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A continuous wave ultraviolet source with extreme frequency stability is described. A ring dye laser with internal electro-optic phase modulator reaches sub-Hertz linewidths relative to a passive reference cavity with the help of an FM stabilization technique. A barium-β-borate frequency doubler crystal inside a second injection-locked ring dye laser generates output powers of 30 mW near 243 nm.

A single-frequency Ti:sapphire laser has been stabilized to a reference cavity with the simple side-of-fringe locking technique and a piezo-controlled mirror as compensating element. A frequency stability of 1 kHz rms with respect to the locking etalon is obtained. This Ti:sapphire laser, optimized for 972.5 nm, will be used for two-photon excitation of the 2S–4S transition in atomic hydrogen.

We have stabilized the frequency of a commercial ring dye laser operating in the blue near 486 nm with an internal electro-optic modulator, using optical heterodyne detection of phase-modulated light reflected from a reference cavity. With a servo bandwidth of 10 MHz, the short-term stability has been reduced below 1 kHz. Frequency doubling of this laser will provide highly monochromatic 243 nm radiation for high resolution spectroscopy of the two-photon hydrogen 1S–2S transition.

We describe a versatile tunable continuous wave ultraviolet source for spectroscopy. An angle-tuned β-barium-borate frequency doubler is placed inside a doubly resonant build-up cavity. By compensating for double refraction, this scheme provides efficient second harmonic generation in a pure TEM00 mode.