Rabi method

Fig. 5.10 Comparison between the conventional Rabi method (a) and its laser version (b)...

The laser version of the Rabi method (Fig. 5.10b) overcomes both limitations. The two magnets A and B are replaced by the two partial beams 1 and 2 of a laser that cross the molecular beam perpendicularly at the positions A and B. If the laser frequency co is tuned to the molecular transition in) the lower level in) is partly depleted due to optical pumping in the first crossing point A. Therefore the absorption of the second beam in the crossing point B is decreased, which can be... 

Optical pumping with lasers offers a new and very convenient variation of the conventional Rabi method, which is illustrated in Figs.10.15b and 10.16. The two inhomogeneous magnetic fields A and B are replaced by two parallel laser beams which cross the molecular beam perpendicularly. The first "pump beam" depletes the population N(i) of the lower level i. This is monitored by the resultant decrease of the fluorescence intensity Ip induced by the probe laser. When the rf field induces transitions k i between other levels k and the depleted level i, the population N(i) is increased, resulting in a corresponding increase of Ip. ... 

The laser version of the Rabi method does not rely on the mechanical deflection of molecules but uses the change of the population density in specified levels due to optical pumping. The conventional technique is restricted to atoms or molecules with magnetic or electric dipole moments and the sensitivity depends on the difference between the dipole moments in the two levels connected by the rf transition. The laser version can be applied to all atoms and molecules which can be optically pumped by existing lasers. The background noise is small because only those molecules which are in the specified level contribute to the probe-induced fluorescence. 

I. I. Rabi (Columbia, New York) resonance method for recording the magnetic properties of atomic nuclei. 

Viruses replicate only in living cells so the first viral vaccines were necessarily made in animals smallpox vaccine in the dermis of calves and sheep and rabies vaccines in the spinal cords of rabbits and the brains of mice. Such methods are no longer used in advanced vaccine production and the only intact animal hosts that are used are embryonated hens eggs. Almost all of the vims that is needed for viral vaccine production is obtained from cell cultures infected with vims of the appropriate strain. 

Calculated to nearest 0.1 G using methods given in ref. 1 by iterative solution of the Breit-Rabi... 

The most commonly used screening method for HIV is an enzyme-linked immunosorbent assay, which detects antibodies against HIV-1 and is both highly sensitive and specific. False positives can occur in multiparous women in recent recipients of hepatitis B, HIV, influenza, or rabies vaccine following multiple blood transfusions and in those with liver disease or renal failure, or undergoing chronic hemodialysis. False negatives may occur if the patient is newly infected and the test is performed before antibody production is adequate. The minimum time to develop antibodies is 3 to 4 weeks from initial exposure. 

The available methods for the determination of diamagnetic susceptibilities in crystals will not be described here. Papers by Rabi (1927), Krishnan and his collaborators (1933, 1934, 1935), and the excellent review of the whole subject by Lonsdale (1937 a) should be consulted. See also Wooster (1957). 

The scheme is illustrated in Fig. 20. In addition to chiral molecules, one can apply this method to two asymmetric quantum wells, to two heteronuclear molecules aligned in an external DC electric field [97]. In the setup of Fig. 20 (lower plot), we consider operating on states i) and their mirror images 1)m by three pulses in a counterintuitive order [92,93], i.e., two pump pulses with Rabi frequencies fl12(0 and fli3(r), which follow a dump pulse H23(0. The Rabi frequencies are defined as, fiy(r) = dtj ij(t)lh — ilij(t) e1 = 0 (0, where dtJ and y(r) are, respectively, the transition dipoles and the envelopes of electric fields, of carrier frequencies a)ij, operating between states i j (i, j = 1,2, 3). If we symmetrically detune the pulse center frequencies, as shown in Fig. 20,... 

Note that there exists a threshold Tc = laJf, the smallest target time satisfying the condition, Eq. (41). If we choose a smaller T than 7), there is no external field that induces the smooth transition described by the CG Rabi state. On the other hand, the numerical method can give finite solutions for such cases because there is no assumption (restriction) about the dynamics except that it obeys the Schrodinger equation. 

On another level, the story of hydrogen reveals how science is conducted. Physical theories are created to provide explanatory schemes whereby the observed world can be understood with quantitative precision. Those theories that capture the support of scientists are those that allow detailed predictions to be made and lead to new insights into the natural world. Good theories are simple theories that unite disparate realms of experience. Physical theories, however, must always yield to the demands of experimental data. Experimental facts are incontrovertible. If they are not accommodated by theory, the theory is held in question. Theories, good theories, are not quickly abandoned. Strenuous effort is exerted to refine a good theory so that experimental facts can be explained. In the final analysis, however, experimental results, once tested and retested, once verified by independent experimental methods, ultimately rule. Dirac s theory was elegant and beautiful, but in the face of data from Lamb and Rabi, it fell short. Their data then became the stimulus for the more powerful theory of quantum electrodynamics. 

The objective of the 1938 experiments was to measure the magnetic moments of the hydrogen and deuterium nuclei as accurately as possible. In 1938, however, a new sense of promise inspired the members of Rabi s group as they prepared to apply the new resonance method to the hydrogens and to measure the magnetic moments of the proton and the deuteron to a new level of precision. Eventually, this objective was accompHshed successfully, but not without surprises that led to new basic knowledge about the atomic nucleus. 

In 1950, Norman Ramsey, a member of the team that developed the magnetic resonance method, made a basic modification to Rabi s molecular beam apparatus that significantly enhanced... 

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