Microchannel plate photomultiplier

MicroChannel plate photomultipliers are preferred to standard photomultipliers, but they are much more expensive. They exhibit faster time responses (10- to 20-fold faster) and do not show a significant color effect (see below). 

With mode-locked lasers and microchannel plate photomultipliers, the instrument response in terms of pulse width is 30-40 ps so that decay times as short as 10-20 ps can be measured. 

For high-frequency measurements, normal photomultipliers are too slow, and microchannel plate photomultipliers are required. However, internal crosscorrelation is not possible with the latter and an external mixing circuit must be used. 

The time resolution of a phase fluorometer using the harmonic content of a pulsed laser and a microchannel plate photomultiplier is comparable to that of a single-photon counting instrument using the same kind of laser and detector. 

A much better time resolution, together with space resolution, can be obtained by new imaging detectors consisting of a microchannel plate photomultiplier (MCP) in which the disk anode is replaced by a coded anode (Kemnitz, 2001). Using a Ti-sapphire laser as excitation source and the single-photon timing method of detection, the time resolution is <10 ps. The space resolution is 100 pm (250 x 250 channels). 

Streak cameras and multianode microchannel plate photomultipliers (MCP-PMs) interfaced to a polychromator also permit multiwavelength fluorescence decay measurements, the spectral response of both being determined by the photocathode composition. 

H. Kume, T. Taguchi, K. Nakatsugawa, K. Ozawa, S. Suzuki, R. Samuel, Y. Nishimura and I. Yamazaki, Compact ultrafast microchannel plate photomultiplier tubes, in Time-Resolved Laser Spectroscopy in Biochemistry III (I. R. Lakowicz, ed.), Proc. SPIE 1640 440-447 (1992). 

H. Kume, K. Koyama, K. Nakatsugawa, S. Suzuki and D. Fatlowitz, Ultrafast microchannel plate photomultipliers, Appl. Opt. 27, 1170-1178 (1988). 

A time-to-amplitude converter (TAC) system was also employed to measure fluorescence decays without the microscope. Then, the fluorescence decay and the fluorescence lifetime were obtained precisely with the microchannel-plate photomultiplier (MCP-PM) as detection. The time resolution of the lifetime was determined, using a convolution method, to be 10ps. 

A laser system that delivers pulses in the picosecond range with a repetition rate of a few MHz can be considered as an intrinsically modulated source. The harmonic content of the pulse train - which depends on the width of the pulses - extends to several gigahertz. The limitation is due to the detector. For high frequency measurements, it is absolutely necessary to use microchannel plate photomultipliers (that have a much faster response than usual photomultipliers). The highest available frequencies are then about 2 GHz. As for pulse fluorometry, Ti sapphire lasers are most suitable for phase fluorometry, and decay times as short as 10-20 ps can be measured. 

It should be noted that internal cross-correlation is not possible with microchannel plate photomultipliers, but an external mixing circuit can be used. 

Hamamatsu Photonics K.K., R3809U-50 series MicroChannel plate photomultiplier tube (MCP-PMTs) (2001)... 

T. Louis, G.H. Schatz, P. Klein-Bolting, A.R. Holzwarth, G. Ripamonti, S. Cova, Performance comparison of a single-photon avalanche diode with a microchannel-plate photomultiplier in time-correlated single-photon counting, Rev. Sci. Instram. 59, 1148-1152 (1988)... 

Other, faster detectors that can be used in place of a conventional PMT include microchannel plate photomultiplier tubes (MCP-PMTs) (31) and streak cameras (37). Because of their expense, the use of these devices is usually confined to home built fluorimeters foimd in dedicated fluorescence laboratories, and is therefore not discussed here. 

The time resolution of a photomultiplier is limited mainly by the variations in the paths that electrons take in reaching the anode. Because of the spread in transit times, the anode pulse resulting from the absorptitm of a single photon typically has a width on the order of 10 -10 s. The spread of transit times is smaller in microchannel plate photomultipliers, which work on the same principles as ordinary photomultipliers except that the electronic amplification steps occur along the walls of small capillaries. The anode pulse width in a microchannel plate detector can be as short as 2 x 10 s. 

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