Imperial College London

ProfessorPeterTörök

Faculty of Natural SciencesDepartment of Physics

Professor of Optical Physics
 
 
 
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Contact

 

+44 (0)20 7594 7753peter.torok Website

 
 
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Location

 

609Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

129 results found

Ghilardi M, Boys H, Torok P, Busfield JJC, Carpi Fet al., 2019, Smart Lenses with Electrically Tuneable Astigmatism, SCIENTIFIC REPORTS, Vol: 9, ISSN: 2045-2322

Journal article

Wu P-J, Masouleh MI, Paterson C, Dini D, Török P, Overby DR, Kabakova IVet al., 2019, Detection of proteoglycan loss from articular cartilage using Brillouin microscopy, with applications to osteoarthritis, Biomedical Optics Express, Vol: 10, Pages: 2457-2466, ISSN: 2156-7085

The degeneration of articular cartilage (AC) occurs in osteoarthritis (OA), which is a leading cause of pain and disability in middle-aged and older people. The early disease-related changes in cartilage extra-cellular matrix (ECM) start with depletion of proteoglycan (PG), leading to an increase in tissue hydration and permeability. These early compositional changes are small (<10%) and hence difficult to register with conventional non-invasive imaging technologies (magnetic resonance and ultrasound imaging). Here we apply Brillouin microscopy for detecting changes in the mechanical properties and composition of porcine AC. OA-like degradation is mimicked by enzymatic tissue digestion, and we compare Brillouin microscopy measurements against histological staining of PG depletion over varying digestion times and enzyme concentrations. The non-destructive nature of Brillouin imaging technology opens new avenues for creating minimally invasive arthroscopic devices for OA diagnostics and therapeutic monitoring.

Journal article

Torok P, Foreman MR, 2019, Precision and informational limits in inelastic optical spectroscopy, Scientific Reports, Vol: 9, Pages: 1-16, ISSN: 2045-2322

Using Fisher information and the Cramér-Rao lower bound, we analyse fundamental precision limits in the determination of spectral parameters in inelastic optical scattering. General analytic formulae are derived which account for the instrument response functions of the dispersive element and relay optics found in practical Raman and Brillouin spectrometers. Limiting cases of dispersion and diffraction limited spectrometers, corresponding to measurement of Lorentzian and Voigt lineshapes respectively, are discussed in detail allowing optimal configurations to be identified. Effects of defocus, spherical aberration, detector pixelation and a finite detector size are also considered.

Journal article

Wu P-J, Kabovka I, Ruberti J, Sherwood J, Dunlop IE, Paterson C, Torok P, Overby Det al., 2018, Water content, not stiffness, dominates Brillouin spectroscopy measurements in hydrated materials, Nature Methods, Vol: 15, Pages: 561-562, ISSN: 1548-7091

Journal article

Wiersma SH, Toeroek P, Visser TD, Varga Pet al., 2018, Comparison of different theories for focusing through a plane interface: reply, JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION, Vol: 35, Pages: 593-593, ISSN: 1084-7529

Journal article

Kabakova IV, Xiang Y, Paterson C, Torok Pet al., 2017, Fiber-integrated Brillouin microspectroscopy: towards Brillouin endoscopy, Journal of Innovative Optical Health Sciences, Vol: 10, ISSN: 1793-5458

Brillouin imaging (BI) for micromechanical characterization of tissues and biomaterials is a fast-developing field of research with a strong potential for medical diagnosis of disease-modified tissues and cells. Although the principles of BI imply its compatibility with in vivo and in situ measurements, the integration of BI with a flexible catheter, capable of reaching the region of interest within the body, is yet to be reported. Here, for the first time, we experimentally investigate integration of the Brillouin spectroscope with standard optical fiber components to achieve a Brillouin endoscope. The performance of single-fiber and dual-fiber endoscopes are demonstrated and analyzed. We show that a major challenge in construction of Brillouin endoscopes is the strong backward Brillouin scattering in the optical fiber and we present a dual-fiber geometry as a possible solution. Measurements of Brillouin spectra in test liquids (water, ethanol and glycerol) are demonstrated using the dual-fiber endoscope and its performance is analyzed numerically with the help of a beam propagation model.

