N2O Laser Research Articles

Planar cw N2O laser with RF excitation

The article presents the results of studying and optimizing the output power and spectral characteristics of radiation of a sealed-off continuous wave (cw) planar N2O laser depending on the input radio frequency power and the size of the interelectrode gap in the discharge, on the composition and pressure of the working gas mixture N2O:N2:He:Xe, on the time of continuous operation of the laser. The effect of adding carbon monoxide CO to the working gas mixture is discussed. The maximum values of the output power—17.5 W and the efficiency—7.3% were obtained in a sealed-off cw N2O laser, which significantly exceed the known values. When N2 was replaced by air in the gas mixture: N2O:Air:He:Xe = 2.3:2.3:5:0.4, the laser output power was 10.6 W. The radiation powers of N2O and CO2 lasers are 13.1 W and 18.6 W, respectively, when the working mixture in the emitter is replaced and the same operating conditions are applied—the input power is 180 W and the pressure of the working gas mixture is 30 Torr.

A shock-tube study of the N2O + M ⇄ N2 + O + M (M = Ar) rate constant using N2O laser absorption near 4.6 µm

The low-pressure limit rate constant k1,0 of the reaction N2O + M ⇄ N2 + O + M was measured in shock-heated mixtures of 0.2% N2O/Ar using 4.56-µm laser absorption of N2O in the temperature range 1546–2476 K near 1.3 atm. Modeling the N2O profiles with a detailed kinetic analysis, which considered non-ideal pressure variations, provided k1,0 values that were best fit by the expression k1,0=1.01×1015exp(−30,050/T), with k1,0 in cm3mol–1s–1 and T in K. Estimated k1,0 uncertainties at 1546, 1821, and 2230 K were respectively 13.0%, 8.9%, and 9.0%. By combining the results of the present study with previous low-temperature data measured in flow/static reactors, the best fit over the temperature range 850–2500 K was determined to be (k1,0 in cm3mol–1s–1, T in K)(R1)k1,0=(1.04±0.04×1015)exp[(−30,098±90)/T]. This is the first study of k1,0 using N2O infrared laser absorption. Through the high signal-to-noise ratios of the experimental N2O profiles and careful consideration of dP/dt effects, this k1,0 determination is in excellent agreement with the large body of historical k1,0 data but demonstrates significantly less scatter than all previous measurements.

Combining Denitrifying Bacteria and Laser Spectroscopy for Isotopic Analyses (δ(15)N, δ(18)O) of Dissolved Nitrate.

We present a novel approach for nitrogen (δ(15)N) and oxygen (δ(18)O) isotopic analysis of nitrate in water based on the isotopic analysis of N2O produced from the conversion of NO3(-) by cultured denitrifying bacteria and off-axis integrated cavity output spectroscopy (OA-ICOS). The headspace N2O was manually injected into an OA-ICOS isotopic N2O laser analyzer through a syringe septum port. Sample analysis time was ∼300 s. The use of OA-ICOS technology yields accurate and precise δ(15)N and δ(18)O results for dissolved nitrate samples when nonlinearity issues are considered. This new isotope analytical technique thus improves the isotopic analysis of nitrates by (i) providing accurate measurements of δ(15)N and δ(18)O without preconcentration, (ii) eliminating interferences by other gas substances (i.e., H2O and CO2), and (iii) reducing extensive maintenance and costs of isotope ratio mass spectrometers (IRMS). This approach will greatly streamline the identification and quantification of nitrate sources in aquatic systems.

IR excitation of ethylene molecules and clusters embedded in He4 droplets

Ethylene and ethylene clusters embedded in superfluid He4 droplets have been spectroscopically investigated with continuous wave line tunable CO2 and N2O lasers, utilizing the strong absorption of the ν7 mode of C2H4. The monomer and the different clusters of ethylene absorb in the same spectral region and show significant overlap of their spectra. By measuring the dependence of the signal on the pick-up pressure and fitting the resulting curves with a Poisson distribution and by further studying the spectral dependence on the droplet size, it was possible to assign two peaks. The origin of the 10 cm−1 broad gas phase dimer spectrum has been the subject of much discussion; we show that the broad peak is not due to homogeneous broadening, because the low temperature of the He droplet leads to a dimer full width at half maximum width of about 1 cm−1.

New FIR Laser Lines from CD3OH

Fourteen new optically pumped far-infrared (FIR) laser lines in the range 46.8 μm to 172.6 μm were discovered in optically pumped CD3OH. The pump sources include both the CO2 laser and the N2O laser. Two theoretically predicted laser lines were observed in this study.

Far-infrared hydrazine laser pumped by an N2O laser

We have used an N2O laser to optically pump N2H4 molecules in a far-infrared cavity and observed 17 new laser lines in the wavelength range 93.0 to 374.2 µm, the 136.8 µm line pumped by 10P(16) being a doublet. We measured the frequencies of the laser lines by heterodyne mixing of the far-infrared radiation with radiation from two frequency-stabilized CO2 lasers.

