Lasers operate through the principle of "stimulated emission," producing powerful beams of light. A laser system consists of three core components:
- Optical Resonator: Functions like an echo chamber, reflecting light back and forth to amplify it.
- Gain Medium: The "fuel" that generates laser light, which can be crystals, gases, or dyes.
- Pump Source: Provides energy to excite the gain medium, such as flash lamps, electrical discharges, or other lasers.
When the pump source energizes the gain medium, light reflects within the optical resonator, amplifying coherent light with identical wavelength and phase. One mirror in the resonator is partially reflective, allowing the amplified light to exit as a laser beam. This process creates light with unique properties: monochromaticity, directionality, and coherence.
Lasers can be categorized by their gain medium (gas, solid-state, or dye lasers) or by their wavelength (ultraviolet, visible, or infrared). These classification systems overlap—for example, a CO2 laser is both a gas laser and an infrared laser.
Diode lasers (semiconductor lasers) generate coherent light through semiconductor materials. Their compact size, high efficiency, and versatility make them increasingly popular.
The core component is a p-n junction where electrons and holes recombine to emit photons. The wavelength depends on the semiconductor material's bandgap. Common materials and their corresponding wavelengths include:
| Material | Wavelength | Color |
|---|---|---|
| Gallium Nitride (GaN) | 405-450 nm | Blue |
| Aluminum Gallium Indium Phosphide (AlGaInP) | 635-680 nm | Red |
| Ytterbium-doped Fiber or Nd:YAG | 1060-1080 nm | Infrared (invisible) |
CO2 lasers emit infrared light at 10,600 nm, making them among the most powerful continuous-wave lasers. They excel in industrial cutting, welding, and engraving applications.
The gain medium is a gas mixture of carbon dioxide, nitrogen, and helium. When excited by electrical discharge, CO2 molecules release photons that stimulate further emission. The optical resonator amplifies this infrared light into a focused, coherent beam.
Fiber lasers use doped optical fibers as their gain medium, offering superior beam quality and efficiency. They're particularly valuable in material processing and telecommunications.
Rare-earth elements like erbium or ytterbium doped into the fiber are excited by diode pump sources. The resulting photons amplify as they travel through the fiber, producing a coherent laser beam. The fiber's waveguiding structure ensures excellent beam quality and stability.
Any laser emitting blue light (typically 473 nm or 445 nm) qualifies as a blue laser, regardless of gain medium. These visible lasers are prominent in projection, biomedical applications, and material processing.
Most blue lasers are diode-pumped solid-state (DPSS) systems using crystals doped with neodymium ions. While compact and efficient, their output power is typically limited to about 50 mW in basic configurations.
Infrared lasers emit light beyond 780 nm, classified as near-infrared (NIR), mid-infrared (MIR), or far-infrared (FIR). Their invisibility to human eyes makes them ideal for high-power industrial applications.
Unlike visible lasers, infrared lasers can achieve their wavelengths through simpler energy transitions in molecules or doped materials. For example, CO2 lasers naturally emit at 10,600 nm through molecular transitions.
- Diode Lasers: Effective on plastics, textiles, thin metals (stainless steel, aluminum), and various organic materials. Blue diodes (445 nm) work well on wood, leather, and opaque acrylic.
- CO2 Lasers: Ideal for non-metallics like acrylic, wood, glass, and ceramics. Can also cut thick industrial metals (aluminum, steel) but struggle with copper and brass.
- Fiber Lasers: Excel with metals including steel, aluminum, and nickel alloys. Generally ineffective on non-metallics like wood or acrylic.
Key operational differences between laser types:
| Parameter | Diode Lasers | CO2 Lasers | Fiber Lasers |
|---|---|---|---|
| Wall-plug Efficiency | 30-60% | 10-15% | 30-60% |
| Max Power | Up to 8kW (industrial) | 100kW+ | 100kW+ |
| Cutting Speed (steel) | ~50 mm/s (6mm thick) | ~83 mm/s (12mm) | ~416 mm/s (25mm+) |
| Maintenance | Minimal (100,000+ hours) | High (gas/mirror replacement) | Moderate (fiber/diode replacement) |
Diode lasers offer the lowest maintenance with semiconductor components lasting up to 100,000 hours. CO2 lasers require regular gas refills and mirror replacements, while fiber lasers need periodic fiber and diode maintenance despite their solid-state design.
In industrial applications, fiber lasers provide the highest cutting speeds for thick metals, while CO2 lasers remain effective for non-metallic materials. Diode lasers serve well in compact, low-power applications where efficiency and longevity are priorities.