Browsing by Author "Han, Molong"

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Computational Imaging at the Infrared Beamline of the Australian Synchrotron Using the Lucy–Richardson–Rosen Algorithm
(2023) Ng, Soon Hock; Anand, Vijayakumar; Han, Molong; Smith, Daniel; Maksimovic, Jovan; Katkus, Tomas; Klein, Annaleise; Bambery, Keith; Tobin, Mark J.; Vongsvivut, Jitraporn; Juodkazis, Saulius
The Fourier transform infrared microspectroscopy (FTIRm) system of the Australian Synchrotron has a unique optical configuration with a peculiar beam profile consisting of two parallel lines. The beam is tightly focused using a 36× Schwarzschild objective to a point on the sample and the sample is scanned pixel by pixel to record an image of a single plane using a single pixel mercury cadmium telluride detector. A computational stitching procedure is used to obtain a 2D image of the sample. However, if the imaging condition is not satisfied, then the recorded object’s information is distorted. Unlike commonly observed blurring, the case with a Schwarzschild objective is unique, with a donut like intensity distribution with three distinct lobes. Consequently, commonly used deblurring methods are not efficient for image reconstruction. In this study, we have applied a recently developed computational reconstruction method called the Lucy–Richardson–Rosen algorithm (LRRA) in the online FTIRm system for the first time. The method involves two steps: training step and imaging step. In the training step, the point spread function (PSF) library is recorded by temporal summation of intensity patterns obtained by scanning the pinhole in the x-y directions across the path of the beam using the single pixel detector along the z direction. In the imaging step, the process is repeated for a complicated object along only a single plane. This new technique is named coded aperture scanning holography. Different types of samples, such as two pinholes; a number 3 USAF object; a cross shaped object on a barium fluoride substrate; and a silk sample are used for the demonstration of both image recovery and 3D imaging applications.
Computational three-dimensional imaging with near infrared synchrotron beam using Fresnel zone apertures fabricated on barium fluoride windows using femtosecond laser ablation
(2023) Smith, Daniel; Han, Molong; Ng, Soon Hock; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Tobin, Mark J.; Vongsvivut, Jitraporn; Juodkazis, Saulius; Anand, Vijayakumar
Extending the Depth of Focus of Infrared Microscope Using a Binary Axicon Fabricated on Barium Fluoride
(2024) Han, Molong; Smith, Daniel; Kahro, Tauno; Stonytė, Dominyka; Kasikov, Aarne; Gailevičius, Darius; Tiwari, Vipin; Xavier, Agnes Pristy Ignatius; Gopinath, Shivasubramanian; Ng, Soon Hock; Rajeswary, Aravind Simon John Francis; Tamm, Aile; Kukli, Kaupo
Axial resolution is one of the most important characteristics of a microscope. In all microscopes, a high axial resolution is desired in order to discriminate information efficiently along the longitudinal direction. However, when studying thick samples that do not contain laterally overlapping information, a low axial resolution is desirable, as information from multiple planes can be recorded simultaneously from a single camera shot instead of plane-by-plane mechanical refocusing. In this study, we increased the focal depth of an infrared microscope non-invasively by introducing a binary axicon fabricated on a barium fluoride substrate close to the sample. Preliminary results of imaging the thick and sparse silk fibers showed an improved focal depth with a slight decrease in lateral resolution and an increase in background noise.
Extraordinary Computational Imaging Technologies with Ordinary Optical Modulators (Invited)
(2022) Anand, Vijayakumar; Ng, Soon Hock; Maksimovic, Jovan; Katkus, Tomas; Han, Molong; Linklater, Denver P.; Klein, Annaleise; Bambery, Keith R.; Tobin, Mark J.; Ivanova, Elena P.; Vongsvivut, Jitraporn; Juodkazis, Saulius
Computational imaging technology (CIT) has revolutionized the field of imaging. CITs based on two genres namely random and deterministic optical fields generated by common optical modulators with extraordinary imaging capabilities are discussed.
