phase contrast microscopy, which was recognized with a Nobel Prize in 1953, revolutionized biomedical imaging by enabling the acquisition of high-resolution images of various transparent and optically thin samples. This discovery led to the development of modern imaging techniques such as digital holography and quantitative phase imaging.
Dr. Radek Lapkiewicz, head of the Quantum Imaging Laboratory at the University of Warsaw’s Faculty of Physics, explains that phase contrast microscopy allows for label-free and quantitative characterization of living specimens, such as cell cultures, and can have applications in neurobiology and cancer research.
However, there is still room for improvement. Interferometry, a commonly used measurement method for precise thickness measurements, only works when the system is stable and not subject to any disturbances. Conducting interferometry tests under dynamic conditions, such as in a moving car or on a shaking table, presents significant challenges.
To address this issue, researchers from the University of Warsaw’s Faculty of Physics, along with colleagues from Stanford University and Oklahoma State University, developed a new method of phase imaging that is immune to phase instability. The idea for this new technique came from the classic experiments of Leonard Mandel and his group in the 1960s, where they demonstrated that even when interference is not detectable in intensity, correlations can reveal its presence.
Inspired by these experiments, the researchers investigated how intensity correlation measurements could be utilized for phase imaging. They found that such measurements contain additional information that cannot be obtained through a single photo based on intensity measurement. By analyzing multiple independent photos of an object, the hidden information in the correlations can be recovered, allowing for the acquisition of perfect interferograms.
In their experiment, the researchers superposed light passing through a phase object with a reference light. A random phase delay was introduced between the object and reference light beams, simulating a disturbance that obstructs standard phase imaging methods. When intensity was measured, no interference was observed, and therefore, no information about the phase object could be obtained. However, the spatially dependent intensity-intensity correlation displayed a fringe pattern containing complete information about the phase object. This correlation was unaffected by any temporal phase noise and could be measured over an arbitrarily long period of time.
To obtain useful information about the object, the researchers recorded a series of frames using a camera and multiplied the measurement values at each pair of points from every frame. By averaging these correlations, they were able to reconstruct a full image of the object.
Stanisław Kurdziałek, the second author of the paper, explains that there are multiple ways to recover the phase profile of an observed object from a sequence of images. However, their method based on intensity-intensity correlation and off-axis holography provides optimal reconstruction precision. This phase imaging approach can be used in highly noisy environments as it works with both classical and quantum light. It can also be implemented in the photon counting regime, such as with single photon avalanche diodes. This technique is particularly useful when there is limited light available or when high light intensity could potentially damage delicate biological samples or works of art.
Dr. Radek Lapkiewicz concludes by stating that this new technique will expand the prospects of phase measurements, including emerging applications in areas such as infrared and X-ray imaging, as well as quantum and matter-wave interferometry. The robustness to phase noise and the ability to operate under low-light conditions make this method highly promising for various fields of research and industry.
