helium neon lasers selection guide    helium neon lasers selection guide

Image credit: Thorlabs | Piezosystems Jena

 

Helium neon (HeNe) lasers are gas lasers which use a mixture of helium and neon to achieve optical gain.

 

Basic HeNe Laser Information

 

Construction and Operation

All lasers consist of three components: an energy source (or pump), a gain medium, and an optical resonator; these components are shown in the diagram below. Essentially, the pump provides energy which is amplified by the gain medium. This energy is eventually converted into light and is reflected through the optical resonator which then emits the final output beam.

 

helium neon lasers selection guide

Image credit: Enlighten Your Mind

 

Considering these commonalities, HeNe lasers must consist of three main component groups:

 

  • A high voltage electrical current source, which functions as the pump.
  • A mixture of helium and neon gases at a concentration of 10:1, which acts as the laser's gain medium.
  • A series of mirrors functioning as the optical resonator. HeNe lasers typically employ at least one highly reflective mirror to redirect the beam to the output point, as well as an output coupler to focus the output beam.

 

 

helium neon lasers selection guide

A cutaway view of a typical HeNe laser.

Image credit: Olympus

 

When voltage is applied from the power supply, the cathode — which is directly connected to the gas reservoir containing the HeNe mixture — supplies electrical current. The introduction of current excites the helium atoms, which in turn excite the neon atoms, causing them to radiate photonic energy at a wavelength of 632.8 nm. This energy is then funneled into the laser's bore, where it is reflected back and forth through the laser by two highly reflective mirrors. Each time the beam is reflected it strengthens in intensity. Since one of the mirrors reflects 100% of the radiation while the other reflects only 99%, the resulting 1% is emitted as a continuous, focused beam.

 

An excellent explanation of HeNe laser operation.

Video credit: University College of London

 

Some HeNe lasers do not use internal mirrors but instead use a single Brewster window. When mounted at a special angle (known as the Brewster angle) the window linearly polarizes the energy, eliminating the need for the radiation to be continuously reflected within the laser. The use of a Brewster window results in an extremely efficient laser due to the fact that all radiation is essentially emitted as an output beam.

 

Helium neon lasers are famed for their long operating lives (up to 50,000 hours of continuous use) mostly due to the fact that only two main conditions can cause a decrease in efficiency or device failure:

 

  • Deterioration of the cathode's oxide coating, which can eventually cause sputtering of aluminum.
  • Helium leakage due to a broken seal or diffusion through glass; this can cause reduced lasing ability until the laser fails completely.

 

Applications

Helium neon lasers are low-cost and simple to use when compared with other gas lasers. They have historically been used for many applications within the fields of microscopy, barcode scanning, spectroscopy, optical disc reading, biomedical engineering, metrology, and holography. Since the introduction and improvement of semiconductor lasers, however, many users are now utilizing smaller and more efficient laser diodes in place of HeNe lasers, especially in confocal microscopy.

 

Specifications

 

Wavelength

As stated above, the interaction of excited helium atoms with neon atoms causes emission of 632.8 nm radiation. For this reason, a large majority of HeNe lasers emit 633 nm (red) beams, as this wavelength results in the simplest laser and relies on the basic interaction of the electrical pump and the gas medium. However, by using specially-coated optical components, the basic 633 nm beam can be altered to other wavelengths and colors. Other common helium neon laser wavelengths include 543.5 nm (green), 594.1 (yellow), 611.9 (orange), and infrared at 1523 or 3921 nm.

 

Power

A laser's power is measured in watts (W) or milliwatts (mW) and is used to describe the strength of the laser's beam. HeNe lasers are relatively low-power devices, especially when compared with carbon dioxide gas lasers, and typically have power ratings between 0.5 mW and 50 mW.

 

Safety

Despite the low power output capabilities, laser safety is an important topic to consider when discussing HeNe lasers despite their typically low power output. Even a split-second direct exposure to a 200 mW laser emitting 100 yards away can cause permanent eye damage.

 

helium neon lasers selection guide

A laser warning sign, including specs and class.

Image credit: Keller Studio

 

To address the concerns above, the Center for Devices and Radiological Health (CDRH) — a division of the US Food and Drug Administration (FDA) — provides a laser safety classification scheme based on six product classes. Lasers are also specified by different classes described in the international IEC 60825 standard. The table below describes both US and international classes for laser safety.

 

helium neon lasers selection guide

Laser safety classes. Image credit: Erchonia

 

 

References

 

Olympus - Helium neon lasers

 

Power Technology Inc. - HeNe lasers (pdf)

 

Sam's Laser FAQ - Helium neon lasers

 

 


Related Products & Services

  • Carbon Dioxide (CO2) Lasers

    Carbon dioxide (CO2) lasers use the energy-state transitions between vibrational and rotational states of CO2 molecules to emit at long IR, about 10 µm, wavelengths. These lasers can maintain continuous and very high levels of power and are typically used in cutting, welding, etching, and marking applications.

  • Helium Cadmium (HeCd) Lasers

    Helium cadmium (HeCd) lasers are relatively economical, continuous-wave sources for violet (442 nm) and ultraviolet (325 nm) output. They are used for 3-D stereolithography applications, as well as for exposing holographs.

  • Ion Lasers

    Ion lasers function by stimulating the emission of radiation between two levels of an ionized gas. They provide moderate to high continuous-wave output of typically 1 mW to 10 W.

  • Laser Pointers

    Laser pointers are compact instruments that produce a low-power, visible laser light. They are often used for pointing out features on a projected visual display.

  • Lasers

    Lasers are devices that produce intense beams of monochromatic, coherent radiation. The word "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation.

  • Nitrogen Lasers

    Nitrogen lasers are an excellent source of high intensity, short pulse, ultraviolet radiation. They can be used as an excitation source, or as a pump for a dye laser.

  • Solid State Lasers

    Solid state lasers use a transparent substance (crystalline or glass) as the active medium, doped to provide the energy states necessary for lasing.  Solid state lasers are used in both low and high power applications.