Cross phase modulation artifact in liquid phase transient absorption spectroscopy

Abstract

We present experimental results for the cross phase modulation (xpm) induced transient absorption signal in a 1 mm thick fused silica plate using a white light continuum as a probe. The fused silica plate mimics the entrance window of a commercial flow cell commonly used in liquid-phase transient absorption measurements. The experimental results are compared with those obtained theoretically by numerically solving the set of nonlinear coupled wave equations describing the propagation of the pump and the probe. The simulations allow for the different group velocities of the pump and probe pulses, and include the influence of the first and second order dispersion on the continuum probe. From the calculations the physical origin of the complex oscillatory feature observed around the zero time delay of each wavelength of the (chirped) continuum has been accurately identified. The influence of propagation effects arising from the finite thickness of the sample is discussed in great detail, and the necessity to work with thin samples, preferably free-flowing jets, is emphasized. The good agreement between theory and experiment indicates that the xpm artifact may be useful for characterizing the continuum probe, in particular its chirp.

Appearance of coherent artifact signals in femtosecond transient absorption spectroscopy in dependence on detector design

“…(The influence of propagation is also seen in the title figure.) In conclusion, employing spectrally resolved detection of the probe light intrinsically leads to the observation of XPM in the transient absorption signals [6][7][8][9]11,12]. Here we illustrate, that characteristic signatures of XPM are observed in the near infrared even when commonly used spectrally integrating silica detectors are employed.…”

“…The presence of coherent artifacts is intrinsic to all time-resolved measurements employing ultrashort pulses and is even observed in media completely transparent for both pump and probe beam [5][6][7][8][9][10]12]. A complex theoretical machinery has been developed to dissect observed short-time signals in femtosecond absorption spec-troscopy [6,11,13], however from an experimental point of view it is important to detail the influence of the detection system and experiment design on the appearance of the non-resonant artifact contributions.…”

Ultrafast Excited State Dynamics of the Perylene Radical Cation Generated upon Bimolecular Photoinduced Electron Transfer Reaction

“…The initial spike at time zero is due to both a resonant contribution from Pe •+ , the so-called coherent spike, 45 and a nonresonant contribution from the solvent, namely cross-phase modulation. 46 Its relatively large magnitude is due to the small transient absorbance around 530 nm. As this spike does not contain any information on the population dynamics of Pe •+ , it has not been included in the analysis.…”

Discerning the Surface and Bulk Recombination Kinetics of Organic–Inorganic Halide Perovskite Single Crystals

“…In fs TA spectroscopy, when the pump and probe beams spatially and temporally overlap, coherent processes such as 2PA, stimulated Raman amplification, etc., can contribute to TA spectra and dynamics. [45,46] Analysis of the "fast" and "slow" processes reveals that the power-dependence of the initial amplitudes from the two processes can be well-fitted with a linear and a quadratic dependence, respectively ( Figure S8, Supporting Information). Hence, we attribute the "fast" process to be a coherent artifact that originates from the nondegenerate (ND)-2PA of the pump and probe (see discussion in the Supporting Information).…”