Imaging with Diffractive Axicons Rapidly Milled on Sapphire by Femtosecond Laser Ablation
(2023) Smith, Daniel; Ng, Soon Hock; Han, Molong; Katkus, Tomas; Anand, Vijayakumar; Juodkazis, Saulius
We show that single-pulse burst fabrication will produce a flatter and smoother profile of axicons milled on sapphire compared to pulse overlapped fabrication which results in a damaged and much rougher surface. The fabrication of large-area (sub-1 cm cross-section) micro-optical components in a short period of time (∼10 min) and with less processing steps is highly desirable and would be cost-effective. Our results were achieved with femtosecond laser fabrication technology which has revolutionized the field of advanced manufacturing. This study compares three configurations of axicons such as the conventional axicon, a photon sieve axicon (PSA) and a sparse PSA directly milled onto a sapphire substrate. Debris of redeposited amorphous sapphire were removed using isopropyl alcohol and potassium hydroxide. A spatially incoherent illumination was used to test the components for imaging applications. Non-linear reconstruction was used for cleaning noisy images generated by the axicons.
Improved Classification of Blurred Images with Deep-Learning Networks Using Lucy-Richardson-Rosen Algorithm
(Licensee MDPI, 2023) Jayavel, Amudhavel; Gopinath, Shivasubramanian; Angamuthu, Praveen Periyasamy; Arockiaraj, Francis Gracy; Bleahu, Andrei; Xavier, Agnes Pristy Ignatius; Smith, Daniel; Han, Molong; Slobozhan, Ivan; Ng, Soon Hock; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Sharma, Rajesh; Juodkazis, Saulius; Anand, Vijayakumar
Pattern recognition techniques form the heart of most, if not all, incoherent linear shift-invariant systems. When an object is recorded using a camera, the object information is sampled by the point spread function (PSF) of the system, replacing every object point with the PSF in the sensor. The PSF is a sharp Kronecker Delta-like function when the numerical aperture (NA) is large with no aberrations. When the NA is small, and the system has aberrations, the PSF appears blurred. In the case of aberrations, if the PSF is known, then the blurred object image can be deblurred by scanning the PSF over the recorded object intensity pattern and looking for pattern matching conditions through a mathematical process called correlation. Deep learning-based image classification for computer vision applications gained attention in recent years. The classification probability is highly dependent on the quality of images as even a minor blur can significantly alter the image classification results. In this study, a recently developed deblurring method, the Lucy-Richardson-Rosen algorithm (LR2A), was implemented to computationally refocus images recorded in the presence of spatio-spectral aberrations. The performance of LR2A was compared against the parent techniques: Lucy-Richardson algorithm and non-linear reconstruction. LR2A exhibited a superior deblurring capability even in extreme cases of spatio-spectral aberrations. Experimental results of deblurring a picture recorded using high-resolution smartphone cameras are presented. LR2A was implemented to significantly improve the performances of the widely used deep convolutional neural networks for image classification.
Mid-infrared Incoherent Three-Dimensional Imaging Using Lucy-Richardson-Rosen Algorithm
(Imaging and Applied Optics Congress 2022 (3D, AOA, COSI, ISA, pcAOP), 2022) Anand, Vijayakumar; Han, Molong; Maksimovic, Jovan; Hock Ng, Soon; Katkus, Tomas; Klein, Annaleise; Bambery, Keith R.; Tobin, Mark J.; Vongsvivut, Jitraporn; Juodkazis, Saulius
Two computational reconstruction methods namely the Lucy-Richardson algorithm and non-linear reconstruction have been combined to develop Lucy-Richardson-Rosen algorithm. This new algorithm has been used to convert a two-dimensional infrared spectral map into a three-dimensional image.
