Optical pumping of rubidium atoms frozen in solid argon

We have grown crystals of solid argon doped with rubidium atoms. The spectrum of the implanted atoms depends on the crystal-growth temperature and annealing history. We have used optical pumping to polarize the spin state of the implanted atoms and polarization spectroscopy to detect the spin state and measure the spin-relaxation time. In addition to the desired optical pumping, we also observed modification of the absorption spectrum of the rubidium due to the applied light.

Figure 1

Spectra of rubidium-doped argon crystals grown at different substrate temperatures. The transmission of the crystal $T=e^{-\mathrm{OD}}$. All spectra were taken at 3.2 K.

Figure 2

Spectra illustrating bleaching of the crystal by the laser for a crystal grown at 15 K (upper trace) and a crystal grown at 10 K (lower trace). All spectra were taken at a 3.2 K substrate temperature. The dashed lines are spectra taken with the crystal exposed to the halogen light source. The solid lines are spectra taken with both the halogen light source and an 802-nm laser with an intensity of 3 mW/cm${}^2$.

Figure 3

Optical pumping of rubidium atoms in an argon matrix grown at 10 K; the data are taken at a temperature of 3.2 K. The probe beam is on continuously; the RHC pumping beam is applied from 0.1 to 0.15 ms. The photodiode signals are shown for both the LHC and RHC detectors; the signals are normalized so that the level is 1 prior to optical pumping. The top graph is with a longitudinal magnetic field applied, and the bottom graph is with a transverse field applied.

Figure 4

The upper graph shows the ratio of the LHC and RHC photodiode signals for longitudinal and transverse magnetic fields; the data are the same as presented in Fig. 3. The lower graph shows the difference between the two upper signals, fit as discussed in the text.