Helium Neon Laser

Summary

This video explains the principles and workings of a Helium-Neon (HeNe) laser, the first gas laser developed in 1961. It is a four-level laser system that utilizes helium and neon gases in a 10:1 ratio for efficient pumping via electrical discharge. The helium atoms help excite neon atoms to higher energy states, facilitating population inversion, which is crucial for laser action. The laser produces two key wavelengths: 632.8 nm (red) and 1.15 µm (infrared). HeNe lasers are widely used in research and educational labs due to their monochromatic, highly directional output and low power requirements.

Takeaways

• 😀 The Helium-Neon (HeNe) laser is a four-level gas laser developed in 1961 by Ali Jawan and his team at Telephund Laboratories.
• 😀 The laser uses an electrical discharge method for pumping, which excites helium and neon atoms to higher energy states.
• 😀 The HeNe laser consists of a long, narrow discharge tube filled with helium and neon gases in a 10:1 ratio.
• 😀 Population inversion is achieved through resonant energy transfer between helium and neon atoms, helping neon atoms reach higher energy levels.
• 😀 Neon atoms accumulate in metastable states (E4 and E6), leading to population inversion necessary for laser action.
• 😀 The HeNe laser emits primarily red light with a wavelength of 632.8 nm, but also emits in the infrared range (1.15 µm and 3.39 µm).
• 😀 The output power of the HeNe laser typically ranges from 1 mW to 50 mW, but the intensity is very high for such low output power.
• 😀 HeNe lasers are highly directional and monochromatic, making them ideal for use in research and educational applications.
• 😀 The design of the HeNe laser does not require complex cooling systems, making it relatively simple to maintain.
• 😀 HeNe lasers are commonly used in laboratory experiments, optical systems, interferometry, holography, and metrology.

Q & A

What is a helium neon laser and who developed it?

A helium neon laser is a four-level gas laser developed by Ali Jawan and his co-workers at Bell Laboratories in the USA in 1961.

What is the pumping method used in a helium neon laser?

The helium neon laser uses the electrical discharge method for pumping, where high voltage is applied to excite the gas atoms, resulting in the ionization of the gas and the acceleration of electrons.

What gases are used in a helium neon laser, and in what ratio?

A helium neon laser uses a mixture of helium and neon gases in a ratio of 10:1, with helium filled at a pressure of 1 millimeter of mercury and neon at a pressure of 0.1 millimeter of mercury.

What is the role of the helium atoms in a helium neon laser?

The helium atoms facilitate the excitation of neon atoms to higher energy levels through a process called resonant energy transfer, where helium atoms transfer their energy to neon atoms.

How does the resonant energy transfer process work in a helium neon laser?

In resonant energy transfer, helium atoms in higher energy states (F2 and F3) collide with neon atoms in the ground state (E1), transferring energy that excites the neon atoms to higher energy levels (E4 and E6).

Why is a metastable state important for laser action in a helium neon laser?

Metastable states are crucial because atoms in these states can retain their energy for a longer period, allowing a population inversion to occur, which is necessary for stimulated emission and laser action.

What are the key energy levels involved in the population inversion of a helium neon laser?

The population inversion in a helium neon laser occurs between the metastable states of neon atoms (E6, E4) and other higher excited states (E5, E3), leading to stimulated emission.

What types of laser radiation are produced by a helium neon laser?

A helium neon laser produces laser radiation at wavelengths of 3.39 micrometers (infrared), 1.15 micrometers (infrared), and the predominant red laser radiation at 632.8 nanometers (visible).

Why is the helium neon laser often used in laboratories despite its low power output?

Despite its low power output (ranging from 1 milliwatt to 50 milliwatts), the helium neon laser is commonly used in laboratories because it provides highly monochromatic, directional light, and requires no special cooling arrangements.

What happens to the neon atoms in the E3 level after the stimulated emission in a helium neon laser?

After the stimulated emission, neon atoms in the E3 level drop spontaneously to the E2 level, which is a metastable state, and can then be pumped back to the ground state (E1) by collision with the discharge tube.