Optical pumping of 5s4d1D2 strontium atoms for laser cooling and imaging

We present a faster repumping scheme for strontium magneto-optical traps operating on the broad 5s^2^1S₀-5s5p^1P₁ laser cooling transition. Contrary to existing repumping schemes, we directly address lost atoms that spontaneously decayed to the 5s4d^1D₂ state, sending them back into the laser cooling cycle by optical pumping on the 5s4d^1D₂-5s8p^1P₁ transition. We thus avoid the 1000. 16em{0ex}s-slow decay path from 5s4d^1D₂ to the 5s5p^3P₁, ₂ states that is part of other repumping schemes. Using one low-cost external-cavity diode laser emitting at 4480. 16em{0ex}nm, we show our scheme increases the flux out of a 2D magneto-optical trap by 600. 16em{0ex}% compared to without repumping. Furthermore, we perform spectroscopy on the 5s4d^1D₂-5s8p^1P₁ transition and measure its frequency ^₈₈Sr= (668917515. 34. 025) 0. 16em{0ex}MHz. We also measure the frequency shifts between the four stable isotopes of strontium and infer the specific mass and field shift factors, ₒ₌ₒ^88, 86=-267 (45) 0. 16em{0ex}MHz and ₅ₒ^88, 86=2 (42) 0. 16em{0ex}MHz. Finally, we measure the hyperfine splitting of the 5s8p^1P₁ state in fermionic strontium and deduce the magnetic dipole and electric quadrupole coupling coefficients A=-4 (5) 0. 16em{0ex}MHz and B=5 (35) 0. 16em{0ex}MHz. Our experimental demonstration shows that this simple and very fast scheme could improve the laser cooling and imaging performance of cold strontium atom devices, such as quantum computers based on strontium atoms in arrays of optical tweezers.