Fig. 4

Cross-beam spectroscopy. (a) Measurement results of the \(^{40}\textrm{Ca}^+\) spectrum. The red curve represents the best-fit Voigt function. (b) Measurement results of the \(^{44}\textrm{Ca}^+\) spectrum. The red curve shows a Voigt function fitted with physically reasonable parameter constraints. The isotope shift of \(^{44}\textrm{Ca}^+\) is approximately 757Â MHz.