Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Overcoming noise with light work

29.09.2014

Researchers overcome noise problems in ultrasensitive measurements of tiny amounts of compounds

As the sensitivity of plasmonic sensors reaches new heights, so does the challenge of using tiny sample volumes. Dmitry Kalashnikov and co-workers at the A*STAR Data Storage Institute in Singapore have devised an innovative way to improve sensor accuracy by exploiting the unique properties of quantum optics.


Dark-field microscopy (top) and scanning electron microscopy (bottom) images showing an array of plasmonic nanoparticles used as a highly sensitive sensor.

Copyright : Reproduced from Ref. 1 and licensed under CC BY 3.0 ©2014 Kalashnikov et al.

Some new sensors based on plasmonic nanostructures can detect responses from samples that contain only about 100,000 molecules. While increased sensitivity is a boon, the low volumes of the sample mean that the light used to probe such tiny amounts can induce unwanted changes in them.

Therefore, it is necessary to probe samples using very low light levels — even down to the ultimate limit of single photons. However, conventional techniques cannot cope with such small amounts of light: the signal strength from a sample becomes low compared with the background noise, rendering accurate detection impossible.

To address this problem, Kalashnikov and his team created a pair of ‘frequency-entangled’ photons by passing laser light through a nonlinear crystal. The frequencies of these two photons add up to that of the photon that initially hit the crystal. Thus, by measuring the frequency of one photon, the researchers could easily calculate the frequency of the other one.

To set up the measurement system, the researchers sent one of the photons to a plasmonic sensor — a hexagonal array of gold nanoparticles — and detected it with a highly sensitive light detector (see image), while using a spectrometer to measure the frequency of the other photon. By measuring the number of photon pairs that are simultaneously spotted by the two light detectors, they could determine the dependence of the transmittance of the sensor on the frequency.

To investigate the robustness of the measurements to background noise, the researchers then artificially introduced noise to the measurement of the photon that passed through the spectrometer. With this, they found that their technique could detect a tiny change in the refractive index (approximately 1 per cent) of a liquid sample placed immediately in front of the plasmonic sensor — even in the presence of severe noise up to 70 times stronger than the signal. When they performed the same measurement using conventional spectroscopy, they found that the noise completely swamped the signal.

“The trick is that both photons reach the detectors at the same moment, whereas noise is completely random, making it highly unlikely to cause both detectors to fire simultaneously,” Dmitry explains.

The extremely low photon levels of the technique make it suitable for measuring photosensitive compounds and ultralow concentrations of other substances.


Reference:
Kalashnikov, D. A., Pan, Z. Kuznetsov, A. I. & Krivitsky, L. A. Quantum spectroscopy of plasmonic nanostructures. Physical Review X 4, 011049 (2014). | article

Associated links

A*STAR Research | Research SEA News
Further information:
http://www.researchsea.com

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent

25.09.2017 | Power and Electrical Engineering

Usher syndrome: Gene therapy restores hearing and balance

25.09.2017 | Health and Medicine

An international team of physicists a coherent amplification effect in laser excited dielectrics

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>