It has been highly developed along with the progress of next-generation atomic clocks in the visible frequency range, which require Hz-level stabilization of the laser [1]. Such an etalon is not expensive and can also be a convenient tool to determine absolute frequencies of lasers. For example, the absolute frequencies of water molecule lines near 790 nm have been accurately determined by using an ultralow-expansion etalon calibrated to the D 1 and D 2 lines of rubidium atoms [2,3]. To investigate many resonance lines spread in a span of a few tens of nanometer using such an etalon, the change of the free spectral range of the etalon due to the dispersion of the mirrors has to be taken into account.In this paper, we report high-resolution spectroscopy for transitions from the ground states of Ca, Rb, In, K, Ga, and Yb atoms in the 398-423 nm spectral range, using this kind of etalon for which small group-delay-dispersion (GDD) mirrors are attached. In this wavelength range the use of the etalon is especially efficient, since it is very difficult to directly measure laser frequencies with optical frequency combs for this range without using a frequency doubling system. The etalon resonance frequencies are calibrated to the absolute frequencies of Ca at 423 nm and Rb at 422 nm, whose uncertainties are less than 0.4 MHz [4,5]. Except these two atomic lines, the absolute frequencies of the atomic lines observed in this paper have not been determined precisely so far. Recent development of violet and blue laser diodes has promoted the spectroscopy of this spectral range, and thus, these atomic line data are of increasing importance. For example, these lines have been utilized for laser cooling, which essentially requires the stabilization of the laser frequency. Bose-Einstein condensates of Ca and Yb have been realized [6,7], and these lines observed in this study are the main cooling transitions. The cooling of In and Ga atomic Abstract We have demonstrated spectroscopy of Ca, Rb, In, K, Ga, and Yb atomic lines in 398-423 nm. Using an etalon of an ultralow-expansion coefficient, we have determined ratios of the resonance frequencies of these atoms. The etalon has small group-delay-dispersion mirrors to be an accurate frequency reference over a wavelength span of a few tens of nanometer. The etalon resonance frequencies are calibrated with accurately known transition frequencies of Ca at 423 nm and Rb at 422 nm. Based on this calibration, the absolute frequencies are also determined for some atomic lines with smaller uncertainties than earlier reports.
