Mathematical modeling of CO2 TEA laser

Five and six-temperature models for the CO₂–N₂–He system are used to describe the process of the dynamic emission in the TEA CO₂ laser. All physical constants and relaxation rates related to these models are examined to estimate the output pulse parameters as a function of the input parameters. The two pumping processes implemented; empirical function and differential equation show a good agreement with the experimental data.     

Tunable electrooptically Q-switched RF excited CO2 waveguide laser with two channels

A tunable electrooptically Q-switched RF excited waveguide CO₂ laser with two channels is presented. Q-switched pulses have been obtained from one of the channels. The peak power is 300 W and the pulse width is 140 ns. CW laser output has been obtained from the other channel, which can been tuned by a PZT. The short-term heterodyne stability can be up to 10⁻⁹.     

Investigation of cutting of engineering ceramics with Q-switched pulse CO2 laser

In this paper, the cutting of Si₃N₄ engineering ceramics with Q-switched pulse CO₂ laser is studied. Considering the influence of the cut front shape on the absorption of the laser beam, a simplified 2D mathematic model is developed based on a pulsed laser vaporization cut process. This model is based on the conservation of energy. The experimental results show that it would realize crack-free cutting by using high-speed and multi-pass feed cutting process.     

Mathematical modeling of TE CO2 laser with SF6 as a saturable absorber

A mathematical model describing the dynamic emission of a single mode TE CO₂ laser with saturable absorber has been adapted. A six-temperature model has been used to describe the amplifying medium, while a four-coupled energy level is used to describe the selective absorbing medium. The suggested mathematical model allows the investigation of the effects of the intracavity absorber on the mode characteristics of the TE CO₂ laser and, moreover, the study of the effect of the laser input parameters on the output laser pulse. The model simulates the passive Q-switch in both low- and high-pressure cases in the absorbing medium.

In addition, numerical solutions of a non-linear rate equation system of the suggested model are quantitatively discussed. The solutions describe the photon number density, the population inversion and the energy transfer processes of amplifying and absorbing media.     

CO2/CO2 isotopic ratio measurements with a continuous-wave quantum cascade laser in exhaled breath

A laser spectrometer based on a continuous-wave thermoelectrically-cooled distributed feedback quantum cascade laser at ∼2308 cm⁻¹ has been evaluated for measurement of ¹³CO₂/¹²CO₂ isotopic ratio (δ¹³C) changes in exhaled breath samples and in CO₂ gas flows in the concentration range 1-5%. Mid-infrared CO₂ absorption spectra were measured in a 54.2-cm long optical cell using balanced detection whereby the beam passing through the cell was ratioed against a reference beam split-off from the main beam before the cell. Signal-to-noise ratios (SNR) were estimated for CO₂ concentration measurements determined from either absorption peak amplitude or absorption peak area. The highest SNR were achieved in the measurements based upon a fitted absorption peak area. Typical short-term δ¹³C precisions of 1.1⁰/₀₀ (1-s integration time) and 0.5⁰/₀₀ (8-12-s integration time) were estimated from the two-sample (Allan) variance plots of data recorded in the optical cell at a pressure of 20 Torr and with no active temperature stabilization of the cell and gas flow. The best precision of 0.12⁰/₀₀ was achieved for averaging 80 successive 1-s integration time measurements.     

Nd:YVO4自受激拉曼激光器调Q锁模特性

利用Nd:YVO4激光晶体的自受激拉曼效应,结合Cr:YAG被动锁模技术和倍频技术,实现了结构紧凑的1176 nm和588 nm黄光锁模激光输出。激光器为LD端面泵浦,三镜折叠腔结构,并且采用了透过率为10%的输出镜。Nd:YVO4晶体长度为10 mm,Nd3+离子掺杂质量分数为0.2%,Cr:YAG晶体的初始透过率为67%。10 W激光泵浦时,1176 nm激光平均输出功率为123 mW,调Q包络宽度为6 ns,调Q包络内的锁模脉冲重复频率高达1 GHz。588.2 nm 黄光的平均输出功率为8 mW。     

Diode laser spectroscopy of CO2 at 790 nm

Absorption lines of ¹²C¹⁶O₂ have been examined by using a tunable diode laser spectrometer in the region around (790 nm). The spectrometer sources are commercially available double heterostructure InGaAlAs tunable diode lasers (TDLs) operating in the “free-running” mode, which allowed the detection of the line positions within . The observed carbon dioxide absorption lines belong to the combination overtone 2ν₂+5ν₃ ro-vibrational band with intensities ranging around .     

