Spectropolarimetry of single plasmonic nanostructures

A novel dark-field Mueller-matrix spectroscopic system facilitates the recording of complete polarization information from a single isolated plasmonic nanorod.
21 September 2016, SPIE Newsroom. DOI: 10.1117/2.1201608.006598

The optimization of plasmonic systems—i.e., those based on ‘plasmons,’ the quanta of plasma oscillations—could enable their use in a range of applications (e.g., biomedical and chemical sensing, imaging, and the development of polarization-based plasmonic metadevices). Information about the polarization properties of scattered light from plasmonic metal nanoparticles and nanostructures is key to achieving this.

The acquisition and subsequent analysis of complete polarization information from plasmonic nanostructures represents a crucial step toward the fundamental understanding of a number of recently observed intricate spin-optical effects,1 and the optimization of experimental parameters for many practical applications.2 Such studies are, however, confounded by the experimental difficulties inherent in recording the full polarization response from plasmonic nanostructures, and by the complexities of the polarization signals that are obtained from such systems. The scattering signal from plasmonic structures (which is relatively weak) is generally swamped by a large amount of unscattered background light. As a result of this, polarimetric measurements on plasmonic nanostructures must be made in a high numerical-aperture (NA) setting.

To address some of the outstanding challenges in plasmon polarimetry, we have developed a novel spectroscopic system based on a Mueller matrix (i.e., a 4×4 matrix representing the transfer function of any optical system in its interaction with polarized light).2 Our system integrates an efficient Mueller-matrix measurement scheme with a dark-field microscopic-spectroscopy arrangement. This arrangement facilitates the detection of weak scattering signals from plasmonic nanostructures. The inherent complexities of measuring polarization in high NA settings (i.e., where one must account for the complex polarization transformation that occurs because of both the focusing and collection geometry of the microscope arrangement) are dealt with by using a robust eigenvalue calibration method, which works over a broad wavelength range.2, 3 The experimental system is also enhanced by our inverse analysis models, which extract and quantify the individual polarization properties of plasmonic samples. Using this approach, the experimental Mueller matrix (M) is decomposed into a product of a depolarizing and a non-depolarizing matrix.3, 4 The latter is then further analyzed to extract the useful polarimetry parameters (i.e., the diattenuation and retardance).

We demonstrated the feasibility and potential utility of our quantitative Mueller-matrix polarimetry on a simple plasmonic system made up of gold nanorods. A schematic of the experimental system (which employs broadband white-light excitation) and the associated calibration results are shown in Figure 1.2 We constructed the wavelength-dependent scattering Mueller matrices for this sample—M(λ)—by combining 16 spectrally resolved intensity measurements (i.e., the scattering spectra) for four different combinations of the optimized-elliptical polarization-state-generator (PSG) and polarization-state-analyzer (PSA) states. We used the eigenvalue calibration method to determine the exact experimental forms of the system’s PSG and PSA matrices (and their associated wavelength dependence), and subsequently used these values to determine the Mueller matrix of the callibrating achromatic quarter waveplate.2, 3 The illustrative Mueller matrices exhibit characteristic features of a pure linear retarder over the entire wavelength (λ) range: see Figure 1(c). We also found the values for linear retardance (δ) and linear diattenuation (d) of the quarter waveplate and linear polarizer (respectively) to be in close agreement (δ∼1.60rad and d∼0.98) with the ideal values (δ=1.57rad and d=1) for the entire range: see Figure 1(d). These (and other) calibration results validate the accuracy of our Mueller-matrix measurements.2

Figure 1. (a) A schematic of the novel dark-field Mueller-matrix spectroscopic-microscopy system. (b) Dark-field (DF) image of a single isolated gold nanorod. NP: Nanoparticle. (c) The spectral Mueller matrices (over λ=500- 700nm) of a calibrating achromatic quarter waveplate (QWP). The matrices exhibit a characteristic feature of a linear retarder (associated with symmetries in the off-diagonal elements of the lower 3×3block, highlighted in red). (d) The Mueller-matrix-derived linear retardance, δ(λ)(red dotted line), and linear diattenuation, d(λ)(blue solid line), of the achromatic QWP and a linear polarizer, respectively. NA: Numerical aperture. PSG: Polarization-state generator. PSA: Polarization-state analyzer.

