15min:

N. PICQUÉ, G. GUELACHVILI, H. HERBIN, R. FARRENQ, V. GIRARD, Laboratoire de Photophysique Moléculaire, Unité Propre du C.N.R.S., Bâtiment 350, Université de Paris-Sud, 91405 Orsay, France, email: nathalie.picque@ppm.u-psud.fr ; E. SOROKIN, I. T. SOROKINA, Institut für Photonik, TU Wien, Gusshausstr. 27/387, A-1040 Vienna, Austria.

Laser operation of Cr²⁺-doped chalcogenides has been demonstrated in the mid-nineties and has led to a new class of efficient mid-infrared laser crystals. Among them, Cr²⁺:ZnSe and Cr²⁺:ZnS represent interesting alternative to difference frequency generation and semiconductor lasers for spectroscopy. They indeed exhibit broad tunability in the 2.5 µm region, high-power room-temperature operation and compactness, especially with fiber or diode lasers pumping.
In this paper, we report application of Cr²⁺:ZnSe and Cr²⁺:ZnS lasers to high-resolution and high-sensitivity intracavity absorption spectroscopy (ICLAS) analyzed by time-resolved Fourier transform (TRFT) spectroscopy. ICLAS with an evacuated tunable Cr²⁺: ZnSe laser is performed with a high-resolution TRFT interferometer with a minimum detectable absorption coefficient equal to 4 10^-9 cm^-1Hz^-1/2 around 2500 nm. This is the extreme limit presently reached in the infrared by ICLAS with Doppler limited resolution. The broad gain band of the crystal allows a spectral coverage at most equal to 125 nm, wide enough to see entire vibration bands. Weak CO₂, N₂O and C₂H₂ bands are observed for the first time in a laboratory and their analysis is discussed. Relatively to Cr²⁺:ZnSe, Cr²⁺:ZnS has a blue-shifted emission, peaking around 2.4 µm, making it especially attractive for applications in this water-free window of the atmosphere. We report first spectroscopic application of a Cr²⁺:ZnS laser. We indeed demonstrate a broadband Cr²⁺:ZnS laser for ICLAS, utilizing Er-fiber or direct diode pumping. Illustration is provided with spectra of weak bands of N₂O.