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Identifying single photon emitters

Antibunching is a characteristic of light with sub-Poissonian statistics. Observation of antibunching (by means of photon coincidence correlation or second-order correlation) for instance reveals whether there is only a single photon emitter present in a sample. The technique is very often employed in the characterization of single quantum systems such as single molecules, quantum dots, carbon nanotubes, and defect centers in diamond nanocrystals, or in applications based on single photons sources. Antibunching experiments can also reveal the degree of multimerization
of fluorophores.

The antibunching dip of the correlation function is based on the fact that a single emitter can only emit one photon at a time. The process can easily be described using a simplified two-level energy diagram, where a molecule in an excited state requires a finite amount of time before it relaxes back to the ground state by emitting a photon. The temporal separation between adjacent photons is therefore determined mostly by the excited-state lifetime. This effect is known as antibunching and represents the sub-Poissonian nature of the emitted light.

Scheme of a typical set-up for antibunching measurementsExperiments probing for photon antibunching are usually performed in a Hanbury Brown-Twiss interferometer set-up, in which the emitted light is split with a 50/50 beam-splitter onto two single photon sensitive detectors. The detector outputs are then connected to a TCSPC (Time-Correlated Single Photon Counting) unit and the time difference between the two signals originating from two emitted photons is repeatedly measured and histogrammed with picosecond resolution. The “stop” channel is usually delayed by a certain amount of time in order to visualize also negative correlations. Antibunching experiments can essentially be performed with pulsed or continous-wave excitation. Using continous-wave excitation, the typical result of an antibunching experiment is a flat line with a notable “intensity dip” at a time difference of zero, because a single molecule can not emit two photons at the same time. With pulsed excitation, the result shows the individual laser pulses spaced by the pulse period with a reduced or missing pulse at the correlation time difference of zero. An alternative way to measure antibunching is to time tag the absolute arrival time of all detected photons and then use a dedicated correlation algorithm.

PicoQuant offers the following system that can be used for antibunching measurements

Time-resolved Confocal Fluorescence Microscope with Unique Single Molecule SensitivityMicroTime 200

Time-resolved Confocal Fluorescence Microscope with Unique Single Molecule Sensitivity

The MicroTime 200 time-resolved fluorescence microscope system is a powerful instrument capable of Fluorecence Corelation Spectroscopy and its daughter techniques as well as Fluorescence Lifetime Imaging (FLIM) with single molecule detection sensitivity. It contains the complete optics and electronics for recording virtually all aspects of the fluorescence dynamics of microscopic samples or femtoliter volumes. The instrument gains its exceptional sensitivity and flexibility in combination with unprecedented ease-of-use from a unique fusion of miniaturized and highly sophisticated state-of-the-art technologies. Although, these technologies enable to run an instrument of comparable complexity and power without having to spend more time on instrument maintenance than on original scientific content, the MicroTime200 remains an open platform that allows the advanced scientist to easily built upon the open character of the instrument in order to realize highly customized applications

Scheme of a typical set-up for antibunching measurementsThe following core components are needed to build a system capable of antibunching measurements, which are (partly) available from PicoQuant:

Nitrogen Vacancy (NV) Centers in Diamond

Nitrogen vacancy centers in diamond: FLIM image (left) and antibuching result (right)Luminescent single-nanometer-sized diamond-like carbon particles have received considerable attention in biophysics, material science, nano-medicine, and photonics. Partly this is related to their extraordinary material properties, such as chemical inertness, biocompatibility, and hardness, and also partly due to their exceptional photo stability. All of these applications desire the availability of sub-10 nm particles that show bright and stable photoluminescence. However, it was questionable if very small crystals in the range below 10 nm would still be photostable. To demostrate that a FLIM image was taken that proved the stability since no distortions in the individual crystals due to photobleaching could be seen. The anitbunching trace also shows that indeed there is only a single fluorescent emitter in the nanocrystal investigated.


  • MicroTime 200
  • Excitation: 532 nm
  • Emission: 600-800 nm
  • image size: 13 x 13 µm (512 x 512 pixels)
  • image: time per pixel: 4.00 ms, total image: 45 min
  • antibunching point measurement: 120 s

Sample courtesy of Fedor Jelezko and Jörg Wrachtrup, University of Stuttgart, Germany

Reference: Tisler J., et.al., Nano, Vol.03, p.1959-1965 (2009)

Antibunching of Atto 655

Antibunching result of a diluted solution of Atto 655 in water

This example shows antibunching measurements of a highly diluted solution of Atto 655 (0.1 nM) in water using pulsed laser excitation. The screenshot shows the results from the antibunching measurements using the standard data acquisition software of the PicoHarp 300. The reduced height of the signal peak around 95 ns due to antibunching can clearly be seen.


  • MicroTime 200
  • Excitation: LDH-P-C-635 at 20 MHz repetition rate
  • Detection: two PDM SPADs in a standard Hanbury Brown Twiss (HBT) setup, signal from one detector delayed by approx. 95 ns
  • Data acquisition: PicoHarp 300 TCSPC module

Latest 10 publications related to Antibunching

The following list is an extract of 10 recent publications from our bibliography that either bear reference or are releated to this application and our products in some way. Do you miss your publication? If yes, we will be happy to include it in our bibliography. Please send an e-mail to info@picoquant.com containing the appropriate citation. Thank you very much in advance for your kind co-operation.

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