Cascaded Kerr-lens partial mode-locking and optimally-coupled cw single-frequency operation of a Nd:YLF/ppKTP ring laser

ZONDY, J.J.; CAMARGO, F.A.; ZANON WILLETTE, T.; PETROV, V.; WETTER, N.U.

Cascaded Kerr-lens partial mode-locking and optimally-coupled cw single-frequency operation of a Nd:YLF/ppKTP ring laser

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2010

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NIKLAUS URSUS WETTER

FABIOLA DE ALMEIDA CAMARGO

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INTERNATIONAL LASER PHYSICS WORKSHO, 19th

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Abstract

Cascaded second-order nonlinearities are often used for picosecond passive mode-locking of diode-pumped Nddoped solid-state lasers via nonlinear mirror mode-locking (NLM) [1] or cascaded-second-order mode-locking (CSM) [2]. Both techniques require standing-wave resonators, where the forwardly generated second-harmonic (SH) wave and/or the fundamental wave (FH) pass more than once through the nonlinear crystal, with a proper phase shift of the back-reflected SH. In this work [3], a self-starting partial mode-locking dynamics triggered by pure cascaded KLM processes arising from an intracavity temperature phase-mismatched ppKTP is demonstrated for the first time in a unidirectional Nd:YLF ring resonator operating on the broad 1321nm transition. In contrast with KLM lasers operating near one of the stability limit of the resonator to enhance the nonlinear gain modulation, our unidirectional intracavity frequency-doubled cw ring laser (ICSHG laser) – originally designed to demonstrate the concept of optimal ICSHG coupling [4,5] – operates at the middle of the resonator stability range with a large laser-crystal to nonlinear-crystal waist ratio w/w0=317m/47m~6.5. When the ppKTP crystal is inserted into the cavity with its temperature substantially phase-mismatched from the gain-center wavelength (1321nm), a strong periodically pulsing dynamics at the cavity free-spectral range repetition rate (frep=421MHz) is systematically observed, whichever the sign of the cascaded Kerr nonlinearity (focusing with k<0 or defocusing with k>0 [6]) – in contrast with CSM lasers. The output of the ICSHG laser consists then of a train of pulses superimposed on a phase-incoherent DC signal background (Fig.1b), and the fundamental or harmonic spectra exhibit a strong spectral gain broadening (Fig.1c) as compared with the narrow-line cw spectrum prior to the ppKTP insertion. This partial KLM regime disappear below a diode pump threshold Pabs~6.5W. The transition from partial KLM to genuinely cw SLM regime could be achieved only with the insertion of a suitable intracavity thin etalon quenching the cascaded second-order nonlinear processes. While under partial KLM regime the maximum average broadband red power (660.5nm) did not exceed P ~0.15W at kL~±3 and Pabs=13W of diode pumping, under cw SLM operation a record P =1.4W in red SLM emission corresponding to ~100% conversion of the 1321nm SLM maximum output power available from the laser (P =1.4W using an optimal T=2% out-coupling mirror) was obtained (Fig.1a), satisfying thus the criterion of optimal ICSHG coupling as theoretically predicted in the late 60’s [3-4,5].

Citation

ZONDY, J.J.; CAMARGO, F.A.; ZANON WILLETTE, T.; PETROV, V.; WETTER, N.U. Cascaded Kerr-lens partial mode-locking and optimally-coupled cw single-frequency operation of a Nd:YLF/ppKTP ring laser. In: INTERNATIONAL LASER PHYSICS WORKSHO, 19th, July 5-9, 2010, Foz do Iguacu, PR. Abstract... p. 254. Disponível em: http://repositorio.ipen.br/handle/123456789/19195. Acesso em: 17 Mar 2025.

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