A fiber-optic instrument for temperature measurement is presented. The sensing element consists of an optical dielectric multilayer system acting as a micro-interferometer which is deposited on a single-mode fiber tip. The sensitivity of the implemented system is theoretically derived and experimentally determined by a calibration measurement. The small size of the probe makes the system well-suited, for instance, for endoscopic in vitro and in vivo measurements in medical applications, especially in small samples. The sensor is used for the investigation of the transient thermal behavior of vitreous during Er:YAG laser irradiation in order to study the local thermal effects that are important to minimize the potential for unintentional injury in laser vitrectomy and laser vitreoretinal surgery.

The accuracy for the direct measurement of the dissociation energy of the N 2 + B2Σ u +-state was significantly improved by using frequency doubled laser light, which enables the authors to excite from lowerv″-levels and additionally to calibrate the fundamental laser wavelength with an iodine cell. The obtained value is:D8(N 2 + )=70248±6 cm−1.

Rotationally cold Na3-molecules are formed during the adiabatic expansion of an argon beam, seeded with 5% sodium vapor. With a single mode tunable dyelaser crossing the molecular beam perpendicularly within the ion source of a mass spectrometer the Na3-molecules are excited into levels of the2A2-state which are then ionized by acw argon-laser. Rotational lines of the electronic2A2 ←X2B2 transition and their hyperfine structure could be resolved using an OODR-technique. A preliminary analysis of the measured spectra is discussed and a comparison of the experimental results with ab initio calculations is presented.

Photofragment spectroscopy of N 2 + has been studied in the wavelength range 343–404 nm using an excimer-pumped dye laser with a spectral resolution of 0.2 cm−1. The observed bands are assigned to transitions from thev″=23−26 levels of theX2Σ g + state to highlying rovibrational levels (v′≈46–48) of theB2Σ u + state, forming quasibound (predissociating) states above the dissociation limit N+(3P)+N(4S0). Measurement of the photofragment kinetic energies allows to establish an absolute energy scale for the transitions with respect to the dissociation limit. Molecular constants for the lower and upper states of the observed transitions are determined. The measurements allow the first direct determination of the N 2 + dissociation energyD 0 0 (N 2 + ). Some high-resolution (0.04 cm−1) measurements show the fine-structure splitting and lifetime broadening of the excitation lines.

Spectra in the visible range of electronically excited atoms, molecules and ions produced in discharges were recorded with sub-Doppler resolution. The advantages and limits of polarization spectroscopy performed in a discharge are discussed by experimental results on helium (3 3S-2 3P and 3 3D-2 3P), molecular nitrogen (B 3Πg-A 3Σu+) and Ar+ ions (4p′ 2Fo [72]-3d′ 2G[92]).

The visible absorption spectra of several heavy diatomic molecules and of many polyatomic molecules show a very complex structure. The spectral line density is often so large that many absorption lines overlap within their Doppler-width. When measured with Doppler-limited spectral resolution, these spectra may therefore appear quasicontinuous, concealing finer details, such as rotational structure or fine- and hyperfine-splittings.

The advantages of collimated cold supersonic beams for sub-Doppler laser spectroscopy of molecules and small clusters are discussed and illustrated by several examples. These include sub-Doppler spectroscopy of the SO2 molecule in the ultraviolet and of NO2 in the visible region. Lifetime measurements under collision-free conditions, stepwise excitation of high lying molecular Rydberg states, and sub-Doppler double resonance spectroscopy of Na3 demonstrate the achievements possible by combining molecular beam techniques with various methods of laser spectroscopy. The relevance of the experimental results for our understanding of the dynamics of molecules in excited states and for the development of new theoretical approaches is emphasized. Some sensitive detection techniques are presented which are in particular useful when cw lasers are used for spectroscopy in cw molecular beams at low densities.

A knowledge of small metal clusters is important for the understanding of the fundamental mechanism of catalysis and surface chemistry. Molecular spectroscopy with lasers is also here a helpful tool to study the electronic potentials and molecular constants.

Several sensitive detection techniques, such as excitation spectroscopy or resonant two-photon ionization spectroscopy are applied to laser spectroscopy with sub-Doppler resolution in collimated molecular beams. Due to internal cooling during the adiabatic expansion in supersonic beams rotational temperatures below 10 K can be reached which results in a drastic simplification of otherwise complex molecular spectra.

