In short
- Four families. Most applications choose between solid-state, fiber, gas and diode lasers. Each has its own strengths, limits and typical uses.
- Efficiency differs widely. Solid-state lasers convert only a few percent of input power, gas lasers about 5–20% and laser diodes about 20–70%.
- Stability or convenience. Gas lasers drift very little in wavelength; laser diodes are cheap, compact and easy to modulate, but their wavelength moves with temperature.
- Start from the critical requirement. Wavelength stability for interferometry, low power where safety comes first, efficiency where heat is a problem. The 10 criteria and the drift calculator below help you decide.
Why the choice of laser matters
Lasers are now used in almost every industry, and choosing the right one can make an application work better, cost less and last longer. They have been around for decades and appear in optics, electronics, communications and surgery, as well as in consumer products such as DVD players.
Four main families are in common use: solid-state, fiber, gas and diode lasers. Each has advantages and drawbacks, so each suits particular purposes. The sections below describe them, and the checklist that follows turns the differences into 10 practical selection criteria.
The four main laser types
Solid-state lasers
Solid-state lasers were the first lasers. The ruby laser was the first to be built, following an earlier device, the ruby maser. A solid-state laser uses a crystal as its gain medium, which gives good stability, so these lasers are useful for laboratory references and testing.
Their efficiency is low, usually a few percent. Their main limits are a restricted choice of wavelengths and narrow tuning. In diode-pumped solid-state (DPSS) lasers the crystal is pumped by a laser diode instead of the traditional xenon flash lamp, which raises efficiency and reduces heat. (For flash-lamp physics, see applications for pulsed flash lamps.)
Fiber lasers
In a fiber laser, stimulated emission takes place inside the doped fiber itself. Fiber Bragg gratings written near each end of the fiber reflect the light and form the cavity that mirrors would form in other lasers. Fiber lasers and amplifiers are a natural fit for fiber-optic and telecom systems; the erbium-doped fiber amplifier (EDFA) is the most widely used fiber amplifier in industry. For the basics of light guiding, see a beginner’s guide to fiber optics.
Gas lasers
Gas lasers use a gas as the gain medium. They offer high gain without external amplifiers, high output power, good stability and very little wavelength drift. The drawback is that the gas must be held in a sealed chamber.
The CO₂ laser is the most common gas laser, especially in surgery and other medical procedures. Helium-neon (HeNe) lasers are used in spectroscopy, interferometry and alignment. Gas lasers cover wavelengths from the ultraviolet through the visible to the infrared. Their efficiency is moderate, about 5–20%, but their stability and reliability are high.
Laser diodes
A laser diode is a p-n or p-i-n semiconductor junction that emits light when current flows through it. There are two main designs: edge-emitting diodes and vertical-cavity surface-emitting lasers (VCSELs). The beam of an edge emitter is elliptical and diverges quickly, so it is usually collimated with a cylindrical lens or reshaped with an anamorphic prism pair. VCSELs emit a round beam and avoid this problem. Diode lasers can be coupled to optical fiber either by direct (butt) contact or through free-space optics.
Laser diodes have a high conversion efficiency, from about 20% to 70% depending on drive current and materials. That makes them the first choice where heat or power consumption must be controlled, and they are low in cost. The drive current sets the output power. Diodes are available at many wavelengths, but the wavelength drifts substantially with temperature, which is why precision diode sources are temperature-controlled with a thermoelectric cooler (TEC).
Laser diodes are easy to integrate into electronic circuits and circuit boards, and they can be simulated in circuit-design software. They need no external shutter or acousto-optic modulator, because the drive current itself modulates the light. A laser diode operated in reverse bias even works as a photodetector.
The four types at a glance
| Type | Efficiency | Strengths | Limits | Typical uses |
|---|---|---|---|---|
| Solid-state | A few % | Stable output | Limited wavelengths, narrow tuning | Laboratory references, testing; DPSS sources |
| Fiber | Typically high | Cavity and gain inside the fiber, fiber-ready output | Best suited to fiber-based systems | Telecom, fiber-optic systems, EDFA amplifiers |
| Gas | About 5–20% | High gain and power, very low wavelength drift, reliable | Sealed gas chamber | CO₂: surgery and medical; HeNe: spectroscopy, interferometry, alignment |
| Diode | About 20–70% | Low cost, compact, direct current modulation, easy circuit integration | Wavelength drifts with temperature; edge emitters need beam shaping | Electronics, sensing, pumping, fiber coupling |
10 criteria for choosing the laser for the job
Choosing a laser starts with the most critical requirement of the system. Work through this list and note which criteria are hard limits and which are preferences:
- WavelengthWhat the target, detector or fiber needs. Gas lasers span UV to IR; diodes come in many wavelengths; solid-state lasers offer fewer choices.
- Wavelength stabilityCritical for interferometry and spectroscopy, minor for illumination or motion detection. Gas lasers drift least; diodes need temperature control.
- Output powerEnough signal, but no more than needed: the lowest practical power improves safety.
- Efficiency and heatA few percent for solid-state, about 5–20% for gas, about 20–70% for diodes.
- Beam shape and qualityEdge-emitting diodes give elliptical, fast-diverging beams that need collimation; VCSELs give round beams.
- ModulationDiodes are modulated directly by the drive current, with no external shutter or acousto-optic modulator.
- Fiber deliveryFiber lasers are fiber-native; diodes couple to fiber by direct contact or through free-space optics.
- Integration and sizeDiodes mount on circuit boards and can be simulated in design software; gas lasers need a sealed tube.
- Stability and reliability over timeGas and solid-state lasers are known for stable output, which suits reference and test set-ups.
- Cost and safetyDiodes are the low-cost option. Wherever people are exposed, choose the lowest power that does the job.
Wavelength drift and interferometric measurements
Wavelength drift matters when a small instability changes the result. In motion detection or illumination it hardly matters. In interferometric measurements of surface texture, thin films or coatings, the wavelength is the ruler: a wavelength error becomes a measurement error, and over a long optical path it becomes a large one. The relative length error equals the relative wavelength error, Δλ/λ, and a fixed optical path difference shifts by ΔN = OPD·Δλ/λ² fringes. The calculator below shows what a temperature change does to a diode-based interferometer. For flatness testing in practice, see interferometer testing for precision flatness measurement.
How much does wavelength drift cost your measurement?
Choose a source or enter its temperature coefficient, then the temperature change and the optical path difference (or measured length). The coefficients are typical values; use your laser’s datasheet value for a real design.
Conclusion: choose, then verify
The type of laser can decide whether a product succeeds. There are many options, so identify the critical requirements first, take expert advice and test thoroughly. Testing means measuring the beam itself: its profile and size with a laser beam profiler, its power with a multi-channel power meter, and, for diode sources, the thermoelectric cooler that holds the wavelength, with the TEC tester. For the full list of laser parameters worth measuring, see essential laser measurements and the essentials of laser beam profiling.
Free engineering tool
Gaussian Beam CalculatorRayleigh range, divergence and beam size at any distance, for the laser you are about to choose.Frequently asked questions
QWhich laser type is the most efficient?
QWhich laser should I use for interferometry?
QWhy does a laser diode’s wavelength change with temperature?
Tzachi Sabati
CEO, IZAK Scientific
Physicist specializing in photonics and quantum technologies, with deep expertise in quantum sensors and advanced optical systems. Leads the Advanced Quantum Lab course at the Technion, bridging academic excellence with industry innovation. At IZAK Scientific, provides cutting-edge photonics-based solutions, developing customized inspection and sensing systems for R&D and production. Passionate about advancing quantum sensing applications and integrating novel technologies to meet industry needs.
