Hybrid Single-Photon Detectors

  • Extremely Fast Response
  • Instrument Response Function (IRF) Down to 18 ps FWHM
  • High Detection Efficiency
  • Large Active Area: 3 mm or 6 mm Cathode Diameter
  • Five Cathode Types Covering 180 nm to 920 nm (Click Here to Compare Spectral Sensitivity)
  • No Afterpulsing Background
  • No Afterpulsing Peak in FCS Measurements
  • Extremely High Dynamic Range of TCSPC Measurements
  • Clean IRF: No Tails or Secondary Peaks
  • High Noise Immunity
  • Internal Generators for PMT Operating Voltages
  • Power Supply and Control via DCC-100 or DCU-400 Modules
  • Overload Protection
  • Direct Interfacing to all bh TCSPC Systems
  • Cooled Version with Reduced Dark Count Rate Available

A hybrid photon detector consists of a photocathode, an electron acceleration system, and a silicon avalanche diode. Photoelectrons emitted by a photocathode are accelerated towards the avalanche diode by a strong electrical field and injected directly into diode material.

When an electron hits the avalanche diode it generates a large number of electron-hole pairs in the silicon. These carriers are further amplified by the linear gain of the avalanche diode. The total gain is on the order of 106, i.e. sufficient to generate a detectable current pulse at the output of the avalanche diode.

Important for TCSPC, the high acceleration voltage between the photocathode and the APD results in low transit time spread. With an acceleration voltage of 8 kV the transit-time spread of the electron time-of-flight is less than 20 ps. Hybrid detectors therefore deliver a very good time resolution in combination with TCSPC. In fact the intrinsic time jitter of the electron amplification system is so low, that the temporal instrument response function (IRF) of a hybrid detector is dominated by the dwell time of the photoelectrons in the photocathode. Detectors with GaAsP photocathodes deliver IRFs on the order of 90 to 120 ps (full width at half maximum, fwhm), detectors with GaAs photocatodes deliver IRFs of 120 to 200 ps fwhm. Bi-alkali and multi-alkali cathodes do not have noticeable electron dwell times. With the bh TCSPC devices such detectors deliver IRF widths of 16 to 20 ps fwhm.

Compared with a conventional PMT, the hybrid PMT has also an advantage in terms of counting efficiency. In a conventional PMT, a fraction of the photoelectrons is lost on the first dynode of the electron multiplication system. There are no such losses in the hybrid PMT: A photoelectron accelerated to an energy of 8 keV is almost certain to generate a carrier avalanche in the avalanche diode. With a high-efficiency GaAsP cathode a hybrid photomultiplier reaches the efficiency of a single-photon avalanche photodiode (SPAD), but with a cathode area several orders of magnitude larger.

The perhaps most significant advantage of the hybrid detector has only been recognised recently: The hybrid PMT is virtually free of afterpulsing. Afterpulsing is the major source of counting background in high-repetition-rate TCSPC applications, and a known problem in fluorescence-correlation (FCS) measurements. The absence of afterpulsing results in high dynamic-range fluorescence-decay recording, and in artefact-free recording of autocorrelation FCS with a single detector.

bh were the first to recognise the potential of hybrid detectors in TCSPC applications. bh were also the first to make the detectors applicable to TCSPC by combining the detector tube, the high-voltage generators, and the low-noise preamplifier in a perfectly shielded metal case.



Cathode Type






Wavelength Range / nm 1)

220 - 650

220 - 850

250 - 720

300 - 850

400 - 900

Detector Quantum Efficiency 1)

28 %

@ 400 nm

26 %

@ 290 nm, 18 %

@ 400 nm

45 %

@ 500 nm

22 %

@ 500 nm

20 %

@ 600 nm


Spectral sensitivity: click here

Dark Count Rate (typ. Value)/ s-1, Tcase = 22 °C


< 300




Dark Count Rate for Actively Cooled HPMs (typ. Value)/ s-1, Tcase = 30 °C

< 15

< 150




Transit Time Spread

(TCSPC IRF / FWHM, typ Value)

< 20 ps

120 ps

150 ps

170 ps

Max. Count Rate (Continuous)

> 10 MHz

Single Electron Response Width (FWHM, typ. Value)

850 ps

Single Electron Response Amplitude (Vapd 95 % of Vmax) 2)

50 mV

Overload Shutdown

> 15 MHz (Higher rates on request)

Signal Output


Output Polarity


Output Connector


Output Impedance

50 Ω

Power Supply

(from DCC-100 Card)

+12 V, +5 V, -12 V


Cathode Diameter

6 mm

3 mm

3 mm

3 mm

3 mm

Dimensions (Width x Height x Depth)

(60 x 90 x 170) mm

Optical Adapter

C-Mount, DCS-120, LSM 710/780/880 NDD and BIG port

All HPM-100 Detectors are available as Cooled Versions

(1) According to Hamamatsu specifications
(2) Varies with cathode type and manufactering lot

Related Literature:

  • W. Becker, B. Su, K. Weisshart, O. Holub, FLIM and FCS Detection in Laser-Scanning Microscopes: Increased Efficiency by GaAsP Hybrid Detectors. Micr. Res. Tech. 74, 804-811 (2011)

The bh TCSPC Handbook
9th edition, September 2021


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