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.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 m–1200 m range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^–4–10^–3 accuracy is achieved in the measurement of the FIR wavelengths.The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^–1 of this main isotope.     

Low-Temperature Midinfrared Absorption in GaSe

We report the measurement of the temperature dependence of the absorption spectra of - GaSe over the temperature range 300 K to 5 K. Measurements have been made for both the e-ray (polarized parallel to the crystals c-axis) and the o-ray (polarized perpendicular to the c-axis), over the spectral range 4000 to 10 cm^–1. Nine absorption lines at 417, 440, 499, 546, 891, 945, 1015, 1093, 1270 cm^–1 were recorded at 300 K for the e- ray spectra. Some of these lines were identified using the results of a modified single layer, linear chain model of GaSe. The lines at 417, 440 and 499 cm^–1 were assigned to local impurity absorption originating from N, Mg and O, respectively. The weak lines at 945, 1015 and 1093 cm^–1 were assigned to hole transitions from the acceptor levels to the top of the valence band. Two absorption lines at 891 cm^–1 and 1270 cm^–1 were assigned to hole transitions from the quasi-local acceptor levels to the double degenerate valence sub-bands ₅ or ₆. The origin of lines recorded in the far IR absorption spectra at 20, 37 cm^–1 and 362 cm^–1 were also identified.     

Saturated absorption Stark spectroscopy of CH3OH with CO2 lasers

The vibration-torsion-rotation spectrum of CH₃OH has been studied by saturated absorption spectroscopy in applied electric fields up to 20 kV/cm, using ¹²C¹⁶O₂ and ¹²C¹⁶O₂ lasers. Frequency offsets for 129 absorption lines were measured relative to the frequency of a fluorescence stabilized reference laser with an accuracy of ±0.5 MHz for 75 lines inside the ±40 MHz tuning range and 2–5% for lines located up to 1.2 GHz outside the tuning range, but Stark tuned into resonance. For 36 lines we obtained fully-resolved Stark spectra, allowing determination of both lower and upper state K. Using this information in combination with information available from optically-pumped FIR laser emission, a total of 44 lines were completely assigned as transitions involving torsional n = 0, 1, 2 and 3 states of the CO stretch. Certain states belonging to n = 1 displayed an anomalous Stark effect which is at present not understood.     

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.     

Stimulated emission and laser action of Pr3+-doped YA1O3

Groundstate absorption, fluorescence, excited-state absorption, and stimulated emission of Pr:YA1O₃ were measured in dependence on the polarization. The results reflect the anisotropy of the host lattice. Especially the polarized spectra of the stimulated emission fit very well with the laser data of this material. Seven cw laser transitions in the visible spectral range obtained so far in Pr:YA1O₃ with argon-ion laser pumping were identified in the spectra of the stimulated emission. In addition, two infrared cw laser transitions were realized. The best results were achieved for the³ P ₀³ F ₄ laser transition at 746.9 nm with a maximum slope efficiency of 24.6%, a maximum output power of 49.6 mW, and a laser threshold of 25 mW.     

New CW FIR laser lines obtained in ammonia pumped by a CO2 laser, using the Stark tuning method

We report fifty seven CW FIR emissions observed in NH₃, by resonant pumping with a CO₂ laser. Exact coincidences between IR absorption lines of the gas and emission lines of the CO₂ laser have been carried out by Stark tuning. IR frequency shifts, up to 30 GHz, have allowed the pumping of forty three NH₃ transitions.These FIR emissions correspond to thirty one different wavelengths in the 50–400 m range; eighteen ones of them are new emitted wavelengths by pumping with the CO₂ laser.     

Multiplasmon laser gain in low-dimensional systems

The light absorption and laser gain in quantum wells are calculated using the cumulant expansion method and the fluctuation-dissipation theorem with allowance made for the strong Coulomb interaction of charge carriers. It is shown that the multiplasmon transitions result in a smoothening of the absorption spectrum and a shift in the absorption edge toward the long-wavelength range. The theoretical laser gain spectra are in agreement with the available experimental data. For In_0.05Ga_0.95As quantum wells, the laser gain g = 50 cm^?1 is reached at an electron density nd₀ = 1.64 × 10¹² cm^?2.     

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.     

