Seres J, Seres E, Serrat C, Young E C, Speck J S, Schumm T
Opt Express. 2019 Mar 4;27(5):6618-6628. doi: 10.1364/OE.27.006618.
We realized a solid-state-based vacuum ultraviolet frequency comb by harmonics generation in an external enhancement cavity. Optical conversions were so far reported by only using gaseous media. We present a theory that allows the most suited solid generation medium to be selected for specific target harmonics by adapting the material's bandgap. We experimentally use a thin AlN film grown on a sapphire substrate to realize a compact frequency comb high-harmonic source in the Deep Ultraviolet (DUV) / Vacuum Ultraviolet (VUV) spectral range. By extending our earlier VUV source [Opt. Express26, 21900 (2018)] with the enhancement cavity, a sub-Watt level Ti:sapphire femtosecond frequency comb is enhanced to 24 W stored average power, its 3rd, 5th, and 7th harmonics are generated, and the targeted 5th harmonic's power at 160 nm increased by two orders of magnitude. The emerging nonlinear effects in the solid medium, together with suitable intra-cavity dispersion management, support optimal enhancement and stable locking. To demonstrate the realized frequency comb's spectroscopic ability, we report on the beat measurement between the 3rd harmonic beam and a 266 nm CW laser reaching about 1 MHz accuracy.
我们通过在外部增强腔中进行谐波产生实现了基于固态的真空紫外频率梳。到目前为止，光学转换仅报道了使用气态介质的情况。我们提出了一种理论，通过调整材料的带隙，可以为特定的目标谐波选择最合适的固态产生介质。我们通过实验使用生长在蓝宝石衬底上的薄氮化铝（AlN）薄膜，在深紫外（DUV）/真空紫外（VUV）光谱范围内实现了一种紧凑的频率梳高谐波源。通过用增强腔扩展我们早期的真空紫外源[Opt. Express 26, 21900 (2018)]，将亚瓦特级的钛宝石飞秒频率梳增强到24 W的存储平均功率，产生了其第3、第5和第7谐波，并且在160 nm处目标第5谐波的功率增加了两个数量级。固体介质中出现的非线性效应，以及合适的腔内色散管理，支持了最佳增强和稳定锁定。为了证明所实现的频率梳的光谱能力，我们报道了第3谐波光束与266 nm连续波（CW）激光之间的拍频测量，精度达到约1 MHz。
