We have realized a 76 MHz white-light differential transmission spectroscopy system. The technique employs a Ti:sapphire laser oscillator and a tapered fiber to generate a white-light continuum spanning almost the full visible to near-infrared spectral range. Using acousto-optical modulation and subsequent lock-in detection, transient relative transmission changes as small as 10 Exp (-5) are detected. The method is applied to study the ultrafast gain dynamics of the active layer of a vertical-external-cavity surface-emitting laser based on a multiple-quantum-well structure.

This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://ol.osa.org/abstract.cfm?id=88963.