Excitation of the /sup 3/P/sub 0 /state is detected in optical-optical double resonance via the dark periods in the fluorescence on the fast /sup 1/S/sub 0/ /sup 3/P/sub 1/ transition. The dye laser formerly used to excite this line was recently replaced by a diode-based laser system: a grating stabilized diode at 922 nm, further frequency stabilized onto a Fabry-Perot interferometer, is seeded into a tapered amplifier. Subsequent frequency-quadrupling employing a periodically poled KTP and a BBO crystal, each placed in an external enhancement cavity, leads to the right frequency at 231 nm. For the /sup 1/S/sub 0/ /sup 3/P/sub 0/ transition a resolution of 1.3 /spl times/ 10/sup -13 /has been achieved so far, limited by the frequency instability of the Nd:YAG laser. The short-term frequency stability of this laser has been strongly improved recently. With a new laser setup a linewidth < 5 Hz (FWHM) for integration times /spl times/30 s has been achieved using active vibration isolation platforms for the reference cavity. Recent progress of that work is reported.
The detailed site-selective and time-resolved fluorescence laser spectroscopy and kinetic measurements with high spectral and nanosecond temporal resolution were applied to analyze the M and N absorption bands at the 4I9/2(1) yields 4G5/2(1) crystal field (CF) transition in the CaF2:Nd3+ crystal at 4.2 K. It was found that at helium temperatures the dynamically split spectral line at the 4I9/2(1) yields 4G5/2(1) CF transition of coherently coupled Nd3+ ions in the pair M- and quartet N-centers is inhomogeneously broadened. Small variation of fluorescence lifetimes of the 4F3/2 and 4D3/2 levels due to small variation of distances between Nd3+ ions in the pairs was found. Approximately 1 percent variation of the Nd-Nd distance in the pair -center was determined form lifetime variation of the 4F3/2 manifold.
Time-resolved collinear fast-beam laser spectroscopy has been used to measure the lifetime of the T=23 537 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, J=9/2 odd-parity [abbreviated as (23 537)${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{9/2}$] level in Nd ii. Nanosecond pulsed excitation was achieved with the Doppler switching technique. The fast ions were selectively excited from the metastable 4${\mathit{f}}^{4}$5d
6K9/2 level to the (23 537)${\mathrm{\ifmmode^\circ\else\textdegree\fi{}}}_{9/2}$ level by the light of a cw dye laser. The decay of the resonance fluorescence photons emitted in the transition to the ground 4${\mathit{f}}^{4}$6s
6I7/2 level, as a function of the flight distance, was observed. The decay length was scaled into the decay time by the ion velocity, which was determined using the optical resonance itself. The lifetime is 27.7(9) ns.