The measurement of chirality and its temporal evolution are crucial for the understanding of a large range of biological functions and chemical reactions. Steady-state circular dichroism (CD) is a standard analytical tool for measuring chirality in chemistry and biology. Nevertheless, its push into the ultrafast time domain and in the deep-ultraviolet has remained a challenge, with only some isolated reports of subnanosecond CD. Here, we present a broadband time-resolved CD spectrometer in the deep ultraviolet (UV) spectral range with femtosecond time resolution. The setup employs a photoelastic modulator to achieve shot-to-shot polarization switching of a 20 kHz pulse train of broadband femtosecond deep-UV pulses (250–370 nm). The resulting sequence of alternating left- and right-circularly polarized probe pulses is employed in a pump-probe scheme with shot-to-shot dispersive detection and thus allows for the acquisition of broadband CD spectra of ground- and excited-state species. Through polarization scrambling of the probe pulses prior to detection, artifact-free static and transient CD spectra of enantiopure ${[\mathrm{Ru}{(\mathrm{bpy})}_3]}^{2+}$ are successfully recorded with a sensitivity of $<2\times {10}^{-5}$ OD ($\approx 0.7\mathrm{mdeg}$). Due to its broadband deep-UV detection with unprecedented sensitivity, the measurement of ultrafast chirality changes in biological systems with amino-acid residues and peptides and of DNA oligomers is now feasible.

中文翻译：

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深紫外中的超快宽带圆二色性

手性及其时间演变的度量对于理解各种生物学功能和化学反应至关重要。稳态圆二色性（CD）是用于测量化学和生物学中手性的标准分析工具。然而，将其推入超快时域和深紫外光仍然是一项挑战，只有亚纳秒级CD的一些孤立报道。在这里，我们介绍了一种具有飞秒时间分辨率的深紫外（UV）光谱范围内的宽带时间分辨CD光谱仪。该设置采用光弹性调制器来实现宽带飞秒深紫外脉冲（250-370 nm）的20 kHz脉冲序列的逐点极化切换。所产生的交替的左旋和右旋圆偏振探头脉冲序列在具有逐次散布检测的泵浦探针方案中使用，因此可以获取基态和激发态物种的宽带CD光谱。通过在检测之前对探针脉冲进行极化加扰，获得对映纯的无伪像的静态和瞬态CD光谱${[茹{（\mathrm{py}）}_3]}^{\mathrm{2个}+}$ 已成功记录，灵敏度为 $<\mathrm{2个}\times {10}^{-5}$ 外径（$\approx 0.7\mathrm{mdeg}$）。由于它具有前所未有的灵敏度的宽带深紫外检测，现在可以测量具有氨基酸残基和肽以及DNA寡聚物的生物系统中超快手性的变化。