Fresnel incoherent correlation holography with single camera shot
Imaging technologies that do not require special light sources such as laser are on-demand due to their broad spectrum of applicability ranging from self-luminous astronomical objects to objects reflecting natural light. Fresnel incoherent correlation holography (FINCH) is one such broad spectrum imaging technology which is also capable of breaking the diffraction limit and achieving super resolution. FINCH is built upon the self-interference phenomenon based on the fundamental property of light that every source point is coherent with respect to itself and therefore when mirrored can coherently interfere. In FINCH, light from an object is split into two, modulated differently from one another and interfered to generate a hologram of a scene. At least three such holograms are recorded with different phase-shifts between the two object waves and the holograms are projected into a complex hologram. The complex hologram is reconstructed into a three-dimensional image by numerically back propagating the hologram to different planes of the object. The time resolution of FINCH is only one-third of that of direct imaging, which is primarily due to the mode of reconstruction.
In this study, the authors have developed a game changing approach and redefined the principle of FINCH using the fundamental property of linear systems. For a single object point in the object space, FINCH generates a point spread hologram (PSH) resembling a Fresnel zone plate (FZP) in the sensor plane. For an object consisting of multiple points distributed in three-dimensional space, the object hologram is formed by the summation of shifted and scaled FZPs. The authors carried out a one-time calibration procedure which involves scanning a point object along the optical axis in the object space and recording the corresponding PSHs and have compiled them into a library. An object is placed within the axial boundaries of the PSH library and the object hologram is recorded. The three-dimensional image of the object is reconstructed by a non-linear adaptive cross-correlation between the object hologram and the PSH library and also using the well-known Lucy-Richardson algorithm. This novel approach opened new possibilities and increased the axial as well as the time-resolution of FINCH. The authors have demonstrated FINCH using a single passive multifunctional diffractive optical element consisting of randomly multiplexed diffractive lenses with different focal lengths for the first time. The multifunctional diffractive optical element has been fabricated using nanolithography and the technique has been successfully demonstrated in a highly compact optical configuration on resolution targets and biological samples.
Dr. Vijayakumar Anand from the research group of Prof. Saulius Juodkazis at Swinburne University of Technology has redefined a well-known incoherent imaging technique called as Fresnel incoherent correlation holography (FINCH) using the fundamental principles of linear systems. FINCH systems have a resolving power 1.5 times higher than that of equivalent lens based incoherent direct imagers and twice that of a coherent direct imager. For this reason, FINCH has been widely used to build super resolution fluorescence microscopes and also used as a resolution enhancer by coupling it with other super resolution techniques such as structured illumination. The super resolution in FINCH also demands many stringent requirements such as special optical configuration, active and passive optical elements such as spatial light modulator, polarizers and lenses and has lower axial and temporal resolutions. This cumbersome requirements and lower axial and temporal resolutions often prevent the wide applicability of FINCH. In this study, the researchers have redefined FINCH in a new light and have succeeded in transferring the enormous optical load consisting of active and passive optical components to nanofabrication and computational optics. Consequently, they were able to realize FINCH with a single diffractive optical element fabricated using nanofabrication. This approach has converted the bulky, expensive and heavy FINCH into a compact, low-cost and light weight version. Furthermore, the new approach has also improved the axial and temporal resolutions of FINCH. This new development will revolutionize the area of incoherent imaging and is expected to create a new generation of advanced FINCH scopes. FINCH is also expected to impact bio-medical imaging and laser-machining applications which are next application targets for the team. This study is published at Opto-Electronic Advances Vol. 8 2020, entitled “Fresnel incoherent correlation holography with single camera shot”.
Fig. 1 | (a) Ideal image synthesized from the direct imaging result. (b) Autocorrelation image of (a). Results of (c) cross-correlation between (a) and Fig. 5 (a), (d) cross-correlation between (a) and Fig. 5 (f), and (e) cross-correlation between (a) and Fig. 5 (c). (f) Plots of the horizontal line data along the origin for (b)–(e). The extracted line data is shown using white dotted line. SSIM index maps calculated by comparing the ideal image with (g) ideal image, (h) direct imaging, (i) FINCH by non-linear reconstruction and (j) FINCH by Lucy-Richardson algorithm.
Fig. 2 | Images of the PSHs recorded for Δz1 = (a) -3 cm, (b) -2.5 cm, (c) -2 cm, (d) -1.5 cm, (e) -1 cm, (f) -0.5 cm, (g) 0.5 cm, (h) 1 cm, (i) 1.5 cm, (j) 2 cm, (k) 2.5 cm, (l) 3 cm and (m) 0 cm. (n) Plot of the variation of IR (x=0, y=0) as a function of Δz1.
About The Group
Prof. Saulius Juodkazis is the Deputy Director of the Optical Sciences Center and Director of Nanotechnology facility of the Swinburne University of Technology. He has established world class state of the art nanofabrication and ultrafast laser fabrication facility – Nanolab - opened in 2011. He is Fellow of OSA and SPIE and ChangJiang scholar. Dr. Vijayakumar Anand (DVCR fellow) has established holography expertise and is developing new applications in bio-medical and laser machining fields. Other authors of this work include research engineer Drs. Tomas Katkus (Nanolab), Soon Hock Ng (industry project fellow), Denver P. Linklater (bio-medical researcher), Stefan Lundgaard (PhD candidate) and Prof. Elena P. Ivanova, who is a Distinguished Professor in the Royal Melbourne Institute of Technology who leads research in the key areas of Nanobiotechnology, Biomaterials, Antibacterial Surfaces, Biodevices and Bacterial Taxonomy.
Vijayakumar A, Katkus T, Lundgaard S, Linklater D P, Ivanova E P et al. Fresnel incoherent correlation holography with single camera shot. Opto-Electron Adv 3, 200004 (2020).