Terahertz Sources Based on Metrological-Grade Frequency Combs

Year: 2023

Authors: Riccardi E., Pistore V., Consolino L., Sorgi A., Cappelli F., Eramo R., De Natale P., Li LH., Davies AG., Linfield EH., Vitiello MS.

Autors Affiliation: CNR Ist Nanosci, Piazza San Silvestro 12, I-56127 Pisa, Italy; Scuola Normale Super Pisa, NEST, Piazza San Silvestro 12, I-56127 Pisa, Italy; European Lab Non Linear Spect, I-50019 Sesto Fiorentino, Italy; CNR Ist Nazl Ott, I-50019 Sesto Fiorentino, Italy; Univ Leeds, Sch Elect & Elect Engn, Leeds LS2 9JT, England.

Abstract: Broadband metrological-grade frequency comb (FC) synthesizers with a rich number of phase locked modes are the ideal sources for quantum sensing and quantum metrology. At terahertz (THz) frequencies, electrically pumped quantum cascade lasers (QCLs) have shown quantum-limited frequency noise operation, phase/frequency absolute referencing and self-starting FC operation, albeit over a rather restricted dynamic range, governed by the nature of the quantum gain media that entangles group velocity dispersion at the different bias points. Here, a technological approach is conceived to achieve FC operation over the entire available gain bandwidth at THz frequencies. The intracavity light intensity of a multistack QCL, inherently showing a giant Kerr nonlinearity, is altered by increasing the mirror losses of its Fabry-Perot cavity through coating the back facet with an epitaxially-grown multilayer graphene film. This enables a frequency modulated THz FC showing a proliferation of emitted modes over the entire gain bandwidth and across more than 60% of its operational range, with approximate to 0.18 mW per mode optical power. The QCL FC is then experimentally characterized to assess its phase coherence, reconstructing its intensity emission profile, instantaneous frequency, and electric field, thus proving its metrological nature.

Journal/Review: LASER & PHOTONICS REVIEWS

Volume: 17 (2)      Pages from:   to:

More Information: This work was supported by the European Research Council through the ERC Consolidator Grant (681379) Ultrashort pulse laser resonators in the Terahertz (SPRINT), by the European Union through the H2020-FET OPEN EXTREME IR (964735), and by the Engineering and Physical Sciences Research Council (EPSRC) (UK) programme grant HyperTerahertz (EP/P021859/1). Open access funding provided by Consiglio Nazionale delle Ricerche within the CRUI-CARE Agreement.
KeyWords: frequency combs; graphene; metrology; quantum cascade lasers; terahertz
DOI: 10.1002/lpor.202200412

Citations: 9
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