Advanced Photon Counting: Applications, Methods, Instrumentation

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Ruedas-Rama, Jose M. Stankowska, Raghu R. Krishnamoorthy, Karol Gryczynski, Badri P. Chizhik, Joerg Enderlein, Alexey I. Du kanske gillar. Lifespan David Sinclair Inbunden. Here are some benchmarks:. At present, commercial instrumentation is available for both time domain and frequency domain luminescence decay measurements.

Applications, Methods, Instrumentation

Although they have different operating principles, both kinds of instruments have similar performance quality criteria for light excitation sources and light detection. Following excitation, luminescence intensity is recorded as a function of time. All of the methods in the benchmark list except for streak cameras normally employ PMT detectors. For the recording and averaging of analog signals, triggered waveform digitizers have essentially supplanted other approaches. Streak cameras offer excellent capabilities but at high prices.

Following the production of photoelectrons at a cathode, a streak camera then deflects the photoelections via a transverse electric field that increases in strength with time; the transversely deflected photoelectrons are amplified by microchannel plates before impacting on a phosphor. The use of CCD cameras allows for detection at a photon counting limit.

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Ultimate resolution would be obtained with light excitation widths of a few ps to sub-ps, requiring expensive laser systems. Sub-ps resolution has been reported with a photon counting streak camera. Laser based fluorescence upconversion detection has a time resolution limited by the laser pulses, potentially down to fs. The potential advantages of TCSPC include high sensitivity, the absence of analog noise, and instrumental response functions that can be as low as several tens of ps.

There are numerous discussions on the details of implementation, with applications. The excitation pulse populates the emitting state, causing luminescence photons to be emitted. Over many such recorded events, a histogram is built up corresponding to photon emission as a function of time. To prevent early photon emissions from having disproportionate weight, the number of detected photons per pulse i.

Since the s, integrated PC boards or standalone electronics have become available that carry out all of these functions. Formerly, such excitation rates were available only with expensive laser systems.

For lower pulse repetition rates, data acquisition times must be significantly longer to acquire decay histograms with satisfactory photon counting statistics. Under normal circumstances, neutral density filters may be needed to attenuate the detected signal.

Advanced Photon Counting, Applications, Methods, Instrumentation - Dimensions

Since there is no analog noise and photon counting statistics prevail, with sufficient time even very weak emission decays can be acquired with good precision but beware the possibility of accompanying weak background emission. With higher photon flux pulses and high pulse repetition rates, the sensitivity can be quite extraordinary. Phase fluorometers are not as well suited for the measurement of extremely weak luminescence. TCSPC is not well suited for the measurement of long lifetimes.

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For these situations, multiscalar electronics modules are available that carry out photon counting within selectable time interval bins that can be as short as 65 ns. In other words, good determination of shorter lifetimes requires higher frequencies. Note that, unlike TCSPC, long as well as short lifetimes the latter as limited by apparatus frequency response can conveniently be measured by the same apparatus.

For a single exponential decay, measurement at a single favorable frequency would suffice, at least in principle. What if the decay really was not single exponential? Fitting over a frequency range would enable fitting to a more realistic multiexponential model. The excitation light intensity can be modulated electro-optically Pockels cell. Lakowicz and collaborators have exploited the properties of cavity dumped 4 MHz 5 ps pulse trains to extend measurements to higher frequencies still, given that the Fourier transform has significant contributions to tens of GHz.

Monitoring of excitation light to GHz ranges can be done with a fast photodiode; a more sensitive detector, a PMT, generally will be required for emitted light. Unlike frequency domain measurements, TCSPC has the ability to produce precise data for weak, even extremely weak, emission. However, Mizuno et al.

The components described are common to time and frequency domain instruments. Similar figures of merit apply in the two cases. Beck improved performance by eliminating some dynodes, with higher voltage at the first stage and last stage to anode. Perhaps the ultimate set of improvements would be afforded by a combination of reducing the number of dynodes, increasing the gain of early and late stages, and precise imaging of the luminescence on the photocathode.

The impediment is the price. For perspective analog applications, total expected anode current should be assessed in order to decide whether it is cost effective to use an MCP-PMT; applications requiring excessive anode currents may not be desirable. Ultimate resolution would be obtained with light excitation widths of a few ps to sub-ps, requiring expensive laser systems.

Sub-ps resolution has been reported with a photon counting streak camera. Laser based fluorescence upconversion detection has a time resolution limited by the laser pulses, potentially down to fs. The potential advantages of TCSPC include high sensitivity, the absence of analog noise, and instrumental response functions that can be as low as several tens of ps.

There are numerous discussions on the details of implementation, with applications. The excitation pulse populates the emitting state, causing luminescence photons to be emitted. Over many such recorded events, a histogram is built up corresponding to photon emission as a function of time. To prevent early photon emissions from having disproportionate weight, the number of detected photons per pulse i.

Since the s, integrated PC boards or standalone electronics have become available that carry out all of these functions. Formerly, such excitation rates were available only with expensive laser systems.

Advanced Photon Counting

For lower pulse repetition rates, data acquisition times must be significantly longer to acquire decay histograms with satisfactory photon counting statistics. Under normal circumstances, neutral density filters may be needed to attenuate the detected signal. Since there is no analog noise and photon counting statistics prevail, with sufficient time even very weak emission decays can be acquired with good precision but beware the possibility of accompanying weak background emission.

With higher photon flux pulses and high pulse repetition rates, the sensitivity can be quite extraordinary. Phase fluorometers are not as well suited for the measurement of extremely weak luminescence. TCSPC is not well suited for the measurement of long lifetimes. For these situations, multiscalar electronics modules are available that carry out photon counting within selectable time interval bins that can be as short as 65 ns.

In other words, good determination of shorter lifetimes requires higher frequencies.

XCounter photon counting detector technology used in Nuclear inspection application

Note that, unlike TCSPC, long as well as short lifetimes the latter as limited by apparatus frequency response can conveniently be measured by the same apparatus. For a single exponential decay, measurement at a single favorable frequency would suffice, at least in principle.

What if the decay really was not single exponential?


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Fitting over a frequency range would enable fitting to a more realistic multiexponential model. The excitation light intensity can be modulated electro-optically Pockels cell. Lakowicz and collaborators have exploited the properties of cavity dumped 4 MHz 5 ps pulse trains to extend measurements to higher frequencies still, given that the Fourier transform has significant contributions to tens of GHz. Monitoring of excitation light to GHz ranges can be done with a fast photodiode; a more sensitive detector, a PMT, generally will be required for emitted light.

Unlike frequency domain measurements, TCSPC has the ability to produce precise data for weak, even extremely weak, emission. However, Mizuno et al. The components described are common to time and frequency domain instruments.

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