Susnjar Peter, Kurdi Gabor, Cinquegrana Paolo, Demidovich Alexander, Nikolov Ivaylo, Sigalotti Paolo, Danailov Miltcho B
Opt Lett. 2024 Apr 15;49(8):2033-2036. doi: 10.1364/OL.519486.
Ultrashort deep ultraviolet (DUV) pulses serve as indispensable tools for investigating molecular dynamics on the femtosecond scale. Nonlinear frequency upconversion of near-infrared (NIR) light sources in a sequence of nonlinear crystals is a common method for their generation. However, preserving the temporal duration of the starting source encounters challenges owing to phase-matching bandwidth limitations within the harmonic generation process. Here we propose an approach for circumventing this limitation and demonstrate it for the case of generation of the third harmonic of 800 nm pulses in a two-stage scheme (second harmonic generation succeeded by sum-frequency mixing of the fundamental and second harmonic pulses). Expanding the bandwidth of the DUV pulse involves the utilization for the last mixing process of two nonlinear crystals, detuned to convert opposite sides of the spectrum. The implementation of this approach yields 20 µJ, 263 nm DUV pulses as short as 19 fs after compression. The setup is very compact and extremely stable due to the common-path scheme, which makes it very interesting for a variety of advanced ultrafast spectroscopy applications.
超短深紫外（DUV）脉冲是研究飞秒尺度分子动力学不可或缺的工具。在一系列非线性晶体中对近红外（NIR）光源进行非线性频率上转换是产生它们的常用方法。然而，由于谐波产生过程中的相位匹配带宽限制，保持起始光源的时间持续时间面临挑战。在此，我们提出一种克服此限制的方法，并在两阶段方案（先进行二次谐波产生，然后是基频脉冲和二次谐波脉冲的和频混合）中对800 nm脉冲产生三次谐波的情况进行了演示。扩展DUV脉冲的带宽涉及在最后一个混合过程中使用两个失谐的非线性晶体，以转换光谱的相反两侧。该方法的实施在压缩后产生了能量为20 μJ、波长为263 nm、脉宽短至19 fs的DUV脉冲。由于采用了共光路方案，该装置非常紧凑且极其稳定，这使其对于各种先进的超快光谱应用非常有吸引力。
