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Sources for TCSPC

The typical excitation sources for TCSPC experiments are listed below. [Pg.263]

The effective resolution of a TCSPC experiment is characterised by its instrument response function (IRF). The IRF contains the pulse shape of the light source used, the temporal dispersion in the optical system, the transit time spread in the detector, and the timing jitter in the recording electronics. With ultrashort laser pulses, the IRF width at half-maximum for TCSPC is typically 25 to 60 ps for microchannel-plate (MCP) PMTs [4, 211, 547], and 150 to 250 ps for conventional short-time PMTs. The IRF width of inexpensive standard PMTs is normally... [Pg.22]

Most endogenous fluorophores are excited efficiently only in the UV, in the range from 280 nm to 400 nm. Suitable light sources for steady-state excitation are mercury or xenon arc lamps. For time-resolved measurements, often nitrogen lasers and nitrogen-laser pumped dye lasers are used. These lasers work at pulse repetition rates of the order of 10 to 100 Hz. Any attempt to use TCSPC at a repetition rate this low is hopeless. Therefore, time-resolved detection is usually done... [Pg.121]

The radiant sensitivity of a detector - or its quantum efficiency - is one of the most important parameters for TCSPC application. Unfortunately absolute measurements of the radiant sensitivity or the quantum efficiency are extremely difficult. The problem is not only that a calibrated light source or a calibrated reference detector are required but also that extremely low light intensities have to be used. However, accurate attenuation of light by many orders of magnitude is difficult. [Pg.241]

Dynode PMTs cost less than MCP PMTs and are adequate for many TCSPC expmments, especially if the excitation source is a flasMamp. Two types of dynode PMTs are used for TCSPC, the side-window and linear-focused PMTs. Their performance is comparable, but there are minor differences. The side-window tubes are less expensive but can still provide good time resolution. Pulse widths from 112 to 700 ps have been obtained with side-window... [Pg.113]

The difficult in resolving (he two intensity decay components is illustrated by the intensity decay of tryptophan at pH 7 (Figure 17.4). The light source was a cavity-dumped rhodamine 6G dye laser, which was frequency-doubled to 29S nm and provided pulses about 7 ps wide. The detector was an MCP PMT detector. This confign-ration of high-speed components represents the state of the art for TCSPC measurements. The data were fit to the single- and double-exponential models,... [Pg.490]

Our objective was to probe fluorescence over a time domain as large as possible. To this end we combined two different detection techniques, FU and TCSPC, allowing us to perform measurements from 100 fs to hundreds of nanoseconds. Notably, we use the same laser excitation source the third harmonic of a titane sapphire laser (267 nm, 100 fs). This is important because the excited state population is created under identical conditions in the two types of experiments. The time-resolution obtained after deconvolution of the recorded signals is 100 fs and 10 ps for FU and TCSPC, respectively. For reasons explained below, FU only detects emission corresponding to highly allowed transitions. TCSPC, on the other hand, is capable to monitor not only allowed but also very weak or forbidden transition. Therefore, particular care must be taken when merging data obtained by these two techniques as described in Ref. 10. [Pg.132]

In the time-correlated single-photon counting (TCSPC) technique, the sample is excited with a pulsed light source. The light source, optics, and detector are adjusted so that, for a given sample, no more than one photon is detected. When the source is pulsed, a timer is started. When a photon reaches the detector, the time is measured. Over the course of the... [Pg.97]

The macro time clock can be started by an external experiment trigger or by a start-measurement command from the operating software. In some TCSPC modules the clock signal source of the macro time clock can be selected. The macro time clock can be an internal quartz oscillator, an external clock source, or the reference signal from the laser. Triggering and external clock synchronisation are absolute requirements for multimodule operation in the time-tag mode, see Sect. 5.11.3, page 189. [Pg.44]

The setup shown in Fig. 5.49 can, in principle, be used to record fast changes in the brain at 4 laser wavelengths and 32 detector positions. However, the limited speed of the fibre switch normally allows one to record sequences only for one or two source positions at a time. The result is a total number of 128 to 256 waveforms each 50 to 100 ms or 32 to 64 per TCSPC module. The corresponding readout rate in the memory swapping mode is well within the range of currently used TCSPC modules. However, improved fibre switches may allow one to multiplex a larger number of source positions at a rate of 100 s" or faster. The data transfer rate then exceeds 10 Mbyte/s, and precautions have to be taken to sustain this rate over a longer time. [Pg.110]

