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.     

Method to investigate the symmetry of saturated absorption signals by means of laser frequency locking techniques

It is shown that the line shape of a saturated absorption signal — especially its symmetry — can be investigated by combining laser frequency locking methods. The laser frequencyv, modulated with a frequencyf, is stabilized alternatively to the zero crossings of the synchronously detected 2f and 3f absorption signals. In addition, almost any other part of the profile can be tested by locking the laser frequency to neighboruing points of the zero crossings by using an offset technique. With two prestabilized Ar⁺ lasers atv=582 THz the symmetry of different¹²⁷ I ₂ hfs signals was investigated with an uncertainty of typically 2×10^–12 v or 10^–3 halfwidths.     

Mixing effect in the NH3 absorption and MIR emission spectra pumped by a continuously tunable CO2 laser

By tuning a high pressure CO2 laser (HPL) around strong ammonia lines nearly coincident with CO2 lines an of-fresonant absorption is observed which can be confirmed by the superfluorescent MIR emission. This effect is related to a two frequency v₁, v₃ HPL emission in the regime of moderate pulling. Around a strong absorption line a mixed v₄=2v₁–v₃ frequency is produced that is strongly absorbed     

Laser investigations at 269 nm for XeF(D-X) in Ne crystals

From line narrowing in amplified spontaneous emission at the D-X transition (269nm) of XeF in solid Ne a gain coefficient of 3.4 cm^–1 has been derived and ground-state losses of 2.8 cm^–1 have been determined by variation of the absorption length. A dielectric laser cavity has been optimized with the reflectivities R₁=100% and R₂=70% for 1 cm long crystals; laser action has been achieved.     

Two-photon resonant four-wave mixing processes in atomic barium

By means of a N₂-laser pumped dye-laser (P _L ≈20kW, Δv _L < 10 GHZ) different two-photon resonant four-wave coupling processes in Ba vapour (n _Ba≈10¹⁶ cm⁻³) using the Ba states 6s8s ¹ S _o and 7s5d ¹ D ₂ were investigated. Coherent line radiation with conversion rates up to 10⁻³ was generated within the range of λ=190–200 nm by sumfrequency mixingv _UV=2v ₁+v ₂ of 3 laser photons and within the range of λ=250–380 nm by couplingv _UV=2v ₁±v _IR of 2 laser photons with one photonv _IR stimulated emitted in laser-induced Ba transitions. For the second coupling type the various nonlinear processes contributing to the formation of the coupling components are discussed. The power of the UV-component as function of inensity and resonance detuning of the laser as well as on the phase-mismatch was calculated on the basis of the small signal theory and compared to the experimental data.     

New cw FIR laser lines from optically pumped ammonia analogues

Two new cw submillimetre lines optically pumped by the 9 μR(30) CO₂ laser have been observed for¹⁴NH₃ and assigned to thea(6,0)→s(5,0) transition and to its cascade transitions(5,0)→a(4,0) in thev ₂=1 state. In addition, six new emission lines have been observed for NH₂D, and one tentatively assigned to the (11,1)→(10,1) transition of ND₃. Methylamine has also been investigated and twenty-eight new emission lines have been discovered.     

Analysis of the high resolution spectrum of the fundamental bandsv2 andv5 of12CH3F and their interactions

Thev ₂(A₁) andv ⁵(E) fundamental vibration-rotation bands of¹²CH₃F have been recorded under high resolution (0.015 to 0.020 cm^–1) in the spectral range of 1460 cm^–1. About 1100 transitions have been assigned. The Coriolis interaction between v₂=1 and v₅=1, and the l(2,-1) interaction in v₅=1 have been rigorously treated. Sixteen molecular constants have been determined from a least squares analysis. They reproduce the observed data with an overall standard deviation of 0.0037 cm^–1.     

Narrow-band extreme-ultraviolet laser radiation tunable in the range 90.5–95 nm

Tunable, narrowband extreme ultraviolet radiation in the range 90.5–95 nm with only limited intensity variations is produced by frequency-tripling ultraviolet light from a frequency-doubled dye laser in a gas-jet of xenon. Acetylene gas is found to be an efficient medium for third-harmonic generation in this wavelength range as well. The extreme-ultraviolet radiation is applied in a spectroscopic study of the b ¹ II _u , v=6–8 and v=10–12, o ¹ II _u , v=0 and b¹ _u ⁺ , v=9 states of molecular nitrogen. From linewidth measurements a value k _p=6×10¹⁰ s^–1 for the predissociation rate of the b ¹ II _u , v=11 state is deduced.     

