Electric field effects on an optically-pumped HCOOH FIR laser and Zeeman laser theory

Electric field effects have been investigated on the output power of six far-infrared (FIR) laser lines from H¹²COOH optically-pumped by a CO₂ laser with its polarization arranged perpendicular to the Stark field. Optoacoustic signals observed on the pump lines were hardly affected by the applied electric field up to 0.6 kV/cm. By neglecting the electric field effects on the pump transitions, Zeeman laser theory has been applied to the FIR laser transitions. Numerical calculation predicts the observed FIR output power as a function of electric field. Experessions for oscillation frequency and intensity in homogeneous limit are given, which may be applicable to any FIR Stark laser so far as the pump transition is free from electric field effects.     

FIR Stark spectroscopy on optically pumped CH3OH laser

An extensive theoretical and experimental analysis of the absorption and emission spectrum of a CH₃OH FIR-laser excited by a conventional CO₂ laser is presented. Particular interest is devoted to the Stark shifts of the pump and lasing lines and to the electric field dependence of the Fir-laser output of the various lines. The offsets with respect to the exciting radiation and the Stark shifts of the IR absorption (pump) lines are measured by means of the transferred Lamb dip technique. The theoretical behaviours of the Stark patterns are calculated for several choices of the quantum numbers and selection rules involved in the transitions. A large variety of experimental results are reported and compared to theory. Non-linear Stark shifts have been observed for the 37.5m FIR laser line and for the IR-pump transitions excited by the 9-P(38) and 10-R(38) CO₂ laser Lines. Line assignments are proposed and new FIR laser lines are reported.     

Laser stark spectroscopy ofSO2 with the HCN laser

The Far Infrared (FIR) laser Stark spectrum ofSO ₂ was investigated using the 337 m line of the HCN laser. Two distinct families, one originating at low field and the other at high field, were observed. The high field transition is identified as theJ _K–1,K+1=22_5,1721_4,18, v₂=1 transition. A significant fourth-order Stark shift was observed for this transition in the presence of a large second-order Stark shift. The zero-field frequency of the assigned transition was obtained by accounting for the fourth-order contribution.Present Adress: Department of Chemistry, University of Rochester, Rochester, NY 14627.     

THz Spectrum of Methanol-D4 and Microwave Spectrum of Methanol-D1

The sub-THz spectra of CD₃OD have been observed in the frequency ranges of 461-486 GHz and 596-610 GHz using the Backward Wave Oscillator based Technique. The 218 transitions of CD₃OD are newly assigned to J=31 and K=12 in the first three torsional states (n=2). The assigned lines include several new series of both a-type and b-type transitions. These THz transitions combined with the previous published millimeter-wave (MMW) and microwave (MW) data and recently observed high resolution Fourier transform far infrared (FIR) spectra have been used in a global fit. The data set contains 1320 MW, MMW, SMMW and FIR transitions with n=2, J=31 and K=12. Using the reduced torsion-rotational Hamiltonian with 67 parameters the fit converges with an RMS deviation of 277 kHz for the MW transitions and of 0.00024 cm^-1 for the FIR transitions. Thus molecular parameters are well determined. The MW spectrum of CH₂DOH (in the range 97.7 -118.0 and 128.5-146.5 GHz) is also presented which will help astronomers for astrophysical detection and theoretical spectroscopists to get further information on torsion-rotation-vibration interaction in an internal rotor with an asymmetric top.     

Laser Stark saturation spectroscopy of the ν2 band of CD3l

The ^QP(4) transitions of the ν₂ band of ¹²CD₃I, which lie close to the P(16) 10.4-μm CO₂ laser line, have been observed by saturation spectroscopy using both an intracavity Stark cell, and a Shimizu-type multipass arrangement. Since both level crossing and Lamb dip signals can be seen using these transitions, they serve to illustrate both the uses of the two types of Stark cell, and also the differences between the two kinds of nonlinear signals. A simple derivation of the quadrupole matrix elements in the uncoupled basis is given. The dipole moments of the molecule in the ground and ν₂ states were determined to be 1.656₂ and 1.652₃ D, from the measurements of the very sharp intracavity level crossing signals.     

