Chopped nonlinear magneto-optic rotation: A technique for precision measurements

Abstract

Magnetooptical and electrooptical spectra and effects PACS 32.80.Xx -Level crossing and optical pumping PACS 42.50.Gy -Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption PACS 32.10.Dk -Electric and magnetic moments, polarizabilitiesAbstract. -We have developed a technique for precise measurement of small magnetic fields using nonlinear magneto-optic rotation (NMOR). The technique relies on the resonant laser beam being chopped. During the on time, the atoms are optically pumped into an aligned ground state (∆m = 2 coherence). During the off time, they freely precess around the magnetic field at the Larmor frequency. If the on-off modulation frequency matches (twice) the Larmor precession frequency, the rotation is resonantly enhanced in every cycle, thereby making the process like a repeated Ramsey measurement of the Larmor frequency. We study chopped-NMOR in a paraffincoated Cs vapor cell. The out-of-phase demodulated rotation shows a Lorentzian peak of linewidth 85 µG, corresponding to a sensitivity of 0.15 nG/ √ Hz. We discuss the potential of this technique for the measurement of an atomic electric-dipole moment.

Permanent EDM measurement in Cs using nonlinear magneto-optic rotation

“…In effect, the other level acts as a co-magnetometer, similar to the use of Rb atoms in a Cs vapor cell as demonstrated by us in Ref. [11] and proposed by others for EDM measurements [14]. The use of the other hyperfine level is a novel feature of our technique, and is reported for the first time for atomic EDM measurements.…”

“…As shown in our earlier work in Ref. [11], the chopped NMOR technique relies on the laser beam measuring the rotation being modulated on and off. During the on time, the atoms are optically pumped into a ∆m = 2 coherence of the ground state (atomic alignment).…”

“…In earlier work [11], we have proposed a new technique to measure the existence of an EDM in Cs atoms using a paraffin-coated vapor cell. This method is also not susceptible to errors due to the motional magnetic field because the average velocity inside a vapor cell is zero.…”

Polarization-dependent tuning of the Hanle effect in the ground state of Cs

“…For example, in the phenomenon of nonlinear magneto-optic rotation (NMOR), a laser field is used to align the atom by inducing coherences among the magnetic sublevels of the ground state. NMOR has important applications in sensitive magnetometry [1], and the search for a permanent electric dipole moment (EDM) in an atom [2]. Another example is an atomic clock, where two laser beams which differ in frequency by the clock transition are used to put the atom in a dark non-absorbing state.…”

Measuring the linewidth of a stabilized diode laser

“…The advent of diode lasers in the last couple of decades has revolutionized laser spectroscopy in atoms, and made possible several experimental studies in fields such as precision measurements [1][2][3], laser cooling and trapping of atoms [4], atomic clocks [5], quantum optics [6][7][8], and so on. This is because most experiments are done using the D lines of alkali atoms, which are in the near infrared (IR) and hence accessible with diode lasers.…”