A single source femtosecond-millisecond broadband spectrometer EC Carroll, MP Hill, D. Madsen, KR Malley, and DS Larsena Department of Chemistry, University of California, Davis, One Shields Avenue, Davis, California 95616, USA Time-resolved measurement of population dynamics extending over femtosecond to millisecond time scales typically requires a combination of transient absorption techniques involving different laser systems and detection schemes. The spectrometer design presented here facilitates transient absorption measurements over 12 decades with a single ultrafast laser system by picking pump and probe pulses independently from the laser oscillator pulse train. Unamplified pulses seed a photonic crystal fiber to a supercontinuum probe source for spectrally resolved measurements. The utility of the system is demonstrated by measuring triplet state dynamics following photoexcitation of vitamin B6 in aqueous solution. Time-resolved transient absorption TA, or optical pump-probe, spectroscopy has become an indispensable technique for characterizing photoinduced population dynamics in biological, chemical, and solid-state chromophores. Dynamics in such samples often occur over multiple time scales ranging from femtoseconds eg photoisomerization to milliseconds eg protein conformational changes. In a TA experiment, a pulsed light source excites a subpopulation of the sample into an electronic excited state and its relaxation dynamics is subsequently probed by …