A few‐cycle, broadband, singly‐resonant optical parametric oscillator (OPO) for the mid‐infrared based on MgO‐doped periodically‐poled LiNbO₃ (MgO:PPLN), synchronously pumped by a 20‐fs Ti:sapphire laser is reported. By using crystal interaction lengths as short as 250 µm, and careful dispersion management of input pump pulses and the OPO resonator, near‐transform‐limited, few‐cycle idler pulses tunable across the mid‐infrared have been generated, with as few as 3.7 optical cycles at 2682 nm. The OPO can be continuously tuned over 2179‐3732 nm (4589‐2680 cm^‐1) by cavity delay tuning, providing up to 33 mW of output power at 3723 nm. The idler spectra exhibit stable broadband profiles with bandwidths spanning over 422 nm (FWHM) recorded at 3732 nm. The effect of crystal length on spectral bandwidth and pulse duration is investigated at a fixed wavelength, confirming near‐transform‐limited idler pulses for all grating interaction lengths. By locking the repetition frequency of the pump laser to a radio‐frequency reference, and without active stabilization of the OPO cavity length, an idler power stability better than 1.6% rms over >2.75 hours is obtained when operating at maximum output power, in excellent spatial beam quality with TEM₀₀ mode profile. Photograph shows a multigrating MgO:PPLN crystal used as a nonlinear gain medium in the few‐cycle femtosecond mid‐IR OPO. The visible light is the result of non‐phase‐matched sum‐frequency mixing between the interacting beams.

中文翻译：

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由20 fs Ti：蓝宝石激光器泵浦的很少周期的宽带中红外光学参量振荡器。

据报道，基于掺有MgO的周期性极化LiNbO ₃（MgO：PPLN），由20 fs Ti：蓝宝石激光器同步泵浦的中红外几个周期，宽带，单谐振光学参量振荡器（OPO）。通过使用短至250 µm的晶体相互作用长度，以及对输入泵浦脉冲和OPO谐振器进行仔细的色散管理，产生了近变换受限的，可在中红外范围内调谐的很少周期的惰轮脉冲，其中只有3.7个2682 nm的光学循环。OPO可以在2179-3732 nm（4589-2680 cm ^-1）范围内连续调谐）通过腔延迟调谐，可在3723 nm处提供高达33 mW的输出功率。惰轮光谱表现出稳定的宽带分布，在3732 nm处记录的带宽超过422 nm（FWHM）。在固定波长下研究了晶体长度对光谱带宽和脉冲持续时间的影响，从而确认了所有光栅相互作用长度的近变换限制的惰轮脉冲。通过将泵浦激光器的重复频率锁定在射频参考上，并且在没有主动稳定OPO腔长度的情况下，以最大输出功率工作时，在大于2.75小时的时间内，惰轮功率稳定性优于1.6％rms。 TEM _00的空间光束质量模式配置文件。照片显示了多光栅MgO：PPLN晶体在几周期飞秒中红外OPO中用作非线性增益介质。可见光是相互作用光束之间非相位匹配的和频混合的结果。