TYPES OF LASER

How many types of laser are there?

The two main types of laser are mentioned as follows:

PYROLITHIC AND PHOTOLITHIC LASER

The laser beam has a high power density, especially when it is focused on a small spot on the surface of the workpiece .

Depending on the wavelength, the light beam interacts with the workpiece material in pyrolithically (thermal) or photolithically .

In the pyrolithic laser, material  is removed by spontaneous melting and evaporation.

This laser is mainly used for cutting, drilling, welding and surface hardening applications.

Removal or processing speed depends on the material to be processed, its thickness and its physical and optical properties, such as specific heat, latent heat of melting and vaporization and surface reflection.

When the above properties decrease, the workability of the material increases.

It also depends on the beam characteristics, especially its power density.

In the field of mechanical processing, pyrolithic lasers are used to process a wide range of metal and non-metal materials.

Considering the thermal diffusitivity, no heat transfer through the processed surface is allowed.

The photolithic laser does not remove the material thermally, but when its bond energy is lower than the photon energy of the beam, it will be affected by the dissociation and the breaking of the chemical bonds between the material molecules.

The photon energy of the beam is inversely proportional to its wavelength.

The fluorine excimer laser is an ultra-short wavelength beam (λ=157 nm); therefore, the has a high photon energy of 7.43 eV (1 eV = 1.6 × 10−19 J), while the CO2 laser has a long wavelength (λ = 10,600 nm) ) and low-wavelength infrared (IR) laser beam photon value is 0.12 eV power.

Therefore, excimer lasers can process plastics and teflon by photolithography, because the photon energy is higher than the chemical bond energy. For most plastics, the chemical bond energy is between 1.8 and 7 eV.

The CO2 laser cannot process plastics by photolithically, but it can be processed pyrolithically.

The removal of photolithic materials requires three stages:

1. Ultrashort wave photons are absorbed to a surface depth of about 200 nm.

2. The chemical bonds between molecules are broken.

3. The reaction products escape in the form of gas and small particles of ashes.

INDUSTRIAL LASERS

Industrial lasers include solid-state lasers in most cases, such as neodymium: yttrium aluminum garnet (Nd: YAG), neodymium: glass, Nd: glass, ruby and gas lasers (CO2, excimer and He/Ne ).

There are four main types of metal processing; namely CO2, Nd: YAG, Nd: glass and excimer laser.

Among  CO2 and YAG are considered to be the most reliable workhorses.

In most cases, the same laser can be used for cutting, welding, machining and surface treatment.

Only the laser beam parameters, such as power density, focal focus diameter,and pulse duration must be adapted to the corresponding machining process.

Explain in brief the four industrial lasers?

The four types of laser related to industrial purposes are as follows:

CO2 LASER:
In these lasers, the active material is CO2 gas. However, a mixture of  gases was used (CO2: N2: He = 0.8: 1: 7).

Helium acts as a coolant in the air cavity.

The CO2 laser is characterized by its long wavelength of 10,600 nm; therefore, the material removal depends only on the thermal interaction with the workpiece.

The CO2 laser provides the highest depth-to-diameter ratio for most metals assisted by gas jet assistance.

However, these lasers are bulky but economical.

There are two types of CO2 laser:

1. Axial flow CO2 laser.

This laser can operate in pulsed mode (P) and continuous wave mode (CW).

For this type, the typical average power of (CW) is in the range of 250 to 5000 W, while in (P) mode, the average power output is reduced to 100 to 2000 W and the pulse frequency is in the range from 1 to 10,000 P/s.

2. Transverse-flow CO2 laser.

This laser only works in (CW) mode.

This type is used when high power of 2500 to 15,000 W is required.

Nd: YAG LASER:

This laser is a single crystal made of YAG doped 1% neodymium as the active laser material.

This laser is compact and economical. Its wavelength is 1060 nm and can be operated in P or CW mode.

It is characterized by high efficiency, high pulse frequency and simple cooling system.

The pulse frequency ranges from 1 to 10,000 p/s, and the pulse energy is 5–8 J/p.

Its average power is close to 1 kW.

Nd: Glass LASER:

This laser is a 2-6% neodymium-doped glass rod, which is an effective laser material.

This type of laser is usually not economical.

It has the same wavelength as Nd: YAG.

It is only applicable to P mode.

Due to the low thermal conductivity of glass, the pulse frequency should be limited.

It is therefore only used for drilling and welding, which requires a higher energy output of the and a lower pulse frequency (1-2 p/s).

EXCIMER LASERS:

Excimer lasers are a family of pulsed lasers operating in the UV region of the spectrum.

Excimer is an abbreviation of “excited dimmer.”

The beam is generated due to fast electric discharges in a mixture of high-pressure dual gas, composed of one from the halogen gas group (F, H, Cl) and another from the rare gas group (Kr, Ar, Xe).

The wavelength of the excimer laser attains a value from 157 to 351 nm, depending on the dual gas combination.

Excimer lasers have low power output, so they remove the material photolithically, and have a remarkably efficient application in the machining of plastics and micromachining as previously mentioned.

ADVANTAGES

High Data Conveying Limit.

Outcome of Electro-attractive Obstruction.

Less sign spillage.

Used in making Fibre Optic Links.

Used in Clinical Field.

Used for Dumping down Adversary tank.

Laser is used in CDs and DVDs.

DISADVANTAGES

It is costly and consequently more consumption to the patients requiring laser-based medicines.

Costly for specialists.

Increases intricacy.

Less uses in Dental method.

Higher forces during the cutting cycle.

Destructive.

Leave a Comment

Your email address will not be published. Required fields are marked *