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Register a new userZeeman-Sisyphus Deceleration of Molecular Beams
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Added by
Benjamin Augenbraun
Publication date
2021
fields
Physics
and research's language is
English
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We present a robust, continuous molecular decelerator that employs high magnetic fields and few optical pumping steps. CaOH molecules are slowed, accumulating at low velocities in a range sufficient for loading both magnetic and magneto-optical traps. During the slowing, the molecules scatter only 7 photons, removing around 8 K of energy. Because large energies can be removed with only a few spontaneous radiative decays, this method can be applied to nearly any paramagnetic atomic or molecular species, opening a general path to trapping of complex molecules.
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Ultracold molecular gases are promising as an avenue to rich many-body physics, quantum chemistry, quantum information, and precision measurements. This richness, which flows from the complex internal structure of molecules, makes the creation of ultracold molecular gases using traditional methods (laser plus evaporative cooling) a challenge, in particular due to the spontaneous decay of molecules into dark states. We propose a way to circumvent this key bottleneck using an all-optical method for decelerating molecules using stimulated absorption and emission with a single ultrafast laser. We further describe single-photon cooling of the decelerating molecules that exploits their high dark state pumping rates, turning the principal obstacle to molecular laser cooling into an advantage. Cooling and deceleration may be applied simultaneously and continuously to load molecules into a trap. We discuss implementation details including multi-level numerical simulations of strontium monohydride (SrH). These techniques are applicable to a large number of molecular species and atoms with the only requirement being an electric dipole transition that can be accessed with an ultrafast laser.
Cold, velocity-controlled molecular beams consisting of a single quantum state promise to be a powerful tool for exploring molecular scattering interactions. In recent years, Stark deceleration has emerged as one of the main methods for producing velocity-controlled molecular beams. However, Stark deceleration is shown not to be effective at producing a molecular beam consisting of a single quantum state in many circumstances. Therefore, quantum state purity must be carefully considered when using Stark decelerated beams, particularly in collision experiments where contributions from all quantum states must be addressed.
Stark deceleration allows for precise control over the velocity of a pulsed molecular beam and, by the nature of its limited phase-space acceptance, reduces the energy width of the decelerated packet. We describe an alternate method of operating a Stark decelerator that further reduces the energy spread over the standard method of operation. In this alternate mode of operation, we aggressively decelerate the molecular packet using a high phase angle. This technique brings the molecular packet to the desired velocity before it reaches the end of the decelerator; the remaining stages are then used to longitudinally and transversely guide the packet to the detection/interaction region. The result of the initial aggressive slowing is a reduction in the phase-space acceptance of the decelerator and thus a narrowing of the velocity spread of the molecular packet. In addition to the narrower energy spread, this method also results in a velocity spread that is nearly independent of the final velocity. Using the alternate deceleration technique, the energy resolution of molecular collision measurements can be improved considerably.
We have recently demonstrated static trapping of ammonia isotopologues in a decelerator that consists of a series of ring-shaped electrodes to which oscillating high voltages are applied [Quintero-P{e}rez et al., Phys. Rev. Lett. 110, 133003 (2013)]. In this paper we provide further details on this traveling wave decelerator and present new experimental data that illustrate the control over molecules that it offers. We analyze the performance of our setup under different deceleration conditions and demonstrate phase-space manipulation of the trapped molecular sample.
Imidogen (NH) radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational and rotational ground state imidogen in collisions with He-3 is measured to be 3.8 +/- 1.1 E-19 cm^2 at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of gamma = 7 E4 in agreement with the recent theory of Krems et al. (PRA 68 051401(R) (2003))
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