Continuous lasers can stably and uninterruptedly output laser beams, and their output power remains constant over time (under ideal conditions).
Core features: Stability and sustainability
Continuous output: This is the most crucial sign. As long as the power is connected and the working conditions are stable, the laser can continuously emit light without interruption.
Power stability: The power of the output laser (the energy emitted per unit time) remains basically constant during operation.
Temporal characteristics: The beam is continuous in the temporal dimension (macroscopically), with no obvious pulse intervals.
Working principle: Continuous pumping, continuous light emission
The working principle of a continuous laser follows the fundamental principle of laser generation (stimulated emission), but its pumping process is continuous:
Continuous pumping: External energy sources (such as current, light energy, chemical reaction energy) are continuously input into the gain medium of the laser (such as gas CO₂, solid crystal Nd:YAG, semiconductor materials, dye solutions).
Population inversion maintenance: The continuous pumping energy excites atoms, molecules or electrons in the gain medium from a low energy level to a high energy level, maintaining a state where the number of particles in the high energy level is greater than that in the low energy level (population inversion).
Stimulated emission continues: A small number of spontaneously emitted photons existing in the resonant cavity (composed of two mirrors), when passing through the gain medium, will cause particles at high energy levels to produce stimulated emission, releasing new photons with exactly the same frequency, phase and direction as the incident photons.
Optical amplification and continuous oscillation: These newly generated photons are reflected back and forth by the resonator mirror and repeatedly pass through the gain medium. Each passage triggers more stimulated radiation, causing the number of photons to continuously increase in an avalanche-like manner and forming powerful coherent light waves.
Stable laser output: When the gain (amplification) obtained by the light oscillating back and forth in the resonant cavity once is sufficient to compensate for the loss of this oscillation (including part of the light transmitted through the output mirror), the laser reaches a stable working state and continuously and stably emits a laser beam from the partially transmitted output mirror.
Key technological advantages
Continuous power output: It provides a stable heat source or light source, suitable for processes that require continuous energy input (such as cutting and welding).
High stability: The output power and beam directivity are usually very stable, which is crucial for precise measurement and communication.
Excellent beam quality: It usually generates high-quality beams with pure modes (such as fundamental mode TEM00) and small divergence angles, which is conducive to focusing and long-distance transmission.
High efficiency (compared with some pulsed lasers) : In scenarios where continuous operation is required, the overall energy utilization efficiency may be higher.
Wide range of application fields
Industrial processing
Laser cutting: Precise and high-speed cutting of metals (such as CO₂ laser cutting machines) and non-metals (such as fabrics, acrylic).
Laser welding: Achieving precise welding with a high aspect ratio and low deformation (commonly used in the automotive and electronics industries).
Laser marking/engraving: Permanent marking on the surface of products (mainly semiconductor and fiber lasers).
Surface treatment: quenching, cladding, alloying, etc.
Medical field
Scalpel: CO₂ laser is used for soft tissue vaporization cutting (such as in ENT surgery), and semiconductor laser is used in ophthalmic surgery and dental treatment.
Photodynamic therapy: Continuous lasers of specific wavelengths activate photosensitive drugs to selectively kill cancer cells or diseased tissues.
Skin treatments: Hair removal (semiconductor, Nd:YAG), vascular treatment, skin rejuvenation, etc.
Communication and Information
Optical fiber communication: Semiconductor lasers are the core light sources of high-speed optical fiber networks, carrying massive amounts of data.
Display and Sensing
Laser display: As a light source for high-brightness, wide-color gamut projectors or televisions.
LiDAR: Some continuous-wave LiDAR is used for speed measurement, distance measurement, gas detection, etc.
Barcode scanning: A common device at supermarket checkout counters.
Continuous lasers are the backbone of the laser family that provide a stable and continuous energy flow. Understanding the working principle and unique advantages of continuous lasers is the foundation for recognizing their core role in contemporary science and technology and industry. They represent the remarkable achievements of humanity in precisely and continuously controlling light energy.