Transfer of Precessing Spin Polarizations between Different Kinds of Atoms with Sameg-Factor
Taro Ito, Noboru Shimomura, T. Yabuzaki
In spin-related fundamental researches, there have been considerable interests in the transfer of microscopic orders between magnetic sublevels of different kinds of atoms. As for gaseous atomic systems, collisional transfer of spin polarization from optically pumped atoms A to atoms B is attained through spin exchange collisions. So far many experiments have been reported on the transfer of longitudinal spin polarization created along a static magnetic field. Transfer of coherence, on the other hand,is possible only when the energy matching condition j!A !Bj < is satisfied, where !A and !B are the Larmor frequencies of atoms A and B, and the line width. This is the reason why transfer of spin polarization precessing around the static magnetic field has not been observed except for a few experiments; The coherence transfer has been observed in the experiments where the atoms are subjected to properly chosen rf magnetic fields. Recently, it has been reported that coherence transfer between different kinds of atoms is possible by using the light field which transversely pumps only one kind of atoms under properly chosen experimetal conditions. It has also been pointed out that, as for the system of Rb and K atoms, which happen to have the same gyro-magnetic ratio, the peculier distortion of the magnetic resonance signal line shapes observed in the collisionally pumped atoms can be explained by the spin exchange coupling between the resonant Rb and K atoms. It is suggested that the precessing spin polarization in Rb can be transferred to K atoms or vice versa, since their Zeeman splittings become equal in the hyperfine multiplets jF 1⁄4 1i and jF 1⁄4 2i of the ground state 2S1=2 with the same gyromagnetic ratio 1⁄4 2 700 kHz/G. The experimental apparatus of the present experiment is shematically shown in Fig. 1. In addition to a droplet of natural rubidium and potassium, the sample cell contains 50mbar Ar as a buffer gas. It is subjected to a static magnetic field of H0 1⁄4 0:786G along the z axis and irradiated transversely to the field by a light beam from a GaAlAs laser A (output power = 10mW, beam diameter = 1mm). It is left-handed circularly polarized and tuned to the Rb absorption lines (S1=2, F 1⁄4 1 ! P1=2, F 1⁄4 1 and 2) which are not resolved owing to the Doppler broadening. The intensity of the laser A is modulated by an AOM (acousto-optic-modulator) at the Larmor frequency !A 1⁄4 2 550 (1⁄4 700 0:786) kHz of Rb in a rectangular shape pulse. As mentioned above the precessing spin polarization in Rb can be transferred to K. The precessing spin polarization of Rb and that of K are detected from the Faraday rotations of the beams of probe lasers B ( 1⁄4 794 nm, output power = 3mW, beam diameter = 2mm) and C ( 1⁄4 769 nm, output power = 3mW, beam diameter = 2mm), respectively. The frequency of laser B is chosen to be a few GHz higher than the Rb absorption lines (S1=2, F 1⁄4 1 ! P1=2, F 1⁄4 1 and 2) to prevent the detection beam from destroying the polarization. Similarly, the frequency of laser C is chosen to be a few GHz higher than the K absorption lines (S1=2, F 1⁄4 1 and 2 ! P1=2, F 1⁄4 1 and 2) which are not resolved owing to the Doppler broadening. They are linearly polarized and counter-propagated against the pumping beam,making angles of about 1 to the pumping beam. In each case the transmitted light beam of probe laser passes through the analyzer which makes an angle 45 to the polarization of the incident beam,and then it is detected by a pin-photo diode. The signals are electronically averaged over a few hundred cycles. Figure 2(a) shows the typical examples of signals on the magnetizations M x and M B x of Rb and K, respectively, Fig. 1. Schematic diagram of the experimetal apparatus. AOM, acoustooptic modulator; PD, pin-photo diode; P, polarizer; A, analyzer.
Journal of the Physical Society of Japan•May 15, 2003•4 citations