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Output Couplers in Laser Systems

Introduction

An output coupler is a crucial component in a laser resonator that plays a significant role in determining the performance of the laser system. It is a semi-transparent dielectric mirror designed to transmit a portion of the intracavity optical power to produce the desired laser output.

Function of an Output Coupler

The primary function of an output coupler is to allow a controlled amount of light to exit the laser resonator, thereby creating the laser beam. By transmitting a specific portion of the circulating optical power, the output coupler enables the generation of a useful laser output.

Output Coupler Transmissivity

One of the key characteristics of an output coupler is its transmissivity, which refers to the efficiency of transmission of optical power through the mirror. The transmissivity of the output coupler impacts factors such as the threshold pump power, laser efficiency, and overall output power of the laser system.

Types of Output Couplers

Output coupler mirrors can have either flat or curved surfaces. Flat output couplers are commonly used to produce collimated laser beams, while curved output couplers may introduce focusing or defocusing effects on the output beam. The choice between flat and curved output couplers depends on the specific requirements of the laser system.

Reflections from the Backside

It is important to consider the reflectivity of the backside of the glass substrate in an output coupler mirror, as it can affect the performance of the laser system. The residual reflectivity of the backside may lead to interference effects that impact the laser bandwidth and stability. To mitigate such issues, slightly wedged output couplers can be used to prevent interference from the reflected light.

Variable Reflectivity Mirrors

In unstable optical resonators, variable reflectivity mirrors are often employed as output couplers. These mirrors have a spatially varying reflectance profile, such as a Gaussian distribution, to control the output characteristics of the laser beam. Variable reflectivity mirrors are utilized in specific laser systems to achieve desired beam properties.

Conclusion

Output couplers are essential components in laser systems that enable the extraction of laser beams with controlled characteristics. Understanding the design and function of output couplers is crucial for optimizing the performance of laser systems across various applications.

Source: Laser Components
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