A laser resonator works by bouncing light back and forth between two mirrors to build up energy and create a strong, directional beam.
Understanding the Laser Resonator
An essential component of most lasers is the optical resonator, also known as a laser cavity. Its primary purpose is to provide feedback for the light generated within the laser medium (the material that emits light when excited). This feedback is crucial for sustaining the laser process.
As stated in the reference: "An optical resonator is needed to build up the light energy in the beam. The resonator is formed by placing a pair of mirrors facing each other so that light emitted along the line between the mirrors is reflected back and forth."
Key Components
The core of a simple laser resonator consists of two main elements:
- Gain Medium: This is where the light is initially generated or amplified (not explicitly mentioned in the reference, but fundamental to laser operation).
- Mirrors: These are positioned facing each other to reflect the light.
Here's a simple representation:
| Component | Function |
|---|---|
| Gain Medium | Amplifies light (Adds energy) |
| Mirror 1 | Reflects light back into the gain medium |
| Mirror 2 | Reflects light back into the gain medium |
One of the mirrors is typically highly reflective (often close to 100%), while the other is partially reflective (e.g., 95-99% reflective). The small percentage of light that passes through the partially reflective mirror forms the usable laser beam.
The Process of Light Build-up
- Light Emission: When the gain medium is excited (e.g., by electricity or another light source), it emits photons (light particles).
- Reflection: Light traveling along the axis between the mirrors hits one mirror and is reflected back.
- Amplification: As the reflected light passes back through the gain medium, it stimulates the emission of more identical photons. This process, called stimulated emission, amplifies the light wave.
- Multiple Passes: The amplified light then travels to the other mirror, reflects back, and passes through the gain medium again for further amplification.
- Energy Build-Up: This continuous back-and-forth travel and amplification causes the light energy within the resonator to build up significantly. Only specific wavelengths (colors) and directions of light that are aligned with the resonator axis and can be sustained by this reflection process will build up into a strong beam.
- Beam Output: The laser beam is extracted from the partially reflective mirror, representing the high-intensity, coherent light that has been amplified within the cavity.
This process effectively traps light, allowing it to make multiple passes through the amplifying medium, thereby building up the necessary energy density and coherence to form a laser beam.