Continuous-wave and Q-switched laser operation of Nd:Gd0.18Y0.82VO4 mixed crystal

Efficient continuous-wave (cw), passively Q-switched, and actively Q-switched laser operations are demonstrated with a mixed vanadate crystal of Nd:Gd_0.18Y_0.82VO₄ under diode pumping. In a cw operation, an output power of 8.25 W is obtained at a maximum available incident pump power (P_in) of 15 W, with a slope efficiency of 56%. Using a Cr⁴⁺:YAG crystal of initial transmission of 62% as the saturable absorber for Q-switching, an average output power of 3.05 W is generated at pulse repetition frequency (PRF) of 16.7 kHz when the laser is pumped with the same maximum P_in. The pulse energy, pulse duration, and peak power are 183.3 μJ, 6.0 ns, and 30.6 kW, respectively. When actively Q-switched by an acousto-optic modulator, the laser produces an average output power of 5.5 W at PRF of 30 kHz with 16.2 W of pump power incident upon the laser crystal. The pulse energy, duration, and peak power are measured to be 183 μJ, 10.5 ns, and 17.5 kW, respectively.     

LD-pumped actively Q-switched Nd:GdVO4/KTP red laser

LD-pumped actively Q-switched intracavity frequency-doubled Nd:GdVO₄/KTP red laser has been introduced. A maximum red average output power of 0.78 W at 671 nm was obtained at pulse-repetition frequency (PRF) of 15 kHz and the optical conversion efficiency was 6.5%. At the incident pump power of 12 W, the shortest laser pulse occurred at PRF of 15 kHz. Its full-width at half-maximum and the highest peak power were measured to be 35.8 ns and 3.38 kW. The largest single pulse energy of 56.3 μJ was achieved at PRF of 10 kHz. The influence factors on the Q-switched Nd:GdVO₄/KTP red laser have been discussed.     

Diode laser overtone spectroscopy of CO2 at 780 nm

Overtone absorption lines of ¹²C¹⁶O₂ have been examined by using a tunable diode laser (TDL) spectrometer in the region around . The spectrometer sources are commercially available double heterostructure InGaAlAs TDLs operating in the “free-running” mode, which allowed the detection of the line positions within . The observed carbon dioxide absorption lines belong to the ν₁+5ν₃ ro-vibrational band with rotational quantum number J up to 48. The minimum absorbance detected by the spectrometer (?5×10^-6) permitted to observe the weakest lines having the absorption cross section of the order of .     

Photoacoustic analysis of CO2 content in annual tree rings

We have used laser photoacoustic gas analysis to study the CO₂ content sorbed by the capillary porous system of annual rings in cross-sectional disks of some conifers. The measurement results showed that in most cases, the CO₂ content in gas samples extracted by the vacuum method from annual rings in the disks is higher than the CO₂ content in atmospheric air. In the disks, we observe an annual trend in the CO₂ concentration, correlating in a number of cases with a rise in atmospheric CO₂. The annual trend in the average value of the CO₂ concentration change sign from positive to negative. We hypothesize that the observed pattern for the annual distribution of CO₂ in the disks is connected with a rise in atmospheric CO₂ and a change in the concentration gradient between stem and atmospheric CO₂. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 477–480, May–June, 2009.     

Oxidation of H2/CO2 mixtures and effect of hydrogen initial concentration on the combustion of CH4 and CH4/CO2 mixtures: Experiments and modeling

An experimental investigation of the oxidation of hydrogen diluted by nitrogen in presence of CO₂ was performed in a fused silica jet-stirred reactor (JSR) over the temperature range 800-1050 K, from fuel-lean to fuel-rich conditions and at atmospheric pressure. The mean residence time was kept constant in the experiments: 120 ms at 1 atm and 250 ms at 10 atm. The effect of variable initial concentrations of hydrogen on the combustion of methane and methane/carbon dioxide mixtures diluted by nitrogen was also experimentally studied. Concentration profiles for O₂, H₂, H₂O, CO, CO₂, CH₂O, CH₄, C₂H₆, C₂H₄, and C₂H₂ were measured by sonic probe sampling followed by chemical analyses (FT-IR, gas chromatography). A detailed chemical kinetic modeling of the present experiments and of the literature data (flame speed and ignition delays) was performed using a recently proposed kinetic scheme showing good agreement between the data and this modeling, and providing further validation of the kinetic model (128 species and 924 reversible reactions). Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in absence and in presence of additives (CO₂ and H₂). The kinetic reaction scheme proposed helps understanding the inhibiting effect of CO₂ on the oxidation of hydrogen and methane and should be useful for gas turbine modeling.     

Absorption coefficients of O3 at CO2 laser wavelengths

The O₃ absorption coefficients for the rotational lines P(12)–P(28) of the 9.4 μm emission band of the CO₂ laser are presented. Measurements were made in O₃–air dilute mixtures (20–600 ppm) at 25°C and a total pressure of 1013.25 h Pa using a frequency stabilized cw CO₂ laser and values have been determined with greater precision than in previously reported studies.     

