Skip to content Short answer: A laser is a device that generates and amplifies light through stimulated emission. Energy is supplied to a gain medium, creating excited states from which photons can trigger the release of further photons with closely related optical properties. The resulting beam can be directed and focused very precisely. In a laser cutter or engraver, concentrating that optical power into a small spot produces enough energy density to heat, melt, decompose or vaporise material.
The word LASER comes from Light Amplification by Stimulated Emission of Radiation. That description is more than a name: stimulated emission is the physical process that distinguishes a laser from an ordinary lamp.
How does a laser work?
A laser begins by supplying energy to a gain medium. Depending on the laser, that medium might be a gas, a semiconductor, a crystal or an optical fibre containing active ions. Supplying energy is normally called pumping.
Pumping raises atoms, molecules or other quantum systems into higher-energy states. Under suitable conditions, enough of the active material is placed into an excited state for the medium to provide optical gain. A passing photon can then stimulate an excited state to release another photon. Repeating that process amplifies the light.
In many laser designs, mirrors form an optical resonator around the gain medium. Light passes repeatedly through the active medium and is amplified on each pass. One end of the resonator allows some of that light to leave as the useful laser beam. Other laser architectures achieve the same basic objective in different ways, so not every practical laser should be imagined as a simple tube with two mirrors.
What is stimulated emission?
Stimulated emission occurs when incoming light interacts with an already excited system and causes it to release additional light. The emitted photon is related to the stimulating photon in frequency and phase, which allows light in the laser cavity to build coherently rather than being emitted randomly in the way it is from many ordinary light sources.
This is the key physical idea behind laser amplification. The gain must be sufficient to overcome optical losses before sustained laser action can occur.
What makes laser light different from ordinary light?
Laser light is not simply “very bright” light. A useful laser beam combines several properties that make it unusually controllable. It commonly occupies a relatively narrow wavelength range, can have high spatial coherence, and can be produced with comparatively low divergence. Those properties allow optical power to be transported and focused into a small, predictable area.
For material processing, this ability to create a small focused spot is crucial. A laser with modest total power can create a very high power density at the workpiece if its beam quality and focusing conditions allow the energy to be concentrated tightly.
What are the main parts of a laser?
Pump or energy source
The pump supplies the energy needed to excite the gain medium. A glass CO₂ laser commonly uses a high-voltage electrical discharge. RF CO₂ sources use radio-frequency excitation. Semiconductor laser diodes are electrically pumped, while many fibre lasers use semiconductor pump diodes to excite a rare-earth-doped fibre.
Gain medium
The gain medium is the active material in which amplification takes place. Examples relevant to laser processing include CO₂ gas mixtures, semiconductor junctions and rare-earth-doped optical fibres. The choice of gain medium is closely connected with the wavelengths that the laser can generate.
Optical resonator or feedback system
Many lasers use mirrors to feed light back through the gain medium so it can be amplified repeatedly. One mirror may be partly transmitting so that a controlled proportion of the circulating light leaves the resonator as the output beam.
Beam delivery and focusing optics
Once the beam has been generated, mirrors, fibres, lenses and other optical components deliver it to the workpiece. In a typical moving-head CO₂ cutter, mirrors steer the beam across the machine and a focusing lens concentrates it onto the material.
Why does laser wavelength matter?
Wavelength is one of the main reasons different lasers behave differently on the same material. Most conventional CO₂ processing lasers operate near 10.6 µm in the infrared, although other CO₂ emission lines are possible. Many common fibre-laser sources operate in the region of 1 µm.
Materials do not absorb and reflect all wavelengths equally. A material that absorbs one laser wavelength strongly may reflect or transmit another. That is why comparing lasers only by their wattage can be misleading: wavelength, beam quality, spot size, pulse behaviour and material absorption all influence the result.
For a CO₂-machine-specific introduction, see What Is a CO₂ Laser Cutter?
How does a laser cut or engrave material?
The processing beam is focused onto the workpiece. Reducing the beam to a small spot concentrates its optical power into a much smaller area, increasing the local power density. The material response then depends on its optical and thermal properties and on the processing conditions.
Depending on the material and process, the interaction may involve heating, melting, decomposition, vaporisation or a change in surface appearance. Motion control then moves the focused spot relative to the workpiece to form a cut, engraving or mark.
Laser power is only one part of that process. The relationship between rated watts, software power settings and actual cutting performance is covered in Laser Cutter Power Guide.
Are all laser beams visible?
No. Many lasers used for cutting, engraving and marking operate outside the visible spectrum. A conventional CO₂ processing beam near 10.6 µm is infrared and invisible to the human eye. Common fibre-laser wavelengths around 1 µm are also outside normal human vision.
A visible red guide beam, where fitted, is normally a separate low-power source used to indicate position. It should not be confused with the actual processing beam.
Are lasers dangerous?
Potentially, yes. Laser hazards depend on wavelength, output, enclosure and operating conditions. Industrial and workshop systems can present eye, skin, fire, fume and electrical hazards. Properly designed enclosed equipment relies on engineering controls such as guarding and safety interlocks to prevent access to hazardous laser radiation during normal operation.
An invisible beam must never be assumed to be harmless. Material suitability also matters because some materials can produce hazardous fumes or present other processing risks. LaserUser maintains a separate CO₂ Laser Material Safety Database for material-specific guidance.
Common questions about lasers
What does LASER stand for?
Light Amplification by Stimulated Emission of Radiation.
Is a laser just a very bright light?
No. Laser light is produced through stimulated emission and can have optical properties that allow it to be directed and focused far more effectively than ordinary broad-spectrum light.
Does every laser use two mirrors?
No. Two-mirror resonators are a useful way to understand many traditional lasers, but practical laser architectures vary. Semiconductor, fibre and other laser systems can use different forms of optical feedback and beam delivery.
Why can one laser process a material that another cannot?
The interaction depends strongly on wavelength and material absorption, together with power density, beam quality, pulse characteristics and process conditions. Two lasers with similar nominal wattage can therefore behave very differently.
Does more laser power always mean a better cut?
No. Greater available power can increase processing capability, but cut quality also depends on focus, beam quality, speed, assist air or gas, material properties, machine condition and the way the material absorbs the laser wavelength.
Where to go next
The next concepts to understand are wavelength, focus and focal length, beam quality and laser power. Together they explain why two machines described simply as “a 60 W laser” can produce very different results.
For manufacturer-specific information, see the Laser Manufacturer Knowledge Guides covering Trotec, Epilog, Universal Laser Systems and GCC LaserPro.
Technical references
The underlying laser-physics explanation on this page was checked against the US National Institute of Standards and Technology’s What Is a Laser? overview. The CO₂ wavelength discussion was cross-checked against the RP Photonics Encyclopedia entry on CO₂ lasers.
