In photonics since 1999. Benelux technical support, answer within one working day.
Why a helium-neon laser is still the alignment reference
A helium-neon laser oscillates on an atomic transition, so its wavelength is fixed by physics rather than by temperature and drive current. For alignment, interferometry and anything calibrated against a known wavelength, that stability is worth more than the convenience of a diode.
THE SHORT ANSWER
A helium-neon laser oscillates on an atomic transition, so its wavelength is fixed by physics rather than by temperature and drive current. For alignment, interferometry and anything calibrated against a known wavelength, that stability is worth more than the convenience of a diode.
| Wavelength | 632,8 nm |
|---|---|
| Wavelength stability | Set by the atomic transition |
| Typical output | 0,5 to 5 mW |
| Beam quality | TEM00, near diffraction limited |
| Polarisation | Linear on polarised models |
| Supply | High voltage, with interlock terminals |
Diode lasers are smaller, cheaper, more efficient and available at almost any wavelength. A helium-neon head is none of those things, and it is still what sits on the bench when the wavelength has to be right.
Physics as the specification
A HeNe oscillates on a neon transition at 632,8 nm. The wavelength is a property of the atom. It does not shift with drive current, it does not walk with heatsink temperature, and it does not mode-hop to somewhere convenient. A diode’s wavelength is set by a semiconductor bandgap and a cavity, and both move.
For imaging or excitation, nobody cares. For interferometry, where fringe spacing is your ruler, a wavelength that drifts is a ruler that stretches.
Beam quality that comes free
The gain geometry of a gas tube produces a clean TEM00 mode with a round, near diffraction limited beam and no astigmatism to correct. Getting comparable quality from a diode means adding circularisation optics, which is exactly what the better diode modules do and part of what they cost.
The real costs
You need a high-voltage supply with proper interlock wiring, several minutes of warm-up before the output settles, and acceptance that efficiency is poor and the tube has a life. In exchange you get a wavelength you can trust and a beam you do not have to fix.
When to choose which
If the wavelength is the measurement, use a HeNe. If the light is only there to illuminate, excite or carry power, use a diode and spend the difference elsewhere.
When to use it
- Interferometry, where a known and stable wavelength is the measurement standard
- Alignment references for optical benches and instruments
- Teaching laboratories, where beam quality and reliability matter
- Calibrating or checking a diode-based system against a trusted source
What to watch out for
- HeNe heads need a high-voltage supply and interlock wiring; treat this as an installation, not a plug-in
- Warm-up takes minutes before the output is stable
- Wall-plug efficiency is poor compared with a diode
- The tube has a finite life and is not repairable in the field
Still deciding?
Tell us the wavelength, the aperture and what you are measuring. We answer with a part number, a price and a lead time, usually the same working day.