singlefrequency

Singlefrequency, in scientific contexts, refers to a signal or wave that contains, in principle, a single frequency component. In mathematics, a perfect single-frequency signal is a pure sinusoid, v(t) = A cos(ωt + φ). In practice, any real source produces additional components or noise, yielding a finite linewidth and spectral shape around a central frequency. In acoustics, a pure tone is the auditory counterpart; in optics, a single-frequency light corresponds to monochromatic, nearly coherent radiation, often produced by lasers.

Single-frequency sources include electronic oscillators, function generators, and stabilized lasers. Frequency stability is achieved through feedback control, temperature stabilization, and high-quality resonators. In optical systems, external cavity lasers, diode lasers with mode selection, and frequency references (such as atomic transitions) are used to minimize linewidth. Signal purity is degraded by amplitude and phase noise, jitter, and modulation.

Characterization uses spectrum analysis, Fourier transform, and phase noise measurements; linewidth is a common metric, defined as the full width at half maximum of the spectral peak. Coherence time is inversely related to linewidth.

Applications of single-frequency signals and light span calibration, testing, and communications, as well as metrology and spectroscopy. Single-frequency light is essential for high-resolution spectroscopy and frequency standards, while single-frequency electrical signals serve as reference tones and carriers in measurement systems and telecommunications. The concept underscores the ideal of a source with minimal spectral content beyond its central frequency, a condition approached but rarely achieved in practice.