where [[GAMMA].sub.nat] is the homogeneous natural linewidth and [DELTA]v is the isotope shift of the specific transition.

In this scheme, the first-step transition at 689.4 nm (5[s.sup.2] [sup.1][S.sub.0]-5s5p [sup.3][P.sup.[omicron].sub.1]) is the so-called intercombination transition with narrow natural linewidth (~7.4kHz).

Measurment of nanoangstrom oscillatory displacements by a gas laser with a small

natural linewidth. Radiophysics and Quantum Electronics, 1998, v.

where [omega] is the laser frequency, T is the temperature of the sample, [E.sup.vJ'.sub.F'p'[beta]], \[[phi].sup.vJ'.sub.F'p'[beta]]>, and [[gamma].sub.v] are the excited state energy, wavefunction, and natural linewidth respectively.

The natural linewidth of the [0.sup.-.sub.g] states is 20 MHz, which is twice the atomic linewidth (20,21).

It is also suggested that if the instrument resolution is similar to the

natural linewidth of the vibrational bands for a given analyte, then a further improvement in resolving power is unwarranted and may prove detrimental in terms of data collection time and data storage space.

5), which has a

natural linewidth of 1/(2[pi][[tau].sub.D]) = 1.7 Hz (where [[tau].sub.D] = 90 ms is the lifetime of the [[blank].sup.2][D.sub.5/2] state), is now being investigated (39).

The lifetime of the upper level is 86(3) ms [2], so the ratio of the

natural linewidth [delta]v to the transition frequency [v.sub.0] is 2 X [10.sup.-15].

The collisional/pressure broadening of absorption line can be quite pronounced [41, 42], especially for gas phase atomic and molecular lines with very low

natural linewidths. This makes most of the species (for extensive list, see [43]), including, for example, atomic oxygen, difficult to detect in atmospheric pressure plasmas.