Laser frequency standards based on gas-filled hollow-core fibres

Marco Triches

Research output: Book/ReportPh.D. thesis

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The work presented in this thesis has been developed within the Marie-Curie Initial Training Network (ITN) called Quantum Sensor Technologies and Applications (QTea), funded under the EU-FP7 program (contract-N MCITN-317485). The ITN QTea project is aimed at preparing a cohort of early-stage researchers for the emerging challenges in quantum technology. The scientific scope of the network is focused on the physics of modern quantum sensors for gravitational probing, rotation sensing, field probes, magnetic surface microscopy,atomic clocks and precision spectroscopy. This work naturally falls within precision spectroscopy with the scope of developing a fiber-based, portable optical frequency standard in the telecommunication band. Nowadays, portable optical frequency standards are important not only in metrology and telecommunication industry but also for remote sensing applications. Since the advent of frequency combs, an optical frequency reference may be used to stabilize the comb in order to achieve an optical clock, which has better specifications than standard Rb and Cs atomic clocks. The realization of such an optical frequency reference is based on the laser frequency stabilization technology, which has been widely investigated in the past decades, using many different molecular and atomic transitions as optical reference. One of the recommended references in the telecommunication region of the light spectrum is given by a specific absorption line in 13C2H2 acetylene. However, many other molecular references (e.g. methane and carbon dioxide) maybe interesting for remote sensing applications in the near infrared region. Typically, molecules are weakly absorbing in the telecommunication band and, hence, they require a long interaction length to be detected. For these reasons,since the advent of the photonic crystal fiber technology, many studies have been performed using various hollow-core fibers used as vapor cells. This hollow-core fiber approach is also meeting the needs of the remote sensing applications, which require size and weight reductions with respect to the conventional optical frequency reference systems based on bulky glass vapor cell and free space optics. All in all, this technology shows great potential but novel solutions in the fiber sealing/encapsulation needs to be developed in order to encounter the market demands. For example, another application looking into the HC fiber technology is represented by high-energy pulse delivery systems. The low non-linearity of the in-air guidance mechanism offers
a unique tool to propagate unperturbed pulses far from the laser source. A tight vacuum sealed encapsulation can avoid the remaining non-linearity generated by in-air Raman scattering, eliminating the remaining obstacle for the implementation of the technology in the laser machining industry.
This thesis presents the development of a compact fiber-based optical frequency standard using acetylene-filled hollow-core fibers. The study focuses both on the technical realization of a portable system and on the theoretical identification of the most important parameters for in-fiber gas spectroscopy applications. The scope of the project is to reduce the gap that prevents the state of the art technology from being commercialized. This thesis aims at:
(a) characterizing of different fibers design; (b) testing the performance of the different fibers; (c) proposing a theoretical explanation for the interaction mechanism inside the gas-filled hollow-core fibers; (d) developing a dedicated solution for the fiber encapsulation; (e) characterizing the instability and reproducibility of the realized optical frequency standard prototype. Furthermore, the research in various encapsulation techniques for the hollow-core fiber ends in a collaboration with other research groups for (f) the development of a proof-of-concept in-fiber Raman sensor for aqueous solutions.
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages173
Publication statusPublished - 2016

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