A lock-in amplifier is a precision instrument used to measure very small AC signals buried in noisy environments by using a technique called phase-sensitive detection.
How It Works:
- A known reference frequency (often from a signal generator or modulator) is supplied to the lock-in amplifier.
- The input signal is multiplied by this reference and then filtered, isolating components at the reference frequency.
- Only signals that match the frequency and phase of the reference are retained; all others (random noise or different frequencies) are suppressed.
Key Features:
- Extremely high sensitivity: Can detect signals millions of times smaller than the noise.
- Narrow bandwidth detection: Effectively ignores all frequencies except the one of interest.
- Phase information: Measures both the amplitude and phase of the signal.
Applications:
- Optical experiments (e.g., modulated laser detection)
- Magnetic resonance and scanning probe microscopy
- Low-level electrical measurements in physics and engineering
- Biophysics and neuroscience experiments with microvolt signals
Lock-in amplifiers are essential tools in experimental physics and engineering for precisely extracting signals that would otherwise be lost in noise.