We report the first direct excitation of the strongly forbidden 5s 2 1 S0 −5s5p 3 P0 transition in 87 Sr. Its frequency is 429 228 004 235 (20) kHz. A resonant laser creates a small leak in a magneto-optical trap (MOT): atoms build up to the metastable 3 P0 state and escape the trapping process, leading to a detectable decrease in the MOT fluorescence. This line has a natural width of 10 −3 Hz and can be used for a new generation of optical frequency standards using atoms trapped in a light shift free dipole trap.

A BaGa₄Se₇ nanosecond optical parametric oscillator (OPO) shows extremely wide idler tunability in the mid-IR (2.7-17 μm) under 1.064 μm pumping. The ∼10  ns pulses at ∼7.2  μm have an energy of 3.7 mJ at 10 Hz. The pump-to-idler conversion efficiency for this wavelength reaches 5.9% with a slope of 6.5% corresponding to a quantum conversion efficiency or pump depletion of 40%.

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Lithium selenoindate (LiInSe 2) is a new nonlinear chalcogenide biaxial crystal, related to LiInS 2 and transparent from 0.54 to 10 µm at the 50% level (10 mm thickness), that has been successfully grown in large sizes and with good optical quality. We report on new physical properties that are relevant for laser and nonlinear optical applications and summarize all relevant characteristics, both from the literature and such measured in the present work. With respect to AgGaS(e) 2 ternary chalcopyrite materials, LiInSe 2 displays a nearly isotropic thermal expansion behavior with 3 to 5-times-larger thermal conductivities associated with high optical damage thresholds, and low intensity-dependent absorption, allowing direct high-power down-conversion from the near-IR, especially 1064 nm, to the deep mid-IR. Continuous-wave difference-frequency generation (5.9-8.1 µm) of Ti:sapphire laser sources is reported for the first time as well as nanosecond optical parametric oscillation with Nd:YAG laser as a pump source at 100 Hz and idler tuning between 4.7 and 8.7 µm.