Optical pumping by a laser pulse traveling in a cavity

We have developed a general method to perform optical pumping by a pulsed laser with the aid of an optical cavity (cavity-assisted optical pumping). Optical pumping is achieved by repetitive interaction of a single laser pulse with a target material in the cavity. This method is demonstrated for manganese ions, ${\text{Mn}}^{+}$, stored in a linear radio-frequency ion trap; about ${10}^8$ ions are spin polarized by a 5-ns laser pulse via ${{}^{7}P}_J\leftarrow {{}^{7}S}_3$ ($J=3$ or 4) transition in the ultraviolet region. The linewidth of the pulsed light source is broad enough to transfer the populations of lower hyperfine levels to the highest one $\left(F=11/2\right)$ in the ${{}^{7}S}_3$ ground state; the nuclear spin is polarized as well.

Figure 1

(Color online) (a) A schematic diagram of the experimental setup. $\lambda /4$ is a quarter-wave plate for generating ${\sigma }^{+}$ polarization. (b) An illustration of spin polarization.

Figure 2

(Color online) Optical absorption spectra of ${\text{Mn}}^{+}$ observed with ${\sigma }^{+}$-polarization laser pulses for (a,b) ${{}^{7}P}_3\leftarrow {{}^{7}S}_3$ and (c,d) ${{}^{7}P}_4\leftarrow {{}^{7}S}_3$ transitions. The pulse energy of the incident laser is either (a,c) 0.2 mJ or (b,d) $2\mu \text{J}$. Solid circles are experimental data. Solid lines show fitting curves (see text for details). Bars indicate wave numbers of absorption lines; the length represents a relative intensity in the condition without spin polarization.

Figure 3

(Color online) (a) The hyperfine energy diagram of ${{}^{7}S}_3$ and ${{}^{7}P}_J$ ($J=3$ and 4) states. (b) An illustration of the optical pumping process for the ${\sigma }^{+}$ transitions between sublevels of $F=11/2$ and those of $F^{\prime }=13/2$; relative absorption intensities are indicated for each sublevel transition. $F\left(M\right)$ and $F^{\prime }$ $\left(M^{\prime }\right)$ denote angular-momentum (magnetic) quantum numbers in the ground and the excited states, respectively.

Figure 4

(Color online) Numerical simulations of the populations in the magnetic sublevels, $M$ $\left(F=11/2\right)$ and $M^{\prime }$ $\left(F^{\prime }=13/2\right)$, as a function of time. The pulse energies of the incident ${\sigma }^{+}$ light are (a) 0.2 mJ and (b) $2\mu \text{J}$. The lifetime of the laser pulse in the cavity is adjusted at $10\mu \text{s}$. Curves for the lower $M$ and $M^{\prime }$ sublevels are not labeled [see the diagram in Fig. 3b].