Output coupler

An output coupler most often consists of a partially reflective mirror, allowing a certain portion of the intracavity beam to transmit through.

In its most common form, an output coupler consists of a partially reflective mirror, sometimes called a beamsplitter.

For lasing to occur, the gain of the active medium must be larger than the total loss, which includes both unwanted effects such as absorption, emission in directions other than the beam path, and the intentional release of energy through the output coupler.

At a specific interval, the beam is redirected, using a device such as a Pockels cell, an acousto-optic modulator, or a fast-rotating prism or mirror.

Cavity dumpers can be used for continuous-wave operation, but their most common use is with mode-locked lasers, to extract a very short pulse at its peak intensity.

Principal components of a laser:
  1. Active laser medium
  2. Laser pumping energy
  3. High reflector
  4. Output coupler
  5. Laser beam
A dielectric output-coupler for a dye laser. Centered at 550 nm, the left photo shows its high reflectance to yellow light and its high transmittance to red and blue light. The right photo shows it reflecting 75% of a laser beam and transmitting 25%, although the beam appears brighter when moving toward the observer than when moving away.
Output coupler of a 594 nm Helium−Neon laser