Abstract
We observe that narrow spectral features in mid-infrared spectra obtained by chirped-pulse up-conversion are strongly distorted by cross-phase modulation between the mid-infrared field and the chirped pulse. We discuss the consequences of this effect on spectral resolution, and introduce a correction method that recovers masked lines. This simple correction can be applied either when the upconverted field is fully characterized, such as in multidimensional spectroscopy, or when causality can be used, such as in absorption spectroscopy, which we demonstrate experimentally.
Highlights
Various methods have been demonstrated for measuring mid-infrared femtosecond pulses directly with a visible detector [1,2,3], and have been subsequently applied to pumpprobe [4,5] and multidimensional [6,7,8] mid-IR spectroscopy
We observe that narrow spectral features in mid-infrared spectra obtained by chirped-pulse up-conversion are strongly distorted by crossphase modulation between the mid-infrared field and the chirped pulse
We discuss the consequences of this effect on spectral resolution, and introduce a correction method that recovers masked lines
Summary
Various methods have been demonstrated for measuring mid-infrared (mid-IR) femtosecond pulses directly with a visible detector [1,2,3], and have been subsequently applied to pumpprobe [4,5] and multidimensional [6,7,8] mid-IR spectroscopy One of these methods, chirpedpulse up-conversion (CPU) [2], consists of mixing the mid-IR field with a stretched pulse, typically the uncompressed output of a chirped pulse amplifier. There must be long features in time In this case, there will be a range of wavelengths, or equivalently, nonlinear phase variations, with which the signal field mixes. In the chirped pump pulse CARS case, the anti-Stokes pulse was characterized in amplitude and phase, and the phase modulation removed [15] This will work for multidimensional spectroscopy, where the upconverted pulse is usually fully characterized. By making use of causality, cases such as pump-probe absorption spectroscopy can be corrected, greatly improving the spectral resolution
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