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Title: Broadly tuneable crystalline Raman lasers
Author: Casula, Riccardo
ISNI:       0000 0004 8509 5706
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2020
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Here is presented the first demonstration of a continuous-wave third-Stokes crystalline Raman laser. This was achieved via intracavity Raman conversion of a vertical external cavity surface emitting laser (VECSEL), also known as a semiconductor disk laser (SDL). The VECSEL-pumped Raman laser achieved Watt-level output and broad tuneability within the water transmission window at 1.7 Âμm, offering potential applications in remote sensing and medical imaging. In this thesis the design and characterization of such a cascaded Raman laser are described. The attractive performance of VECSELs based on InGaAs for emission around 1 Âμm, now being implemented in commercial cw laser systems, has spurred the VECSEL research community to widen the fundamental spectral coverage beyond 1.2 Âμm via more sophisticated and at the same time more complex growth and fabrication processes. These devices nonetheless lend themselves very well to nonlinear frequency conversion, primarily owing to the high-intensity fields generated intracavity, thus bypassing diffcult epitaxy and processing to access long wavelengths with high power and low output coupling. Raman media, as x(3)-type materials, are powerful tools as wavelength converters thanks to the simplified optics required to achieve stimulated Raman scattering -which is the basis of the Raman laser- when compared to most common x(2)-based systems. This thesis reports 1.1 W continuous-wave Raman laser emission centred at 1.73 Âμm from third-Stokes generation in a KGW crystal within an InGaAs-based VECSEL designed for fundamental emission at 1.18 Âμm. This system also demonstrated broad tuneability from 1696-1761 nm when the VECSEL was tuned from 1163-1193.2 nm, exceptional beam quality (M2 ≈ 1) and instrument-limited narrow linewidth of 48 pm FWHM. In addition, simultaneous output coupling at the first and second Stokes was also attained, with maximum output power of 1.1 and 0.8 W at 1.5 Âμm and 1.32 Âμm,respectively tuneable from 1473-1522 nm and 1300-1338 nm. Having originally intended to reach 1.7 Âμm with a synthetic crystal of diamond and two Stokes shifts (the Raman shift is larger than in KGW), in this work three Stokes shifts in KGW were utilized since the deposition of robust anti-reflection coatings was more feasible on this crystal for such a broad wavelength range (1.1-1.7 Âμm). Nevertheless, the first Stokes shift in diamond, being AR-coated for 1.1-1.4 Âμm operation and pumped by the same VECSEL structure, resulted in Raman laser emission at an important water absorption region around 1.4 Âμm, with maximum 2.3 W output power and tuneable over a range of 42 nm.
Supervisor: Hastie, Jennifer ; Kemp, Alan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral