We designed a stable laser system capable of swiftly switching among various target wavelengths. The switching times can be less than 1 microsecond, limited by electro-optic switching times. The system consists of several key components: a continuous-wave, stable laser locked to a frequency reference; a flat frequency comb; a frequency filter; and a high-speed frequency shifter. In this approach, the laser is never required to change its frequency and acts as a stable frequency reference for the system. A comb line generated from the stable frequency reference near to the target wavelength is selected, amplified and fine-tuned to the target Rydberg state.
In order to demonstrate the system’s versatility, we utilized the system for Rydberg atom-based radio frequency sensing in vapour cells. The observed spectral profile of the frequency comb is shown in Fig. 2 and is remarkably flat. All 61 lines are within a 3dB bandwidth across a wavelength range of 8 nm.
In Fig. 3(a), we show the system switching between two different Rydberg states. The switching action starts at t = 10 ms, as marked by the dashed vertical line in Fig. 3(a). The falling edge on the graph shows the delay time in the switching process. The switching time was 400 μs in the case shown in the figure. By utilizing the frequency sweeping capability of the frequency shifter, the laser system’s output can be scanned across the Rydberg spectral features, Fig. 3(b).
We improved the system’s switching speed by constructing a ping-pong scheme for changing the sensing frequency, Fig. 4. The RF detection process alternates between two RF sensing frequencies: one at 9.6 GHz with 100 kHz modulation and one at 8.3 GHz with 65 kHz modulation, Fig. 5. Ultimately, the switching speed was < 50 microseconds, limited by the re-locking time of the frequency shifter.
- “Tuning the output of a laser,” C. Liu, K.A. Nickerson, M. Hajialamdari, and J.P. Shaffer, US patent 11,658,461 B1 (2023).
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If you are interested in collaborating with us or becoming a technical staff member, including student internships and postdoctoral training, please contact James Shaffer at [email protected].