Laser spectroscopy : 5. Raman spectroscopy

This article in the series reviews the application of lasers in Raman spectroscopy.     

Laser spectroscopy : 1. Principal problems

Laser spectroscopy has made it possible to solve, or at least to begin solving, a number of important problems to which classical spectroscopy could not be applied. These problems are defined in this, the first in a series of articles reviewing the subject of laser spectroscopy. This is followed by an outline of the present status of tunable lasers — the basic instruments used in developing the techniques of laser spectroscopy.     

Laser systems specialized for laser spectroscopy at storage rings

Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported. Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator. It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz. This laser can be advantageous for laser cooling of ion beams. This revised version was published online in August 2006 with corrections to the Cover Date.     

Laser spectroscopy 4. Nonlinear high resolution spectroscopy

This paper in the series gives a brief outline of the main ideas, methods and types of nonlinear laser spectrometer used for atomic and molecular spectroscopy without Doppler broadening. This is the most developed area of laser spectroscopy and has recently been the subject of several papers^1,2 to which readers are reffered for more detailed information.     

Laser spectroscopy : II. Applications in quantum metrology

Applications of sub-Doppler optical resonances to the spectral lines of atoms and molecules giving laser standards of wavelength and frequency are presented. The problems of precise measurement of length and absolute measurement of light frequency are considered. Prospects of elaborating fundamental experiments with laser ultra-stable frequency are discussed.     

Laser spectroscopy : 10. Applications in nuclear physics

This article describes recent progress in the application of laser atomic spectroscopy to study parameters of nuclei available in very small quantities; radioactive nuclei, rare isotopes, nuclear isomers, etc, for which study by conventional spectroscopic methods is difficult.     

Laser spectroscopy : 7. Multiphoton and multistep methods

Multiphoton and multistep spectroscopy of atoms and molecules is a rapidly developing branch of laser spectroscopy which relies almost exclusively on the application of tunable lasers. This article reviews the different techniques which have been developed.     

Site-selective laser spectroscopy of BaF2:Eu3+

The selective laser excitation of the flourescence of Eu³⁺ ions is used to investigate the defect sites in BaF₂:Eu³⁺ for Eu³⁺ concentrations ranging from 0.03 to 2.43 mol%. We identified the fluorescence lines arising from the (Eu³⁺, F^-_i) dipole of C_3v symmetry and established its energy level diagram. The compensating ion is an interstitial F^-_i ion located in the next-nearest-neighbour site, with respect to the Eu³⁺ ion. This (Eu³⁺, F^-_i) dipole dominates in BaF₂. Fluorescence lines assignable to next-nearest-neighbour pairs of (Eu³⁺, F^-_i) dipoles have been found above 0.1 mol% dopant concentration.     

Laser spectroscopy 8. Picosecond processes

Picosecond laser spectroscopy is a rapidly developing field, the applications of which extend to the adjacent subjects of chemistry and biology. Here, the various methods and areas of application are classified and compared. Some experiments and results are mentioned for illustration.     

LiGdF4:Tm3+: spectroscopy and diode-pumped laser experiments

A novel LiGdF₄ crystal doped with Thulium ions has been grown using the Czochralski technique. Three samples with doping concentrations of 0.3 at.%, 8 at.%, and 12 at.% have been extensively spectroscopically analyzed. We also performed room-temperature preliminary laser experiments, pumping the samples with a laser diode at 792 nm obtaining 53% as maximum slope efficiency with a maximum output power of 205 mW and a minimum lasing threshold of 22 mW. The laser emission spectrum in free running condition typically spans between 1990 and 2018 nm.     

Laser spectroscopy 9. Prospects and applications

This concluding article in the series discusses the prospects of realizing the ultimate parameters — spectral resolving power and sensitivity — and some fields of application — nuclear physics, chemical kinetics and molecular physics, quantum metrology — of laser spectroscopy.     

Optoacoustic Laser Stark spectroscopy and FIR laser action on CH3Br using a waveguide CO2 laser

The optoacoustic spectrum of CH₃Br around 10 m band lines of a tunable cw waveguide CO₂ laser is investigated. Several new infrared absorptions are observed and most of the correspond ing molecular transitions are assigned. Far infra red laser action is reported by pumping with the same CO₂ laser: pump offsets are given using the Transferred Lambs dip (TLD) technique. A new FIR laser emission is obtained and assigned. An optoacoustic Laser Stark spectroscopy technique is used to investigate off resonance infrared tran sitions.     

