Absorption of 9.6-micron CO2 laser radiation by CO2 at elevated temperatures

Absorption of 9.6-micron CO2 laser radiation by CO2 at temperatures between 296 and 625 K has been measured at a pressure of 200 Torr. Experimental results for the R1O-R26 and P1O-P28 transitions have been obtained and compared with computed values of absorption. The relative optical broadening coefficients due to He and N2 have been measured on the R16-R22 and P16-P22 transitions over the same temperature range.     

Effect of CO2 laser irradiation on the refractive-index change in optical fibers

The effect of CO2 laser irradiation on the refractive-index change in optical fibers is investigated by measuring the interference fringe shift formed by a long-period fiber grating pair. The refractive-index decrease on CO2 laser irradiation was due to relaxation of the residual stress, which was formed in optical fibers during the drawing process, and the refractive-index decrease was found to increase linearly with the drawing force. The effect of the CO2 laser output power on residual-stress relaxation, and fiber elongation was also studied.     

Linear excitation schemes for IR planar-induced fluorescence imaging of CO and CO2

A detailed discussion of linear excitation schemes for IR planar-induced fluorescence (PLIF) imaging of CO and CO2 is presented. These excitation schemes are designed to avoid laser scattering, absorption interferences, and background luminosity while an easily interpreted PLIF signal is generated. The output of a tunable optical parametric amplifier excites combination or overtone transitions in these species, and InSb IR cameras collect fluorescence from fundamental transitions. An analysis of the dynamics of pulsed laser excitation demonstrates that rotational energy transfer is prominent; hence the excitation remains in the linear regime, and standard PLIF postprocessing techniques may be used to correct for laser sheet inhomogeneities. Analysis of the vibrational energy-transfer processes for CO show that microsecond-scale integration times effectively freeze the vibrational populations, and the fluorescence quantum yield following nanosecond-pulse excitation can be made nearly independent of the collisional environment. Sensitivity calculations show that the single-shot imaging of nascent CO in flames is possible. Signal interpretation for CO2 is more complicated, owing to strongly temperature-dependent absorption cross sections and strongly collider-dependent fluorescence quantum yield. These complications limit linear CO2 IR PLIF imaging schemes to qualitative visualization but indicate that increased signal level and improved quantitative accuracy can be achieved through consideration of laser-saturated excitation schemes.     

超临界CO2清洗技术的应用研究进展

超临界CO2清洗在技术、经济和环保领域的独特优势,使其具有广阔的应用前景。文章主要介绍了超临界CO2清洗技术在电子元器件、核工业、精密机械、医疗器械、纺织领域、光学工业和国防工业的应用进展。     

High-energy-density extended CO solid

Covalently bonded extended phases of molecular solids made of first- and second-row elements at high pressures are a new class of materials with advanced optical, mechanical and energetic properties. The existence of such extended solids has recently been demonstrated using diamond anvil cells in several systems, including nitrogen, carbon dioxide and carbon monoxide. However, the microscopic quantities produced at the formidable high-pressure/temperature conditions have limited the characterization of their predicted novel properties, including high-energy content. In this paper, we present experimental evidence that these extended low-Z solids are indeed high-energy-density materials, by milligram-scale high-pressure synthesis, recovery and characterization of polymeric CO (p-CO). Our spectroscopic data reveal that p-CO is a random polymer made of lactonic entities and conjugated C=C with an energy content rivalling or exceeding that of HMX (cyclo-tetramethylene tetranitramine, a commonly used conventional high explosive). Solid p-CO explosively decomposes to CO(2) and glassy carbon, and thus might be used as an advanced energetic material.     

Prototype CO2 laser-induced long-period fiber grating variable optical attenuators and optical tunable filters

Prototype devices capable of variable attenuation at a fixed wavelength, wavelength tuning at a constant attenuation, and combinations of these spectral characteristics are demonstrated in CO2 laser-induced long-period fiber gratings (LPFGs). These devices are based on controlled flexure by means of a piezoceramic platform. CO2 laser-induced LPFG characteristics along with the fabrication and testing processes of these gratings are discussed. Devices with a optical attenuation of 13 dB and a wavelength tuning of 7 nm are reported.     

