Magnetoplasmonics Lab

Archives August 2022

News On Atomic Clock

Laser tweezers help stabilize atomic clock

A team of physicists in the US has reported that an atomic clock based on laser tweezers offers some “unique possibilities” for a future generation of super-precise timepieces.

Demonstrated at JILA (formerly the Joint Institute for Laboratory Astrophysics) at the University of Colorado in Boulder, the new design uses a grid-like array of laser light to trap and control an individual strontium atom in each beam.

The approach, described by Adam Kaufman and colleagues in the latest issue of the journal Science appears to offer a combination of near-continuous operation with both strong signals and high stability – a set of features not previously found together.

doi: 10.1126/science.aat4586

Isolated atoms
Part of the reason for the good stability is the isolation of individual atoms made possible by the laser tweezers, which makes them less likely to interfere with each other. That, along with good uptime, is a property it shares with state-of-the-art clocks that are based on a single ion – but the tweezer clock manages to combine these features with the strong signals and stability of a multi-atom lattice clock.

“The tweezer design’s long-term promise as a competitive clock is rooted in its unique balancing of these capabilities,” Kaufman said in a JILA release.

Next-generation optical atomic clocks are able to stabilize a laser frequency to atoms “ticking” between two energy levels, with their extraordinary precision equivalent to gaining or losing less than one second over the known age of the universe.

The tweezer clock looks to improve performance even more. By trapping and controlling atoms individually, to maintain ticking stability, they can reuse the same atoms several times without needing a constant supply of new ones.

“Using our technique, we can hold onto atoms and reuse them for as long as 16 seconds,” Kaufman added. “[This] improves the duty cycle – the fraction of time spent using the atoms’ ticking to correct the laser frequency – and precision. The tweezer clock can also get a single atom very rapidly into a trap site, which means there is less interference and you get a more stable signal for a longer time.”

Redefining the second
Ultimately, the JILA team and others working on similar technology at physical standards laboratories around the world are preparing for a future redefinition of the second, which since 1967 has been based on a microwave transition within a cesium atom.

In the new JILA tweezer clock, an infrared laser is aimed into a microscope and focused to a small spot. Radio waves at ten different frequencies are applied sequentially to a special deflector that creates ten spots of light to trap individual atoms. The traps are refilled every few seconds from a pre-chilled cloud of atoms overlapped with the tweezer light.

The strontium atoms held by the tweezers are then excited by another laser, which is stabilized by a silicon crystal cavity. Described by the team as “clock laser” light, this was provided by co-author Jun Ye’s JILA laboratory.

However, if there are too many atoms in the system, collisions between them can destabilize the clock. To get rid of extra atoms, a pulse of light is applied to create weakly bound molecules, which then break apart and escape the trap.

According to JILA, this means that tweezer sites are left with either a single atom or empty, meaning that during an experimental “run”, each tweezer has about a 50/50 chance of being empty or containing a single atom. “Having at most one atom per site keeps the ticking stable for longer time periods,” explains the team.

They are now planning to build a larger clock featuring about 150 atoms, and to evaluate the performance formally. Kaufman also wants to add entanglement, which as well as improving clock sensitivity and performance, could provide a new platform for quantum computing and simulation.

Plasmonics-Based COVID-19 Test Delivers Results in POC Settings

In this days, the Journal of Nature Nanotechnology publishes a new paper entitled as “Multiplexed reverse-transcriptase quantitative polymerase chain reaction using plasmonic nanoparticles for point-of-care COVID-19 diagnosis”

Quantitative polymerase chain reaction (qPCR) offers the capabilities of real-time monitoring of amplified products, fast detection, and quantitation of infectious units, but poses technical hurdles for point-of-care miniaturization compared with end-point polymerase chain reaction. Here we demonstrate plasmonic thermocycling, in which rapid heating of the solution is achieved via infrared excitation of nanoparticles, successfully performing reverse-transcriptase qPCR (RT-qPCR) in a reaction vessel containing polymerase chain reaction chemistry, fluorescent probes and plasmonic nanoparticles. The method could rapidly detect SARS-CoV-2 RNA from human saliva and nasal specimens with 100% sensitivity and 100% specificity, as well as two distinct SARS-CoV-2 variants. The use of small optical components for both thermocycling and multiplexed fluorescence monitoring renders the instrument amenable to point-of-care use. Overall, this study demonstrates that plasmonic nanoparticles with compact optics can be used to achieve real-time and multiplexed RT-qPCR on clinical specimens, towards the goal of rapid and accurate molecular clinical diagnostics in decentralized settings.