Laser Stark spectroscopy of the coriolis coupled ν2 and ν5 bands of CD3Cl

About 940 Stark resonances for CD₃³⁵Cl and 610 resonances for CD₃³⁷Cl have been measured by using a CO₂ laser with the 9- and 10-μm regions. They were assigned to 59 rovibrational transitions of ν₂ (J′ ≤ 37, K ≤ 14) and 200 of ν₅ (J′ ≤ 47, ?14 ≤ k′l′ ≤ +10) for ³⁵Cl, and 31 of ν₂ (J′ ≤ 12, K ≤ 10) and 175 of ν₅ (J′ ≤ 46, ?14 ≤ k′l′ ≤ +9) for ³⁷Cl. These data, combined with the microwave and FIR data in the ν₂ and ν₅ states, were analyzed by taking account of the Coriolis interaction between ν₂ and ν₅, and the (2, 2) and (2, ?1) interactions in ν₅. Several ΔK = +2 transitions of the ν₅ band were observed in the Stark spectra, and the ground state constants, A₀ and D_K0, were determined precisely for both ³⁵Cl and ³⁷Cl species. Also, the vibrationally induced dipole moments were obtained. The molecular constants and the zero-field transition frequencies of the ν₂ and ν₅ bands were determined.     

Measurement of the dipole moment of CF3CN

The Stark effect was observed for K = 0 and K = 1, J = 1 → 2 transitions in CF₃CN. Measurements were made in a Stark modulated microwave spectrometer. The dipole moment obtained was μ = 1.262 ± 0.010 D. An analysis of the effects of electric field inhomogeneities on the observed Stark shifts for K = 0 and K = 1 states is included. Appropriate corrections are given for measuring linear Stark effects in a standard waveguide cell calibrated using a molecule with second-order Stark effect.     

Fir laser stabilization using stark effect: Data on CH3Br and CH3Cl

Data on the influence of the Stark Effect on an optically pumped FIR laser with CH₃Cl or CH₃Br as active medium are given for various wavelengths. A very simple method for an effective FIR power stabilisation based on the Stark Effect is described. Its working is illustrated with the EPR signal of a 10% diluted DAG sphere.     

IR and FIR Spectroscopy of 13CH3I

We have investigated the ¹³CH₃I isotopomer of methyl iodide as a source of Far Infrared (FIR) laser radiation using the optical pumping technique. The molecule is pumped by using a pulsed waveguided CO₂ laser, driven by a novel all solid state power supply that lases on the 10HP band as well as the regular bands. We discovered and assigned two new FIR laser emissions and we give further spectroscopic information about polarization and pump frequency offset for five already known lines.     

Stark splitting of the optically pumped 118.8-μm CH3OH laser line

We report the first observation that the optically pumped 118.8-μm CH₃OH laser line splits into two components corresponding to ΔM = ±1 transitions in the presence of the Stark field. The splitting shows linear dependence on the Stark field and well amounts to about 34 MHz at the Stark field of 1300 V/cm. The cases are discussed in which a far infrared laser line splits into ΔM = ± 1 components in the presence of the Stark field. Stark field dependence of the 118.8- and 170.6-μm output power is also given.     

13CH3OH and13CD3OH optically pumped fir laser: New large offset emission and optoacoustic spectroscopy

27 new, large offset, FIR laser lines from¹³CH₃OH and one from¹³CD₃OH have been discovered by pumping with a high tunability waveguide CW CO₂ laser. Optoacoustic measurements of isotopic methyl alcohol have also been performed and the pump offsets of the new and of previously known lines have been measured and checked. Frequency tunability by Stark effect has been observed for 6 strong lines. Some assignments are discussed.     

