Infrared laser stark shift spectroscopy in ammonia

The Stark effect in ammonia has been theoretically and experimentally analyzed using lead salt tunable diode laser absorption spectroscopy and CO₂ laser absorption spectroscopy of several absorption lines around 1050 cm^–1 applied to an all-optical sensor for measuring of electric field strength. Measurements of the Stark splitting effect of theaR(5,K) ammonia lines forK=1–5 as well as for the sR(3,K) lines forK=0–3 have been made at Doppler broadening pressures and for several different electric field strengths. Theoretical electric field dependent energy levels have been evaluated by diagonalization of a 6×6 energy matrix constructed using both electric field independent and dependent terms. From the theoretical analysis the resolution can be predicted and optimized both in the Doppler broadened and in the pressure broadened regimes. The predicted resolution is 0.5% at an electric field strength of 20 kV/cm. The theoretical calculations and the experimental data recorded with the tunable diode laser system were compared with independent measurements made with a CO₂ laser system. The agreement between experimentally recorded and theoretically calculated spectra is good which indicates that the theoretical model is satisfactory for our purposes. The contribution from the normally forbidden ssR(5, 3) ammonia line to the absorption at theP(12) CO₂ laser line in the 9 m band is briefly discussed.     

Direct observation of the second-order Stark effect of theX-B transition in molecular iodine

The second-order Stark shift of the components of the hyperfine structure of the transition¹ _g ⁺ ( = 0,j = 13, 15) ³ _ou ⁺ ( = 43,j = 12, 16) (of molecular iodine have been studied by means of saturated absorption spectroscopy in an external cell with the I₂ vapour located in an electric field. The anisotropic polarizabilities of the upper and lower levels together with the difference between the isotropic polarizabilities of the levels of the transition have been obtained.     

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.     

Laser spectroscopy of Eu<Superscript>3+</Superscript> cubic centers in the CaF<Subscript>2</Subscript> bulk single crystal

The optical transitions ⁵ D _{0, 1} → ⁷ F _J (J = 0, 1, ..., 6) of Eu³⁺ cubic centers in the CaF₂ single crystal are investigated using combined excitation and emission spectroscopy at different time delays after the excitation pulse. The energies of the Stark sublevels of the ⁷ F _J ground states are determined.     

Nonlinear level crossing in the infrared transitions of optically pumped far infrared laser media

In conjunction with the Stark field induced power enhancement in optically pumped far infrared lasers, absorption transitions in a degenerate two level system under the influence of an weak static Stark field have been analyed. A third order theory to the density matrix formalism leads to zero field level crossing signals for absorption in rate equation approximation and in Doppler limit. For fast relaxation among Zeeman sublevels, the zero field level crossing signal arises from population effect. Optoacoustic measurements have been carried out on the ₅,^qQ(16,8) absorption line of CH₃OH which produces the familiar 119-m laser with the CO₂ 9P(36) pump line. The optoacoustic absorption signals observed are well reproduced by the theoretical expression.     

Determination of electron density in a wall stabilized Ar-CO ${\mathsf{_2}}$ thermal plasma

The electron density is measured in an argon-CO₂ thermal plasma by optical emission spectroscopy. Electron density is deduced from the Stark broadening of the argon line and hydrogen (H ) line. Different theories are used and compared. The effect of CO₂ molecule upon this plasma is studied as a function of the Ar-CO₂ mixture composition and discharge current. The electron density is ranging from 3 x 10²¹ m^-3 to 5.6 x 10²² m^-3. The influence of the arc confinement is studied and the electron density gradients are evaluated. Departure from local thermal equilibrium is also discussed.Received: 5 September 2003, Published online: 21 October 2003PACS: 52.70.Kz Optical (ultraviolet, visible, infrared) measurements - 52.80.Mg Arcs; sparks; lightning; atmospheric electricity     

The high resolution infrared spectrum and laser Stark spectroscopy of thev8 band of propyne

The perpendicularv ₈ band lying in the 1000–1100 cm^–1 region has been studied from infrared and laser Stark, spectra. We were interested in the part of spectrum corresponding to the spectral range of the 9 m CO₂ laser lines. Assignments of rovibrational lines with J'<40 and K'<6 have been made. About 100 Stark resonances have been assigned to 12 rovibrational transitions. Effective molecular constants and dipole moment have been determined with high accuracy. A list of close resonances with CO₂ laser lines is given and may be used for optical pumping experiments.     

Optical 4<Emphasis Type="Italic">f</Emphasis>-4<Emphasis Type="Italic">f</Emphasis> transitions in multiferroic HoMnO<Subscript>3</Subscript>

In the absorption spectra of the hexagonal single-crystal manganite HoMnO₃ in the paramagnetic ferroelectric state, lines near 1.1 and 2.0 μm were observed associated with the transitions ⁵ I ₈ → ⁵ I ₆ and ⁵ I ₈ → ⁵ I ₇, respectively, within the 4f ¹⁰ configuration of the Ho³⁺ ion. At T = 80 K, to the ⁵ I ₈ → ⁵ I ₇ transition corresponds one band at 1.9 μm for both polarizations E ∥ c and E ⊥ c. As the temperature increases from 80 to 293 K, a low-energy band with a peak at 2.04 μm for E ⊥ c and a peak at 2.07 μm for E ∥ c arises associated with transitions from an excited Stark level of the ground ⁵ I ₈ multiplet to the Stark levels of the ⁵ I ₇ multiplet and with an increase in the population of the initial Stark level, the energy of which is ～100 K.     

Far-Infrared Laser Stark Spectroscopy of 1,1 Difluoroethylene

The far-infrared laser Stark spectrum of 1,1 difluoroethylene (H₂C=CF₂) has been investigated with the 311 m line of the hydrogen cyanide (HCN) laser. Numerous families of absorption lines have been observed for both parallel and perpendicular polarizations up to 60 000 V/cm. Three families of resonances have been identified as J(K_a,K_c) = 41(35,7) 40(33,8), 40(36,5) 39(34,6) and 43(35,8) 42(33,9). The Stark shift for the first two transitions can be adequately explained by quasi-first-order calculations, whereas the Stark shift for the third transition requires second-order corrections. The zero-field frequencies for these transitions have been experimentally determined and are reported with fractional uncertainties up to a few parts in 10⁶.     

Specific features of magneto-optical spectra of Tb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript>

The spectra of magnetic circular dichroism in the range of the ⁷ F ₆→⁵ D ₄ absorption band and the spectra of magnetic circular polarization of luminescence in the range of the ⁵ D ₄→⁷ F ₅ band in the terbium-gallium garnet Tb₃Ga₅O₁₂ are studied at a temperature of 80 K. The optical transitions between the Stark sublevels of the ⁷ F ₆, ⁷ F ₅, and ⁵ D ₄ multiplets are identified based on the analysis of the magneto-optical and optical spectra. It is shown that the experimentally determined symmetry and energy of the Stark sublevels of these multiplets confirm the results of numerical calculations of the energy spectrum of the Tb³⁺ rare-earth ion in terbium-gallium garnet.