November 2020
Spotlight Summary by Eric Cormier
Self-frequency-doubling Yb:CNGS lasers operating in the femtosecond regime
Within an EU-China collaboration, researchers have demonstrated the generation of green femtosecond pulses from an optical cavity by means of self-frequency-doubling in an ytterbium doped laser material. Lasers emitting in the visible are often based on solid states materials doped with Er3+, Pr3+ or Tb3+ ions or gaseous Ar+ lasers. However, operation of these media in a mode-locked regime unfortunately provides pulses with durations longer than several tens of picoseconds. Equivalent materials emitting in the near infrared spectral range provides bandwidths supporting sub 100 fs pulses. A strategy could then consist in using a femtosecond Yb-doped mode-locked laser and frequency doubling it to the green via second-harmonic-generation (SHG) in a χ(2) non-linear material. This approach is perfectly viable but requires an independent additional module and suffers from the limited conversion efficiency, in particular if short pulses are targeted. A smarter strategy, perhaps, could fill the bill by capitalizing on the so-called self-frequency-doubling active crystals.
In this article, the authors have identified a novel birefringent non-centrosymmetric crystal, Yb:CNGS, whose properties are (i) to amplify 1 micron radiation by stimulated emission and (ii) to frequency double to green through SHG. By mode-locking a laser cavity with such a crystal, they were able to generate, directly within the cavity, a beam at 525 nm with pulses potentially compressible down to 240 fs at a repetition rate of 78 MHz with several tens of mW. Such a design provides a very simple, compact and efficient architecture for further conversion to the UV or frequency comb spectroscopy in the visible.
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In this article, the authors have identified a novel birefringent non-centrosymmetric crystal, Yb:CNGS, whose properties are (i) to amplify 1 micron radiation by stimulated emission and (ii) to frequency double to green through SHG. By mode-locking a laser cavity with such a crystal, they were able to generate, directly within the cavity, a beam at 525 nm with pulses potentially compressible down to 240 fs at a repetition rate of 78 MHz with several tens of mW. Such a design provides a very simple, compact and efficient architecture for further conversion to the UV or frequency comb spectroscopy in the visible.
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Maciej Kowalczyk
11/24/2020 11:18 AM
We are very glad to see that you found our research exciting! In case of any questions on this topic please do not hesitate to contact me (email in the paper). Cheers!