  We describe the development of a broadband magneto-optical spectrometer with
femtosecond temporal resolution. The absorption spectrometer is based on a
white-light supercontinuum (ca. 320 - 750 nm) using shot-to-shot temporal and
spectral referencing at 1 kHz. Static and transient absorption spectra using
circularly polarised light are collected in a magnetic field. The difference
spectra with respect to the external field direction give the static and
transient magneto-optical Faraday rotation (magnetic optical rotary dispersion)
and ellipticity (magnetic circular dichroism) spectra. An achromatic
quarter-wave plate is used and the impact of the deviation from ideal
retardance on the spectra is discussed. Results from solution-based and
thin-film samples are used to demonstrate the performance and wide
applicability of the instrument. The sensitivities for the static and
time-resolved data were found to be 5 and 0.4 mdeg, respectively. The method
presents a simple way to measure magneto-optical spectra using a transient
absorption spectrometer and an electromagnet.
