Laser Cavity

A laser cavity, also known as an optical resonator, forms the fundamental architecture that enables laser operation. It consists of a precisely aligned system of mirrors that create a closed path for light amplification and oscillation.

Core Components

Mirror Configuration

• High Reflector (HR): A mirror with nearly 100% reflectivity
• Output Coupler (OC): A partially reflective mirror that allows some light to escape
• The space between these mirrors contains the gain medium

Cavity Geometries

1. Linear Cavity

   • Most basic design
   • Two mirrors facing each other
   • Standing waves form between reflectors

2. Ring Cavity

   • Three or more mirrors arranged in a closed loop
   • Allows unidirectional operation

Physical Principles

Resonant Modes

The cavity supports specific electromagnetic modes that satisfy the resonance condition:

• Longitudinal modes (along cavity axis)
• Transverse modes (perpendicular to axis)
• Mode spacing determined by cavity length

Stability Criteria

Cavity stability depends on:

• Mirror curvature
• Cavity length
• Gaussian beam propagation characteristics

Applications

Different cavity designs serve various purposes:

• Q-switching for pulsed operation
• Mode locking for ultrashort pulses
• Single-frequency operation for precise wavelength control

Key Parameters

1. Cavity Length

   • Determines mode spacing
   • Affects stability
   • Influences pulse duration

2. Mirror Properties

   • Reflectivity
   • Curvature
   • Coating damage threshold

3. Alignment Sensitivity

   • Critical for performance
   • Requires precise mechanical stability

Advanced Concepts

The cavity design significantly impacts:

• Beam quality
• Spectral properties
• Power handling
• Thermal effects

Optimization Considerations

Cavity design must balance:

1. Desired output characteristics
2. Physical constraints
3. Thermal management
4. Cost and complexity
5. Maintenance requirements

The laser cavity represents a crucial intersection of optical, mechanical, and thermal engineering, forming the heart of any laser system. Its design fundamentally determines the characteristics and capabilities of the resulting laser output.