The high signal-to-noise ratio of photomultiplier tubes (PMTs) is mainly due to their unique multiplication mechanism and design characteristics. The following are the reasons for the high signal-to-noise ratio of photomultiplier tubes:

Multiplication mechanism:

The photomultiplier tube achieves electron multiplication through the secondary electron emission effect. When photons collide with the photocathode, they release photoelectrons. These photoelectrons are accelerated and collided with the doubling pole under the action of an electric field, producing more secondary electrons. This process repeats between multiple doubling poles, resulting in a geometric increase in the number of electrons.
Due to the highly controllable doubling of electrons, the gain of PMT can be precisely adjusted to adapt to different light signal intensities. This high gain characteristic enables PMT to detect very weak optical signals and output strong electrical signals.

Low noise characteristics:

The noise of photomultiplier tubes mainly comes from thermal electron emission noise, secondary emission noise, ionization noise, and dark current noise. However, through reasonable design and manufacturing processes, these noises can be effectively suppressed.
For example, by controlling the operating temperature of PMT, the impact of hot electron emission noise can be reduced. Meanwhile, optimizing the material and structure of the multiplier can reduce secondary emission noise and ionization noise.
Dark current is an inherent characteristic of PMT, but its magnitude can be reduced by selecting appropriate materials and processes. In addition, through reasonable circuit design, the impact of dark current on signal-to-noise ratio can also be further reduced.

High sensitivity:

Photomultiplier tubes have extremely high sensitivity to light signals. Due to the doubling effect of electrons, even very weak light signals can be effectively detected and amplified. This makes PMT widely applicable in the field of weak light detection.
High sensitivity means that PMT can detect more photons and generate stronger electrical signals. Therefore, under the same optical signal intensity, the output signal amplitude of PMT is larger and the signal-to-noise ratio is also higher.

Good stability:

The photomultiplier tube has good stability and reliability. Through reasonable design and manufacturing processes, it can be ensured that PMT maintains stable performance during long-term operation.
Good stability means that the output signal of PMT will not undergo significant changes due to environmental changes or the passage of time. This helps to maintain a high signal-to-noise ratio and ensures the accuracy and reliability of measurement results.

The reason why photomultiplier tubes have a high signal-to-noise ratio is mainly due to their unique multiplication mechanism, low noise characteristics, high sensitivity, and good stability. These characteristics make PMT have broad application prospects in the field of weak light detection.