Time-Resolved Fluorescence Wiki

differential_count_rate

Anonymous (anonymous@undisclosed.example.com) — 2017-09-26T11:46:03+00:00

2017/09/24 05:34		current
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	Not really. In case of pulsed signals the average count rate is a misleading quantity. An average count rate value does not take into account when and how those photons are emitted and detected. Interpreting a 100 kcps intensity as a constant emission rate (Poisson mean rate, in math terms) is a misconception. The physics of the measurement is completely different. These photons are obviously not emitted evenly, one by one over the whole one second period. They arrive to the detector bunched, as flashes. These are short time intervals with huge photon density (rate), separated by long "dark", quiet periods.		Not really. In case of pulsed signals the average count rate is a misleading quantity. An average count rate value does not take into account when and how those photons are emitted and detected. Interpreting a 100 kcps intensity as a constant emission rate (Poisson mean rate, in math terms) is a misconception. The physics of the measurement is completely different. These photons are obviously not emitted evenly, one by one over the whole one second period. They arrive to the detector bunched, as flashes. These are short time intervals with huge photon density (rate), separated by long "dark", quiet periods.

-	Getting a final count at "1% of SYNC rate" is a result of **low sampling rate of a high rate signal**.	+	In yet another words, achieving a final count rate at "1% of SYNC rate" is a result of **sparse sampling with dead time**. The sampled signal features much higher photon density, but lasts only for a short time.

	In mathematical terms, "average count rate of 1..2% of SYNC rate" means the overall detection probability, integrated over the whole duration of a measurement. The concept of //differential count rate// is related to the //probability density function//. The detected signal in TCSPC has a very inhomogeneous time distribution.		In mathematical terms, "average count rate of 1..2% of SYNC rate" means the overall detection probability, integrated over the whole duration of a measurement. The concept of //differential count rate// is related to the //probability density function//. The detected signal in TCSPC has a very inhomogeneous time distribution.

	Note: for detectors that exhibit count rate dependent shifting of the IRF, extra care has to be taken when measuring the IRF and directly using it for decay analysis. ((Takuhiro Otosu, Kunihiko Ishii and Tahei Tahara, Note: Simple calibration of the counting-rate dependence of the timing shift of single photon avalanche diodes by photon interval analysis, Rev. Sci. Instrum. 84, 036105 (2013); [[http://dx.doi.org/10.1063/1.4794769]]))		Note: for detectors that exhibit count rate dependent shifting of the IRF, extra care has to be taken when measuring the IRF and directly using it for decay analysis. ((Takuhiro Otosu, Kunihiko Ishii and Tahei Tahara, Note: Simple calibration of the counting-rate dependence of the timing shift of single photon avalanche diodes by photon interval analysis, Rev. Sci. Instrum. 84, 036105 (2013); [[http://dx.doi.org/10.1063/1.4794769]]))

dead_time

Anonymous (anonymous@undisclosed.example.com) — 2015-06-03T15:04:41+00:00

2015/06/03 17:04		current
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	In TCSPC the term dead time refers to the time the TCSPC system needs armed again after detecting an event. During the dead time the TCSPC system is blind.		In TCSPC the term dead time refers to the time the TCSPC system needs armed again after detecting an event. During the dead time the TCSPC system is blind.

-	If for example two photons are detected with the dead time of the TCSPC device the second photon will be lost. This leads to the so called [[glossary:Pile Up Effect]].	+	If for example two photons are detected with the dead time of the TCSPC device the second photon will be lost. This leads to the so called [[glossary:Pile-up Effect]].

	Note that not only TCSPC devices but also photon counting devices exhibit dead times.		Note that not only TCSPC devices but also photon counting devices exhibit dead times.

hybrid_pmt

Anonymous (anonymous@undisclosed.example.com) — 2015-11-03T15:00:37+00:00

2015/11/03 15:59		current
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	"The hybrid photodetector's structure is similar yet different from a conventional PMT. Like PMTs, the HPD is a vacuum tube with a photocathode that detects light, an electron multiplier that multiplies electrons, and an output terminal that outputs an electrical signal. But unlike PMTs which use multiple dynodes as electron multipliers, the HPD uses a silicon avalanche diode (AD) instead"((continue reading on the [[http://www.hamamatsu.com/us/en/community/optical_sensors/tutorials/what_is_hpd/index.html\|Hamamatsu]] website.))		"The hybrid photodetector's structure is similar yet different from a conventional PMT. Like PMTs, the HPD is a vacuum tube with a photocathode that detects light, an electron multiplier that multiplies electrons, and an output terminal that outputs an electrical signal. But unlike PMTs which use multiple dynodes as electron multipliers, the HPD uses a silicon avalanche diode (AD) instead"((continue reading on the [[http://www.hamamatsu.com/us/en/community/optical_sensors/tutorials/what_is_hpd/index.html\|Hamamatsu]] website.))

-	PicoQuant integrates various Hybrid PMT tubes into a convenient assembly called [[https://www.picoquant.com/products/category/photon-counting-detectors/pma-hybrid-series-hybrid-photomultiplier-detector-assembly\|PMA Hybrid]].	+	PicoQuant integrates Hybrid PMT tubes into a convenient assembly called [[https://www.picoquant.com/products/category/photon-counting-detectors/pma-hybrid-series-hybrid-photomultiplier-detector-assembly\|PMA Hybrid]].