Optical Kerr switching technique for the production of a picosecond,multiwavelength CO2 laser pulse

A wavelength-independent method for optical gating, based on the optical Kerr effect, has been demonstrated. Using this method, we produced 100-ps, 10-kW, two-wavelength pulses (10.3 and 10.6 microm) with a signal-to-background ratio contrast of 10(5) by slicing a long CO2 pulse. The capability of gating consecutive pulses separated on a picosecond time scale with this method is also shown.     

Localized CO2 laser annealing induced dehydrogenation/ablation and optical refinement of silicon-rich silicon dioxide film with embedded si nanocrystals

CO2 laser annealing induced effects of dehydrogenation, Si nanocrystal precipitation, ablation, and optical refinement in PECVD grown SiO1.25 film are investigated. Dehydrogenation shrinks SiO1.25 thickness by 40 nm after annealing at laser intensity (Plaser) of 4 kW/cm(2) for 1.4 ms. As Plaser increases to 6 kW/cm(2), the photoluminescence (PL) red-shifts to 806 nm due to the size enlargement of Si nanocrystals, while a reduced optical bandgap energy from 3.3 to 2.43 eV and an enlarged refractive index from 1.57 to 1.87 are also observed. Transmission electron microscopy analysis reveals that the randomly oriented Si nanocrystals exhibit an average diameter of 5.3 nm and a volume density of 1.9 x 10(18) cm(-3). CO2 Laser ablation initiates at intensity higher than 7 kW/cm(2), which introduces numerous structural defects with a strong PL at 410 nm. Such an ablation inevitably leads to a blue-shifted optical bandgap energy from 2.43 to 2.76 eV as Plaser enlarges from 6 to 12 kW/cm(2) are concluded.     

Measurement of CO2-laser-irradiation-induced refractive index modulation in single-mode fiber toward long-period fiber grating design and fabrication

We report a new method to measure the CO(2)-laser-irradiation-induced refractive index modulation in the core of a single-mode optical fiber for the purpose of design and fabrication of long-period fiber gratings (LPFGs) without applying tension. Using an optical fiber Fabry-Perot interferometer, the laser-induced axial refractive index perturbation was measured. We found that the CO(2)-laser-irradiation-induced refractive index change in the fiber core had a negative value and that the magnitude was a sensitive function of the laser exposure time following almost a linear relation. Under the assumption of a Gaussian-shaped refractive index modulation profile and based on the first two terms of Fourier series approximation, the measured refractive index perturbations were used to simulate the LPFG transmission spectra. LPFGs with the same laser exposure parameters were fabricated without applying tension, and their spectra were compared with those obtained by simulations.     

Optical Transmission Measurements on Phase Transitions of O2 and CO in Mesoporous Glass

The optical transmission of O₂ and CO condensates embedded in porous Vycor glass has been studied as function of the filling fraction and of the thermal history of the samples. The freezing transition as well as the solid-solid transitions (β-α of CO and γ-β of O₂) induce a coarsening of the separation into empty and filled regions which results from the hysteretic behavior of the transitions in the presence of a pore size distribution. In the birefringent β phase of O₂ domains with a fixed crystallographic orientation extend over distances much larger than the pore diameter (10 nm).     

In situ combustion measurements of CO, H2O, and temperature with a 1.58-microm diode laser and two-tone frequency modulation

An optical near-infrared process sensor for electric arc furnace pollution control and energy efficiency is proposed. A near-IR tunable diode laser has performed simultaneous in situ measurements of CO (1577.96 nm), H(2)O (1577.8 and 1578.1 nm), and temperature in the exhaust gas region above a laboratory burner fueled with methane and propane. The applicable range of conditions tested is representative of those found in a commercial electric arc furnace and includes temperatures from 1250 to 1750 K, CO concentrations from 0 to 10%, and H(2)O concentrations from 3 to 27%. Two-tone frequency modulation was used to increase the detection sensitivity. An analysis of the method's accuracy has been conducted with 209 calibration and 105 unique test burner setpoints. Based on the standard deviation of differences between optical predictions and independently measured values, the minimum accuracy of the technique has been estimated as 36 K for temperature, 0.5% for CO, and 3% for H(2)O for all 105 test data points. This accuracy is sufficient for electric arc furnace control. The sensor's ability to nonintrusively measure CO and temperature in real time will allow for improved process control in this application.     