Si-Cr Nano-Alloys Fabricated by Direct Femtosecond Laser Writing
(2023) Maksimovic, Jovan; Mu, Haoran; Han, Molong; Smith, Daniel; Katkus, Tomas; Anand, Vijayakumar; Nishijima, Yoshiaki; Hock Ng, Soon; Juodkazis, Saulius
Ultra-short 230 fs laser pulses of 515 nm wavelength were tightly focused into 700 nm focal spots and utilised in opening ∼400 nm nano-holes in a Cr etch mask that was tens-of-nm thick. The ablation threshold was found to be 2.3 nJ/pulse, double that of plain silicon. Nano-holes irradiated with pulse energies below this threshold produced nano-disks, while higher energies produced nano-rings. Both these structures were not removed by either Cr or Si etch solutions. Subtle sub-1 nJ pulse energy control was harnessed to pattern large surface areas with controlled nano-alloying of Si and Cr. This work demonstrates vacuum-free large area patterning of nanolayers by alloying them at distinct locations with sub-diffraction resolution. Such metal masks with nano-hole opening can be used for formation of random patterns of nano-needles with sub-100 nm separation when applied to dry etching of Si.
Single Shot Lensless Interferenceless Phase Imaging of Biochemical Samples Using Synchrotron near Infrared Beam
(Licensee MDPI, 2022) Han, Molong; Smith, Daniel; Ng, Soon Hock; Katkus, Tomas; Rajeswary, Aravind Simon John Francis; Praveen, Periyasamy Angamuthu; Bambery, Keith R.; Tobin, Mark J.; Vongsvivut, Jitraporn; Juodkazis, Saulius; Anand, Vijayakumar
Phase imaging of biochemical samples has been demonstrated for the first time at the Infrared Microspectroscopy (IRM) beamline of the Australian Synchrotron using the usually discarded near-IR (NIR) region of the synchrotron-IR beam. The synchrotron-IR beam at the Australian Synchrotron IRM beamline has a unique fork shaped intensity distribution as a result of the gold coated extraction mirror shape, which includes a central slit for rejection of the intense X-ray beam. The resulting beam configuration makes any imaging task challenging. For intensity imaging, the fork shaped beam is usually tightly focused to a point on the sample plane followed by a pixel-by-pixel scanning approach to record the image. In this study, a pinhole was aligned with one of the lobes of the fork shaped beam and the Airy diffraction pattern was used to illuminate biochemical samples. The diffracted light from the samples was captured using a NIR sensitive lensless camera. A rapid phase-retrieval algorithm was applied to the recorded intensity distributions to reconstruct the phase information. The preliminary results are promising to develop multimodal imaging capabilities at the IRM beamline of the Australian Synchrotron.
Three-dimensional phase imaging with near infrared synchrotron beam using phase-retrieval algorithm
(2023) Han, Molong; Anand, Vijayakumar; Juodkazis, Saulius; Vongsvivut, Jitraporn; Tobin, Mark J.; Praveen, Periyasamy Angamuthu; Rajeswary, Aravind Simon John Francis; Katkus, Tomas A.; Ng, Soon Hock; Smith, Daniel
THz Filters Made by Laser Ablation of Stainless Steel and Kapton Film
(2022) Han, Molong; Smith, Daniel; Hock Ng, Soon; Vilagosh, Zoltan; Anand, Vijayakumar; Katkus, Tomas; Reklaitis, Ignas; Mu, Haoran; Ryu, Meguya; Morikawa, Junko; Vongsvivut, Jitraporn; Appadoo, Dominique; Juodkazis, Saulius
THz band-pass filters were fabricated by femtosecond-laser ablation of 25-μm-thick micro-foils of stainless steel and Kapton film, which were subsequently metal coated with a ∼70 nm film, closely matching the skin depth at the used THz spectral window. Their spectral performance was tested in transmission and reflection modes at the Australian Synchrotron’s THz beamline. A 25-μm-thick Kapton film performed as a Fabry–Pérot etalon with a free spectral range (FSR) of 119 cm−1, high finesse Fc≈17, and was tuneable over ∼10μm (at ∼5 THz band) with β=30∘ tilt. The structure of the THz beam focal region as extracted by the first mirror (slit) showed a complex dependence of polarisation, wavelength and position across the beam. This is important for polarisation-sensitive measurements (in both transmission and reflection) and requires normalisation at each orientation of linear polarisation.