Excimer laser

Since the 1960s, excimer lasers have been widely used in high-resolution photolithography machines, one of the critical technologies required for microelectronic chip manufacturing.

[1] The excimer laser development started with the observation of a nascent spectral line narrowing at 176 nm  reported in 1971[2] by Nikolai Basov, V. A. Danilychev and Yu.

Definitive evidence of a xenon excimer laser action at 173 nm using a high pressure gas at 12 atmospheres, also pumped by an electron beam, was first presented in March 1973, by Mani Lal Bhaumik of Northrop Corporation, Los Angeles.

Under the appropriate conditions of electrical stimulation and high pressure, a pseudo-molecule called an excimer (or in the case of noble gas halides, exciplex) is created, which can only exist in an energized state and can give rise to laser light in the ultraviolet range.

However, when in an excited state (induced by electrical discharge or high-energy electron beams), they can form temporarily bound molecules with themselves (excimer) or with halogens (exciplex) such as fluorine and chlorine.

The excited compound can release its excess energy by undergoing spontaneous or stimulated emission, resulting in a strongly repulsive ground state molecule which very quickly (on the order of a picosecond) dissociates back into two unbound atoms.

[17] While electron-beam pumped excimer lasers can produce high single energy pulses, they are generally separated by long time periods (many minutes).

[19][20] Their significantly higher pulse repetition rates (of order 100 Hz) and smaller footprint made possible the bulk of the applications listed in the following section.

This laser used a high power thyratron and magnetic switching with corona pre-ionization and was rated for 100 million pulses without major maintenance.

This challenge was overcome when in a pioneering development in 1982, deep-UV excimer laser lithography was proposed and demonstrated at IBM by Kanti Jain.

In 1980–1983, Rangaswamy Srinivasan, Samuel Blum and James J. Wynne at IBM's T. J. Watson Research Center observed the effect of the ultraviolet excimer laser on biological materials.

In 2012, the team members were honored with National Medal of Technology and Innovation by the President Barack Obama for their work related to the excimer laser.

[36] Xenon chloride (308 nm) excimer lasers are also used to treat a variety of dermatological conditions including psoriasis, vitiligo, atopic dermatitis, alopecia areata and leukoderma.