HeNe Lasers: Red
(Center to Outer Cylinder)
(Parallel to Outer Cylinder)
|Starting Voltage||<10,000 VDC|
|Shock for 11 ms||25 g|
|Operating Temperature||-40 to 70 °C|
|Storage Temperature||-40 to 150 °C|
|Relative Humidity (Non-Condensing)||0 to 100%|
|Operating Altitude||0 to 10,000 ft|
|Storage Altitude||0 to 70,000 ft|
- 14 Models with 632.8 nm Central Wavelength
- Linearly or Randomly Polarized Output Beams
- Output Powers from 0.8 mW - 22.5 mW
- Includes Power Supply
- Confocal Microscopy
- Laboratory Use in Polarization Experiments
- DNA Sequencing
- Flow Cytometry
- Semiconductor Inspection
Thorlabs offers an extensive selection of CE compliant 632.8 nm (red) Helium-Neon (HeNe) Lasers with powers from 0.8 mW to 22.5 mW from stock. In addition to the applications listed above, HeNe lasers are widely used in education and as alignment tools due to their excellent beam quality and gas discharge laser characteristics. Depending upon the model, the output beam is either linearly polarized or randomly polarized (unpolarized). The polarization state of a randomly polarized HeNe changes on nanosecond timescales.
Specifications common to all of the lasers featured on this page are listed in the table above, and model-dependent information is given in the tables below. The packages here all feature remote interlock connections and integrated shutters.
For specialized applications, Thorlabs offers a Stabilized Red HeNe Laser, which is capable of either ±2 MHz stabilization in frequency stabilization mode, or ±0.2% power stabilization in intensity stabilization mode.
A Helium-Neon laser, typically called a HeNe laser, is a small gas laser with many industrial and scientific uses. These lasers are primarily used at 632.8 nm, which is in the red portion of the visible spectrum. Thorlabs' line of red Helium-Neon gas lasers have stable output powers from 0.5 to 22.5 mW and a fundamental Gaussian beam. Depending on the model chosen, the output will be either linearly polarized or randomly polarized (unpolarized).
The gain medium of a HeNe laser is a mixture of helium and neon gases in a 5:1 to 20:1 ratio that is contained at low pressure in a sealed glass tube. The excitation source for these lasers is a high-voltage electrical discharge through an anode and cathode at each end of the glass tube. The optical cavity of the laser consists of a flat, high-reflecting mirror at one end of the laser tube and an output coupler mirror with approximately 1% transmission at the other end (see figure below). HeNe lasers tend to be small, with cavity lengths from around 15 cm to 0.5 m and optical output powers ranging from 1 mW to 100 mW. Thorlabs offers output powers up to 22.5 mW.
Optical Resonator Cavity
(1) Laser Bore, (2) Intracavity Beam, (3) Collimating Lens, (4) Output Beam
|Typical HeNe Parameters|
|Beam Diameter||1 mm|
|Full Angle Beam Divergence (α)||1.5 mrad|
|Cavity Length (L)||0.15 m (0.5 mW) to 1 m (50 mW)|
|Reflectivity at High Reflector (HR)||>99.99%|
|Transmission at Output Coupler (OC)||~1%|
Unpolarized (Randomly Polarized) Beam
Most common HeNe laser tubes are randomly polarized since for many applications the polarization of the beam does not matter. The term "random" here does not mean that the polarization is changing to totally arbitrary orientations or at high frequency. In fact, such behavior would be rather unusual. It just means that nothing special is done to control the polarization. The typical random polarized HeNe laser will lase on several longitudinal modes (how many will depend on the tube length of the resonator), with adjacent modes having polarizations orthogonal to each other, and the polarization axes fixed for the life of the tube. Each of the modes will change their relative intensities periodically over time, most notably during warmup as the cavity length changes due to thermal expansion.
Random polarized lasers are acceptable for applications where there are no polarizing elements in the beam path. Depending on the time scale of an application, polarizing elements could result in large power fluctuations. Reorienting the laser head (about its axis) may help to minimize these, but the use of a linearly polarized laser is the best solution.
The state of polarization in a polarized HeNe laser beam is linear, making these lasers ideal for polarization-sensitive applications.
A red HeNe laser outputs at 632.816 nm in air, although it is often reported as either 632 nm or 633 nm. The wavelength gain curve of a HeNe laser is actually made up of several longitudinal modes that fluctuate within the gain curve due to thermal expansion of the cavity and other external factors.
The linewidth of a HeNe laser is specific to the application. The longitudinal mode structure of the HeNe laser is characterized by the number of modes, the free spectral range (FSR), and the Doppler width (see figure below). The linewidth of individual longitudinal modes is usually small (~kHz) and is primarily determined by external factors and measurement timescales, rather than fundamental laser parameters. In most interferometric applications, the most relevant parameter is the coherence length, which is determined by the longitudinal modes that are farthest apart. For a red HeNe laser, the coherence length is approximately 30 cm.
HeNe Gain Curve
HeNe Energy Levels
HeNe Energy Levels
The laser process in a HeNe laser starts with the collision of electrons from the electrical discharge with the helium atoms in the gas. This excites helium from the ground state to a long-lived, metastable excited state. Collision of excited helium atoms with ground-state neon atoms results in excited neon electrons.
The number of neon atoms entering the excited states builds up until population inversion is achieved. Spontaneous and stimulated emission between the states results in emission at 632.82 nm, along with other emission wavelengths (see figure at right). From these states, the electrons quickly decay to the ground state. The HeNe laser's power output is limited because the neon upper level saturates with higher current, while the lower level varies linearly with current.
