noise floor

**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.