Noise Floor is the minimum signal level below which the instrument cannot distinguish a real signal from noise — defined by the intrinsic noise of the detector, electronics, and measurement system, the noise floor sets the ultimate sensitivity limit of the instrument.

Noise Floor Components

• Thermal Noise (Johnson): Electronic noise from resistive components — proportional to temperature and bandwidth.
• Shot Noise: Statistical fluctuation in photon or electron counting — proportional to $sqrt{signal}$.
• 1/f Noise (Flicker): Low-frequency noise that increases at lower frequencies — drift and instabilities.
• Readout Noise: Electronic noise from signal digitization and amplification circuits.

Why It Matters

• Sensitivity Limit: The noise floor determines the minimum detectable signal — no amount of averaging can go below it.
• Cooling: Detector cooling (cryo, Peltier) reduces thermal noise — lowers the noise floor for better sensitivity.
• Bandwidth: Narrower measurement bandwidth reduces noise — but may also reduce signal (temporal resolution trade-off).

Noise Floor is the instrument's hearing limit — the irreducible minimum signal level below which measurements are indistinguishable from random noise.