Frequency-Comb Velocity-Modulation Spectroscopy

We have developed a novel technique for broad spectral bandwidth rapid ion-sensitive spectroscopy. This technique combines the high sensitivity of velocity-modulation spectroscopy with the parallel nature and high frequency accuracy of cavity-enhanced direct frequency comb spectroscopy. Prior to this research, no techniques have been capable of high sensitivity velocity modulation spectroscopy on every parallel detection channel over such a broad spectral range. We have demonstrated the power of this technique by measuring the $A^{2}\Pi_{u} - X^{2}\Sigma^{+}_{g}$ (4,2) band of N$^{+}_{2}$ with an absorption sensitivity of $10^{-6}$ for each of 1500 simultaneous measurement channels spanning 150 cm$^{-1}$. A fully sampled spectrum with 75 MHz spacing consisting of interleaved measurements is acquired in under an hour. Currently, this technique is being used to map the electronic transitions of HfF$^{+}$ for the JILA electron electric dipole moment experiment. This work was funded by the NSF.