vågplatta

Vågplatta is a term used in optics to describe a wave plate or retardation plate, a flat piece of birefringent material that introduces a controlled phase shift between the ordinary and extraordinary polarization components of light passing through it. The plate’s retardance depends on the material’s birefringence and its thickness, and is typically designed for a specific wavelength or a narrow wavelength range. Commonly used retardances are quarter-wave (λ/4) and half-wave (λ/2).

The operating principle relies on birefringence: the two polarization components travel at different speeds inside the material, resulting in a phase difference when they exit the plate. By orienting the fast axis of the plate relative to the input polarization, the wave plate can convert linear polarization to circular or elliptical polarization, or rotate the polarization orientation. The output polarization state is sensitive to wavelength, temperature, and plate orientation, so precise alignment and calibration are essential.

Types and materials vary. Quarter-wave and half-wave plates are widely used in laser optics and microscopy. Materials commonly employed include quartz, magnesium fluoride, mica, and birefringent polymers, sometimes with anti-reflection coatings to reduce losses. Broadband or achromatic wave plates use stacks of plates to achieve relatively uniform retardance over a range of wavelengths.

Applications span polarization control, ellipsometry, interferometry, and quantum optics, as well as instrumentation in communication systems. While the term analogous to “vågplatta” appears in some Scandinavian languages, in English technical usage the device is typically referred to as a wave plate or retardation plate.