Di Gaetano, E. , Keliehor, B., Griffin, P., Sorel, M. , Riis, E. and Paul, D. (2023) Sub-4 kHz Linewidth Distributed Feedback Lasers at 778.1 nm Wavelength for Two-Photon Rb Spectroscopy. SPIE Photonics West 2023, San Francisco, CA, USA, 28 Jan - 02 Feb 2023.
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Abstract
Short-wavelength GaAs/AlGaAs-based semiconductor lasers are of interest for emerging quantum technologies such cold atom systems. However, such technologies require high-power, stable single-mode, and narrow linewidth sources at specific target wavelengths, e.g. 780.24 nm for D2 87Rb transitions. Several material properties, such as propagation losses, self-heating, and far-field emission pattern, are critical for laser performance, including maximum power output before damage, coupling efficiency into optical components, and linewidth, in accordance with the Schawlow-Townes formula. In our work, an aluminum-free active area is designed with InGaAsP quaternary compounds and sandwiched between AlGaAs cladding layers. The presence of an asymmetrical mode expander into both p- and n-doped AlGaAs cladding shapes mode profile to achieve a Gaussian-like emission pattern. The asymmetrical mode expander configuration reduces propagation losses, modal confinement within the active region, and decrease the vertical beam divergency. A 3 mm-long phase-shifted laterally-coupled DFB laser is fabricated by reactive ion etching of the reported epilayer material, with weak coupling grating that contributes to narrow the laser linewidth. The AR/HR laser device exhibits single-mode emission at the wavelength of 778.1 nm with a tunability of 0.8 nm, power output of 48 mW, SMSRs exceeding 35dB, and vertical beam divergence of 20.5. Instantaneous Lorentzian linewidth, measured by homodyne technique with automated noise characterisation tool, proved as narrow as 3.67 kHz. The laser is employed to probe the 87Rb two-photon transitions employing a heated Rb cell in retroreflection configuration. Using an acousto-optical modulator for frequency scan, the laser resolved hyperfine levels for the 87Rb two-photon transition.
| Item Type: | Conference or Workshop Item |
|---|---|
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Sorel, Professor Marc and Paul, Professor Douglas and Di Gaetano, Dr Eugenio |
| Authors: | Di Gaetano, E., Keliehor, B., Griffin, P., Sorel, M., Riis, E., and Paul, D. |
| Subjects: | Q Science > Q Science (General) T Technology > T Technology (General) |
| College/School: | College of Science and Engineering > School of Engineering > James Watt Nanofabrication Centre |
| Copyright Holders: | Copyright © 2023 The Authors |
| Publisher Policy: | Reproduced with the permission of the authors |
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