Detailed vibrational population distributions in a CO2 laser discharge as measured with a tunable diode laser

A tunable diode laser (TDL) operating in the 2150–2350 cm^–1 wavenumber region is used to probe a conventional cw CO₂ laser discharge. Absorption lines in more than 25 different vibrational bands are observed, enabling us to determine absolute vibrational populations inall levels of concern to the dynamics of the 10 m CO₂ laser. Levels in thev ₃ mode of CO₂ as high as 00°9 are monitored, and it is found that anharmonic effects play a significant role in the populations of such levels. Thev ₁ andv ₂ mode populations are also investigated in detail, and it is found that these modes are strongly coupled and maintain a common vibrational temperature under all discharge conditions. The use of a TDL is shown to be a powerful technique for investigating the dynamics of infrared molecular lasers.This work was supported in part by the National Science and Engineering Research Council, Canada     

Infrared absorption of silane,ammonia, acetylene and diborane in the range of the CO2 laser emission lines: Measurements and modelling

Absorption spectra of the gases SiH₄, NH₃, C₂H₂ and of SiH₄/Ar and SiH₄/B₂H₆ mixtures have been measured in the spectral range of the CO₂ laser from 9.2 to 10.8 µm. In agreement with literature, silane shows the highest absorption (absorption coefficient = 3.3 × 10^–2 Pa^–1 m^–1). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment. This is confirmed by a rate-equation model involving the basic mechanisms of V-V and V-T energy transfer between vibrationally excited silane molecules. In contrast to silane, the absorption coefficient of NH₃ at the 10P(20) laser line is 4.5 × 10^–4 Pa^–1 m^–1 atp = 20 kPa and has its maximum of 4.5 × 10^–3 Pa^–1 m^–1 at the 10R(6) laser line. For C₂H₂ and B₂H₆, is even less ( 2.1 Ò 10^–5 Pa^–1 m^–1 for C₂H₂).     

Double resonance and collision-induced transitions in the radiofrequency spectra of H2CO and HDCO observed inside the cavity of a CO2 laser

Many radiofrequency resonances corresponding to transitions between the two components of a K-type doublet in H₂CO and HDCO have been observed using infrared-radiofrequency double resonance inside a CO₂ laser cavity. For strong resonances, additional transitions induced by collisions have also been observed and these provide information on collisional processes. The collision-induced transitions also provide a method for assigning the K doublet frequencies in the ground and v₄ = 1 states of H₂CO, and in the ground, v₅ = 1, and v₆ = 1 states of HDCO; the rovibrational transitions pumped by the CO₂ laser can therefore be determined. The upper state rotational transitions and the infrared frequencies for the transitions in exact coincidence with the CO₂ laser lines provide accurate additional data in the analysis of the conventional infrared spectrum of the ν₅ and ν₆ bands of HDCO. In addition, the 195-μm far-infrared laser line in HDCO, observed by Dangoisse et al. [J. Quantum Electron. QE-13, 730–731 (1977)] has been assigned as the 24_6,19→23_6,18 transition in the v₆ = 1 state.     

Sensitivity of approximate formulas for determining optical constants of thin films

The sensitivity of approximate formulas for determining the optical constants of thin films using measurement of reflectancesR and transmittancesT at normal incidence have been investigated theoretically. The ranges of refractive indexn, absorption indexk,2nk (=₂) andn ²–k ²(=₁) within relative errors of 5%, 10%, and 20% may be obtained. Selected signs of (₁)⁺ or (₁)^– have been determined. Validity of the condition n₀ A=n _s A has been also evaluated (A=1–R –T andA=1–R–T).     

Application of a CW chemical laser for remote pollution monitoring and process control

The measurement of the concentration of gaseous hydrogen fluoride in the exhaust of an aluminum plant by resonance absorption of the radiation of a cw chemical HF laser is reported. The HF concentration has been evaluated taking into account the simultaneous absorption of water vapor and carbon dioxide at the HF laser frequencies. The absorption cross sections for H₂O and CO₂ at the HF laser lines have been determined in laboratory experiments.     

Fourier transform infrared spectrum of the ν3 band of HCO

The ν₃ fundamental band of the formyl radical, HCO, in the 5.3-μm region has been observed at high resolution (0.0025 cm⁻¹, unapodized) using a Fourier transform spectrometer. The HCO radicals were formed by the reaction of F atoms with H₂CO in a fast-flow multiple-traversal absorption cell. A total of 298 lines were measured with an accuracy of about 0.0004 cm⁻¹ and assigned to transitions with values of the rotational quantum numbers N and K_a up to 20 and 5, respectively. These data greatly improve the knowledge of the HCO ν₃ line positions and (v₁v₂v₃) = (001) vibrational state molecular parameters as compared to earlier laser magnetic resonance studies of this band, especially for higher values of N. The ν₁ fundamental band of HCO was also observed and an analysis of these data agrees well with the recent study of Dane et al. [J. Chem. Phys. 88, 2121–2128 (1988)].     