Two-micrometer heterodyne differential absorption lidar measurements of the atmospheric CO2 mixing ratio in the boundary layer

A 2 microm heterodyne differential absorption lidar (HDIAL) has been operated at the Inst?tut Pierre Simon Laplace, Laboratoire de Météorologie Dynamique (Paris) to monitor the CO(2) mixing ratio in absolute value at high accuracy in the atmospheric boundary layer. Horizontal measurements at increasing range are made to retrieve the optical depth. The experimental setup takes advantage of a heterodyne lidar developed for wind velocity measurements. A control unit based on a photoacoustic cell filled with CO(2) is tested to correct afterward for ON-line frequency drift. The HDIAL results are validated using in situ routine measurements. The Doppler capability is used to follow the change in wind direction in the Paris suburbs.     

Optical performance of a burst-mode multikilowatt CO(2) laser

A unique advancement in the flexibility of high-power lasers is presented. Operation of a 20-kW, continuous-wave, CO(2) laser with a burst excitation technique produces a broad range of optical output characteristics. A detailed discussion of the discharge excitation of this system demonstrates some unique features of the process. Control of burst frequency and duty cycle provides a convenient means to alter the time-varying nature of the output beam. Laser output can be varied from distinct, independent pulses through to a continuous wave. Optical pulse shape varies from triangular to square in profile. The primary focus of this study lies in the regime with distinct, separate pulses. Empirical relationships that summarize the dependence of optical duty cycle and peak laser power on discharge control parameters are developed. Use of these relations imparts control of the optical parameters of importance in deep penetration welding.     

Observation of CO and CO(2) absorption near 1.57 microm with an external-cavity diode laser

Near-IR and visible room-temperature diode lasers in broadly tunable external-cavity configurations are becoming commercially available for gas-sensing applications. Near 1.57 mum, a coincidence of overtone and combination-band transitions from CO, CO(2), OH, and H(2)O is particularly interesting for combustion and combustor emissions monitoring. We report initial observations of the room-temperature absorption of CO and CO(2) made with a commercial external-cavity diode laser.     

Characteristics of a submicrosecond transverse discharge in mixtures of helium with N2 and CO molecules and xenon atoms

An investigation is made of the electrical and optical characteristics of a moderate-pressure transverse discharge in typical active media of infrared CO lasers. The discharge was ignited in a system of unprofiled “ grid-plane” electrodes with automatic ultraviolet preionization by a corona discharge and had a 2×3 cm aperture. The pulse repetition frequency was 1–10 Hz, the current pulse length was ≤0.5 μs, and the pressure of the working mixtures was 10–100 kPa. Studies were made of the transverse discharge current voltage pulses, and also the spectral and temporal characteristics of the plasma radiation in N₂:CO, He:N₂:CO, and He: N₂:CO:Xe mixtures in the ultraviolet and visible ranges. Pis’ma Zh. Tekh. Fiz. 23, 71–76 (October 12, 1997)     

Side-line tunable laser transmitter for differential absorption lidar measurements of CO2: design and application to atmospheric measurements

