Gaussian mirrors produce high quality laser beams

9th August 2016
Daisy Stapley-Bunten

Gaussian mirrors, or variable reflecting mirrors, are characterised by a degree of reflection which slopes radially from the centre of the optic in a Gaussian distribution. These mirrors are used in unstable resonators to produce high quality laser beams with low divergence at high pulse energies. In frequency-doubled systems they are used to achieve a greater pump efficiency. Gaussian mirrors are extremely stable and suitable for high power applications.

These optics are based on the principle of a Fabry Perot interferometer, with a position dependant mirror spacing. Dielectric coatings with a defined reflectivity value as a function of radius are generally monochromatic. The Gaussian profile is only valid for a single specified wavelength. Gaussian mirrors are manufactured with high precision, usually to customer specification by LASER COMPONENTS, one of the few companies worldwide offering this type of mirror.

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The working principle of Gaussian mirrors is based on a Fabry Pérot interferometer with a fixed mirror spacing – a so-called etalon. In this way, the phase shift caused by the coating is minimized. Also, the wavefront distortion of coherent radiation is reduced.

The image here shows the cross-section of a coating that exhibits a gradual change in the reflection R(r) for monochromatic light depending on its position.

A so-called distance layer S with varying thickness d is surrounded by two identical mirror layers M. If d is an even multiple of l/4, the system is transparent for the wavelength and does not exhibit a reflection for l. If d is an odd multiple of l/4, the total reflection is determined by the reflection of the mirror layers M.

Special substrates are used for Gaussian mirrors. LASER COMPONENTS offers meniscus, plano convex, and other custom-made substrates.

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