Detection of the linear carbon cluster C10: rotationally resolved diode-laser spectroscopy.

Detected in interstellar space and as intermediates in soot formation, molecules of pure carbon in the form of linear chains or ring structures have interested researchers for several decades, who attempt to elucidate their physical properties and the processes govering their formation. A high-resolution infrared spectrometer housing a tunable diode laser and combined with an effective laser ablation source for the cluster production has been used to study the molecular properties of small carbon clusters; reported herein is the first gas-phase spectrum of linear C10.

High precision frequency calibration of tunable diode lasers stabilized on an internally coupled Fabry-Perot interferometer.

For very high precision molecular spectroscopy we use a tunable diode laser which is frequency locked to an internally coupled Fabry-Perot interferometer (icFPI). The spectra are calibrated by means of the interference pattern of an iodine stabilized He-Ne reference laser which is simultaneously coupled into the icFPI. In this paper the exact relation between the diode laser frequency and the He-Ne fringe number is derived and a convenient calibration procedure yielding a frequency accuracy of 5 x 10(-5) cm(-1) at 10 microm is described.

High-sensitivity mid-infrared heterodyne spectrometer with a tunable diode laser as a local oscillator.

A new mid-IR heterodyne spectrometer, which is intended to be applied for atmospheric and astrophysical studies, is presented. The spectrometer uses a frequency-stabilized tunable diode laser as a local oscillator. Owing to the low output power of available single-mode diode lasers, a newly developed confocal-ring resonator, the diplexer, is used to superimpose the source signal efficiently with that of the local oscillator. Additionally, the diplexer serves as an optical filter that establishes controlled optical feedback between the laser diode and the detector, which allows stable laser operation with linewidths of the order of 1 MHz. The heterodyne signal from the HgCdTe detector is analyzed by means of a 1.4-GHz acousto-optical spectrometer. With this setup we find system temperatures as low as 4400 K (double sideband), that is, approximately a factor of 6 of the quantum limit.

Temperature-Dependent Line Shift and Broadening of CO Infrared Transitions.

The temperature dependence of lineshift and broadening of the rovibrational transitions R(18) and R(20) of the CO fundamental band, perturbed by Ar, N2, O2, and H2, have been measured with high frequency accuracy and at temperatures between 160 and 270 K in steps of 20 K. A wavelength stabilized tunable diode laser spectrometer has been combined with a low temperature long path cell of 134 m absorption length and 1 m basis length. For all measurements the CO pressure was below 0.1 mbar to avoid self-shift and self-broadening. In case of line broadening the temperature dependence is quite well reproduced by an exponential relation, b(T) = b(T0)(T/T0)-n. For all foreign gases, the exponent n has been obtained (0.53