What kind of mirrors can you use in laser cavities?

Mirrors in Laser Cavities

The mirrors used in laser cavities are crucial components that define the characteristics of the laser beam. These mirrors serve to reflect light back and forth within the cavity, amplifying the light through stimulated emission and shaping the resonator mode. There are several types of mirrors specifically designed for use in laser cavities, each tailored for different applications and laser types.

Plane Mirror

A plane or flat mirror is a common type used in laser cavities where a simple reflective surface is required. These mirrors are typically used in long laser cavities where the distance between the mirrors is large compared to the diameter of the laser beam.

Curved Mirrors

Curved mirrors such as concave and convex mirrors are used to focus or diverge the light within the cavity. Concave mirrors are often used in the design of stable laser resonators where they can help to maintain a consistent beam diameter over multiple passes through the gain medium.

Partially Transparent Mirror (Output Coupler)

A partially transparent mirror, also called an output coupler, is one of the two mirrors in a laser cavity. It possesses a specific degree of reflectivity that allows for a certain percentage of the laser beam to transmit through, providing the output laser beam while reflecting the remaining light back into the cavity for further amplification.

Dielectric Mirror

Dielectric mirrors consist of multiple layers of dielectric material designed to reflect specific wavelengths of light very efficiently, often with reflectivities greater than 99.9%. They are typically used where high reflectivity or specific wavelength selectivity is required.

Bragg Mirror (Distributed Bragg Reflector)

Bragg mirrors, or distributed Bragg reflectors, are mirrors made from alternating layers of different refractive indices, creating a structure that reflects certain wavelengths of light through constructive interference. They are useful in semiconductor lasers and other applications requiring precise wavelength control.

Metallic Mirror

Metallic mirrors are used in laser cavities for their broad bandwidth and high reflectance. Common metals used include gold, silver, and aluminum, each providing high reflectivity over different spectral ranges. They are particularly valuable in ultrafast lasers and other applications requiring broadband reflectors.

Reflectivity

This is the percentage of incident light that the mirror reflects. High reflectivity is essential for efficient operation of a laser cavity.

Damage Threshold

The damage threshold indicates the maximum amount of laser power or energy that a mirror can handle before it is damaged or destroyed. This is particularly important in high-power laser applications.

Wavelength Selectivity

Mirrors can be designed to highly reflect certain wavelengths while allowing others to pass through. This is key in creating lasers that emit a specific color or wavelength of light.

Coating Materials

Dielectric coatings are usually made from materials such as tantalum pentoxide or silicon dioxide while metallic coatings employ metals like gold or silver for reflective purposes.

Choosing the appropriate type of mirror for a laser cavity depends on the specific application and desired properties of the laser. Factors like power, wavelength, beam diameter, and stability all influence the selection of mirror types used in laser systems.