An instrument for optical biopsy of bones based on a diode laser and a single TCSPC channel is described in [151, 152]. Other instruments use a tuneable synchronously pumped dye laser and a Ti Sapphire laser [414]. The lasers are switched into a single source fibre by a fibre switch. A single TCSPC channel records the diffusely reflected light and a reference signal split off from the source fibre. [Pg.112]

Of course, a TCSPC system works effieiently only with a high-repetition-rate excitation source. Diode lasers ean be built with any repetition rate up to about 100 MHz and are available with 375 nm, 405 nm, 440 nm, and 473 nm emission wavelength. Diode lasers are cost-effieient and ean be multiplexed at ps rates see Excitation Wavelength Multiplexing, page 87. For shorter wavelengths, frequency-doubled or frequency-tripled titanium-sapphire or neodymium-YAG lasers can be used. [Pg.122]

The Na source is placed between two identical samples. Two XP 2020 photomultipliers equipped with scintillators are attached directly to the two samples. The pulses from the photomultipliers are used as start and stop pulses for the TCSPC module. The pulses from PMT 2 are delayed by a few nanoseconds so that a stop pulse arrives after the corresponding start pulse. Eaeh y quantum generates a large number of photons in the scintillator. Therefore, the PMT pulses are multiphoton signals, and the time resolution can be better than the transit time spread of the PMTs. Moreover, the amplitudes of the photomultiplier pulses are proportional to the energy of the particle that caused the scintillation. Therefore the amplitudes can be used to distinguish between the 511 keV events of the positron decay and the 1.27 MeV events from the Na. The discriminator thresholds for start and stop are adjusted in a way that the stop channel sees all, the start channel only the larger Na events. The rate of the Na events is of the order of a few kHz or below. [Pg.207]

The chip laser is actually a miniaturised version of the Nd-YAG laser. It contains a diode laser pump, an active laser medium, a saturable absorber, and a frequency multiplier in a solid block. Chip lasers are an inexpensive and reliable source of UV radiation. Unfortunately they cannot be made with repetition rates higher than a few tens of kHz. The pulse width is of the order of 1 ns. Chip lasers are sometimes used in TCSPC systems for environmental research, e.g. to trace contamination of water by polycyclic hydrocarbons. [Pg.267]

TCSPC needs a timing reference signal from the light source. This is no problem for picosecond diode lasers, which deliver a trigger output pulse from the laser diode driver. For free-running solid-state lasers or jet-stream dye lasers, a suitable synchronisation signal can be generated by a photodiode. A simple solution is to use a fast PIN photodiode in one of the circuits shown in Fig. 7.42. [Pg.304]

Cables are available for Z= 50, 60, 75 and 100 Q. For measurement equipment and other wide-band systems only Z = 50 Q is used. The CFD inputs of TCSPC modules, amplifiers, or routers have internal matching resistors of 50 Q. However, the input impedance of amplifiers or of the pulse shaping network used in CFDs is often far from being ideally resistive. Moreover, PMTs and photodiodes are current sources. Matching at the detector side is avoided because it would decrease the signal amplitude. The resulting reflections at the input cables of a TCSPC device can normally be tolerated, especially if some precaution is taken in adjusting the CFD thresholds. [Pg.309]


See other pages where Sources for TCSPC is mentioned: [Pg.104]    [Pg.104]    [Pg.106]    [Pg.1367]    [Pg.104]    [Pg.104]    [Pg.106]    [Pg.1367]    [Pg.494]    [Pg.273]    [Pg.108]    [Pg.137]    [Pg.187]    [Pg.242]    [Pg.268]    [Pg.1063]    [Pg.104]    [Pg.105]    [Pg.107]    [Pg.107]    [Pg.116]    [Pg.485]    [Pg.514]    [Pg.131]    [Pg.152]    [Pg.434]    [Pg.92]    [Pg.554]    [Pg.555]    [Pg.434]    [Pg.23]    [Pg.104]    [Pg.107]    [Pg.108]    [Pg.186]    [Pg.268]    [Pg.302]    [Pg.348]   


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TCSPC

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