Abstract
We present a technique that uses noisy broadband pulse bursts generated by modulational instability to probe nonlinear processes, including infrared-inactive Raman transitions, in molecular gases. These processes imprint correlations between different regions of the noisy spectrum, which can be detected by acquiring single shot spectra and calculating the Pearson correlation coefficient between the different frequency components. Numerical simulations verify the experimental measurements and are used to further understand the system and discuss methods to improve the signal strength and the spectral resolution of the technique.
Highlights
Low noise trains of ultrashort pulses are a powerful tool for studying the properties of matter
We present a technique that uses noisy broadband pulse bursts generated by modulational instability to probe nonlinear processes, including infrared-inactive Raman transitions, in molecular gases
The faint horizontal bar are caused by Kerr-related four-wave mixing that generates a side-band at the filter cut-off frequency
Summary
Low noise trains of ultrashort pulses are a powerful tool for studying the properties of matter. Free electron lasers (FELs) can deliver high energy fs pulses in the x-ray spectral region [4,5], but usually exhibit strong stochastic fluctuations, which permits their use in ghost imaging [13,14]—an absorption-based method that relies on simultaneous measurements at multiple points and that has been demonstrated with both classical and quantum sources in the spatial, temporal and spectral domains. The energy conversion between different frequencies due to such nonlinear processes can be tracked by correlation maps These maps have been used in different fields such as quantum optics [17], mass spectroscopy [18,19], nuclear magnetic resonance spectroscopy [20], nonlinear fiber optics [21,22], and very recently, Tollerud et al used them to characterise solid samples by stimulated Raman scattering (SRS) of broadband incoherent femtosecond pulses [6]
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