The analysis of measured hyperfine splittings in the 2B2 ← X2A1 spectrum of NO2 shows that the major cause of the observed hfs splittings in the excited 2B2 state is vibronic coupling between a single level of the 2B2 state and many high lying vibrational levels of the X2A1 ground state. Only a minor part of the hfs splitting may be due to spin polarization of the core. These results agree with the simple MO picture of NO2 which predicts no Fermi interaction type hfs in the pure 2B2 state.

Sub-Doppler excitation spectra of NO2, covering four vibronic bands within the spectral range from 16 861 to 16 903 cm−1, were measured with a resolution of down to 10 MHz in a collimated supersonic molecular beam. Unambiguous assignment of all prominent lines in the 42-cm−1-wide interval of the 2B2 ← 2A1 excitation spectrum was achieved by recording for each excitation line at least four vibrational bands of the corresponding fluorescence spectrum with completely resolved rotational lines. From least-squares fits to the line positions in the excitation spectra the rotational, fine, and hyperfine structure of the 2B2 state was analyzed. A perturbation analysis, based on information from both types of spectra, confirms earlier models of vibronic coupling with high-lying vibrational levels of the 2A1 ground state and gives evidence for spin-orbit coupling. Possible models are discussed which may explain the observed perturbations.

In a high resolution laser excitation spectrum of NO2, lines were recorded which do not follow the selection rule ΔN = ΔJ = ΔF of “spin allowed” transitions. Line positions and intensities of these “spin forbidden” lines were investigated for all rotational lines up to N″ = 12 of the Ka = 0 subband around λ = 592.5 nm. While the observed line intensities of “spin allowed” transitions can be well described by the J-coupling scheme, neither the J- nor the G-coupling scheme sufficiently describes the “spin forbidden” transitions. The observations can be fitted satisfactorily by perturbation theory, in which the Fermi interaction in 2A1 is treated as the perturber. This looks similar to a superposition of J and G scheme in the 2A1 ground state.

Frequency differences between hyperfine structure (HFS) components of 129I2 at the He-Ne laser emission range at 612 nm wavelength are determined by using the saturated absorption technique. The weaker lines are attributed to the R(113)14-4 transition of 129I2. Computer fits have been made to the HFS splittings of the 129I2 transitions. The best fits resulted in quadrupole coupling constants of ΔeqQ = 1365.30 MHz for P(11) 10-2 and constants of ΔC = 17.62 kHz and ΔC = 21.22 kHz respectively. A fluorescence analysis confirming the assigned transitions has been made.

High-resolution excitation spectra of some NO2 bands around λ = 592.5 nm have been taken with a linewidth down to 10 MHz. The experimental arrangement consists of a collimated supersonic NO2 beam crossed perpendicularly with the beam of a tunable single-mode dye laser. The wavelengths of the NO2 lines were measured with a “Lambdameter” of the Michelson-type with an absolute accuracy of 10−3 cm−1. The analysis of a K−1 = 0 subband showed strong anomalies of the spin splittings in the upper 2B2 state. It was possible to fit the completely resolved hyperfine structure splittings of most lines with a standard deviation of less than 5 MHz, although a few transitions showed significant perturbations. Possible causes of perturbations for fine-structure splittings are discussed. The analysis yields some molecular constants for the 2B2 state. The ground-state splittings obtained from this work agree with the infrared and microwave results.

Three different techniques of laser spectroscopy with sub-Doppler resolution are discussed which have been applied to the investigation of diatomic and triatomic molecules. These are linear laser spectroscopy in collimated molecular beams, polarization spectroscopy and a combination of both methods with optical-optical double resonance techniques. The methods are illustrated by high resolution spectra of the molecules NaK, Cs2 and NO2. A section on time resolved spectroscopy, applied to lifetime measurements and to the deterniination of collision induced relaxation processes concludes the paper.

The hfs components of a weak rotational line of 127I2, assigned as the R(98) line of the 58→1 band, are resolved by saturated intermodulated fluorescence and a third-derivative technique using a single-mode Ar+-laser at 514.5 nm. The spacings between different hfs components are measured by a heterodyne technique with an accuracy of 30 kHz. The differences between the upper and lower coupling constants obtained by a fit giving a standard deviation of 15.2 kHz, are: δeqQ = 1880.198 ± 0.09 MHz; δC = 829.20 ± 0.04 kHz for the spin-rotation constant; δD = −501.9 ± 3.5 kHz for the scalar spin-spin and δA = 356.8 ± 1.1 kHz for the tensor spin-spin interaction. The results are compared with data for other vibrational transitions.