Structuring light in multiple degrees of freedom has become a powerful approach to create complex states of light for fundamental studies and applications. Here, we investigate the light field of an ultrafast laser beam with a wavelength-dependent polarization state, which we term a spectral vector beam. We present a simple technique to generate and tune such structured beams and demonstrate their spectroscopic capabilities. By measuring only the polarization state using fast photodetectors, it is possible to track pulse-to-pulse changes in the frequency spectrum caused by, e.g.,  narrowband transmission or absorption. In our experiments, we reach readout rates of around 6 MHz, which is limited by our technical ability to modulate the spectrum and can in principle reach GHz readout rates. In simulations we extend the spectral range to more than 1000 nm by using a supercontinuum light source, thereby paving the way to various applications requiring high-speed spectroscopic measurements.

Structured light harnessing multiple degrees of freedom has become a powerful approach to use complex states of light in fundamental studies and applications. Here, we investigate the light field of an ultrafast laser beam with a wavelength-depended polarization state, a beam we term spectral vector beam. We demonstrate a simple technique to generate and tune such structured beams and demonstrate their spectroscopic capabilities. By only measuring the polarization state using fast photodetectors, it is possible to track pulse-to-pulse changes in the frequency spectrum caused by, e.g. narrowband transmission or absorption. In our experiments, we reach read-out rates of around 6 MHz, which is limited by our technical ability to modulate the spectrum and can in principle reach GHz read-out rates. In simulations we extend the spectral range to more than 1000 nm by using a supercontinuum light source, thereby paving the way to various applications requiring high-speed spectroscopic measurements.