Abstract
We present the design and commissioning of a resonant microwave cavity as a novel diagnostic for the study of ultracold plasmas. This diagnostic is based on the measurements of the shift in the resonance frequency of the cavity, induced by an ultracold plasma that is created from a laser-cooled gas inside. This method is simultaneously non-destructive, very fast (nanosecond temporal resolution), highly sensitive, and applicable to all ultracold plasmas. To create an ultracold plasma, we implement a compact magneto-optical trap based on a diffraction grating chip inside a 5GHz resonant microwave cavity. We are able to laser cool and trap (7.25 ± 0.03) × 107 rubidium atoms inside the cavity, which are turned into an ultracold plasma by two-step pulsed (nanosecond or femtosecond) photo-ionization. We present a detailed characterization of the cavity, and we demonstrate how it can be used as a fast and sensitive probe to monitor the evolution of ultracold plasmas non-destructively. The temporal resolution of the diagnostic is determined by measuring the delayed frequency shift following femtosecond photo-ionization. We find a response time of 18 ± 2 ns, which agrees well with the value determined from the cavity quality factor and resonance frequency.
Highlights
A new exotic category of plasmas currently under investigation is that of ultracold plasmas (UCPs)
We find a response time of 18 ± 2 ns, which agrees well with the value determined from the cavity quality factor and resonance frequency
We will briefly discuss the concept of the diffraction grating chip used to create a compact magneto-optical trap inside the cavity, how the plasma is created from the laser-cooled gas, and how the shift in the cavity’s resonance frequency can be used to determine the electron density of a UCP
Summary
A new exotic category of plasmas currently under investigation is that of ultracold plasmas (UCPs). The diagnostic is based on a resonant microwave cavity for probing the plasma in combination with a compact, diffraction grating-based magnetooptical trap inside the cavity to laser cool and trap 85Rb atoms. It uses the shift in the cavity’s resonance frequency induced by the UCP to obtain information about the electron density as a function of time. We will briefly discuss the concept of the diffraction grating chip used to create a compact magneto-optical trap inside the cavity, how the plasma is created from the laser-cooled gas, and how the shift in the cavity’s resonance frequency can be used to determine the electron density of a UCP. We will end with some concluding remarks and an outlook for further developments
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