Quantum Limit to Precision of Wavelength Determination

The precision of wavelength determination is ultimately limited by noise arising from the quantum nature of light and light detection. Expressions are derived for the limiting precision attainable by various interferometers and conventional spectrometers in terms of parameters characterizing the instruments, the source, and the detector. A comparison of five different instruments shows the superiority of the interferometers and indicates that they are divided into three classes, according to the role played by the half-width of the radiation from the source.