Due to different refractive index of light in glass (red, orange, yellow, green) all wavelength of the white light does not reach the sample at the same time (chirp). This results in different time=0 for different wavelength which distorts the TA spectrum. This however does not affect the kinetics. In only affects the t=0. The extent of chirp (in time) depends on amount of glass the light passes and your wavelength window. If you are working in UV the chirp could be 2-3 ps. If you are in the region above 600 nm the chirp may be less than 500 fs.
Article Sub-50 fs broadband absorption spectroscopy with tunable exc...
To do chirp correction: you can put instead of your sample a quartz plate or a cuvette with any solvent (water) and scan TA at times 0-3 ps with step 0.05 ps. Excitation power about 0.2-0.5 mW. You will see a transient signal, positive and negative. Plot the maximum of the TA signal vs the time, fit with any function and use this function for the chirp correction of your TA 3D spectra.
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