The characteristics of multiple-photon absorption of SF6 molecules cooled in free jet expansion from a pulsed supersonic nozzle

The multiple-photon absorption of pulsed TEA CO₂ laser radiation by SF₆ molecules cooled toT _R40K andT _v160K in the free jet expansion from a pulsed supersonic nozzle has been investigated at energy fluences of 0.1 to 3.0 J·cm^–2.For practically all laser lines which coincide with the linear absorption spectrum of thev ₃ vibrational mode of SF₆ [P(12)...P(28), 10,6 m], the dependence of the absorbed energyE _ab on the exciting energy fluence was found to be steeper than linearE _abⁿ, wheren=(1.1 to 1.8). Considerable increases of the absorption cross sections with increasing energy fluence were observed.The fraction of the molecules interacting with the laser radiation is estimated.     

Femtosecond-pulse laser ablation of human corneas

A femtosecond pulse laser in the visible spectral region shows promise as a potentially new powerful corneal sculpting tool. It combines the clinical and technical advantages of visible wavelengths with the high ablation quality observed with nanosecond-pulse excimer lasers at 193 nm. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs and 7 ns, and centre wavelengths at 615 nm and 600 nm, respectively, both focused to an area of the order of 10^–5 cm², have been applied to human corneal ablation. Nanosecond laser pulses caused substantial tissue disruption within a 30–100 m range from the excision edge at all fluences above the ablation threshold of F _th60 J cm^–2 (I _th9 GW cm^–2). Completely different excisions are produced by the femtosecond-pulse laser: high quality ablations of the Bowman membrane and the stroma tissue characterised by damage zones of less than 0.5 m were observed at all fluences above ablation threshold of F _th1 J cm^–2 or I _th3 TW cm^–2 (3×10¹² W cm^–2). The transparent cornea material can be forced to absorb ultrashort pulses of extremely high intensity. The fs laser generates its own absorption by a multiphoton absorption process.     

Tunable diode laser absorption measurement of oxygen A-band line strengths

Line strength measurements and pressure-broadening coefficients for the oxygen A-band (b¹Σ_g ⁺ X³Σ_g ^-) at 13122 cm^-1 using tunable diode laser absorption spectroscopy are reported. Diode lasers are scanned over individual lines and the absorption at different pressures is recorded; from these data the line strength for each transition is obtained. Average values for each transition are compared to those previously published, and in particular a comparison with the HITRAN database is presented. Line strengths reported here are 5–10% lower than the HITRAN values. PACS 33.20.-t; 33.70.Fd     

Selective optothermal detection of NO2 and H2O with a frequency-tuned CO waveguide laser

The results are reported of the CO-laser optothermal (OT) detection of impurity gases when their absorption spectra overlap with those of an interfering gas. The influence of the latter was avoided using low gas pressures corresponding to a maximum of the OT sensitivity. Frequency tuned in the 5.2–6.3 m wavelength range, ¹²C¹⁶O and ¹³C¹⁶O waveguide lasers were used. The fine frequency tuning at 490 MHz was achieved for 150 laser transitions of both molecules. The OT sensitivity was estimated by NO₂ detection in the presence of water vapor. The minimal detectable concentration proved to be 60 ppb at P _19–18(14) transition of a ¹²C¹⁶O laser for NO₂ and 75 ppb on P _12–11(13) transition of a ¹³C¹⁶O laser for H₂O.     

Comprehensive analysis of the FASSST rotational spectrum of S(CN)2

Results are reported of a comprehensive investigation of an almost continuous rotational spectrum of S(CN)₂ recorded over the frequency region 110-374 GHz by means of the FASSST spectroscopic technique. The spectrum was analysed in detail and over 22 000 transitions were assigned in total. Precise, octic order spectroscopic constants in the asymmetric rotor Hamiltonian have been determined for the ground state and 12 different vibrationally excited states of the parent isotopologue, including first excited states of five different normal modes. Three states near 370 cm⁻¹ and four states near 490 cm⁻¹ above the ground state were found to be mutually interacting and were successfully analysed in terms of a triad and a tetrad of coupled states, respectively. Rotational transitions in the ³⁴S, ¹³C, and ¹⁵N isotopologues of S(CN)₂ have also been assigned and fitted, and newly determined rotational constants were used to derive the geometry of the molecule. The complex multistate analysis of the spectrum was carried out with the newly developed AABS software package for Assignment and Analysis of Broadband Spectra.     