We subsequently employed the system to record a spectroscopic-scattering Mueller matrix from a single isolated gold nanorod (with a diameter of 14±3nm and a length of 40±3nm): see Figure 2. The scattering spectra from the gold nanorod exhibits two distinct peaks, which correspond to the two electric dipolar plasmon resonances. One of the peaks occurs at λ∼525nm due to transverse resonance along the short axis, and the second occurs at λ∼650nm due to longitudinal resonance along the long axis.

Figure 2. (a) The wavelength dependence of the decomposition-derived, non-depolarizing (diattenuation retarder) Mueller matrix, obtained from a single gold nanorod. (b) The decomposition-derived wavelength variation of the linear retardance—δ(λ), red dotted line—and linear diattenuation—d(λ), blue solid line—parameters of the gold nanorod.

The corresponding scattering Mueller matrices encode several interesting and potentially useful pieces of information. Despite considerable depolarization effects, which occur due to the high-NA imaging geometry, the decomposed non-depolarizing component (i.e., the diattenuating retarder matrix) shown in Figure 2(a) can be interpreted to extract the spectral diattenuation and retardance—d(λ) and δ(λ), respectively—of the plasmonic sample. We interpret these effects via the relative amplitudes and phases of the two orthogonal dipolar plasmon polarizations of the gold nanorod. The d(λ) parameter is a measure of the relative amplitudes of the transverse and longitudinal dipolar polarizabilities, and therefore peaks at wavelengths that correspond to their resonances (525 and 650nm for transverse and longitudinal, respectively). The δ(λ) parameter, on the other hand, quantifies the phase difference between the two orthogonal polarizabilities, and thus reaches its maximum value in the spectral overlap region of the two resonances (∼575nm): see Figure 2(b). The d(λ) and δ(λ) parameters therefore capture and quantify unique information on the relative strengths and phases (respectively) of the two dipolar plasmon polarizabilities of the gold nanorod. We can use this polarization information to probe, manipulate, and tune the interference of neighboring resonant modes (i.e., orthogonal dipolar modes in plasmonic nanorods), and the resulting spectral line shape of the plasmonic system, via polarization control.2

In summary, we have developed a novel experimental system for recording full 4×4 spectroscopic-scattering Mueller matrices from single isolated plasmonic nanoparticles or nanostructures. Inverse Mueller-matrix analysis on a single plasmonic gold nanorod yields intriguing spectral diattenuation and retardance effects that encode potentially valuable information about the relative strengths and phases of the resonant modes in plasmonic structures. These polarization parameters therefore hold considerable promise as novel experimental metrics for the analysis of a number of interesting plasmonic effects. The parameters could, for example, be used to probe, manipulate, and tune the interference of neighboring modes in complex coupled plasmonic structures, or to study spin-orbit interaction and the spin Hall effect of light.1, 5 Results from such studies could be used to develop and optimize novel polarization-controlled plasmonic sensing schemes. We are currently expanding our investigations in these directions. Our next steps include the analysis, interpretation, and control of the plasmonic Fano resonance using Mueller-matrix-based polarization analysis. We are also employing polarization-based weak-measurement schemes to observe and amplify tiny spin-optical effects in plasmonic structures. It is our hope that these studies will aid in the development of novel polarization-controlled optical metadevices for diverse applications.

News source:http://spie.org/newsroom/6598-spectropolarimetry-of-single-plasmonic-nanostructures?highlight=x2400&ArticleID=x120092

Shubham Chandel, Subir Kumar Ray, Jalpa Soni, Satyabrata Raj, Nirmalya Ghosh

Indian Institute of Science Education and Research, Kolkata

Mohanpur, India

Shubham Chandel is currently pursuing his doctoral research in the Bio-Optics and Nano-Photonics Group, where his research focuses on the use of polarimetry. He obtained his MSc from the International School of Photonics, India.

Nirmalya Ghosh is a physicist with a specialization in optics and photonics. He is currently an associate professor in the Department of Physical Sciences, and heads the Bio-Optics and Nano-Photonics Group.


