A ruby laser works by using a ruby crystal to generate a beam of coherent light through a process called stimulated emission. Here's a breakdown of how it works:
The Ruby Crystal
- The core of a ruby laser is a synthetic ruby crystal. This crystal is made of aluminum oxide (Al₂O₃) with a small amount of chromium (Cr³⁺) ions added as impurities. These chromium ions are the key players in the laser process.
The Pumping Process
- The process begins when the ruby crystal is pumped with a high-intensity light source, typically a xenon flash lamp.
- The chromium ions in the ruby crystal absorb photons of light, specifically visible light at wavelengths of approximately 400 nm or 550 nm.
- This absorption causes some of the electrons within the chromium ions to jump from their ground state (E₀) to higher energy levels (E₁ or E₂).
Energy Levels and Spontaneous Emission
| Energy Level | Description |
|---|---|
| E₀ | Ground State |
| E₁ | Excited Energy State |
| E₂ | Excited Energy State |
- After being excited to E₁ or E₂, the electrons quickly drop to an intermediate, metastable energy level. From this level, they can then decay spontaneously to the ground state, E₀, releasing photons of a certain wavelength (694.3 nm). This is a process called spontaneous emission. The emitted photons are random in direction and phase.
Stimulated Emission and Coherent Light
- When a photon encounters an excited chromium ion in the metastable state, it can trigger the release of another identical photon. This process, known as stimulated emission, is what leads to laser action.
- This emitted photon is an exact copy of the incident photon; it has the same wavelength, phase, and direction.
- As this process continues, many identical photons are produced, resulting in a coherent, focused, and intense beam of red light.
Components for Laser Operation
- To amplify the light and make a laser, the ruby crystal is placed inside an optical cavity or resonator. This is typically formed by two mirrors, one of which is partially reflective.
- The photons are reflected back and forth within the cavity, continuing to stimulate more emissions as they pass through the ruby crystal.
- A portion of the coherent light is transmitted through the partially reflective mirror as the laser beam.
Summary of Ruby Laser Operation:
- Pumping: A xenon flash lamp pumps the ruby crystal with intense light.
- Absorption: Chromium ions in the crystal absorb light and jump to higher energy levels.
- Metastable State: The electrons decay to a metastable energy level.
- Stimulated Emission: Photons trigger the release of identical photons from the chromium ions.
- Laser Beam: Coherent light is amplified by the optical cavity and emitted as the laser beam.
