A method is provided for optimizing the performance of laser-pumped atomic frequency references with respect to the laser detuning and other operating parameters. The strap assembly includes a top flange, a bottom flange and a strap extending between the top flange and bottom flange. The main fine tune branch includes at least one variable capacitor whose capacitance varies according to a tuning voltage. In addition, the single-string LED lamp provides the standardization design for connectors of the driving circuit used to connect to the single-string LED lamp so that the driving circuit has a better common-use characteristic.