Abstract
We report the wavelength tuning, linewidth narrowing and power enhancement of a continuous-wave intracavity Raman laser by incorporating solid etalons in the high-Q fundamental resonator. With a-cut Nd:GdVO4 and a-cut BaWO4 serving as the laser and Raman crystals respectively, tilting of a 50 μm-thick etalon in the high-Q fundamental cavity enabled the fundamental to be tuned from 1061.00 nm to 1065.20 nm. This gave rise to Stokes output which was tunable from 1176.46 nm to 1181.63 nm whilst the narrowed fundamental linewidth resulted in higher effective Raman gain and as a consequence enhanced output power, as well as the narrow-linewidth Stokes output. Frequency-doubling of the Stokes field resulted in yellow output tunable from 588.23 nm to 590.81 nm, which covers the guide star wavelength of 589.16 nm.
Highlights
Solid-state Raman lasers have been established as efficient coherent radiation sources in spectral regions inaccessible to inversion lasers, from ultraviolet to mid-infrared regions [1,2,3]
The broadened fundamental laser linewidth results in wider Stokes spectrum which could be inconvenient for some practical applications, and, more importantly, it was shown in [9] that spectral broadening of the fundamental can reduce the effective Raman gain coefficient by over 70% of its narrow linewidth steady state value
Threshold for stimulated Raman scattering (SRS) occurred for a diode pump power of 0.8 W, and 1.73 W Stokes output at 1179 nm was obtained for the maximum incident pump power of 18.7 W with corresponding optical efficiency being 9.3%
Summary
Solid-state Raman lasers have been established as efficient coherent radiation sources in spectral regions inaccessible to inversion lasers, from ultraviolet to mid-infrared regions [1,2,3]. By locating the Raman crystal within the high-Q fundamental laser cavity with minimized losses, the circulating fundamental power could achieve cw SRS threshold (usually hundreds of watts) with primary diode pump power as low as several hundred milliwatts [4,5]. Intracavity Raman lasers exhibit some complex dynamics, and it has been shown in recent years that their efficiency can be impacted by broadening of the fundamental linewidth, as the SRS presents a spectrally-varying loss to the fundamental laser [6,7,8,9]. The broadened fundamental laser linewidth results in wider Stokes spectrum which could be inconvenient for some practical applications, and, more importantly, it was shown in [9] that spectral broadening of the fundamental can reduce the effective Raman gain coefficient by over 70% of its narrow linewidth steady state value. There has been a less emphasis given to the potential for wavelength tuning the output of crystalline Raman lasers
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