For example, the term subwavelength-diameter optical fibre means an optical fibre whose diameter is less than the wavelength of light propagating through it. A subwavelength particle is a particle smaller than the wavelength of light with which it interacts (see Rayleigh scattering). Subwavelength apertures are holes smaller than the wavelength of light propagating through them. Such structures have applications in extraordinary optical transmission, and zero-mode waveguides, among other areas of photonics. Subwavelength may also refer to a phenomenon involving subwavelength objects; for example, subwavelength imaging. Angular wavelength A quantity related to the wavelength is the angular wavelength (also known as reduced wavelength), usually symbolized by ƛ (lambda-bar). It is equal to the "regular" wavelength "reduced" by a factor of 2π (ƛ = λ/2π). It is usually encountered in quantum mechanics, where it is used in combination with the reduced Planck constant (symbol ħ, h-bar) and the angular frequency (symbol ω) or angular wavenumber (symbol k). It is also used to measure the amplitude of mechanical waves, where the amplitude is equal to displacement divided by reduced wavelength. See also Emission spectrum Envelope (waves) Fraunhofer lines – dark lines in the solar spectrum, traditionally used as standard optical wavelength references Index of wave articles Length measurement Spectral line Spectroscopy Spectrum References External links Conversion: Wavelength to Frequency and vice versa – Sound waves and radio waves Teaching resource for 14–16 years on sound including wavelength The visible electromagnetic spectrum displayed in web colors with according wavelengths Waves Length