Journal article

Karampatzakis A, Song CZ, Allsopp LP, Filloux A, Rice SA, Cohen Y, Wohland T, Török Pet al., 2017, Probing the internal micromechanical properties of Pseudomonas aeruginosa biofilms by Brillouin imaging., NPJ Biofilms Microbiomes, Vol: 3, ISSN: 2055-5008

Biofilms are organised aggregates of bacteria that adhere to each other or surfaces. The matrix of extracellular polymeric substances that holds the cells together provides the mechanical stability of the biofilm. In this study, we have applied Brillouin microscopy, a technique that is capable of measuring mechanical properties of specimens on a micrometre scale based on the shift in frequency of light incident upon a sample due to thermal fluctuations, to investigate the micromechanical properties of an active, live Pseudomonas aeruginosa biofilm. Using this non-contact and label-free technique, we have extracted information about the internal stiffness of biofilms under continuous flow. No correlation with colony size was found when comparing the averages of Brillouin shifts of two-dimensional cross-sections of randomly selected colonies. However, when focusing on single colonies, we observed two distinct spatial patterns: in smaller colonies, stiffness increased towards their interior, indicating a more compact structure of the centre of the colony, whereas, larger (over 45 μm) colonies were found to have less stiff interiors.

Journal article

Mack, Cortes, Giannini, Torok, Roschuk, Maier SAet al., 2017, Decoupling absorption and emission processes in super-resolution localisation of emitters in a plasmonic hotspot, Nature Communications, Vol: 8, ISSN: 2041-1723

The absorption process of an emitter close to a plasmonic antenna is enhanced due to strong local electromagnetic (EM) fields. The emission process, if resonant with the plasmonic system, re-radiates to the far-field by coupling with the antenna due to the availability of plasmonic states. This increases the local density of states (LDOS), effectively providing more, or alternate, pathways for emission. Through the mapping of localized emission events from single molecules close to plasmonic antennas – performed using far-field data – one gains combined information on both the local EM field strength and the LDOS available. The localization from these emission-coupled events generally do not, therefore, report the real position of the molecules, nor the EM enhancement distribution at the illuminating wavelength. Here we propose the use of a fluorescent molecule with a large Stokes shift in order to spectrally decouple the emission process of the dye from the plasmonic system, leaving only the absorption strongly in resonance with the enhanced EM field in the antenna’s vicinity. We demonstrate that this technique provides an effective way of exploring either the EM field or the LDOS with nanometre spatial resolution.

Journal article

Chen WT, Torok P, Foreman MR, Liao CY, Tsai W-Y, Wu PR, Tsai DPet al., 2016, Integrated plasmonic metasurfaces for spectropolarimetry, Nanotechnology, Vol: 27, ISSN: 1361-6528

Plasmonic metasurfaces enable simultaneous control of the phase, momentum, amplitude and polarization of light and hence promise great utility in realization of compact photonic devices. In this paper, we demonstrate a novel chip-scale device suitable for simultaneous polarization and spectral measurements through use of six integrated plasmonic metasurfaces (IPMs), which diffract light with a given polarization state and spectral component into well-defined spatial domains. Full calibration and characterization of our device is presented, whereby good spectral resolution and polarization accuracy over a wavelength range of 500–700 nm is shown. Functionality of our device in a Müller matrix modality is demonstrated through determination of the polarization properties of a commercially available variable waveplate. Our proposed IPM is robust, compact and can be fabricated with a single photolithography step, promising many applications in polarization imaging, quantum communication and quantitative sensing.

Journal article

Antonacci G, Pedrigi R, Krams R, Torok Pet al., 2016, Quantification of plaque stiffness by Brillouin microscopy (Conference Presentation), 3rd Conference on Optical Elastography and Tissue Biomechanics III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

Conference paper

Antonacci G, Pedrigi RM, Kondiboyina A, Mehta VV, de Silva R, Paterson C, Krams R, Toeroek Pet al., 2015, Quantification of plaque stiffness by Brillouin microscopy in experimental thin cap fibroatheroma, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 12, ISSN: 1742-5689

Journal article

Antonacci G, Lepert G, Paterson C, Toeroek Pet al., 2015, Elastic suppression in Brillouin imaging by destructive interference, APPLIED PHYSICS LETTERS, Vol: 107, ISSN: 0003-6951

Journal article

Macias-Romero C, Munro PRT, Toeroek P, 2014, Polarization-multiplexed encoding at nanometer scales, OPTICS EXPRESS, Vol: 22, Pages: 26240-26245, ISSN: 1094-4087

Journal article

Macias-Romero C, Foreman MR, Munro PRT, Toeroek Pet al., 2014, Confocal polarization imaging in high-numerical-aperture space, OPTICS LETTERS, Vol: 39, Pages: 2322-2325, ISSN: 0146-9592

Journal article

Mazumder N, Hu C-W, Qiu J, Foreman MR, Romero CM, Toeroek P, Kao F-Jet al., 2014, Revealing molecular structure and orientation with Stokes vector resolved second harmonic generation microscopy, METHODS, Vol: 66, Pages: 237-245, ISSN: 1046-2023