Energy levels and crystal-field analysis of Tm in YAl3(BO3)4 crystals

The electronic structure of the Tm³⁺ in YAl₃(BO₃)₄ crystals has been investigated by means of low temperature absorption and emission spectroscopy in the 5000-30,000 cm⁻¹ range. The assignment of the lines composing the observed manifolds to transitions between the Stark levels of Tm³⁺ is complicated by the presence of extra features having different origins. The energy levels scheme of the doping ion has been compiled after a careful analysis of the spectra by reproducing the observed transitions by means of theoretical calculations based on a Hamiltonian, including the free ion and the crystal field (CF) terms. The agreement between experimental and calculated energy values was reasonably good, the overall r.m.s. deviation being 16 cm⁻¹. The resulting CF parameters have been tabulated and compared with those reported in literature for other rare earth ions doped in YAB. The analysis of trends observed along the lanthanide series evidences some inconsistencies and the necessity of a systematic investigation of these systems.     

10-μm sub-doppler laser-Stark spectroscopy of methyl chloride: Analysis of the ν6 bands of the CH335Cl and CH337Cl

About 900 Stark transitions from 70 vibration-rotation transitions in CH₃³⁵Cl and about 400 transitions from 38 transitions in CH₃³⁵Cl in the ν₆ band have been assigned. These data were analyzed simultaneously with previously published microwave data on the ν₆ = 1 state. The fit has a standard deviation of about 2 MHz for the data for both isotopes. The isoptopic shift ν₆35 ? ν₆37 = 0.3766(6) cm^?1. Rotational dependence of the dipole moment was also just apparent at about μ_J = μ_K = 1 × 10^?5 D, and a complete set of molecular constants is given.     

Optically pumped submillimeter laser lines from CH2F2 and CD2Cl2 using a12C18O2 CW laser

Thirty-nine new submillimetre laser lines in CH₂F₂ and twelve in CD₂Cl₂ have been obtained in a Fabry-Perot FIR resonator by optically pumping with a CW¹²C¹⁸O₂ laser. The wavelength range obtained for CH₂F₂ is 126m to 1091m and for CD₂Cl₂ 212m to 774m. The wavelength measurements are accurate to within 5.10^–3. The relative polarisations of the pump laser and the FIR laser output were also determined. Tentative assignments of the IR and FIR transitions were made using existing microwave data.     

Measurements and assignments of new large offset CD3OH FIR laser lines

By using an acoustooptic modulator we extend the 300 MHz tunability of a waveguide CO₂ laser to 480 MHz. The CD₃OH was optically pumped by the 10R(32), 10R(34), and 10R(36) CO₂ laser lines, and 17 new FIR laser lines were discovered. The Stark effect on previously known FIR laser lines was investigated, and some tentative FIR laser lines assignments are suggested.     

Crystal field splittings and luminescence properties for Nd3+, Er3+ and Dy3+ in yttrium orthoaluminate (YAlO3)

This report contains information appropriate for a theoretical analysis of the optical spectra of triply ionized lanthanides in YAlO₃. Starting with the best-fit crystal field parameters, the crystal field splitting schemes, multiplet-to-multiplet line strengths, radiative lifetimes, branching ratios, line-to-line square matrix elements and g-factors for the triply ionized Nd, Er and Dy in YAlO₃ have been calculated. In this paper detailed discussions were made on the luminescence properties of the principal transitions of Nd-doped YAlO₃ emanating from the metastable ⁴F_{$\text{3}\text{2}$} state to Stark components of multiplets of the ground ⁴I_J term and compared to similar results of Y₃Al₅O₁₂ (YAG). The line-to-line branching ratios were calculated including J-mixing effects. In the calculations, only electric dipole transitions were considered because of odd-parity. The results predicted some interesting differences in the optical behavior of Nd³⁺ in these two host materials. It has been observed that there is a reasonable agreement between the theoretical data and those reported experimentally for YAlO₃ and YAG. The theoretical studies undertaken here were chosen to supplement or extend the optical data for these two host materials.     

