Browsing by Author "Juodkazis, S"

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    Estimating dielectric parameters by reflecting evanescent waves at THz frequencies
    (Society of Photo-Optical Instrumentation Engineers (SPIE), 2021-04-20) Vilagosh, Z; Foroughimehr, N; Lajevardipour, A; Appadoo, D; Juodkazis, S; Wood, AW
    The THz/Far-IR Beamline at the Australian Synchrotron was used to demonstrate a novel method of estimating the dielectric properties of homogenous substances in the 1.0 THz to 4.0 THz region. Attenuated total reflection (ATR) coupled with synchrotron sources allow rapid evaluation of samples. The source is incoherent, thus normally only reflectance can be derived, as phase shift data cannot be obtained with this arrangement. A method is presented of deriving the full complex dielectric parameters by a modified frustrated internal reflection technique which reflects the evanescent wave using a gold plated mirror. Oil and alcohol samples were used in the study. With the mirror in situ, the reflectance changed from being enhanced at some frequencies to undergoing a frequency dependent destructive interference at other frequencies. The change in different samples was noted to vary according to the refractive index (but not the absorption coefficient) of the sample. © (2022) Society of Photo-Optical Instrumentation Engineers (SPIE)
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    Femtosecond laser fabrication of diffractive optics for spatial and spectral imaging at synchrotron infrared beamlines
    (Society of Photo-Optical Instrumentation Engineers (SPIE), 2021-03-06) Anand, V; Katkus, T; Ng, SH; Vongsvivut, JP; Maksimovic, J; Klein, AR; Bambery, KR; Lundgaard, S; Linklater, D; Ivanova, EP; Tobin, MJ; Juodkazis, S
    Infrared (IR) microspectroscopy is a powerful molecular fingerprinting tool widely used for the identification of structural and functional composition of biological and chemical samples. The IR microspectroscopy beamline at the Australian Synchrotron can be operated either with a single-point narrow-band mercury cadmium telluride (MCT) detector or a focal plane array (FPA) imaging detector with 64 × 64 pixels. For the implementation of indirect nonscanning imaging technology, the system was operated with the FPA detector. In this study, we propose an indirect IR imaging technique based on the principles of correlation optics using diffractive optical elements such as random pinhole array (RPA) and Fresnel zone plate (FZP). The spatial and spectral variations of point spread functions (PSFs) of the RPA and FZP were simulated for the synchrotron configuration. Intensity responses for 2D objects were simulated using the same simulation conditions and reconstructed using Lucy-Richardson algorithm. Fabrication of diffractive elements for IR wavelengths is often a challenging task as the IR transparent material substrates, such as barium fluoride and calcium fluoride, are highly susceptible to thermal shocks and brittle by nature. The diffractive elements were fabricated by ablating directly on a 100 nm thick gold coated substrate using femtosecond laser pulses. The simulation results and the fabrication outcomes demonstrate the feasibility of indirect imaging at the synchrotron IR beamline. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)
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    Orientation information added to IR hyperspectral imaging: silk and paracetamol
    (Society of Photo-Optical Instrumentation Engineers (SPIE), 2019-12-30) Ryu, M; Ng, SH; Vongsvivut, JP; Tobin, MJ; Morikawa, J; Juodkazis, S
    Malus (1809) and Beer-Lambert (1729) laws can be combined to separate birefringence and dichroism contributions in IR hyperspectral imaging. This is achieved by using two optically aligned polarisers for the highest transmittance. By rotation sample between the two aligned polarisers, spectra are taken at several angles for a better fit. This method is shown to resolve orientation of sub-diffraction patterns which are ~50 times smaller than the diffraction limit of 5:1 μm (at the wavelength 3.3 μm). Application potential for very different fields ranging from microscopy of bio- and pharmaceutical materials (silk and paracetamol) to satellite imaging of ocean waves with altimeter at K∝ band of 35.75 GHz or 8.39 cm wavelength will be discussed. © 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
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    Three-dimensional phase imaging with near infrared synchrotron beam using phase-retrieval algorithm
    (Society of Photo-Optical Instrumentation Engineers (SPIE), 2023-03-08) Han, M; Smith, D; Ng, SH; Katkus, TA; Simon, A; Rajeswary, JF; Praveen, PA; Tobin, MJ; Vongsvivut, JP; Juodkazis, S; Anand, V
    The near infrared (NIR) part of the infrared synchrotron beam is usually dumped to improve the signal to noise ratio of spectral imaging. In this study, this NIR synchrotron beam has been extracted and used for three-dimensional (3D) phase imaging. A pinhole was inserted in the path of the fork shaped NIR synchrotron beam and the Airy diffraction pattern was aligned with biochemical samples and the diffracted intensity distribution was captured using an image sensor sensitive to NIR. A phase retrieval algorithm was used to estimate the 3D phase distribution at the object plane from the recorded intensity distribution. © (2023) Society of Photo-Optical Instrumentation Engineers (SPIE)