Congratulations for our new paper in Journal of Superconductivity and novel magnetism

Congratulations for our new paper in Journal of Superconductivity and novel magnetism:

Longitudinal Magneto-optical Kerr effect in Insulator/ Metal/ Insulator Grating structure

N. S. Shnan1,2, S. Sadeghi1, M. Farzaneh1, S. M. Hamidi1*, V. I. Belotelov3,4,5, A. I. Chernov3,4

Herein, we have investigated theoretically and experimentally the longitudinal magneto-optical Kerr effect in a one-dimensional magneto-plasmonic grating structure combining Insulator/ Metal/ Insulator materials. One-dimensional grating substrate was covered by MgF2 that formed a first insulator layer, followed by gold, serving as a plasmonic middle metal layer, and finally cerium substituted iron garnet magneto-optical thin film covers all of them to reach Insulator/Metal/Insulator structure. The magneto-optical film is formed by the pulsed laser deposition method at high vacuum. The effect of a surface lattice resonance of a plasmonic layer onto the overall magneto-optical activity of the structure shows two well-pronounced peaks in magneto-optical spectra due to electric and magnetic dipole in this new magneto-plasmonic device.

News On Plasmonics

In this days, the Journal of Nano Letters published a new paper entitled as “Elevating Surface-Enhanced Infrared Absorption with Quantum Mechanical Effects of Plasmonic Nanocavities”

Plasmonic nanocavities, with the ability to localize and concentrate light into nanometer-scale dimensions, have been widely used for ultrasensitive spectroscopy, biosensing, and photodetection. However, as the nanocavity gap approaches the subnanometer length scale, plasmonic enhancement, together with plasmonic enhanced optical processes, turns to quenching because of quantum mechanical effects. Here, instead of quenching, we show that quantum mechanical effects of plasmonic nanocavities can elevate surface-enhanced infrared absorption (SEIRA) of molecular moieties. The plasmonic nanocavities, nanojunctions of gold and cadmium oxide nanoparticles, support prominent mid-infrared plasmonic resonances and enable SEIRA of an alkanethiol monolayer (CH3(CH2)n−1SH, n = 3–16). With a subnanometer cavity gap (n < 6), plasmonic resonances turn to blue shift and the SEIRA signal starts a pronounced increase, benefiting from the quantum tunneling effect across the plasmonic nanocavities. Our findings demonstrate the new possibility of optimizing the field enhancement and SEIRA sensitivity of mid-infrared plasmonic nanocavities.

Congratulations for our new Paper in Journal of Optics and Laser Technology

Coupled modes enhance random lasing in plasmonic double grating

S.F. Haddawi, N. Roostaei, S.M. Hamidi*

In this work, we experimentally and theoretically proved a flexible fine random laser from a two-face double grating plasmonic structure based on PDMS. Accordingly, PDMS was fabricated using the nanoimprint lithography method and coated by a thin gold layer with a thickness of 35 nm using a PVD device and light-emitting polymer (F8PT) to enhance the scattering and efficiency of the random laser. Using a plasmonic gold grating as a substrate, the simulation results compared the upside and downside of the plasmonic double grating structure. Moreover, an enhancement was observed in light transmission, and it is common to predict high efficiency in random lasing properties. The experimental results showed a comparison between normal plasmonic double grating samples and symmetric and asymmetric double grating -based nanostructures with thicknesses of 200, 400 and 600 and reported that random lasing properties had better results for samples with thinner spaces based on coupled mode effects. Correspondingly, this was done by increasing the intensity and decreasing the lasing threshold from 22 μJ in normal double grating to 16 in the thinnest double grating structure.

Congratulations for our new paper in Journal of Nanomeghyas

فیلتر خط اتمی کوک پذیر مبتنی بر جفت شدگی قوی اتم-پلاسمون

*محمد مصلح، مهناز اسدالله سلمانپور، ملیحه رنجبران و سیده مهری حمیدی

 آزمایشگاه مگنتوپلاسمونیک، پژوهشکده لیزر و پلاسما، دانشگاه شهید بهشتی، تهران

 گروه فیزیک، دانشکده علوم پایه، واحد تهران مرکزی، دانشگاه آزاد اسلامی، تهران

محدود کردن نور در ابعاد نانو در ساختارهای اتمی-پلاسمونی، می‌تواند کاربردهای بسیاری از جمله ساخت فیلترهای خط اتمی داشته باشد. در چنین سامانه‌های تشدیدی جفت‌شده‌ای، تشدید پهن پلاسمونی در مقابل تشدید باریک اتمی قرار می‌گیرد که منجر به شکل‌گیری یک فیلتر باریک در طیف بازتاب می‌گردد. در این مقاله با طراحی و ساخت سلول اتمی-پلاسمونی، طیف بازتاب از یک لایه نازک طلا که در مجاورت بخار روبیدیم در هندسه کرشمن قرار گرفته است، با استفاده از روش مدولاسیون فرکانسی اندازه‌گیری شد. با تنظیم زاویه نور فرودی، فرکانس تشدید مد پلاسمون-پلاریتون نسبت به فرکانس مرکزی خطوط جذب اتمی تغییر کرده و پدیده تبدیل تشدید فانو به شبه EIT و سپس، بازگشت به شکل خط فانو مشاهده شد. بنابراین، پدیده شبه EIT مشاهده شده به عنوان یک فیلتر خط اتمی کنترل پذیر با زاویه فرود نور معرفی شد.