References:
1. K. Y. Bliokh, F. J. Rodríguez-Fortuño, F. Nori, A. V. Zayats, Spin-orbit interactions of light,Nat. Photon. 9, p. 796-808, 2015. doi:10.1038/nphoton.2015.201
2. S. Chandel, J. Soni, S. K. Ray, A. Das, A. Ghosh, S. Raj, N. Ghosh, Complete polarization characterization of single plasmonic nanoparticle enabled by a novel dark-field Mueller matrix spectroscopy system, Sci. Rep. 6, p. 26466, 2015.doi:10.1038/srep26466
3. J. Soni, H. Purwar, H. Lakhotia, S. Chandel, C. Banerjee, U. Kumar, N. Ghosh, Quantitative fluorescence and elastic scattering tissue polarimetry using an Eigenvalue calibrated spectroscopic Mueller matrix system, Opt. Express 21, p. 15475-15489, 2013.doi:10.1364/OE.21.015475
4. S. Y. Lu, R. A. Chipman, Interpretation of Mueller matrices based on polar decomposition, J. Opt. Soc. Am. A 13, p. 1106-1113, 1996.
5. J. Soni, S. Ghosh, S. Mansha, A. Kumar, S. Dutta Gupta, A. Banerjee, N. Ghosh, Enhancing spin-orbit interaction of light by plasmonic nanostructures, Opt. Lett. 38, p. 1748-1750, 2013.



‘Sniffer plasmons’ could detect explosives

Physicists from the Moscow Institute of Physics and Technology (MIPT) have found that the two-dimensional form of carbon, known as graphene, might be the ideal material for manufacturing plasmonic devices capable of detecting explosive materials, toxic chemicals, and other organic compounds based on a single molecule, says an article published in Physical Review B.

 

Plasmons in constructing high-accuracy electronics and optics

 

Scientists have long been fascinated by the potential applications of a quasiparticle called the plasmon, a quantum of plasma oscillations. In the case of a solid body, plasmons are the oscillations of free electrons. Of special interest are the effects arising from the surface interactions of electromagnetic waves with plasmons—usually in the context of metals or semimetals, as they have a higher free electron density. Harnessing these effects could bring about a breakthrough in high-accuracy electronics and optics. One possibility opened up by plasmonic effects is the subwavelength light focusing, which increases the sensitivity of plasmonic devices to a point where they can distinguish a single molecule. Such measurements are beyond what any conventional (classical) optical devices can achieve. Unfortunately, plasmons in metals tend to lose energy quickly due to resistance, and for this reason they are not self-sustained, i.e. they need continuous excitation. Scientists are trying to tackle this issue by using composite materials with predefined microstructure, including graphene.

 

Graphene is an allotrope of carbon in the form of a two-dimensional crystal. It can be visualised as a one-atom-thick honeycomb lattice made of carbon atoms. Two MIPT graduates, Andre Geim and Konstantin Novoselov, were the first to isolate graphene, which won them a Nobel Prize in Physics. Graphene is a semiconductor with extremely high charge carrier mobility. Its electrical conductivity is also exceptionally high, which makes graphene-based transistors possible.

 

Theoretical physicists give the okay

 

Although, plasmonic devices have seemed an exciting prospect to pursue from the start, to take advantage of them, it was first necessary to find out whether the technology behind them was feasible. To do this, scientists had to find a numerical solution to the relevant quantum-mechanical equations. This was accomplished by a team of researchers at the Laboratory of Nanostructure Spectroscopy headed by Prof. Yurii Lozovik: they formulated and solved the necessary equation. Their research has led them to develop a quantum model that predicts plasmonic behaviour in graphene. As a result, the scientists described the operation of a surface-plasmon-emitting diode (SPED) and the nanoplasmonic counterpart of the laser—known as the spaser—whose construction involves a graphene layer.spaser_слайдер.png

Pic.: Design of the spaser with the graphene layer shown as a honeycomb lattice above the dielectric layer (blue). The spaser is optically pumped through the active (gain) medium shown in orange.

 

A spaser could be described as a device similar to a laser and operating on the same basic principle. However, to produce radiation, it relies on optical transitions in the gain medium, and the particles emitted are surface plasmons, as opposed to photons produced by a laser. An SPED is different from a spaser in that it is an incoherent source of surface plasmons. It also requires considerably lower pump power. Both devices would operate within the infrared region of the spectrum, which is useful for studying biological molecules.

 

‘The graphene spaser could be used to design compact spectral measurement devices capable of detecting even a single molecule of a substance, which is essential for many potential applications. Such sensors could detect organic molecules based on their characteristic vibrational transitions (‘fingerprints’), as the light emitted/absorbed falls into the medium infrared region, which is exactly where the graphene-based spaser operates,’ says Alexander Dorofeenko, one of the authors of the study.

Source news: https://mipt.ru/english/news/_sniffer_plasmons_could_detect_explosives?sphrase_id=143931




The Institute of Physics of Kazan Federal University opened a seminar on modern trends in materials science

In September 26 at the Institute of Physics of Kazan Federal University, a joint seminar was launched with researchers from Shahid Beheshti University of Tehran.

