signal-to-noise ratio

**SNR** (Signal-to-Noise Ratio) is the **ratio of the analytical signal to the noise level** — $SNR = S / N$ where $S$ is the signal intensity and $N$ is the noise amplitude, quantifying the quality and reliability of a measurement. Higher SNR means more reliable measurements. **SNR in Analytical Metrology** - **Detection**: $SNR = 3$ at the detection limit — signal is just distinguishable from noise. - **Quantification**: $SNR = 10$ at the quantification limit — signal is reliable for quantitative measurement. - **Improving SNR**: Longer measurement time ($SNR propto sqrt{t}$), higher source intensity, better detector, or signal averaging. - **Peak-to-Peak vs. RMS**: Noise can be measured as peak-to-peak (worst case) or RMS (statistical) — RMS is more common. **Why It Matters** - **Measurement Quality**: Higher SNR = more precise and reliable measurements — the fundamental quality metric. - **Trade-offs**: Improving SNR often requires longer measurement time — throughput vs. quality trade-off. - **Semiconductor**: High SNR is critical for sub-ppb contamination detection and sub-nm CD measurement. **SNR** is **signal quality** — the ratio that determines whether the analyte signal can be reliably distinguished from measurement noise.