Measurement of the 88Sr+ reference transition frequency with a new probe laser system

The authors have designed and implemented a new 674 nm (445 THz) laser system for probing the ultranarrow 5s²S_1/2-4d²D_5/2 reference (clock) transition of the trapped and laser-cooled ⁸⁸Sr⁺ ion. The authors describe briefly the double-stage probe laser system; linewidths of (50 plusmn 9) Hz FWHM were observed for the clock transition with this source. Results on the determination of the temperature of zero thermal expansion coefficient of the reference cavity were also presented. Preliminary measurement of the absolute frequency of the ⁸⁸Sr⁺ clock transition frequency gives a frequency of (444779044095472 plusmn 15) Hz