A continuously tunable long-wavelength cw IR source for high-resolution spectroscopy and trace-gas detection

A new widely tunable source in the infrared for use in high-resolution spectroscopy and trace-gas detection is described. This spectroscopic source is based on Difference Frequency Generation (DFG) in gallium selenide (GaSe) and is continuously tunable in the 8.8–15.0 m wavelength region. Such a DFG source operates at room temperature which makes it a useful alternative to a lead-salt diode-laser- based detection system that requires cryogenic temperatures and numerous individual diode lasers.Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Widely tunable mode-hop free external cavity quantum cascade laser for high resolution spectroscopic applications

An external cavity (EC) quantum cascade laser (QCL) configuration with the thermoelectrically cooled gain medium fabricated using a bound-to-continuum design and operating in continuous wave at ∼5.2 μm is reported. The EC architecture employs a piezo-activated cavity mode tracking system for mode-hop free operation suitable for high resolution spectroscopic applications and multiple species trace-gas detection. The performance of the EC-QCL exhibits coarse single mode tuning over 35 cm^-1 and a continuous mode-hop free fine tuning range of ∼1.2 cm^-1. PACS 07.07.Df; 42.55.Px; 42.62.Fi; 42.60.Fc     

Widely tunable mode-hop free external cavity quantum cascade lasers for high resolution spectroscopy and chemical sensing

Recent progress in the development of room temperature, continuous wave, widely tunable, mode-hop-free mid-infrared external cavity quantum cascade laser (EC-QCL) spectroscopic sources is reported. A single mode tuning range of 155 cm^-1 (∼ 8% of the center wavelength) with a maximum power of 11.1 mW and 182 cm^-1 (∼ 15% of the center wavelength) with a maximum power of 50 mW was obtained for 5.3 and 8.4 μm EC-QCLs respectively. This technology is particularly suitable for high resolution spectroscopic applications, multi species trace-gas detection and spectroscopic measurements of broadband absorbers. Several examples of spectroscopic measurements performed using EC-QCL based spectrometers are demonstrated. PACS  42.55.Px; 42.60.-v; 42.62.Fi; 07.07.Df     

Saturation spectroscopy of BO2 at 5145 Å

The hyperfine structure of one of the transitions of BO₂ coincident with the 5145 Å argon-ion laser line has been resolved by the technique of intermodulated fluorescence. The splitting has been interpreted in terms of the hyperfine constants of the excited A ²Π_u electronic state.     

Fluorescence spectrum of chlorine dioxide induced by the 4765 Å argon-ion laser line

The fluorescence spectrum induced in ClO₂ by excitation with the 4765 Å argon-ion laser line has been studied under moderate resolution with the laser in single mode operation and under high resolution with the laser in multimode operation. The most intense features of the fluorescence have been assigned to excitation by the 23_{2, 22} ← 24_{2, 23} transition of the (0, 0, 0) ← (0, 0, 0) band of ³⁷ClO₂. Another set of features has been assigned to excitation by the 38_{0, 38} ← 37_{0, 37} transition of the (0, 0, 0) ← (0, 0, 0) band of ³⁷ClO₂.The vibrational structure and the ν₁ vibrational dependence of the rotational structure in the fluorescence have been least squares fitted giving a new set of vibrational constants and vibration-rotation interaction constants, $\text{α}{}_1{}^{\mathrm{B}}$ and $\text{α}{}_1{}^{\mathrm{C}}$.     

Computer-Assisted Structural Interpretation of 1H-NMR. Spectral Data

Interactive computer programs for the establishment and maintenance of a ¹H-NMR. data base, the prediction of ¹H-NMR. shifts and the rank-ordering of structural candidates based on comparison between observed and predicted spectra are presented. The programs take into account configuration, at stereocenters and double bonds, as well as diastereotopy. We demonstrate how, for purposes of structure elucidation, these new programs can be linked to the GENOA and STEREO programs.     

Saturation spectroscopy of NH2 using a CW dye laser

Hyperfine structure in the electronic spectrum of NH₂ has been resolved using the technique of intermodulated fluorescence with CW dye laser excitation. From the observed spacings values for the ¹⁴N Fermi contact and dipole-dipole coupling terms have been estimated for both the ground state and the Π(0,10,0) vibrational level of the à ²A₁ excited electronic state.     

Jet-cooled infrared spectrum of methoxy in the CH stretching region

Observations of the jet-cooled infrared spectrum of CH(3)O in the CH stretching region have been extended, down to 2756 cm(-1) and up to 3003 cm(-1). In the lower frequency extension, a single vibronic band has been assigned. In the higher frequency region, the spectrum becomes complex above 2900 cm(-1) and remains so until near 2970 cm(-1) where it rapidly becomes sparse. Including the single vibronic band previously reported, a total of four bands have been assigned. Two bands including the original one follow a perpendicular DeltaP = +1 rotational selection rule and the other two bands follow a parallel DeltaP = 0 selection rule. In addition to these in the congested region between 2900 and 2970 cm(-1), ten isolated sub-bands (two P' = -1/2, two P' = +1/2, and six P' = +1.5) have been assigned, but it has so far not been possible to connect these together to form bands. Taken together these observations suggest that there are strong vibronic couplings between the two CH stretching vibrations and the overtone and combination levels in the region.