What is Nd:YAG Laser? Construction, Working, Advantages, Disadvantages, and Applications.

Definition of Nd:YAG Laser

ND YAG laser is the short form used for Neodymium Yttrium Aluminum Garnet. Neodymium ion (Nd³⁺) Is a very effective laser medium. When it is doped in YAG (YAG which Y₃Al₅O₁₂ ) host material or glass host material.

In ND: YAG laser, The laser emission takes place at 1.06μm. Whereas in Nd : glass, the laser emission takes place at 1.05μm. Nd YAG laser has a four-level laser system that means these four energy levels take a part in laser action.

YAG is a very good host material. For Nd³⁺(Active medium) as it is very strong and has very high thermal conductivity. Therefore, this laser is capable of producing high power output without the breakage of Crystal.

Population inversion in Nd : YAG laser is achieve either by flash lamps or by GaAs semiconductor diode laser.

Nd:YAG Laser Working, Construction, Advantages, Disadvantages and Applications.

Construction of Nd:YAG Laser

The basic laser components are active or gain medium, pumping device or source and resonant cavity

1. The Active Medium ( or laser gain medium).

The main component of a laser is. A certain medium in the form of solid, liquid, or gas called an active medium. The active medium is Nd:YAG. The main characteristics of the active medium are as follow :

• It must have a pair of energy levels separate by a certain amount of energy. The energy level having high energy is known as upper energy level or higher excited state level. And the energy level having low energy is known as low energy level or ground state.
• it must allow a population inversion between two energy levels.

Active Medium:

Dielectric solid like neodymium atoms doped in YAG to make ND YAG crystals.

2. A Pumping Device.

It is an external source of energy. Which provides the necessary energy to the active medium to produce a state of the population inversion. And it is essential for lasing action.

The most commonly used methods of pumping are : (a) Optical Pumping. (b) Electric discharge (c) Inelastic atomic collision, (d) chemical reaction energy called chemical pumping.

3. Resonant Cavity.

Population inversion is achieved to amplify the signal by stimulated emission. However, in practice, most atoms in the excited state emit Spontaneously and do not contribute to the overall output. Only a few atoms in the excited state emit via stimulated emission.

Hence overall gain of the output is small. Therefore, we require a positive feedback mechanism to make most of the atom in the excited state.

And to emit via stimulated emission for contributing to the coherent output. A device used to have a positive feedback mechanism for Maximum coherent output is known as Resonator or resonant cavity.

Thus, resonant cavity or resonator is a feedback device. This makes the photon move back and forth through the active medium. In this process, the number of photons emitted due to stimulated emission are multiplied.

Resonant cavity consists of pair of planes or spherical Mirrors placed parallel to each at the end of the active medium. One of the mirror is a fully reflecting mirror and the other is a partially transmitting mirror.

The laser output is taken out through the partially transmitting mirror which is also called the output coupler mirror.

ND YAG Laser Working

The Nd:YAG laser is a four level laser and the energy diagram of Nd³⁺ ion.

In ND : YAG laser, Nd³⁺ ion is an active medium. Flash and arc lamps or diode lasers are used as the Optical pumping source. For the transition from energy level 4I  9/2 to 4F 5/3 energy level.

The excited electrons in the 4F5/3 energy level immediately fall to excited energy level 4F 3/2 through a radiationless transition.

The excited Nd³⁺ ions stay for a longer time ( approx 230μs) in the 4F 3/2 Energy level. These ions make a transition from 4F 3/2 energy to 4I 11/2 energy level by emitting a photon of wavelength 1.06μm.

The ions in the energy level 4I 11/2 Jump quickly to the ground level (4I 9/2) through the radiationless transition. The population of ions in the lower laser level (4I 11/2) is less than the population of ions in the upper laser level (4F 3/2). Hence population inversion is achieved.

The photon emitted ( λ = 1.06μm) during the transition from energy level 4F 3/2 to the energy level 4I 11/2 oscillates in the resonant cavity. And stimulate the transition from energy level F3/2 to the energy level 4I 11/2. Thus, a coherent beam of laser is obtained.

CHARACTERISTICS OF Nd:YAG LASER

Advantages of Nd:YAG Laser

• Nd:YAG laser has high energy output.
• Nd:YAG laser has very high repetition rate operation.
• It is much easy to achieve population inversion in Nd:YAG laser.

Disadvantage of Nd: YAG Laser

It is very hard to study the electron energy level structure of Nd3+ in YAG .

Applications of Nd:YAG Laser 

Nd:YAG Laser use for welding. 

In welding, a very high temperature is needed to melt and then join material. In the process of welding, material is added to join two components. For welding, laser beams must have high power rather than high peak power.

Carbon dioxide laser and neodymium – YAG laser are most commonly used in welding. However, laser power should not be high to evaporate the material.

Lasers are used in the manufacturing of aircraft and automobiles. Laser welding is easily formed between two dissimilar metals. Hence, a Thermocouple can be easily welded to a substrate without damaging and neighbouring material. 

Laser welding is also used effectively in electronics and microelectronics. Where precise welding of very thin wire and two thin film is required. Since laser welding is done in a very small interval of time.

Therefore welding with a laser is performed in a region in the neighborhood of the heat-sensitive area without damage.

For example, welding of part of a transistor is performed by a laser. Welding of components of inaccessible regions like inside a glass envelope can be done using lasers.

The main advantage of laser welding. Over the gas, welding is that the purity of material welded is not altered in case of laser welding. 

ND YAG Laser use for cutting. 

The removal of a part of material along the cut from a substance is known as the cutting process. To cut metal or nonmetal like stainless steel, Titanium, ceramics,glass, plastic, wood, paper etc.

The repetition frequency of the pulse of a laser and the motion of the laser across the substance. The material is adjusted in such a way that a series of overlapping holes are produced.

Carbon dioxide laser is commonly used in the cutting process due to its output power. The efficiency of laser cutting can be increased by making use of a gas Jet coaxial with the laser. 

In cutting hard material like stainless steel, carbon steel, Titanium etc. A highly reactive gas like oxygen is used along with a laser beam.

When a laser beam heats the material, it interacts with oxygen and get burnt. The Oxygen gas that also helps in expelling the molten material.

In cutting less hard material like good, plastic, paper etc. Inert gases like nitrogen and argon are used along with laser beams. This technique of cutting is very efficient for material absorbing most radiation of laser wavelength. The gas that you used helps in expelling the molten material. 

Laser cutting is used in the aircraft and automobile industries, diamond industry and in the textile industry for cutting clothes.

Nd:YAG Laser used in Medicine

ND YAG LASER for eye surgery.

Lasers have brought revolution in the field of medicine especially in eye surgery. The large scale use of lasers in eye surgery is due to the fact that the outer transparent region of the eye.

Allow light at a suitable wavelength to pass through for subsequent absorption by the tissues at the back of the eye. 

Laser beam is used in treating the detached retina. In this case, a laser beam (or laser pulse) is focused precisely at the desired spot on the retina. Where it produces a tiny spot weld ( the typical diameter of the spot is about 50 micrometers). 

Lasers are also used for vision correction. LASIK  ( Laser In-Sites Keratomileusis ) surgery is used to treat vision correction ( i.e. focusing defects) of the eye.

In this technique, the cornea of the eye is crafted to adjust its curvature. So that the proper focusing of light by the eye lens takes place on the retina.

4. ND YAG Laser used for induced thermotherapy.
5. The ND YAG Laser used to cure skin cancer. 
6. ND YAG Laser used in rangefinders.