Rydberg masers

With the use of a resonant cavity the threshold for collective emission is lower by the magnitude of the cavity finesse. Using a cavity finesse of a 100 or so Rydberg maser action on sodium has been observed. In this case the field ionisation signal was used to monitor the population as a function of time for the states 27S, 26P and 25P corresponding to transitions An = 1 at X = 1 470 mm and An = 2... 

For the Rydberg maser experiment [15] an atomic beam of highly excited Rydberg atoms was used. The beam oven is carefully heat-shielded from the cavity by copper plates cooled by water, liquid nitrogen and liquid helium the atoms pass through small apertures into the liquid... 

Moi et reported the first direct detection of Rydberg maser... 

The threshold condition for collective emission (superradiance) or maser action (gain in the medium exceeding the losses) is much lower for Rydberg atoms than it is for the same number density of atoms in low n states. To obtain an order of magnitude estimate for the point at which collective fects occur we estimate the amplitude of the electric dipole field E radiated by an atom at a distance corresponding to a neighbouring atom. That is, if we let L represent a linear dimension in the sample which contains N atoms,... 

Fig. 9.73 Schematic experimental setup for the one-atom maser with resonance cavity and state-selective detection of the Rydberg atoms [1294]...

In the following we will briefly review the most important properties of Rydberg atoms and then discuss the QED in a cavity and in the last chapter we will describe the present status of our one-atom maser experiment. 

In the case of measurements at a cavity temperature of 2K [15], a reduction of the signal could be clearly seen for atomic fluxes as small as 800 atoms/s. An increase in flux caused power broadening and finally an asymmetry and a small shift (Fig. A). This shift is attributed to the ac Stark effect, caused predominantly by virtual transitions to the 6ld level, which is only 50MHz away from the maser transition (Fig. 3). the fact that the field ionization signal at resonance is independent of the particle flux (between 800 and 22 x 10 atoms/s) indicates that the transition is saturated. This, and the observed power broadening show that there is a multiple exchange of photons between Rydberg atoms and the cavity field. 

Ensembles of N Rydberg atoms prepared in the cavity also exhibit interesting effects. The atoms couple symmetrically to the field mode and collective radiative effects are observable even if the atomic sample is made of a few radiators only. Tests of superradiance theory and related radiative effects have been studied on these systems which-when N goes down to unity-constitute the smallest maser systems ever achieved. 

The statistical properties of the field radiated by these masers have been analyzed and it has been shown that they should exhibit large amount of "squeezing". Most of the Rydberg atom radiation experiments so far have been... 

The Rydberg atom experiments described above are well adapted to the study of the atomic observables via the very sensitive field ionization method. The observation of the field itself and its fluctuations would also be very interesting. (In the Bloch vector model, the field variables are associated to the pendulum velocity whereas the atomic ones are related to its position). It has recently been shown either by full quantum mechanical calculations or by the Bloch vector semi-classical approach that if the system is initially triggered by a small external field impinging on the cavity, the fluctuations on one phase of the field become at some time smaller than in the vacuum field. This is a case of radiation "squeezing" which would be very interesting to study on Rydberg atom maser systems. 

Fig. 14.49. (a) Level diagram of the maser transition in rubidium. The transition frequencies are given in MHz. (b) Measured ion signal, which is proportional to the number of Rydberg atoms in level n), as a function of the cavity resonance frequency. Maser operation of the one-atom maser manifests itself in a decrease in the number of atoms in level n) [14.130]... 

Rydberg Atoms as Masers attd Radiatiori Detectors... 

Further experimental studies concern microwave superradiance. It is interesting to mention that blackbody radiation rather than spontaneous emission initiates superradiance and maser activity in the systems described above. Using a beam of Rydberg atoms Ducas et detected far-infrared... 

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