How to Perform Antibunching Measurements
During Antibunching Measurements the afterglow effect of the SPADs may become visible as (un)expected additional peaks near the expected antibunching dip (see figure 2). These peaks might be useful to find the location of the dip, they are however artifacts caused by photons emitted (after the detection of a genuine photon) by one SPAD detected by the second SPAD. The distance of the expected dip and the afterglow peak is characteristic for the setup.
To get rid of the afterglow peak it has been proven useful to introduce 2 identical bandpasses directly in front of each SPAD and to use a 50:50 beamsplitter plate instead of a beamsplitter cube or to misalign the detectors slightly.1)
Antibunching using Symphotime
Changing from Normal Acquisition (T3-mode) to Antibunching (T2-mode)
Disconnect SPAD 1 Signal from Router (PHR800
Connect SPAD 1 to PicoHarp 300
Ch0 (Do not use the attenuator).
Adjustment of the CFD Level for Ch 0 (Sync Channel) might be necessary.
if Laser is attached via SEPIA II
driver, it's enough to disable the SYNC in the SEPIA software ⇒ no cable change necessary
Software Settings during Acquisition
Figure 1: Correlation of Antibunching Measurement. Sample Diamond_NV_centers
. Laser rep. rate 10 MHz
Figure 2: Correlation of Antibunching Measurement. Sample Diamond NV centers
. Laser repetition rate 40 MHz
. Note the peak near the expected dip at lag-time=0 due to SPAD afterglow. Compared with figure 1 the expected dip has not been shifted to the center of the x-axis and the emission bandpasses have not been placed directly in front of the detectors but in the emission filter wheel in front of the tube lens.
typically just point measurement in T2-mode
imaging in T3-mode
followed by point measurements in T2-mode
depending on preference set laser repetition rate in order to allow full fluorescence to fully decay or highest possible rate or cw-excitation. The advantage of the highest possible repetition rate (or even cw) is better resolvability of the dip, disadvantage is that fluorescence does not decay completely during the pulses. (Compare figure 1 (10MHz) rep. rate and figure 2 (40 MHz
) rep rate).
Analysis in SymPhoTime
select few multiples of the Laser Repetition Rate (e.g. for 10 MHz
select 700 ns – so you will see 7 peaks)
is the step width of the lag-time axis in units of the PicoHarp 300
e.g. for 32 ps Resolution Setting, selecting a Delta = 128 will result in approx. 4 ns steps for the x-Axis of the correlation.
Start with lag-time/200/T2-resolution (e.g. 700ns/200/32ps ~=110; this means your x-scale will have 198 points, resolution will be 3.52 ns).
Higher Delta values will speed up the calculation but result in a coarser correlation curve.
The symmetric correlation, which is shown automatically will only show a small “dip” as it is the average of AxB AND BxA in the case of figure 1 AxB will have its dip at 350 ns and BxA will have its dip at -350 ns. Therefore only one of both correlation (here AxB) should be displayed.
Some MT200 based literature about Antibunching
Yuan C. T., Yu P., Ko H. C., Huang J., Tang J.: Antibunching single-photon emission and blinking suppression of CdSe/ZnS quantum dots. In: ACS Nano. Vol. 03, p.3051-3056 (2009).
Koberling F., Kraemer B., Buschmann V., Rüttinger S., Kapusta P., Patting M., Wahl M., Erdmann R: Recent advances in photon coincidence measurements for photon antibunching and full correlation analysis. In: Proceedings of SPIE. Vol.7185, 71850Q (2009).
Fore S., Laurence T.A., Hollars C. W., Huser T.: Counting constituents in molecular complexes by fluorescence photon antibunching IEEE Journal of Selected Topics. In: Quantum Electronics. Vol.13, p.0996-1005 (2007)
Nettels D., Gopich I. V., Hoffmann A., Schuler B: Ultrafast dynamics of protein collapse from single-molecule photon statistics. In: Proceedings of the National Academy of Sciences of USA. Vol.104, p.02655-02660 (2007)
Ta H., Kiel A., Wahl M., Herten D.-P.: Experimental approach to extend the range for counting fluorescent molecules based on photon-antibunching Physical Chemistry Chemical Physics, Vol.12, p.10295-10300 (2010)