Laser system based on a picosecond dye laser with combined feedback for spectroscopy

A laser system comprising a synchronously pumped picosecond dye laser with combined cavity-distributed feedback and a two-stage dye amplifier is described. The dependence of the laser pulse duration on the detuning of the cavity length, the pumping level of the active medium, and the pulse number in the pulse train was investigated. It is shown that the combination of the two types of feedback provides more than ten-fold shortening of the dye laser ultrashort pulse duration. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 47–55, January–February, 1998.     

Laser Stark and laser microwave double-resonance spectroscopy of deuterated fluoroacetylene with the CO2 laser

The CO₂ laser Stark spectrum of deuterated fluoroacetylene was identified with the aid of the double-resonance technique for the ν₃, ν₃ + ν₅ ? ν₅, ν₃ + ν₄ ? ν₄, ν₃ + 2ν₅ ? 2ν₅, and ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅ vibrational bands. Laser microwave double-resonance signals were observed in the presence of the Stark field. From the analysis of the double-resonance signals precise values of the dipole moment were obtained for 10 vibrational states, in Debye, with the uncertainties in parentheses: ground, 0.73292(22); ν₅, 0.75656(17); ν₄, 0.68412(24); 2ν₅(Σ⁺), 0.78063(21); ν₄ + ν₅(Σ⁺ or Σ^?), 0.70698(19); ν₃, 0.75772(30); ν₃ + ν₅, 0.78270(18); ν₃ + ν₄, 0.70822(17); ν₃ + 2ν₅(Σ⁺), 0.80808(25); ν₃ + ν₄ + ν₅(Σ⁺ or Σ^?), 0.73329(17). The band origins were determined (in cm^?1); ν₃, 1045.9242(8); ν₃ + ν₅ ? ν₅, 1049.6441(8); ν₃ + ν₄ ? ν₄, 1047.8700(8); ν₃ + 2ν₅ ? 2ν₅(Σ⁺-Σ⁺), 1053.0374(8); ν₃ + ν₄ + ν₅ ? ν₄ ? ν₅(Σ⁺?Σ⁺ or Σ^??Σ^?), 1051.5040(8).     

Laser Stark and laser microwave double resonance spectroscopy of fluoroacetylene with the CO2 laser

The CO₂ laser Stark spectrum of fluoroacetylene was identified for the ν₃, ν₃ + ν₄ ? ν₄, and ν₃ + ν₅ ? ν₅ vibrational bands. The origins of these bands were precisely determined (±0.0003 cm^?1) to be 1061.4452, 1059.0639, and 1064.6960 cm^?1. A CO₂ laser microwave double resonance experiment in the presence of the Stark field is described. This technique was applied to assignment of the Stark spectrum, calibration of the Stark electrode spacing, and precise determination (±0.0003 D) of dipole moment. The dipole moments of the HCCF molecule in the ground, ν₃, ν₄, ν₅, ν₃ + ν₄, and ν₃ + ν₅ vibrational states are 0.7207, 0.7447, 0.6557, 0.7441, 0.6769, and 0.7689 D.     

Laser spectroscopy of CaF2:Eu:Sm thin films grown by pulsed laser deposition

Thin films of CaF₂ co-doped with low concentrations of Eu and Sm ions were grown by pulsed laser deposition (PLD) using a KrF (λ=248 nm) as the ablation source. To the best of our knowledge, the work presented here is the first report of rare-earth-doped CaF₂ films grown by PLD with this source. Combined laser excitation-emission spectroscopy was used to map out electronic transitions of Eu³⁺ with ⁷F₀→⁵D₁ excitation and the ⁵D₀→⁷F₁ emission. At the low concentrations used here the crystal field center of cubic symmetry is dominant in the films that are same for laser targets. However, charge compensated centers are present in the bulk crystal precursor. The removal of the charge compensated centers in the films and the target is likely caused by the target preparation where high pressure and temperature were applied.