Infrared photofragmentation spectra of size-selected SF6⋅Ar+n cluster ions

Results are presented of a detailed experimental study of the infrared photofragmentation patterns of size-selected SF6⋅Ar+n cluster ions for n in the range 3 to 70. Line-tuneable CO2 and N2O lasers have been used to excited the ν3 vibrational mode of the SF6 molecule which is followed by the loss of one and two argon atoms as the principal fragmentation routes. Which of the two processes is dominant depends quite strongly on the size of the cluster ion concerned, with very pronounced fluctuations in the relative intensities of photofragments being observed for cluster ions in the range SF6⋅Ar+3 to SF6⋅Ar+25. Only for SF6⋅Ar+3 is the fragmentation pattern markedly different from that found for the other ions; an observation that supports an earlier conclusion regarding the relative ionisation energies of the two constituents [Stace et al. J. Phys. Chem. 97, 11363 (1993)]. A summation of fragment ion intensities as a function of laser wavelength is used to determine infrared absorption profiles and these have been recorded for individual clusters containing up to 70 argon atoms. Clusters containing fewer than 40 argon atoms appear to form single structures, with both the absorption profile shapes and selected hole-burning experiments suggesting that the number of isomers is small. The presence of isomers only appears to become significant when the clusters contain more than 40 argon atoms. The observation of site splittings for the triply degenerate ν3 vibrational mode of SF6, together with the comparatively narrow linewidths seen for clusters containing between 15 and 40 rare gas atoms, indicates the presence of ordered structures. Such a conclusion implies that the clusters are solidlike rather than liquidlike. Overall, the results demonstrate that there is a clear correlation between those criteria previously used to identify the presence of stable cluster ion structures, i.e., mass spectra and unimolecular fragmentation patterns, and the corresponding infrared fragmentation patterns and absorption profiles. Of the ions studied, SF6⋅Ar+21 stands out as being particularly stable and worthy of future theoretical attention.

Gain and emission spectrum of a pulsed electron-beam-controlled N2O laser

An experimental and theoretical investigation was made of the small-signal gain in a pulsed electron-beam-controlled N2O laser. The gain was found to exceed ~ 1 m−1. A comparison of the experimental and calculated gain values was used as the basis for estimating the pumping efficiency of N2O molecules in an electron-beam-controlled discharge and the relaxation constant of the upper active level. The lasing frequency of the N2O laser was tunable in spectral ranges corresponding to vibrational–rotational transitions from R (46) to R (2) and from P (2) to P (46). The laser output energy, at its maximum in the distribution over the rotational numbers, was ~ 8 J (~ 16 J liter−1 amagat−1).

Discharge ignition phenomena in CO2 and N2O lasers with preliminary filling of the interelectrode gap by electrons

A comprehensive model is presented that describes preionization and discharge ignition processes in large-aperture molecular-gas lasers. By initially filling the interelectrode gap with electrons and establishing a space-charge screen at the cathode, electron avalanche begins adjacent to the anode. Cathode-directed ionization waves develop and ignite the discharge. Dynamic profiling of the electric-field distribution and Penning ionization of a readily ionizable additive combine to decrease both the ignition and quasi-steady-state voltages.

High-power molecular lasers pumped by a volume self-sustained discharge

The basic principles that underlie the initiation of a volume self-sustained discharge, which is to be used for pumping CO2 and N2O lasers, are discussed. The experimental results for discharge stability, optical homogeneity, and scalability of the laser active medium are reported. Characteristics of CO2 lasers with apertures of up to 70 cm and active volumes of up to 400 L, as well as of N2O lasers with apertures of up to 20 cm and active volumes of up to 60 L, are presented.

High-resolution Fourier-transform infrared spectroscopy of thev3(F2) fundamental of RuO4

The v 3(F2) fundamental band of ruthenium tetroxide (RuO4) vapour is investigated by high-resolution (0·004 cm-1 FWHM) interferometric FTIR spectroscopy in the range 850–1000 cm-1. The rotational fine structure is largely resolved and accurately analysed on the basis of third- and fourth-order (diagonal) effective Hamiltonians in the theory of Moret-Bailly. The analysis of the enriched isotopomer spectra gives m = 921·6514 cm-1 (102RuO4) and m = 920·0674 cm-1 (104RuO4). Many other constants for these are summarized in tables. For other isotopomers we find m(96) = 926‥d83 cm-1, m (99) = 924·14 cm-1, m(100) = 923·31 cm-1 and m(101) = 922·46 cm-1 from an approximate analysis of the spectrum of the natural isotope mixture. Many coincidences of rovibrational transitions in RuO4 with N2O and CO2 laser lines are predicted and assigned. The importance of the results for sub-Doppler spectroscopy, IR-laser isotope separation and the analysis of symmetry (and parity) selection rules is discussed briefly.

