Dicke narrowing

Besides the initial object of CARS as a tool for the determination of molecular energy levels and its application to combustion studies and related areas, there are several other scientific applications of academic interests. These include spectral lineshape studies, collisional effects, Dicke narrowing, nonadditivity effects, and motional narrowing. CARS turned out to be an excellent method for these studies (Berger et al., 1992 and references therein). 

One additional subtlety if the coordinate displacement of the ion 6z during the time 6t is smaller than the wavelength of the radiation. the radiation cannot sense the off-resonance (Dicke narrow-ing9 >93). Thus for the last case of the above numerical examples, 6v will be smaller than the calculated value. 

In the infrared and microwave ranges, collisions may sometimes cause a narrowing of the linewidth instead of a broadening Dicke narrowing) [3.34]. This can be explained as follows if the lifetime of the upper molecular level (e.g., an excited vibrational level in the electronic ground state) is long compared to the mean time between successive collisions, the velocity of the oscillator is often altered by elastic collisions and the mean velocity compo-... 

Under certain conditions, if the mean free path A of the molecules is smaller than the wavelength of the radiation field, velocity-changing collisions may also result in a narrowing of a Doppler-broadening line profile (Dicke narrowing. Sect. 3.3.3). 

Figure 3.17 Dicke narrowing and pressure broadening of a rotational line of a vibrational transition in H2O at 1871 cm (A = 5.3 xm) as a function of Ar and Xe pressure [103]...

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