The design and performance of a femtosecond timeresolved mid-infrared transient absorption spectrometer is illustrated. The spectrometer was developed from a set of commercially available Ti: sapphire femtosecond lasers utilizing difference frequency mixing technique. With this spectrometer, the transient absorption in the mid-infrared region from 800 to 2800 cm
-1 was detected with a sensitivity of 1×10
-4 for difference ab-sorbance. With a sub-picosecond visible or ultraviolet pump, a time-resolution of 250 fs has been obtained. A study on the binding and dissociation processes of carbon monoxide in myoglobin is presented as an example of its applications.
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