Pulsed electron-beam-controlled N2O laser with 100 J output energy

An experimental investigation was made of the influence of the molecular (N2, CO) and atomic (He, Ar, Xe) gases on the energy characteristics of a pulsed electron-beam-controlled N2O laser. The active mixture composition was optimized. In a device having an optical volume V ≈ 10 liters at a gas pressure of 0.25 atm, the laser output energies were ~ 80 J (a specific output energy of ~ 30 J liter−1 atm − 1) for an active medium temperature T = 20°C, and 106 J (36 J liter − 1 amagat − 1) for T ≈ – 30 °C (N = 0.3 amagat). An efficiency of ~ 10% was achieved.

N2O laser pumped by a self-sustained volume discharge

An investigation was made of the parameters of an N2O laser pumped by a self-sustained volume discharge with the aim of improving the output characteristics of this laser. The discharge was ignited as a result of a preliminary filling of the discharge gap with electrons and preionization of the gas in the gap by a low-current beam of accelerated electrons. In this way it was possible to reach an output energy up to 465 J, a specific output energy up to 16.4 J · liter − 1 · atm − 1, and an efficiency of 6.7%, all of which exceeded the earlier values reported for N2O lasers pumped by a self-sustained volume discharge.

Chaotic passive Q-switching pulsation in a N_2O laser with a saturable absorber

A single-mode N2O laser with NH3 as a saturable absorber is found to exhibit chaotic passive Q switching with multipeaked pulses. The chaotic dynamics is strongly correlated with vibrational relaxation mechanism in the laser medium. The phenomenon is predicted, and its characteristic behavior is well explained, by the rate-equation analysis recently developed for the case of instability in CO2 lasers.

Coherent tunable far infrared radiation

Tunable, cw, far infrared (FIR) radiation has been generated by nonlinear mixing of radiation from two CO2 lasers in a metal-insulator-metal, (MIM) diode. The FIR difference-frequency power was radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO2 lasers. Using the combination of lines from a waveguide CO2 laser, with its larger tuning range, with lines from CO2, N2O, and CO2 isotope lasers promises complete coverage of the entire far infrared band from 100 to 5000 GHz (3–200 cm−1) with stepwise-tunable cw radiation.

New strong CW FIR laser actions and assignments in COF2

Thirty one new cw far-infrared laser lines have been discovered in COF2 optically pumped by a CO2 laser and a N2O laser, in a metallic waveguide resonator. This number appreciably increases the number of eighteen lines appearing in the literature. Moreover, some of the new lines show that intense far-infrared laser action might be obtained with an optimized cavity, as it was the case for some of the previously reported lines. Twenty-seven, amongst the thirty one new lines, have been fully identified.

Passive Q-switching instability and bistability of a N_2O laser with intracavity saturable absorber

Several types of instability in passive Q switching and optical bistability are observed in a number of 10-μm laser lines in a N2O laser with intracavity saturable absorbers such as NH3, SF6, C2H4, C2H3Cl, and CCl2F2. The observed pulse shapes are reproduced well by a calculation based on the recently proposed rate-equation model. Characteristic dependences of passive Q switching and bistability on the laser parameters are explained with a phase diagram derived theoretically.

Electron-beam-controlled N2O laser

The development of a pulsed N2O electron-beam-controlled laser (V ~ 2 liter) with a radiation energy, specific output energy, and efficiency (8 J, 16 J???liter??1???atm??1, and 9%, respectively) substantially higher than the values known for electric-discharge N2O lasers is reported. The addition of CO to an N2O?N2?He active mixture (or complete substitution of N2 by CO) improved the energy characteristics of an electron-beam-controlled N2O laser by more than an order of magnitude.

Laser Stark spectroscopy of phosphine

A laser Stark spectrum of PH3 has been observed by using 12C16O2, 13C16O2, 12C18O2, and N2O lasers. Coincidences have been found for 44 ν2 band lines and 31 ν4 band lines for Stark fields up to 60 kV/cm. Zero-field frequencies of the ν2 and ν4 band lines and several A1A2 splittings in the ν2 and ν4 states have been determined. Effective dipole moments for rotational levels in the ν2 and ν4 states have been determined and analyzed by taking into account the mixing of the states resulting from the Coriolis interaction between the ν2 and ν4 states and by introducing the transverse dipole moment between the two states.

The ?2 and ?5 bands of CD3Cl. Assignments and predictions of far infrared laser emission lines

Infrared spectra of the υ2 and υ5 bands of CD3Cl have been recorded with a resolution of about 0.015 cm−1 and assigned. An agreement quite perfect was found with the spectra calculated using last molecular constants. Assignments of most of the optically pumped emission lines have then been derived and coincidences with all CO2 and N2O laser lines in the 10 μm region have been predicted.