A beam of ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons, i.e., rotons which have oppositely directed group velocity and momentum, is reated by condensing an atom beam onto the surface of liquid $^{4}\mathrm{He}$ . ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons are identified by quantum evaporation and their time of flight. Measured signal shapes agree well with those modeled. Signal sizes are compared with those from atoms specularly reflected from the He surface, from which it is estimated that the quantum efficiency for the condensation or evaporation process is high and of the order of 0.5 for angles of incidence where mainly rotons are created. ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons can specularly reflect from a solid-liquid He interface with high probability, if the interface is particularly good.A beam of ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons, i.e., rotons which have oppositely directed group velocity and momentum, is reated by condensing an atom beam onto the surface of liquid $^{4}\mathrm{He}$. ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons are identified by quantum evaporation and their time of flight. Measured signal shapes agree well with those modeled. Signal sizes are compared with those from atoms specularly reflected from the He surface, from which it is estimated that the quantum efficiency for the condensation or evaporation process is high and of the order of 0.5 for angles of incidence where mainly rotons are created. ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons can specularly reflect from a solid-liquid He interface with high probability, if the interface is particularly good.

Physical Review LettersJul 16, 199014 citations

Quantum liquids in correlated systems

Silvia Viola Kusminskiy

Jan 1, 20100 citations

Theory of Collimated Atomic Beam Formation

Cyril Bernard Lucas

If a beam is to be produced from a material that is solid or liquid at laboratory temperature, then it must be converted to a vapour in an oven before it passes through the beam-forming impedance. In the reviews mentioned in Section 1.2, the approach has usually been to give details of numerous designs. In this chapter, we discuss the general design principles, and then the next two chapters become more of a reference source for the evaporation of different substances. We thus include the experience of a large number of experimenters who have needed to heat a liquid or solid substance to form it into an atomic or molecular beam. If the material can be evaporated and raised to a temperature to give the required input pressure at the input to the impedance at a temperature less than about 1500 K, it is usual to describe the heating device as an oven. At higher temperatures, the device is usually called a furnace, but the distinction is not really necessary. Hence we will avoid the term except for thermal dissociation of a molecular species, discussed in Chapter 6, when very high temperatures are usually needed, so a furnace is a more appropriate term. For convenience we will also term a completely different approach, namely, the evaporation of the material by direct electron beam heating of the surface (Section 3.2.5) as an oven. ‘Crucible’ is used by many authors interchangeably with ‘oven,’ but it often implies a container for the material to be evaporated that is placed within a heated envelope.If a beam is to be produced from a material that is solid or liquid at laboratory temperature, then it must be converted to a vapour in an oven before it passes through the beam-forming impedance. In the reviews mentioned in Section 1.2, the approach has usually been to give details of numerous designs. In this chapter, we discuss the general design principles, and then the next two chapters become more of a reference source for the evaporation of different substances. We thus include the experience of a large number of experimenters who have needed to heat a liquid or solid substance to form it into an atomic or molecular beam. If the material can be evaporated and raised to a temperature to give the required input pressure at the input to the impedance at a temperature less than about 1500 K, it is usual to describe the heating device as an oven. At higher temperatures, the device is usually called a furnace, but the distinction is not really necessary. Hence we will avoid the term except for thermal dissociation of a molecular species, discussed in Chapter 6, when very high temperatures are usually needed, so a furnace is a more appropriate term. For convenience we will also term a completely different approach, namely, the evaporation of the material by direct electron beam heating of the surface (Section 3.2.5) as an oven. ‘Crucible’ is used by many authors interchangeably with ‘oven,’ but it often implies a container for the material to be evaporated that is placed within a heated envelope.

CRC Press eBooksNov 27, 20130 citations

Theory of quantum evaporation from superfluid helium

S. Stringari, F. Dalfovo, M. Guilleumas +2 more

Czechoslovak Journal of PhysicsJun 1, 19966 citations

A beam of ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons, i.e., rotons which have oppositely directed group velocity and momentum, is reated by condensing an atom beam onto the surface of liquid

^{4}\mathrm{He}

. ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons are identified by quantum evaporation and their time of flight. Measured signal shapes agree well with those modeled. Signal sizes are compared with those from atoms specularly reflected from the He surface, from which it is estimated that the quantum efficiency for the condensation or evaporation process is high and of the order of 0.5 for angles of incidence where mainly rotons are created. ${\mathit{R}}^{\mathrm{\ensuremath{-}}}$ rotons can specularly reflect from a solid-liquid He interface with high probability, if the interface is particularly good.