Atomic spectroscopy linewidth

Linewidth is also affected by pressure broadening from collisions between atoms. Collisions shorten the lifetime of the excited state. The uncertainty in the frequency of atomic absorption and emission lines is roughly numerically equal to the collision frequency between atoms and is proportional to pressure. The Doppler effect and pressure broadening are similar in magnitude and yield linewidths of 10-3 to I0-2 nm in atomic spectroscopy. 

Subnatural Linewidths in Atomic Spectroscopy, Dennis P. O Brien, Pierre Meystre, and Herbert Walther... 

D.P. O Brien, P. Meystre, H. Walther Subnatural linewidths in atomic spectroscopy, in Advanced Atomic and Molecular Physics, Vol.21, ed. by D.R. Bates, B. Bederson (Academic, Orlando 1985)... 

High-resolution spectroscopy used to observe hyperfme structure in the spectra of atoms or rotational stnicture in electronic spectra of gaseous molecules connnonly must contend with the widths of the spectral lines and how that compares with the separations between lines. Tln-ee contributions to the linewidth will be mentioned here tlie natural line width due to tlie finite lifetime of the excited state, collisional broadening of lines, and the Doppler effect. 

Atomic absorption spectroscopy (AAS) was practiced in the mid-nineteenth century by passing a small sample into a flame and noting the color of the flame. Compared to molecular absorption, atomic absorption lines are very narrow. The linewidth is defined as the width of the signal at halfheight Ali/i, which for atoms is of the order of 0.002-0.005 nm. Al /2 consists of the natural linewidth plus the Doppler37 linewidth. 

For almost three decades, the S-2S two-photon transition in atomic hydrogen with its natural linewidth of only 1.3 Hz has inspired advances in high-resolution spectroscopy and optical frequency metrology. This resonance [the 1S-2S transition] has become a de facto optical frequency standard. More importantly, it is providing a cornerstone for the determination of fundamental constants and for stringent tests of quantum electrodynamic theory. In the future, it may unveil... 

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