VUV-Free Laser Cooling of Neutral Carbon using Metastable State
POSTER
Abstract
Neutral carbon atom plays a central role in chemistry, astrophysics, and atmospheric science but has not yet been laser cooled. The main problem is that the closed cycling transitions from the ground state lie in the vacuum ultraviolet (VUV, 166 nm). It makes a conventional cooling scheme technically demanding. To circumvent this, we propose an alternative route that operates entirely on long-lived metastable states 1D2 and 1S0 levels. Metastable states enable laser cooling of carbon by maintaining optical cycles without the need for a VUV laser. Carbon atoms are excited from the 1S0 to the 1P1 state using a 247.8 nm laser, followed by spontaneous decay to both the 1S0 and 1D2 states. Population in the metastable 1D2 state is repumped to 1S0 via the electric-quadrupole transition at 872.7 nm.
In this study, we design a multi-stage protocol for laser cooling neutral carbon. Carbon vapor is first produced via laser ablation of a highly oriented pyrolytic graphite (HOPG) target, then thermalized in a cryogenic helium buffer-gas cell to form a cold, slow atomic beam. Under typical buffer-gas conditions, collisional quenching of the metastable manifold is expected to remain sufficiently weak, allowing a sizable fraction of atoms to survive in the 1D2 and 1S0 states for subsequent optical manipulation. We then employ the strong electric-dipole transition 247.8 nm from 1S0 to 1Po1 for the main cooling line.
A key challenge is using the weak electric-quadrupole transition from 1D2 to 1S0 as a repump transition line. We demonstrate that by optimizing the polarization geometry under a biased magnetic field, the effective coupling strength can be maximized by mixing the dark magnetic substates. Our calculations show that a scattering rate of approximately 30 kHz is achievable using attainable laser parameters with a combined main and repump laser scheme. We further report recent experimental progress toward generating a cryogenic buffer-gas beam of neutral carbon atoms.
In this study, we design a multi-stage protocol for laser cooling neutral carbon. Carbon vapor is first produced via laser ablation of a highly oriented pyrolytic graphite (HOPG) target, then thermalized in a cryogenic helium buffer-gas cell to form a cold, slow atomic beam. Under typical buffer-gas conditions, collisional quenching of the metastable manifold is expected to remain sufficiently weak, allowing a sizable fraction of atoms to survive in the 1D2 and 1S0 states for subsequent optical manipulation. We then employ the strong electric-dipole transition 247.8 nm from 1S0 to 1Po1 for the main cooling line.
A key challenge is using the weak electric-quadrupole transition from 1D2 to 1S0 as a repump transition line. We demonstrate that by optimizing the polarization geometry under a biased magnetic field, the effective coupling strength can be maximized by mixing the dark magnetic substates. Our calculations show that a scattering rate of approximately 30 kHz is achievable using attainable laser parameters with a combined main and repump laser scheme. We further report recent experimental progress toward generating a cryogenic buffer-gas beam of neutral carbon atoms.
Presenters
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yongwoong lee
- Korea University