21 June 2004 High-spectral-resolution multiplex CARS spectroscopy using chirped pulses
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A novel technique for achieving high spectral resolution with a femtosecond laser system is presented. Transform-limited 800 nm, 90 femtosecond (fs) pulses pass off two gratings, stretching the pulse in time to a pulse width of several picoseconds due to an induced linear temporal chirp directly proportional to the grating separation. This chirped pulse is the degenerate pump (ωP) and probe (ωp) pulse for the CARS experiment. When overlapped in time with the 1050 nm, 90 fs transform-limited Stokes (ωS) pulse, only a fraction of the chirped ωp pulse generates the CARS signal, thereby creating a temporal slit that defines the spectral resolution of the technique. Spectra for liquid methanol and liquid isooctane are presented, with ~6 cm-1 spectral resolution achieved for isooctane. Resonance enhancement and the mechanism of achieving high spectral resolution are shown by adjusting the ωS wavelength and ωp delay relative to the ωS pulse.
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Kelly P. Knutsen, Kelly P. Knutsen, Justin C. Johnson, Justin C. Johnson, Abigail E. Miller, Abigail E. Miller, Poul B. Petersen, Poul B. Petersen, Richard James Saykally, Richard James Saykally, } "High-spectral-resolution multiplex CARS spectroscopy using chirped pulses", Proc. SPIE 5323, Multiphoton Microscopy in the Biomedical Sciences IV, (21 June 2004); doi: 10.1117/12.527830; https://doi.org/10.1117/12.527830

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