Abstract
We demonstrate high efficiency second harmonic generation (SHG) of near infrared femtosecond pulses using a $\text{BiB}_{3}\text{O}_{6}$ crystal in a single-pass tight focusing geometry setup. A frequency doubling efficiency of $63\%$ is achieved, which is, to the best of our knowledge, the highest value ever reported in the femtosecond regime for such low energy (nJ-level) pumping pulses. Theoretical analyses of the pumping scheme focusing waist and the SHG efficiency are performed, by numerically solving the three wave mixing coupled equations in the plane-wave scenario and by running simulations with a commercial full 3D code. Simulations show a good agreement with the experimental data regarding both the efficiency and the pulse spectral profile. The simulated SHG pulse temporal profile presents the characteristic features of the group velocity mismatch broadening in a ‘thick’ crystal.
Highlights
IntroductionIn the past few decades, an increasing demand for coherent and ultrafast laser sources in the 350–530 nm spectral range, ultraviolet (UV) to visible, has been arising for significant industrial and scientific applications[1,2,3,4]
In the past few decades, an increasing demand for coherent and ultrafast laser sources in the 350–530 nm spectral range, ultraviolet (UV) to visible, has been arising for significant industrial and scientific applications[1,2,3,4]. This has resulted in the development and use of nonlinear second harmonic generation (SHG) of near infrared radiation, from commercial Ti:sapphire lasers (700–1060 nm)
High repetition rate (HRR) SHG is extensively employed, for example, in quantum optics[2, 5], enabling low probability events to be studied with adequate statistics
Summary
In the past few decades, an increasing demand for coherent and ultrafast laser sources in the 350–530 nm spectral range, ultraviolet (UV) to visible, has been arising for significant industrial and scientific applications[1,2,3,4]. Conversion efficiency is increased and harmonic temporal pulse broadening is minimized in the ultrashort laser pulse regime if the group velocity mismatch (GVM) in the nonlinear crystal is sufficiently small compared to the fundamental pulse duration This requirement is met by using a thin crystal, but this condition results in a low conversion efficiency for most of the frequency doubling crystals, unless high intensity pump pulses are used. BiBO presents some disadvantages, such as a larger walk-off angle, which can be minimized by employing a thin crystal thanks to the high nonlinear coefficient Another option for having a nonlinear coefficient higher than that of BiBO is KNbO3[24], but its opaqueness below 420 nm, the requirement of large negative/positive temperatures for phase matching and losses due to blue light induced infrared absorption effect, limits its use[25, 26]. The spectral bandwidth retrieved matches the experimental data and the temporal profile is retrieved
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