26 сентября в Институте физики КФУ начал свою работу совместный  семинар с исследователями из Университета им. Шахида Бехешти из Тегерана.

Основная цель форума – прямое общение между физиками Казанского университета и участниками семинара из Ирана и установление взаимовыгодного сотрудничества. Семинар начался с устных сессий; а во вторник, 27 сентября, запланировано посещение коллегами из Ирана лабораторий Института физики.

Тегеранский университет им. Шахида Бехешти  готовит студентов по различным отраслям – от гуманитарных до естественнонаучных – уже 57 лет. По данным различных рейтингов, он входит в 500 известных вузов мира. Его сотрудничество с российскими вузами ведет свою двухдесятилетнюю историю. А студенты из Ирана учатся в КФУ уже 2 года. Иранские ученые приехали лично познакомиться с коллегами из Казанского университета и надеются на дальнейшее сотрудничество.

 

Иранцы ,КФу, Институт физики, университет имени шахида бехешти

dr-hamidi

 

News source:http://kpfu.ru/news/irancy-247132.html




Thesis Defense

Congratulations to Ms Borumand for her master thesis defense!

 

ms-borumand-en




Thesis Defense

Congratulations to Mr Behjati for his master thesis defense!

1en-behjati

 




Thesis Defense

Congratulations to Ms Jafari for her master thesis defense!

 

jafari-en

 

 




Silicon brings more color to holograms

Silicon holograms harness the full visible spectrum to bring holographic projections one step closer.

We can’t yet send holographic videos to Obi-Wan Kenobi on our droid, but researchers at Agency for Science, Technology and Research (A*STAR), Singapore, have got us a little bit closer by creating holograms from an array of silicon structures that work throughout the visible spectrum.

Many recent advances in hologram technology use reflected light to form an image; however the hologram made by Dong Zhaogang and Joel Yang from the A*STAR Institute of Materials Research and Engineering uses transmitted light. This means the image is not muddled up with the light source.

The team demonstrated the hologram of three flat images at wavelengths ranging from blue (480 nanometers) to red (680 nanometers). The images appeared in planes 50 microns apart for red and higher spacings for shorter wavelengths.

“In principle, it can be tuned to any wavelength,” says Yang.

Holograms can record three-dimensional images, which mean they can store large amounts of information in increasingly thin layers.

Recently, holograms that are mere hundredths of the thickness of a human hair have been made from metal deposited onto materials such as silicon. The holograms are created by nanoscale patterns of metal that generate electromagnetic waves that travel at the metal-silicon interface; a field called plasmonics.

Silicon holograms are slightly thicker than the metal-based ones, but have the advantage of being broadband. Plasmonic holograms only operate in the red wavelengths because they undergo strong absorption at blue wavelengths.

A disadvantage of the silicon holograms is their poor efficiency at only three per cent; however Dong estimates this could easily be tripled.

“The losses can be lowered by optimizing the growth method to grow polycrystalline silicon instead of amorphous silicon,” he says.

The hologram is an array of tiny silicon skyscrapers, 370 nanometers tall with footprints 190 nanometers by 100 nanometers. Unlike a city grid, however, the tiny towers are not laid out in neat squares but at varying angles.

The hologram operates with circularly polarized light, and the information is encoded on to the light beam by the varied angles of the skyscrapers. These alter the phase of the transmitted light through the ‘Pancharatnam-Berry effect’.

“What’s interesting about this hologram is that it controls only the phase of the light by varying the orientation of the silicon nanostructures. The amplitude is the same everywhere; in principle you can get a lot of light transmitted,” says Yang.

The A*STAR researchers focused on nanofabrication and measurements and collaborated with Cheng-Wei Qiu from National University of Singapore, whose team specializes in hologram design.


Story Source:

The above post is reprinted from materials provided by The Agency for Science, Technology and Research (A*STAR).Note: Content may be edited for style and length.


Journal Reference:

  1. Kun Huang, Zhaogang Dong, Shengtao Mei, Lei Zhang, Yanjun Liu, Hong Liu, Haibin Zhu, Jinghua Teng, Boris Luk’yanchuk, Joel K.W. Yang, Cheng-Wei Qiu. Silicon multi-meta-holograms for the broadband visible light. Laser & Photonics Reviews, 2016; 10 (3): 500 DOI:10.1002/lpor.201500314

News source: The Agency for Science, Technology and Research (A*STAR). “Silicon brings more color to holograms.” ScienceDaily. ScienceDaily, 12 August 2016. <www.sciencedaily.com/releases/2016/08/160812190822.htm>.