Title: Multi-pass configuration for Improved Squeezed Vacuum Generation in Hot Rb Vapor,
Abstract: We study a squeezed vacuum field generated in hot Rb vapor via the
polarization self-rotation effect. Our previous experiments showed that the
amount of observed squeezing may be limited by the contamination of the
squeezed vacuum output with higher-order spatial modes, also generated inside
the cell. Here, we demonstrate that the squeezing can be improved by making the
light interact several times with a less dense atomic ensemble. With
optimization of some parameters we can achieve up to -2.6 dB of squeezing in
the multi-pass case, which is 0.6 dB improvement compared to the single-pass
experimental configuration. Our results show that other than the optical depth
of the medium, the spatial mode structure and cell configuration also affect
the squeezing level.