CO2 laser cutting of slate

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate.Following the previous work focused on the drilling and cutting of slate tiles using a Nd : YAG laser, we present in this paper the results of the work carried out to explore the possibilities to cut slate plates by using a CO₂ laser. A 1.5 kW CO₂ laser was used to perform different experiments in which, the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO₂ laser is a feasible tool for a successful cutting of slate.     

Absorption spectra of CO2 and CO2 near 1.05 μm

The absolute line intensities of the Fermi triad 2003i-00001 (i = 1, 2, 3) of ¹²C¹⁶O₂ and ¹³C¹⁶O₂ isotopic species of carbon dioxide were retrieved from Fourier-transform spectra recorded at Doppler limited resolution in the region 9200-9700 cm⁻¹. The accuracy of the line intensity determination is estimated to be better than 15% for most lines. The vibrational transition dipole moments squared and Herman-Wallis coefficients have been determined. The global fittings of the observed line intensities within the framework of the effective operators method have been performed. The fitting results reproduce the data within experimental uncertainty.     

Integral plug-in RF module in a CO2 hybrid-waveguide laser: Its performance and overall evaluation

This work describes the performance of a compact “in-house built” radio–frequency (RF)-excited CO₂ slab waveguide laser which has the innovation of having a plugged-in RF generator–amplifier module directly connected into the positive electrode of the laser head. The design circuit parameters include a matching circuit and a feed-through element as a whole. The overall laser performance takes into account the waveguide dimension (y-axis) as approximately one-tenth of the free space transverse dimension (x-axis). The optical resonator is calculated to be in the regime of the negative branch for unstable confocal resonators, having focal lengths of and with geometrical amplification of 1.108. Optical output coupling mirror was set to 9.7%. The calculated waveguide length is 37.73 cm whilst the total resonator length was adjusted to 42 cm to allow coupling losses less than 1%. The laser operational efficiency was about 12% and the output beam quality of 1.13 which is close to the ideal Gaussian beam. The optical output power was accomplished by playing with different gas compositions to have a final optimized gas proportion of 1:1:2.7:0.3 correspondingly to CO₂, N₂, He and Xe as admixture.     

Neon matrix isolation spectroscopy of CO2 isotopologues

The solid neon matrix isolated spectrum of CO₂ are recorded in the 2–5 μm region. Natural and ¹³C or ¹⁸O enriched CO₂ samples were used and the nν₁ + ν₃ (n = 0, 1, 2) series bands of different CO₂ isotopologues have been observed. The solid neon matrix shift due to Fermi-resonance of bands within the same vibrational polyad is analyzed.     

Kinetic modelling of electrooptically Q-switched CO2 laser

In this paper, a six-temperature model for CO₂ lasers is used to describe the process of the dynamic emission in the electrooptically Q-switched laser. The dissociation of CO₂ molecules, the electron excitation and the energy-transfer of vibrational levels and the rotational relaxation of rotational levels are involved. The calculated pulse waveforms are in good agreement with the experiment.     

Diode-pumped passively Q-switched intracavity frequency doubled Nd:GdVO4/KTP green laser

A compact diode-pumped passively Q-switched intracavity frequency-doubled Nd:GdVO₄/KTP green-pulse laser was demonstrated, using Cr⁴⁺:YAG as a saturable absorber in a simple flat–flat cavity. With a 5.9 W incident pump power, a passively Q-switched green laser was obtained with an average power of 397 mW, repetition rate of 40 kHz, and pulse width of 40 ns, when the initial transmission of Cr⁴⁺:YAG was 85%. The shortest pulse width of 30 ns, the highest green peak power of 696 W and the maximum pulse energy of 21 μJ were obtained when the initial transmission of Cr⁴⁺:YAG was 70%. Under CW green operation, we obtained 440 mW output power.     

A complete study of CO2 line parameters around 4845 cm for Lidar applications

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO₂ line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from 4843 to 4848 cm⁻¹, which is suitable for the measurement of atmospheric carbon dioxide (CO₂) mixing ratios was studied using a new generation-commercial diode laser from Nanoplus. Three lines of the (20°1)_III←(0 0 0) band of CO₂ have been studied. The results of intensity measurements and self-broadening coefficients are compared with previous determinations and available databases. Furthermore, the air-broadening coefficients for these transitions are also reported and analyzed. Finally, these new parameters are used for the measurement of atmospheric CO₂ mixing ratio with the 2 μm heterodyne differential absorption Lidar from the Laboratoire de Météorologie Dynamique at Palaiseau (France). These new parameters demonstrate a dramatic improvement of the retrieved atmospheric CO₂ concentrations.