C8991

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Product Specifications: Hamamatsu C8991

Category	Parameter	Specification / Description
General Information	Product Code	C8991
	Product Type	Hybrid Photo-Detector (HPD)
	Description	A vacuum tube device where photoelectrons are accelerated by a high voltage and directly bombarded onto a large-area avalanche diode, achieving high gain with exceptionally low noise.
Photocathode	Type	Bialkali
	Form	Transmissive
	Effective Area	Diameter: 8 mm
	Window Material	UV-glass
Spectral Response	Range	300 nm to 650 nm
	Peak Wavelength	~420 nm
	Cathode Luminous Sensitivity	70 μA/lm (Typ., at 2856 K)
Semiconductor Target	Type	Avalanche Diode
	Operating Principle	Electron Bombardment Gain: Photoelectrons are accelerated by high voltage (e.g., 8 kV) and gain enough energy to create thousands of electron-hole pairs upon impact with the diode.
Gain	Mechanism	Electron Bombardment + Avalanche Multiplication
	Typical Value	2,000 to 10,000 (Much lower than a PMT, but with superior signal-to-noise ratio)
	Key Advantage	The gain process is virtually noiseless (excess noise factor F ≈ 1.0), unlike the multiplicative noise in PMT dynodes.
Voltage	Operating Voltage (Cathode to Target)	-8 kV DC (Typical)
	Avalanche Diode Bias	Requires an additional +100 V to +200 V DC bias for the internal semiconductor target.
	Polarity	Negative High Voltage on photocathode.
Performance	Dark Count Rate	Extremely Low: ~100 counts per second (cps) typ. at room temperature.
	Photon Counting	Excellent capability due to narrow pulse height distribution (low noise).
	Rise Time	1.5 ns (Extremely fast)
	TTS (Transit Time Spread)	150 ps (Excellent timing resolution)
	Magnetic Field Immunity	High. Much more resistant to magnetic fields than traditional PMTs.
Output	Signal	Anode Output
	Connector	BNC connector (standard)
Mechanical	Housing	Metal-bodied, head-on type.
	Dimensions	Larger than a PMT module due to internal high-voltage requirements.
	Key Feature	Integrated focusing electrode to ensure accelerated photoelectrons bombard the target correctly.
Applications		Ultra-low-light photon counting, High-energy physics, Fluorescence Lifetime Imaging Microscopy (FLIM), Time-Correlated Single Photon Counting (TCSPC), LIDAR.