Recent experiments 1-4 on laser induced breakdown in compressed helium gas and in liquid helium suggest that optical breakdown is caused by an electronic avalanche mechanism5. According to this mechanism the threshold power for optical breakdown should increase with decreasing electronic scattering rate, or with atomic density since electrons are mainly scat­ tered by atoms. This close relation...

The Sinano~lu solvent effect method is here modified to include the exchange-overlap three-body SCF term in addition to the usual triple-dipole term. This is accomplished using an analytical fit which gives a better picture of short range non-additive interactions. The application of this modified model to the dimers (4He)~, (aHe)2 and ~He-4Hc in a liquid ~He environment leads to the lowering o...

The specific heat of liquid helium was calculated theoretically in the Landau theory . The results deviate from experimental data in the temperature region of 1.3 2.1 K. Many theorists subsequently improved the results of the Landau theory by applying temperature dependence of the elementary excitation energy , . As well known, many-body system has a total energy of Galilean covariant form. The...

We have used a Hartree-type electron-helium potential together with a density functional description of liquid 4He and 3He to study the explosion of electron bubbles submitted to a negative pressure. The critical pressure at which bubbles explode has been determined as a function of temperature. It has been found that this critical pressure is very close to the pressure at which liquid helium b...

We describe an approach to detecting ionizing radiation that combines the special properties of superfluid helium with the sensitivity of quantum optics techniques. Ionization in liquid helium results in the copious production of metastable He2 molecules, which can be detected by laser-induced fluorescence. Each molecule can be probed many times using a cycling transition, resulting in the dete...

We report stimulated Brillouin gain spectra of bulk superfluid helium-4. Stimulated spectroscopy is a powerful optical method to probe the acoustic properties liquid helium in narrow spatio-temporal domain with moderate power and fast acquisition rates. determine velocity first sound helium-4 from between 0.90 2.17 K compare it well-known available data, which validate our experimental method.