A 2 microm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely tune and lock the wavelength at a desired offset up to 2.9 GHz from the center of a CO(2) absorption line. Once detuned from the line center the laser wavelength is actively locked to keep the wavelength within 1.9 MHz standard deviation about the setpoint. This wavelength control allows optimization of the optical depth for a differential absorption lidar (DIAL) measuring atmospheric CO(2) concentrations. The laser transmitter has been coupled with a coherent heterodyne receiver for measurements of CO(2) concentration using aerosol backscatter; wind and aerosols are also measured with the same lidar and provide useful additional information on atmospheric structure. Range-resolved CO(2) measurements were made with <2.4% standard deviation using 500 m range bins and 6.7 min? (1000 pulse pairs) integration time. Measurement of a horizontal column showed a precision of the CO(2) concentration to <0.7% standard deviation using a 30 min? (4500 pulse pairs) integration time, and comparison with a collocated in situ sensor showed the DIAL to measure the same trend of a diurnal variation and to detect shorter time scale CO(2) perturbations. For vertical column measurements the lidar was setup at the WLEF tall tower site in Wisconsin to provide meteorological profiles and to compare the DIAL measurements with the in situ sensors distributed on the tower up to 396 m height. Assuming the DIAL column measurement extending from 153 m altitude to 1353 m altitude should agree with the tower in situ sensor at 396 m altitude, there was a 7.9 ppm rms difference between the DIAL and the in situ sensor using a 30 min? rolling average on the DIAL measurement.     

Interactions between reducing CO2 emissions, CO2 removal and solar radiation management

We use a simple carbon cycle-climate model to investigate the interactions between a selection of idealized scenarios of mitigated carbon dioxide emissions, carbon dioxide removal (CDR) and solar radiation management (SRM). Two CO(2) emissions trajectories differ by a 15-year delay in the start of mitigation activity. SRM is modelled as a reduction in incoming solar radiation that fully compensates the radiative forcing due to changes in atmospheric CO(2) concentration. Two CDR scenarios remove 300 PgC by afforestation (added to vegetation and soil) or 1000 PgC by bioenergy with carbon capture and storage (removed from system). Our results show that delaying the start of mitigation activity could be very costly in terms of the CDR activity needed later to limit atmospheric CO(2) concentration (and corresponding global warming) to a given level. Avoiding a 15-year delay in the start of mitigation activity is more effective at reducing atmospheric CO(2) concentrations than all but the maximum type of CDR interventions. The effects of applying SRM and CDR together are additive, and this shows most clearly for atmospheric CO(2) concentration. SRM causes a significant reduction in atmospheric CO(2) concentration due to increased carbon storage by the terrestrial biosphere, especially soils. However, SRM has to be maintained for many centuries to avoid rapid increases in temperature and corresponding increases in atmospheric CO(2) concentration due to loss of carbon from the land.     

Gliding arc plasma processing of CO2 conversion

Conversion of carbon dioxide (CO2) using gliding arc plasma was performed. The research was done to investigate the effect of variation of total gas flow rates and addition of auxiliary gases--N2, O2, air, water--to the CO2 conversion process. This system shows higher power efficiency than other nonthermal plasma methods. Experiment results indicate the conversion of CO2 reaches 18% at total gas flow rate of 0.8 L/min and produces CO and O2 as the main gaseous products. Among auxiliary gases, only N2 gives positive effect on CO2 conversion and the power efficiency at N2 concentration of 95% and total gas flow rate of 2 L/min increases about three times compared to pure CO2 process.     

基于激光干涉法的CO2气体压力测量

气体压力无接触式测量,是激光技术应用的重要研究方向。为解决气体压力测量过程中的溯源问题,设计了一种基于激光干涉技术的压力测量方法,通过洛伦兹-洛伦茨方程、气体状态方程和光程差方程的理论研究,建立了基于光程差的压力测量模型,将压力测量问题追溯到光程变化量上。并以CO2为研究对象,搭建压力测量实验系统,开展了293K,313K,333K温度条件下,压力范围为1~3atm的压力测量实验。实验结果显示：压力测量值与实际值有较高的吻合度,相对误差在5%以内,证明压力测量溯源模型的正确性。     

二氧化碳制冷技术

CO2作为一种天然工质，是目前CFCs工质替代的一个重点研究方向。根据CO2作为制冷剂的相关热物理和化学性质及CO2制冷循环，说明采用CO2作制冷剂、采用跨临界循环的优越性。介绍CO2制冷循环系统关键设备——压缩机、膨胀机、气体冷却器／蒸发器的研究进展情况，并对采用CO2作制冷剂的汽车空调、热泵系统的应用进行综述，指出今后研究的发展方向。