Journal article

Antonacci G, Foreman MR, Paterson C, Toeroek Pet al., 2013, Spectral broadening in Brillouin imaging, APPLIED PHYSICS LETTERS, Vol: 103, ISSN: 0003-6951

Journal article

Foreman MR, Giusca CL, Toeroek P, Leach RKet al., 2013, Phase-retrieved pupil function and coherent transfer function in confocal microscopy, JOURNAL OF MICROSCOPY, Vol: 251, Pages: 99-107, ISSN: 0022-2720

Journal article

Mazumder N, Qiu J, Foreman MR, Romero CM, Toeroek P, Kao F-Jet al., 2013, Stokes vector based polarization resolved second harmonic microscopy of starch granules, BIOMEDICAL OPTICS EXPRESS, Vol: 4, Pages: 538-547, ISSN: 2156-7085

Journal article

Foreman MR, Giusca CL, Coupland JM, Török P, Leach RKet al., 2013, Determination of the transfer function for optical surface topography measuring instruments—a review, Measurement Science and Technology, Vol: 24, Pages: 052001-052001, ISSN: 0957-0233

Journal article

Foreman MR, Sivan Y, Maier SA, Toeroek Pet al., 2012, Independence of plasmonic near-field enhancements to illumination beam profile, PHYSICAL REVIEW B, Vol: 86, ISSN: 2469-9950

Journal article

Mazumder N, Qiu J, Foreman MR, Romero CM, Hu C-W, Tsai H-R, ToeroeK P, Kao F-Jet al., 2012, Polarization-resolved second harmonic generation microscopy with a four-channel Stokes-polarimeter, OPTICS EXPRESS, Vol: 20, Pages: 14090-14099, ISSN: 1094-4087

Journal article

Foreman MR, Toeroek P, 2012, Fundamental limits in determining the orientation of single molecules An information theoretic approach, 9th IEEE International Symposium on Biomedical Imaging (ISBI) - From Nano to Macro, Publisher: IEEE, Pages: 916-918

Conference paper

Macias-Romero C, Toeroek P, 2012, Eigenvalue calibration methods for polarimetry, JOURNAL OF THE EUROPEAN OPTICAL SOCIETY-RAPID PUBLICATIONS, Vol: 7, ISSN: 1990-2573

Journal article

Macias-Romero C, Foreman MR, Toeroek P, 2011, Spatial and temporal variations in vector fields, OPTICS EXPRESS, Vol: 19, Pages: 25066-25076, ISSN: 1094-4087

Journal article

Foreman MR, Toeroek P, 2011, Fundamental limits in single-molecule orientation measurements, NEW JOURNAL OF PHYSICS, Vol: 13, ISSN: 1367-2630

Journal article

Macias-Romero C, Lim R, Foreman MR, Toeroek Pet al., 2011, Synthesis of structured partially spatially coherent beams, OPTICS LETTERS, Vol: 36, Pages: 1638-1640, ISSN: 0146-9592

Journal article

Foreman MR, Torok P, 2011, Spin-orbit coupling and conservation of angular momentum flux in non-paraxial imaging of forbidden radiation, New Journal of Physics, Vol: 13, Pages: 063041-063041

Rigorous, closed form expressions are derived for non-paraxial imaging of sources of multipole radiation from which conservation of angular momentum (AM) flux is established. Coupling of spin and orbital optical AM flux is also quantitatively investigated, highlighting the importance of spin–orbit interactions in high numerical aperture imaging.

Journal article

Foreman MR, Torok P, 2010, Information and resolution in electromagnetic optical systems, PHYS REV A, Vol: 82, Pages: 1-9, ISSN: 1050-2947

Quantitative analysis can play a vital role in a number of polarization-based optical systems, yet to date no definition regarding resolution in the polarization domain exists. By adopting a stochastic framework, a suitable metric is developed in this article, allowing a number of polarimetric systems to be assessed and compared. In so doing, the performance dependencies of polarization-based systems are demonstrated and fundamental trends are identified.

Journal article

Romero CAM, Van de Nes AS, Foreman MR, Munro P, Toeroek Pet al., 2010, Multiplexed optical data storage and vectorial ray tracing, 1st NanoCharM Workshop on Advanced Polarimetric Instrumentation (API), Publisher: E D P SCIENCES, ISSN: 2100-014X

Conference paper

Foreman MR, Torok P, 2010, Computational methods in vectorial imaging, Journal of Modern Optics, ISSN: 0950-0340

Journal article

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