The sub-micrometer thickness n-InSb/i-GaAs epilayers for magnetoresistor applications at room temperatures of operation

Magnetotransport at fields up to 500 mT and LF-noise characteristics are reported for miniature magnetoresistors with ferrite concentrators based on Sn-doped n-InSb/i-GaAs heterostructures grown by MBE. The thickness of the InSb epilayers lie in the range 0.55–1.5 μm giving room temperature mobilities of 2.5–5.5 m² V⁻¹ s⁻¹ with carrier densities of (0.5–1.5)×10¹⁷ cm⁻³. The room temperature magnetoresistance (MR) for our two terminal devices could be as high as 115% at 50 mT which is comparable to the extraordinary MR (ExMR) recently reported in microscopic composite van der Pauw disks four terminal devices [Science 289 (2000) 1530]. In addition, a high signal-to-noise ratio and a good temperature stability of R(B)/R₀=0.5–0.83% K⁻¹ was observed for B<60 mT (below the saturation field B_sat for ferrite). Device resistance stability R₀(T) was equal to 0.27–0.66% K⁻¹ in zero field with a nominal device resistance R₀=197–224 Ω for DC currents in the range I=0.01–1.0 mA. The minimum detectable magnetic field is estimated from the reduced differential MR (∂R/∂B)/R=2000% T⁻¹ at B=31 mT and normalised 1/f current noise power spectral density measured at the same field. The resolution limit B_min=2.6 nT at 10² Hz and B_min=0.82 nT at 10³ Hz. These resolution limits are seven times better than those recently reported for the same material n-InSb/i-GaAs and ferrite fabricated Hall sensors [Magnetotransport and Raman characterization of n-InSb/i-GaAs epilayers, for Hall sensors applications over extremely wide ranges of temperature and magnetic field, Proceedings NGS 10, IPAP Conference Series 2, IPAP, Tokyo, 2001, pp. 151–154].     

A tunable frequency stabilized Ar+ laser

The frequency of a single-mode Ar⁺ laser atv=582 THz (=515 nm) is stabilized by means of an external iodine cell to a Doppler broadened absorption profile. The —unmodulated — stabilized laser frequency is reproducible to ±1 MHz or ±1.5×10^–9 v and can be shifted within a 180 MHz wide range.     

Vector-spinor space and field equations

Generalizing the work of Einstein and Mayer, it is assumed that at each point of space-time there exists a vector-spinor space with N_v vector dimensions and N_s spinor dimensions, where N_v=2k and N_s=2 ^k, k3. This space is decomposed into a tangent space with4 vector and4 spinor dimensions and an internal space with N_v–4 vector and N_s–4 spinor dimension. A variational principle leads to field equations for geometric quantities which can be identified with physical fields such as the electromagnetic field, Yang-Mills gauge fields, and wave functions of bosons and fermions.     

Determination of the deuterium abundance in water using a cw chemical DF laser

This paper describes a new method for the determination of the deuterium content in water samples. The absorption of the radiation of a cw deuterium fluoride laser by HDO in water vapor is measured by means of a nonresonant spectrophone (optoacoustic detector). This method enables one to evaluate the isotope ratio of hydrogen in a rather simple and straightforward way. Advantage is taken of the fact that HDO absorbs some of the DF laser lines whereas H₂O shows no absorption. Due to the small concentration in natural water deuterium is practically entirely present as HDO. Therefore a selective determination of the deuterium content is possible. In the course of the investigation the absorption coefficients of HDO for the different laser lines were determined. It was thereby established that there exists a strong coincidence of an HDO absorption line with the 2P2 DF laser line. The detection sensitivity of the method was then examined for some selected laser lines. The concentration of HDO in natural water samples could be determined with an accuracy of better than 10%. The experiments, however, show that with appropriate improvements it should be possible to achieve an accuracy of better than 1%. This makes the method very interesting as an analytical tool in hydrology.     

Laser-induced fluorescence of Na2 at the Na(3s → 5s) two-photon transition (6022.3 Å)

Na₂ excited from the X¹Σ_g⁺ state to the A¹Σ_u⁺ state by a narrow band (3 MHz) Rhodamine-6G dye laser at 6022.3 Å, the same wavelength at which Na undergoes the 3s–5s two-photon transition, gives four fluorescence series from A¹Σ_u⁺ levels (v′ = 21, J′ = 26), (18, 33), (33, 19), and (34, 50). The last two series are much weaker in intensity, and at long wavelengths many doublets are lost in the background noise. The same (34, 50) fluorescence series was found by other workers in the lab using a Kr⁺ (5682 Å) laser as excitation source. Their analysis agrees very well with the findings in the work.     

Spectroscopic Study of the Na2 2Σg State by cw Perturbation-Facilitated Optical-Optical Double-Resonance Spectroscopy

The Na₂(3sσ_g)(4sσ_g) 2³Σ⁺_g state of Na₂ has been observed and studied by cw perturbation-facilitated optical-optical double-resonance (PFOODR) spectroscopy for the first time. A single-mode dye laser and a Ti-sapphire laser served as the pump and the probe lasers, respectively. A total of 543 PFOODR excitation signals have been assigned to the 2³Σ⁺_g ← b³Π_1u transitions. Absolute vibrational numbering was determined by counting nodes in the 2³Σ⁺_g → a³Σ⁺_u bound-free spectra. Spectroscopic constants and the corresponding RKR potential energy curve are presented in this vsork. The values of T_e, R_e, and D_e, are found to be 25 551.237(49) cm⁻¹, 3.53463(35) Å, and 6211.5(1) cm⁻¹ respectively.