Possible two-photon absorption in the near-infrared region observed by cavity ring-down spectroscopy.

Two-photon absorption spectra are difficult to observe using direct absorption spectroscopy especially in the near-infrared region. Cavity ring-down spectroscopy is a promising absorption spectroscopy technique which has been widely applied to linear and saturated single-photon absorption spectra. In the present study, we report the observation of a possible two-photon absorption in the near-infrared using cavity ring-down spectroscopy, namely a two-photon resonance of methane. Using an optical frequency comb, the single-photon wavenumber of the double-quantum transition has been determined to be 182 207 682.645 MHz with a standard deviation of 75 kHz.

Nd:YLF laser at 1.3 microm for calcium atom optical clocks and precision spectroscopy of hydrogenic systems.

We describe single-frequency operation of a diode-pumped Nd:YLF laser in the range 1311.9-1317.2 nm. It can be used for the interrogation of the clock transition in calcium (1314.0 nm) or spectroscopy in hydrogen and metastable singly ionized helium (1312.6 nm). By using a twisted-mode cavity, we have obtained output powers of 830 and 970 mW at 1312.6 and 1314.0 nm, respectively, in a single longitudinal mode.

Doubled single-frequency Nd:YLF ring laser coupled to a passive nonresonant cavity.

We demonstrate an original solution to obtain a single-frequency ring laser coupled to an external passive nonresonant ring cavity, which plays the role of an optical diode. This system provides more output power than systems with an intracavity unidirectional device. To the best of our knowledge, this work marks the first demonstration of a unidirectional planar ring laser at 1.3 microm. Using 12 W at 797 nm to pump a Nd:YLF laser, combined with intracavity second-harmonic generation, we achieve yields of 440 mW at 661.3 nm and 340 mW at 656.0 nm.