Krypton-fluoride laser

A krypton-fluoride laser (KrF laser) is a particular type of excimer laser, which is sometimes (more correctly) called an exciplex laser. With its 248 nanometer wavelength, it is a deep ultraviolet laser which is commonly used in the production of semiconductor integrated circuits, industrial micromachining, and scientific research. The term excimer is short for "excited dimer", while exciplex is short for "excited complex". An excimer laser typically contains a mixture of a noble gas, such as argon, krypton, or xenon, and a halogen gas such as fluorine or chlorine. Under suitably intense conditions of electromagnetic stimulation and pressure, the mixture emits a beam of coherent stimulated radiation as laser light in the ultraviolet range.

KrF and ArF excimer lasers are widely incorporated into high-resolution photolithography machines, one of the critical tools required for microelectronic chip manufacturing in nanometer dimensions. Excimer laser lithography has enabled transistor feature sizes to shrink from 800 nanometers in 1990 to 10 nanometers in 2016.

Theory

A krypton-fluoride laser absorbs energy from a source, causing the krypton gas to react with the fluorine gas, producing the exciplex krypton fluoride, a temporary complex in an excited energy state:

2 Kr + F2 → 2 KrF

The complex can undergo spontaneous or stimulated emission, reducing its energy state to a metastable, but highly repulsive, ground state. The ground state complex quickly dissociates into unbound atoms:

2 KrF → 2 Kr + F2

The result is an exciplex laser which radiates energy at 248 nm, near the ultraviolet portion of the spectrum, corresponding to the energy difference between the ground state and the excited state of the complex.

Example Systems

There have been several of these lasers built for ICF experiments; examples include:

Los Alamos built a KrF laser in 1985 to prove test firing of a beam with an energy level of 1×104 Joules.