Helium–neon laser

A red laser makes a bright beam.

It uses two kinds of gas. These gases live in a glass tube.

One gas is helium. It helps the other gas, neon. Electricity makes the helium move fast. The helium hits the neon. This makes the neon glow red.

This light can scan things at a store. It is also used in science labs. Some lasers can even show many colors like green or orange.

It is a very useful tool.

A helium-neon laser makes a very steady beam of light.

Most people know them as red lasers. This is because they shine in the red part of the rainbow.

Inside a glass tube, there is a mix of two gases. This mix is mostly helium. There is also some neon.

To start the laser, electricity flows through the gas. This electricity makes the helium atoms move with a lot of power. These fast helium atoms hit the neon atoms. This process passes power from the helium to the neon.

When the neon atoms get this power, they become excited. They then give off light. To make a laser beam, the tube has two mirrors at the ends. One mirror reflects almost all the light back. The other mirror lets a small part of the light out. This light travels in a straight line.

These lasers are very useful. They were once used in barcode scanners at stores. Scientists also use them in labs to study light. They can even help define how long a meter is.

A helium-neon laser is a special kind of gas laser. It creates a very steady and narrow beam of light.

Most people recognize these lasers by their bright red color. This color comes from the light being in the red part of the visible spectrum. These lasers are very important for science and industry. They are used for things like making holograms or studying light in labs. They were even used in barcode scanners at grocery stores for a long time.

Inside a glass tube, there is a mixture of two gases. This mixture is mostly helium, with some neon added. The ratio of helium to neon is usually between 5:1 and 10:1.

To make the laser work, electricity flows through the gas. This electrical discharge gives energy to the helium atoms. These excited helium atoms then bump into the neon atoms. This collision transfers the energy to the neon. This step is what allows the neon to produce the laser light.

Scientists first created these lasers at Bell Telephone Laboratories. The very first helium-neon lasers were shown in December 1960. These early models did not shine with visible light. Instead, they emitted infrared light at a wavelength of 1150 nm. Researchers wanted a laser that people could actually see. They studied many different neon transitions to find the best one. They eventually found that the 633 nm line gave the best results for visible light. This became the standard for most helium-neon lasers.

Most common red lasers work at a wavelength of 632.8 nm. In a vacuum, this wavelength is exactly 632.991 nm. The laser tube is usually quite small. Most cavities are between 15 and 50 cm long. Some very powerful versions can be up to 1 meter long. The light power is often between 0.5 and 50 mW. To guide the light, the tube uses two mirrors at the ends. One mirror reflects 99.9% of the light back inside. The other mirror is an output coupler that lets about 1% of the light escape.

You might see these lasers used in high-tech tools. For example, they are used in laser gyroscopes. These devices help with navigation in some commercial aircraft.

They are also used in making tiny computer parts. Because they are so precise, they help define how long a meter is. In the past, they were even inside LaserDisc players. Even though new types of lasers exist now, helium-neon lasers remain very useful in research labs. They help scientists see and measure the world with great detail.

A helium–neon laser, or He–Ne laser, is a specific type of gas laser. It uses a mixture of helium and neon gases to create a steady beam of light.

This device is highly valued for its high spectral purity. This means the light it produces is very concentrated in a narrow range of colors. Most people recognize these lasers by their bright red light. This light comes from a specific wavelength in the red part of the visible spectrum. Because they produce such high-quality light, these lasers are vital tools in scientific research and industrial manufacturing.

The mechanism of the laser begins with a gas mixture inside a glass envelope. The mixture consists of helium and neon in a ratio between 5:1 and 10:1.

The total pressure inside the tube is kept low, at approximately 1 Torr. To start the process, a high-voltage electrical discharge is passed through the gas between an anode and a cathode. This discharge provides the energy needed to excite the atoms. A DC current of 3 to 20 mA is typically used to maintain this continuous operation. This electrical energy is the "pump" that drives the entire system.

Once the electricity flows, the helium atoms begin to react. Energetic electrons from the discharge collide with ground-state helium atoms. These inelastic collisions push the helium atoms into higher, metastable excited states.

Because the mixture contains mostly helium, there are many excited helium atoms ready to interact. These excited helium atoms then collide with the neon atoms. Through this process, the energy is transferred from the helium to the neon atoms. This transfer increases the population of certain neon energy levels, such as the 4s2 and 5s2 levels. When more atoms exist in these upper levels than in the lower levels, a state called population inversion is achieved.

Population inversion is the key to light amplification. In a He–Ne laser, the neon atoms eventually drop from these excited states to a lower level called 3p4. As they drop, they release energy in the form of light. This is known as stimulated emission. To turn this light into a concentrated beam, the laser uses an optical cavity. This cavity usually consists of two mirrors at the ends of the tube. One mirror is highly reflective, often reflecting 99.9% of the light. The other mirror, called the output coupler, allows about 1% of the light to pass through. As the light bounces back and forth between these mirrors, it passes through the gas repeatedly. Each pass amplifies the light until a stable, continuous beam exits through the output coupler.

The history of the He–Ne laser is tied to the early days of laser science. The first gas lasers were developed at Bell Telephone Laboratories. In December 1960, researchers demonstrated the first continuous-wave infrared He–Ne laser. This first version emitted light at a wavelength of 1150 nm, which is invisible to the human eye. Scientists soon realized that visible light was in much higher demand. They investigated many different neon transitions to find the best visible light source. They discovered that the 633 nm line provided the highest gain in the visible spectrum. This discovery led to the development of the red He–Ne lasers we use today.

Most standard red He–Ne lasers operate at a center wavelength of 632.8 nm in air. In a vacuum, this wavelength is precisely 632.991 nm.

The laser's output power is generally quite low, ranging from 0.5 to 50 mW. The length of the laser cavity typically stays between 15 and 50 cm, though some high-power versions reach 1 meter. These lasers are incredibly precise. For example, frequency-stabilized versions can specify a wavelength to within 1 part in 10^8. Using an iodine absorption cell, scientists can achieve absolute frequency stabilization as fine as 2.5 parts in 10^11. This level of precision makes them essential for measuring the physical world.

Because of this precision, He–Ne lasers have many important applications. They are used in holography and as wavelength references for spectroscopy. In the past, they were common in supermarket barcode scanners. They were also used in LaserDisc players from 1978 until the mid-1980s. Today, they are vital for nano-positioning in semiconductor device fabrication. They are also used in high-precision laser gyroscopes for navigation in commercial aircraft.

These gyroscopes use a ring laser configuration to help planes stay on course. From helping build computer chips to navigating the skies, the He–Ne laser remains a cornerstone of modern technology.