Optical absorption electron, liquid helium

Our first steps toward the single-molecule regime arose from work at IBM Research in the early 1980s on persistent spectral hole-burning effects in the optical transitions of impurities in solids (for a review, see [20]). Briefly, if a molecule with a strong zero-phonon transition and minimal Franck-Condon distortion is doped into a solid and cooled to liquid helium temperatures, the optical absorption becomes inhomogeneously broadened (Fig. 2.2A). The width of the lowest electronic transition for any one molecule (homogeneous width, Yjj) becomes very small because few phonons are present, while at the... 

For the detection of the optical absorption of excess electrons in liquid helium, eight interchangeable IR semiconductor lasers immersed in the liquid were employed. A schematic of the setup is shown in Figure 25. Excess electrons were injected into the liquid from a metal cathode on which a titanium tritide P-source was deposited. Concentrations of 10 cm could be produced. The change in laser light intensity was measured by a boron-doped silicon photoresistor. 

Parshin, A. Y. and Pereverzev, S. V., Direct observation of optical absorption by excess electrons in liquid helium, JETP Lett., 52, 282,1990. 

In liquid helium ( He), the electron trap is thought to consist of a spherical void in the liquid of about 2-nm radius (see Section 7.2). Grimes and Adams (1990) produced electrons in liquid helium by field emission from tungsten tips and measured their optical absorption. The absorption spectrum is shown in Figure 33. 

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