Mid-infrared diode laser spectroscopy of SO

The absorption spectrum of the fundamental band of SO⁺ (X²Π) has been recorded using a mid-infrared tunable diode laser spectrometer with the velocity modulation technique in an AC glow discharge of He/SO₂. Forty-two lines of SO⁺ were identified in the spectral range of 1230-1330 cm⁻¹. The observed rovibrational transitions together with the microwave data published previously were fitted to a standard effective Hamiltonian for ²Π states. Molecular constants for the ground and υ = 1 vibrational states were derived. The band origin was determined to be 1291.5299(27) cm⁻¹.     

Spectral studies of Nd3+ and Er3+ ions in POCl3:SnCl4 laser liquid

The optical absorption spectra of triply ionized neodymium and erbium ions in POCl₃SnCl₄ laser liquid have been studied for the first time in the UV-VIS and NIR regions. Spectroscopic and Judd-Ofelt intensity parameters are evaluated from the observed band positions and their intensities. Radiative lifetimes and the luminescent branching ratios for the excited fluorescent levels of Nd³⁺ and Er³⁺ ions are theoretically estimated and the possible laser transitions are indicated. From the observed splittings of certain bands in the second-derivative spectrum of the Nd³⁺ ion, the crystal field (A ₂₀,A ₄₀) parameters are evaluated assumingC _3h symmetry for the ion.     

Optical study of praseodymium doped yttrium aluminium garnet

The absorption and fluorescence spectra of YAG crystals doped with praseodymium at 1% level are investigated through dye laser spectroscopy. The spectra can be interpreted as evidence for at least three series of crystallographic sites for Pr³⁺, but only the transitions which involve the ground state are really complex, that is multi-sites like. It is suggested that an electronphonon interaction occurs through resonance with peaks in the density of phonon states and ground state Stark levels in the range 350–750 cm^–1. This creates new vibronic states and the appearance of a large number of lines for transitions involving ground state especially if laser excitation of the fluorescence is used.Presented at the International Symposium on Solid State Chemistry, October 28–31, 1986, Karlovy Vary, Czechoslovakia.     

High sensitivity absorption spectroscopy of HDO by ICLAS-VeCSEL between 9100 and 9640 cm

The absorption spectrum of monodeuterated water has been recorded between 9100 and 9640 cm⁻¹ using intracavity laser absorption spectroscopy (ICLAS) based on a vertical external cavity system emitting laser (VeCSEL). Overall 1706 lines were attributed to the HDO species. The spectrum assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge. A set of 746 energy levels was derived from transitions assigned to 13 upper vibrational states, 300 of them being reported for the first time. Resonance interactions leading to an important strengthening and observations of the very weak 7ν₂ and ν₁ + 5ν₂ bands are discussed. A detailed line list has been generated.     

Spectroscopic and laser properties of Er3+-doped monoclinic BaY2F8 single crystals

The luminescence and absorption properties of Ba(Y_1–x Er _x )₂F₈ (x=0.001, 0.01, 0.05, 0.1, 0.2 and 0.3) and the Er³⁺-ion decay kinetics of luminescent transitions from three initial laser states, the⁴S_3/2,⁴F._9/2 and⁴I_11/2 manifolds, were measured. The crystal-field splitting schemes for allJ-manifolds which are involved in (J J)-luminescence transitions and stimulated emission parameters of Er³⁺ -ions in BaY₂F₈ were determined. A comparison of laser powers and efficiencies of BaY₂F₈ and Y₃Al₅O₁₂, Lu₃Al₅O₁₂ and LiYF₄ single crystals doped with Er³⁺-ions shows the similar performance of these materials.     

High-precision pressure shifting measurement technique using frequency-stabilized cavity ring-down spectroscopy

We describe a high-precision method for measuring pressure shifting of absorption lines. The technique involves the acquisition of high-resolution spectra using a cavity ring-down spectrometer whose length is continuously locked to a frequency-stabilized reference laser over a range of sample pressures. We discuss a relatively large correction arising from the pressure-dependence of dispersion in the cavity modes, and we demonstrate pressure shifting measurements in air for transitions in the ¹⁶O₂A-band. Pressure shifts in the range -0.011 to are reported. We measured relative positions of line centers to within 70 kHz and determined pressure shifting coefficients over a 5 kPa pressure range with relative uncertainties approximately equal to 1.0%, which constitutes a five-fold improvement over previous measurements.