Reduced optical shielding of collisional loss for laser-cooled atoms

Collisional loss rates of ultracold atoms in a laser trap (formed by red-detuned laser beams) can be suppressed by using a sufficiently intense blue-detuned optical shielding laser to repel the atoms before they collide. We present calculations that reveal an additional mechanism for collisional loss in the presence of a blue-detuned laser that reduces optical shielding as the blue-detuned laser intensity increases, and even causes enhancement of collisional loss effects with increased blue-detuned intensity. This mechanism can strongly affect the saturation of the optical shielding.