Dual optical frequency combs are an appealing solution to many optical measurement techniques due to their high spectral and temporal resolution, high scanning speed, and lack of moving parts. However, industrial and field-deployable applications of such systems are limited due to a high-cost factor and intricacy in the experimental setups, which typically require a pair of locked femtosecond lasers. Here, we demonstrate a single oscillator which produces two mode-locked output beams with a stable repetition rate difference. We achieve this via inserting two 45°-cut birefringent crystals into the laser cavity, which introduces a repetition rate difference between the two polarization states of the cavity. To mode-lock both combs simultaneously, we use a semiconductor saturable absorber mirror (SESAM). We achieve two simultaneously operating combs at 1050 nm with 175-fs duration, 3.2-nJ pulses and an average power of 440 mW in each beam. The average repetition rate is 137 MHz, and we set the repetition rate difference to 1 kHz. This laser system, which is the first SESAM mode-locked femtosecond solid-state dual-comb source based on birefringent multiplexing, paves the way for portable and high-power femtosecond dual-combs with flexible repetition rate. To demonstrate the utility of the laser for applications, we perform asynchronous optical sampling (ASOPS) on semiconductor thin-film structures with the free-running laser system, revealing temporal dynamics from femtosecond to nanosecond time scales.

中文翻译：

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飞秒双梳Yb：CaF ₂激光器，来自一个自由运行的偏振多路复用腔，用于光学采样应用

双光频率梳由于其高光谱和时间分辨率，高扫描速度和缺少活动部件，因此是许多光学测量技术的理想解决方案。然而，由于高成本因素和复杂的实验装置，这种系统的工业和现场可部署的应用受到限制，这通常需要一对锁定的飞秒激光器。在这里，我们演示了一个振荡器，该振荡器产生两个锁模输出光束，并具有稳定的重复速率差。我们通过将两个45°切割的双折射晶体插入激光腔来实现此目的，这会在腔的两个偏振态之间引入重复率差异。为了同时锁模两个梳子，我们使用了半导体可饱和吸收镜（SESAM）。我们在1050 nm处实现了两个同时工作的梳，持续时间为175 fs，3.2 nJ脉冲，每束平均功率为440 mW。平均重复率是137 MHz，我们将重复率差设置为1 kHz。该激光系统是第一个基于双折射多路复用技术的SESAM锁模飞秒固态双梳光源，为具有灵活重复率的便携式高功率飞秒双梳奠定了基础。为了演示激光器在应用中的实用性，我们使用自由运行的激光器系统对半导体薄膜结构执行了异步光学采样（ASOPS），揭示了从飞秒到纳秒级的时间动态。并将重复率差异设置为1 kHz。该激光系统是第一个基于双折射复用技术的SESAM锁模飞秒固态双梳光源，为具有灵活重复率的便携式高功率飞秒双梳奠定了基础。为了演示激光器在应用中的实用性，我们使用自由运行的激光器系统对半导体薄膜结构执行了异步光学采样（ASOPS），揭示了从飞秒到纳秒级的时间动态。并将重复率差异设置为1 kHz。该激光系统是第一个基于双折射多路复用技术的SESAM锁模飞秒固态双梳光源，为具有灵活重复率的便携式高功率飞秒双梳奠定了基础。为了演示激光器在应用中的实用性，我们使用自由运行的激光器系统对半导体薄膜结构执行了异步光学采样（ASOPS），揭示了从飞秒到纳秒级的时间动态。