Rydberg Gas Sensors
Goals and background
A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, n. Rydberg atoms have a number of peculiar properties, including an exaggerated response to electric and magnetic fields. 
The swift development of narrowband lasers, especially in the ultraviolet domain allows for expanding the proficiency of atomic vapor spectroscopy to molecular gases. With a multistep excitation scheme, partners from STUTT could realize highlying Rydberg states of nitric oxide (NO) with unmatched precision. In combination with integrated electronics, a direct current of ionized molecules was detected, making the whole system a substantial bandwidth, a highly sensitive detector for NO. The flexibility offered by such a Rydberg gas sensor will benefit current small-sized and integrable systems that are currently limited to a few gases of interest. In the medical context of breath analysis, one molecule of interest is NO as an indicator for several severe conditions.
In macQsimal, the partners collaborated closely under the lead of STUTT to design and develop a microfabricated Rydberg-based Gas Sensor demonstrator for the detection of NO.
Key results and impact
- Performed Sub-doppler spectroscopy of nitric oxide
- Realization of Rydberg states of nitric oxide
- Direct current detection of Rydberg states
- Realization of integrated vapor cells with onboard electronics
- Development of large bandwidth and low current trans-impedance amplifiers
- Performance test of rubidium in nitrogen resulted in ppb sensitivities
- Exploring the potential to extend this scheme to other relevant molecules
- An optogalvanic gas sensor based on Rydberg excitations
Schmidt, J., Münzenmaier, Y., Kaspar, P., Schalberger, P., Baur, H., Löw, R., Fruehauf, N., Pfau, T., Kübler, H. (2020) Journal of Physics B: Atomic, Molecular and Optical Physics, 53(9), 1-5.
- Towards an Optogalvanic Flux Sensor for Nitric Oxigene Based on Rydberg Excitation (PDF), Kaspar P. et al., OSA Optical Sensing and Sensors Congres 2021, online.
The macQsimal partners produced four deliverables on Rb gas sensors. Please refer to the publicly available deliverables for more details.
- Towards an Optogalvanic Flux Sensor for Nitric Oxigene Based on Rydberg Excitation STUTT, OSA Optical Sensing and Sensors Congres 2021, online.
The sensing principle of the Rb gas sensors developed in macQsimal is illustrated below. The violet arrow represents a gas mixture of unknown composition entering the gas cell. Within the cell, the NO molecules get excited to a Rydberg state through the laser system visualised in pink and via the excitation scheme on the left. The following ionisation of the molecules results from collisions with other particles. The small voltage applied to the electrodes guides the ionised particles towards the electrical circuit, where a trans-impedance amplifier (TIA) generates the signal of interest.
In macQsimal, the research team developed a prototype of a through-flow gas cell. An unknown concentration of NO including background gases passes the cell from left to right. With the laser excitation scheme involving three wavelengths, we excited the NO to a Rydberg state which subsequently ionises due to collisions. The resulting charges are then collected by field plates within the cell and afterwards detected by a trans-impedance amplifier, which was designed at the Institute of Smart Sensors.
In order to maintain the laser linewidth of each transition as narrow as possible, we installed a locking setup capable of providing feedback, that was applied to our laser systems. The master laser (780 nm) was locked to an ultra-low expansion cavity. The incorporation of electrooptical modulators enabled the locking of the required wavelength for the measurement of particles. The light of the laser was delivered to the table via optical fibres. For protective reasons, the table was hidden in special boxes.
Towards market applicability
Within the project, the macQsimal partners have demonstrated the feasibility of the developed Rb gas sensors for the detection of nitric oxide and rubidium in gas mixtures. In order to bring the innovation closer to the market, the development will focus on the improvement of trans-impedance amplifiers as well as overcoming the current gas mixture limit of 10 ppb by improving the gas mixing strategy.