I can open the data files in MS Excel as comma-separated columns of data, but there are a lot of entries saying either ‘Inf’ or ‘NaN’. I guess these entries are for the wavelength ranges at the edges and outside the range of the white light spectrum. Is this normal and can I still plot the data with standard analysis software? (I just expected to have zeros for filling).

The Inf and NaN values appear when there was not enough probe light at that wavelength. They mean that you do not have any information about the transient signal at those points. They are different from zero, which is a valid value for transient absorption. In most spreadsheet programs, such points will be represented by empty cells. When you see Inf and/or NaN, it means that the data were imported as text instead of numbers. This would need to be changed before plotting the data. Also, keep in mind that older versions of MS Excel allow for only up to 256 columns in the tables. Therefore, if you have more than 256-time points in the data file, some of them will be cut off.