Dye laser spectrometer for ultrahigh spectral resolution: design and performance.

A dye laser spectrometer for ultrahigh spectral resolution is described. The laser frequency is stabilized to the side of a transmission fringe of an optical cavity by means of the usual differencing servo technique. With an intralaser-cavity AD(*)P phase modulator, driven by improved fast servo electronics, the linewidth of the jet stream dye laser was reduced to 1.8 kHz rms. With fast amplitude stabilization a 1.0-kHz line-width was observed. Good long-term stability and digital frequency scanning (with a step resolution of 1 kHz and a continuous tuning range of 900 MHz) are accomplished by transferring the long-term stability of an I(2)-stabilized He-Ne laser to the dye laser via a second optical cavity and an offset locked He-Ne laser. A drift rate of <1 kHz/min was obtained while using this dye laser spectrometer to investigate two-photon optical Ramsey fringes. A fringe width of the Ramsey features of 17 kHz has been observed, confirming for the first time the high resolution capability of two-photon optical Ramsey resonances.