The laser cavity can be designed with the correct mirrors and length to promote other wavelengths of laser emission. There are infrared transitions at 3.39 µm and 1.15 µm wavelengths and a variety of visible transitions, including a green (543.365 nm), yellow (593.932 nm), yellow-orange (604.613 nm), and orange (611.802 nm) transition (see figure below). The typical red 632.8 nm wavelength output of a HeNe laser has a much lower gain compared to other wavelengths, such as the 1.15 µm and 3.39 µm lines.
- Cleanroom Monitoring Equipment
- Food Sorting
- Flow Cytometry
- Confocal Microscopy
- Imaging and Medical Equipment
- Opacity Monitoring
- Maritime Visual Guidance Systems
Environment is an important factor in achieving optimum laser performance. In dirty environments, the optics can become contaminated, which causes the power output to drop below expected levels. Unstable output beams can be caused by noisy environments with large sources of vibrations. Proper mounting on an optical table can reduce the effects of ambient vibrations. If the environment where the laser is being used fluctuates in temperature, the output power can experience a large amplitude change. While a HeNe laser is less sensitive to variations caused by back reflections, large retro-reflections into the laser can cause unpredictable power changes. A free-space isolator can be used to reduce or eliminate these effects. This line of HeNe lasers is ill-suited to any application or experiment where single frequency or long coherence length is required. For questions about the suitability of a HeNe laser to a particular application, please contact Technical Support.
Laser Safety and Classification
Safe practices and proper usage of safety equipment should be taken into consideration when operating lasers. The eye is susceptible to injury, even from very low levels of laser light. Thorlabs offers a range of laser safety accessories that can be used to reduce the risk of accidents or injuries. Laser emission in the visible and near infrared spectral ranges has the greatest potential for retinal injury, as the cornea and lens are transparent to those wavelengths, and the lens can focus the laser energy onto the retina.
Safe Practices and Light Safety Accessories
- Thorlabs recommends the use of safety eyewear whenever working with laser beams with non-negligible powers (i.e., > Class 1) since metallic tools such as screwdrivers can accidentally redirect a beam.
- Laser goggles designed for specific wavelengths should be clearly available near laser setups to protect the wearer from unintentional laser reflections.
- Goggles are marked with the wavelength range over which protection is afforded and the minimum optical density within that range
- Laser Barriers and Blackout Materials can prevent direct or reflected light from leaving the experimental setup area.
- Thorlabs' Enclosure Systems can be used to contain optical setups to isolate or minimize laser hazards.
- All beams should be terminated at the edge of the table, and laboratory doors should be closed whenever a laser is in use.
- Do not place laser beams at eye level.
- Carry out experiments on an optical table such that all laser beams travel horizontally.
- Remove unnecessary reflective items such as reflective jewelry (e.g., rings, watches, etc.) while working near the beam path.
- Be aware that lenses and other optical devices may reflect a portion of the incident beam from the front or rear surface.
- Operate a laser at the minimum power necessary for any operation.
- If possible, reduce the output power of a laser during alignment procedures.
- Use beam shutters and filters to reduce the beam power.
- Post appropriate warning signs or labels near laser setups or rooms.
- Use laser sign lightboxes if operating Class 3R or 4 lasers (i.e., lasers requiring the use of a safety interlock).
- Do not use Laser Viewing Cards in place of a proper Laser Barrier or Beam Trap.
Lasers are categorized into different classes according to their ability to cause eye and other damage. The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic, and related technologies. The IEC document 60825-1 outlines the safety of laser products. A description of each class of laser is given below:
|1||This class of laser is safe under all conditions of normal use, including use with optical instruments for intrabeam viewing. Lasers in this class do not emit radiation at levels that may cause injury during normal operation, and therefore the maximum permissible exposure (MPE) cannot be exceeded. Class 1 lasers can also include enclosed, high-power lasers where exposure to the radiation is not possible without opening or shutting down the laser. |
|1M||Class 1M lasers are safe except when used in conjunction with optical components such as telescopes and microscopes. Lasers belonging to this class emit large-diameter or divergent beams, and the MPE cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. However, if the beam is refocused, the hazard may be increased and the class may be changed accordingly. |
|2||Class 2 lasers, which are limited to 1 mW of visible continuous-wave radiation, are safe because the blink reflex will limit the exposure in the eye to 0.25 seconds. This category only applies to visible radiation (400 - 700 nm).|
|2M||Because of the blink reflex, this class of laser is classified as safe as long as the beam is not viewed through optical instruments. This laser class also applies to larger-diameter or diverging laser beams. |
|3R||Lasers in this class are considered safe as long as they are handled with restricted beam viewing. The MPE can be exceeded with this class of laser, however, this presents a low risk level to injury. Visible, continuous-wave lasers are limited to 5 mW of output power in this class. |
|3B||Class 3B lasers are hazardous to the eye if exposed directly. However, diffuse reflections are not harmful. Safe handling of devices in this class includes wearing protective eyewear where direct viewing of the laser beam may occur. In addition, laser safety signs lightboxes should be used with lasers that require a safety interlock so that the laser cannot be used without the safety light turning on. Class-3B lasers must be equipped with a key switch and a safety interlock.|
|4||This class of laser may cause damage to the skin, and also to the eye, even from the viewing of diffuse reflections. These hazards may also apply to indirect or non-specular reflections of the beam, even from apparently matte surfaces. Great care must be taken when handling these lasers. They also represent a fire risk, because they may ignite combustible material. Class 4 lasers must be equipped with a key switch and a safety interlock. |
|All class 2 lasers (and higher) must display, in addition to the corresponding sign above, this triangular warning sign|