Thev2 andv5 bands of CD3Cl: Infrared spectra and stark patterns with hyperfine structure

Infrared spectra of theV ₂ andV ₅ bands of CD₃Cl have been recorded with a resolution of about 0.015 cm^–1 and assigned. Moreover Stark patterns of the trideuterated methyl chloride for two CO₂ laser lines with saturated Lamb dips have been analysed. Many new strong coincidences showing hyperfine structure are observed and assigned.     

R branch tuning characteristics of the13CH3F Raman FIR laser

Summary We described a¹³CH₃F Raman laser pumped by a grating tuned 20 atmospheres CO₂ laser. The emission characteristics of the¹³CH₃F laser extends from 14 cm^–1–35 cm^–1 and from 49 cm^–1–72 cm^–1; about 65% of these frequency ranges can be covered with tunable radiation. The characteristics shows a strong dependence on the rotaional quantum numbers of the states involved in the Raman laser transitions and, within each tuning interval, on the frequency offset with respect to the frequencies of resonant transitions. We obtained, at 51 cm^–1, a maximum FIR laser pulse energy of about 800 J (at a pump energy of 200 mJ), corresponding to a photon conversion of about 8%. In some cases we have observed simultaneous emission at a Raman and a cascade frequency. In addition, FIR emission power dependence on¹³CH₃F gas pressure and pump pulse power were investigated for different J quantum numbers.     

Spectra, energy levels, and symmetry assignments for Stark components of Eu(4f) in gadolinium gallium garnet (Gd3Ga5O12)

Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu³⁺(4f⁶) in single-crystal Czochralski-grown garnet, Gd₃Ga₅O₁₂ (GGG). The spectra represent transitions between the ^2S+1L_J multiplets of the 4f⁶ electronic configuration of Eu³⁺ split by the crystal field of the garnet. In absorption, Eu³⁺ transitions are observed from the ground state, ⁷F₀, and the first excited multiplet, ⁷F₁, to multiplet manifolds ⁵D₀, ⁵D₁, and ⁵D₂. The Stark splitting of the ⁷F_J multiplets (J=0-6) was determined by analyzing the fluorescence transitions from ⁵D₀, ⁵D₁, and ⁵D₂ to ⁷F_J. The Eu³⁺ ions replace Gd³⁺ ions in sites of D₂ symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2J+1 non-degenerate Stark levels characterized by one of four possible irreducible representations (irreps) assigned by an algorithm based on the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels in D₂ symmetry. The quasi-doublet in ⁵D₁ was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between ⁵D₁ and ⁷F₁. A parameterized Hamiltonian defined to operate within the entire 4f⁶ electronic configuration of Eu³⁺ was used to model the experimental Stark levels and their irreps. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental Stark levels is 5.9 cm⁻¹. The choice of coordinate system, in which the nine are real and the crystal-field z-axis is parallel to the [0 0 1] crystal axis and perpendicular to the xy plane, is identical to the choice we used previously in analyzing the spectra of Er³⁺ and Ho³⁺ garnets.     

Determination of electric dipole moment for the ν2 vibrational state of 15NH3 by infrared-infrared double resonances

An infrared-infrared double-resonance technique, employing the sidebands produced by electro-optic amplitude modulation of a single-frequency CO₂ laser, is used to observe the second-order Stark effect of the ν₂asR(2, 0) transition of ¹⁵NH₃. The technique enables the Stark shifts in ground and vibrationally excited states to be observed separately and yields the electric dipole moments: μ(v₂ = 1) = 1.253 ± 0.003 D, μ(v = 0) = 1.469 ± 0.004 D. The relative intensity distribution, linewidths, and line shapes of features in the double-resonance Stark spectra are also examined.