What is an Excimer LASER?
Excimer laser or Exciplex laser is a type of laser that uses ultraviolet light to produce microelectronic devices, semiconductor integrated circuits, and micro-machines. Nikolai Basov, Yu. M. Popov, and V. A. Danilychev invented the excimer laser in 1970 at Lebedev Physical Institute, Moscow. The word excimer is short for “Excited dimer” and the word exciplex is short for “Excited complex”. Initially, Nikolai Basov, Yu. M. Popov, and V. A. Danilychev used a Xenon dimer or Xe2 that was excited by using an electron beam to produce a stimulated emission having a wavelength of 172 nm.
How is an excimer laser constructed?
An Excimer or Exciplex laser is generally constructed by using noble gases like Argon, Krypton or Xenon along with reactive halogen gas like fluorine or chlorine. The gases are then subjected to electrical stimulation and high pressure resulting in the formation of an energized pseudo molecule known as excimer or exciplex (for noble gas halides). These pseudo molecules can exist only in energized states producing a laser beam of ultraviolet light. An excimer molecule has a bound excited state and a repulsive ground state that is responsible for the molecule’s laser action.
Noble gases like Argon, Krypton or Xenon do not generally react with other molecules but in an electrically excited state these molecules can combine with themselves (excimer) or with halogen molecules (exciplex). The excited molecule tends to release its excess energy in the form of spontaneous or stimulated emission. This results in an extremely repulsive ground state molecule that swiftly dissociates into its unbound atoms by population inversion.
Excimer Molecule – Wavelength Table
The wavelength of light remitted by an excited excimer or exciplex molecule depends on the elements that the molecule is composed of.
|Xe2*||172 & 175 nm|
What are the applications of Excimer Laser?
Excimer laser generates ultraviolet light that is well absorbed by organic compounds and biological matter. The intensity of UV light energy provided by the excimer laser is sufficient to disturb the molecular bonds present in the surface of tissue without burning or cutting. Excimer lasers dissociate fine layers over tissue surfaces through controlled ablation instead of burning. This makes it extremely effective in removing fine layers of tissue without disturbing the deep layers and organs.
The large size of these lasers act as a disadvantage for medical applications. However, nowadays with development of new technologies the size is considerably reduced.
Excimer lasers are used for a variety of scientific experimental purposes. These lasers are also used for further producing blue-green dye lasers by exciting that region of the spectrum. The short wavelength, large fluence and non-continuous beam properties of these lasers are used for ablating several materials in pulse laser deposition systems.
Excimer lasers play an important role in manufacturing microelectronic chips (i.e., semiconductor integrated circuits) by using photolithography machines. Currently, deep ultraviolet (DUV) light from KrF and ArF excimer lasers are used to shrink the size of the transistors to 7 nanometers. Excimer lithography has immensely contributed in the field of semiconductor devices.
What is the pulse repetition rate of excimer lasers?
Excimer or exciplex lasers that are pumped by electron beams can high single energy pulses that are usually parted by long time periods. Comparatively, excimer lasers pumped by discharge produces a steady stream of pulses. These lasers have a significantly higher pulse repetition rate of about 100 Hz and a much smaller footprint.
The average output of an excimer laser is the product of the repetition rate or the number of pulses per second with pulse energy (in Joules). The average power of an excimer or exciplex laser ranges from 1 Watt to 100 Watt. Similar average power does not necessarily mean that the laser output would be the same. Once the repetition rate exceeds a certain value the energy produced per pulse gets reduced.
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