	The PMA Hybrid is a compact single photon sensitive detector based on a fast hybrid photomultiplier tube with peltier cooler to reduce the dark count rate. The detector includes a high voltage power supply and pre-amplifier with overload protection and emergency shut down procedure if the detector count rate reaches a critical limit.		The PMA Hybrid is a compact single photon sensitive detector based on a fast hybrid photomultiplier tube with peltier cooler to reduce the dark count rate. The detector includes a high voltage power supply and pre-amplifier with overload protection and emergency shut down procedure if the detector count rate reaches a critical limit.

mcp

Anonymous (anonymous@undisclosed.example.com) — 2015-11-03T13:27:59+00:00

2013/08/05 13:45		current
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	====== MCP ======		====== MCP ======

-	Microchannel Plate PMT (MCP)	+	Microchannel Plate [[PMT]] (MCP)

-	A microchannel plate PMT is a sensitive photon detector. It consists of an array of glass capillaries (10-25 μm inner diameter) that are coated on the inside with a electron-emissive material. The capillaries are biased at a high voltage. Like in the PMT, an electron that strikes the inside wall of one of the capillaries creates an avalanche of secondary electrons. This cascading effect creates a gain of 103 to 106 and produces a current pulse at the output. The timing jitter of MCPs is sufficiently small to perform time-resolved photon counting on a sub-nanosecond- scale, usually outperforming PMTs. Good but also expensive MCPs can achieve timing uncertainties as low as 20ps. Microchannel plates are also used as an intensifier for low-intensity light detection with array detectors.	+	A microchannel plate [[PMT]] is a sensitive photon detector. It consists of an array of glass capillaries (10-25 μm inner diameter) that are coated on the inside with a electron-emissive material. The capillaries are biased at a high voltage. Like in the PMT, an electron that strikes the inside wall of one of the capillaries creates an avalanche of secondary electrons. This cascading effect creates a gain of 103 to 106 and produces a current pulse at the output. The timing jitter of MCPs is sufficiently small to perform time-resolved photon counting on a sub-nanosecond- scale, usually outperforming PMTs. Good but also expensive MCPs can achieve timing uncertainties as low as 20ps. Microchannel plates are also used as an intensifier for low-intensity light detection with array detectors.

pile-up_effect

Anonymous (anonymous@undisclosed.example.com) — 2015-06-03T15:09:55+00:00

2015/06/03 17:09		current
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-	{{tag>pile-up TCSPC pile-up dead_time}}	+	{{tag> TCSPC pile-up dead_time}}
	~~TOC~~		~~TOC~~

spad

Anonymous (anonymous@undisclosed.example.com) — 2017-05-17T08:37:15+00:00

2013/08/06 16:53		current
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	SPAD means Single Photon counting Avalanche photo-Diode. It stands commonly for a complete module including an Avalanche Photodiode, working temporary above the breakdown voltage in reverse bias. One photon may trigger the avalanche process and generates a time-corresponding electrical pulse. The avalanche must be "quenched" in order to prevent destructive current flow. This is achieved by passive or active quenching circuits. Passive quenching requires basically just a resistor but is slow and causes longer deadtimes. Active quenching is standard for all modules used by PicoQuant.		SPAD means Single Photon counting Avalanche photo-Diode. It stands commonly for a complete module including an Avalanche Photodiode, working temporary above the breakdown voltage in reverse bias. One photon may trigger the avalanche process and generates a time-corresponding electrical pulse. The avalanche must be "quenched" in order to prevent destructive current flow. This is achieved by passive or active quenching circuits. Passive quenching requires basically just a resistor but is slow and causes longer deadtimes. Active quenching is standard for all modules used by PicoQuant.

-	/*
-	[[Howto:How to unmount a SPAD from the MT200]]
-	*/

t3-mode

Anonymous (anonymous@undisclosed.example.com) — 2015-02-10T16:27:57+00:00

2015/02/10 17:27		current
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	- the arrival time of the event pair on the overall experiment time scale (the time tag).		- the arrival time of the event pair on the overall experiment time scale (the time tag).

-	The latter was originally obtained from an independent asynchronous clock. This made it difficult to combine the start-stop timing with the time tag or to know the sync period the event belonged to. For the PicoHarp's T3 Mode a smarter approach was chosen:\\	+	The latter was originally obtained from an independent asynchronous clock. This made it difficult to combine the start-stop timing with the time tag or to know the sync period the event belonged to. For the *Harp's T3 Mode a smarter approach was chosen:\\
	The time tag is now obtained by simply counting sync pulses. From the T3 Mode event records it is therefore possible to precisely determine which sync period a photon event belongs to. Since the sync period is also known precisely, this furthermore allows to reconstruct the arrival time of the photon with respect to the overall experiment time.		The time tag is now obtained by simply counting sync pulses. From the T3 Mode event records it is therefore possible to precisely determine which sync period a photon event belongs to. Since the sync period is also known precisely, this furthermore allows to reconstruct the arrival time of the photon with respect to the overall experiment time.