Parameters of Pulsed Chemical Lasers

Three steps may be distinguished in the operation of a pulsed chemical laser  

2) the formation (and subsequent partial decay) of the inversion in the reaction 

Other sources of energy input that have been used are dissociation by shock waves and by high-energy electron beams. A further possibility which has been discussed but not realized so far is to supply the energy by means of another laser, preferably in the infrared 64 . 

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Contents Population Inversion and Molecular Amplification. Energy-partitioning in Elementary Chemical Reactions Vibrational Relaxation. Requirements for Laser Oscillation. Design Parameters of Pulsed Chemical Lasers. Specific Chemical Laser Systems. Future Chemical Lasers. Present Perspectives of High-Power Chemical Lasers. Kinetic Information through Chemical Laser Studies. 

In some cases the measured V-V transfer rates differ from theoretical predictions, which indicates that some improvement is needed in theoretical models. Sophisticated computer analysis has to be employed to transform the experimental data to theoretical parameters The spectroscopic studies of cw and pulsed chemical lasers including the local variation of laser output on different vibration-rotation transitions as a function of distance froih the injectory array has been a useful tool, too, for elucidating the different reaction paths and the excited molecular levels involved... 

An intuitive method for controlling the motion of a wave packet is to use a pair of pump-probe laser pulses, as shown in Fig. 13. This method is called the pump-dump control scenario, in which the probe is a controlling pulse that is used to create a desired product of a chemical reaction. The controlling pulse is applied to the system just at the time when the wave packet on the excited state potential energy surface has propagated to the position of the desired reaction product on the ground state surface. In this scenario the control parameter is the delay time r. This type of control scheme is sometimes referred to as the Tannor-Rice model. 

The influence of the laser and plasma parameters (such as wavelength, laser power density, pulse length, plasma temperature, electron and ion density and others) on the physical and chemical processes in a laser induced plasma with respect to the formation of polyatomic and cluster ions has been investigated for different materials (e.g. graphite, boron nitride, boron nitride/graphite mixture, boron carbide, tungsten oxide/graphite mixture and superconductors ). 

To conclude, we have synthesized VO2 with a perfect crystal stmcture in opal pores using the chemical bath deposition technique. The parameters of the semiconductor-metal phase transition in the prepared material indicate the presence of a small amount of oxygen defects. We have achieved a controllable and reproducible variation of the PEG properties of the opal-V02 composite and inverted VO2 composite during heating and cooling. This is due to the change in the dielectric constant of VO2 at the phase transition. We demonstrated dynamical tuning of the PEG position in synthetic opals filled with VO2 imder laser pulses. 

Laser surface treatment can be used either below or beyond the ablation threshold of the surface. Laser treatment is more often used below the ablation threshold of the material, thus inducing efficient modification of the surface composition [12, 18]. Various laser parameters, such as the wavelength, the fluence (laser intensity), the nature of the environmental gas, or the pulse number, may be changed in order to modify the characteristics of the treated surface as the treatment induces the formation of polar chemical species (hydroxyls, carboxyls, peroxides, etc.). Therefore, the use of laser treatment below the ablation threshold induces adhesion improvement mainly through thermodynamic and chemical parameters. 

The morphology of an ablated microfluidic channel is determined by a number of parameters. These include the laser irradiance, spot size, speed of the x-y stage, repetition rate of the laser, properties and characteristics of the substrate being ablated, and the chemical environment under which the ablation occurs. It is also dependent on the temporal and spatial profile and wavelength of the laser pulse. Waddell et al. determined that as the fluence is increased... 

In this sense, the control of electronic transitions of wavepackets using short quadratically chirped laser pulses of moderate intensity is a very promising method, for two reasons. First, only information about the local properties of the potential energy surface and the dipole moment is required to calculate the laser pulse parameters. Second, this method has been demonstrated to be quite stable against variations in pulse parameters and wavepacket broadening. However, controlling of some types of excitation processes, such as bond-selective photodissociation and chemical reaction, requires the control of wavepacket motion on adiabatic potential surfaces before and/or after the localized wavepacket is made to jump between the two adiabatic potential energy surfaces. 

Optimization of internal engine combustion in respect of fuel efficiency and pollutant minimization requires detailed insight in the microscopic processes in which complex chemical kinetics is coupled with transport phenomena. Due to the development of various pulsed high power laser sources, experimental possibilities have expanded quite dramatically in recent years. Laser spectroscopic techniques allow nonintrusive measurements with high temporal, spectral and spatial resolution. New in situ detection techniques with high sensitivity allow the measurement of multidimensional temperature and species distributions required for the validation of reactive flow modeling calculations. The validated models are then used to And optimal conditions for the various combustion parameters in order to reduce pollutant formation and fuel consumption. 

Also, the method how the ablation parameters are acquired can have a pronounced influence on the results. The ablation rate can be defined either as the depth of the ablation crater after one pulse at a given fluence, or as the slope of a linear fit of a plot of the ablation depth versus the pulse number for a given fluence. Very different ablation rates can result from the two different measurement methods. This is especially the case for materials where ablation does not start with the first pulse, but after multiple pulses, or if the ablation crater depth after one pulse is too small to be measured. The process that occurs if ablation does not start with the first laser pulse is called incubation. It is related to physical or chemical modifications of the material by the first few laser pulses, which often results in an increase of the absorption at the irradiation wavelength [32,33], for example, the formation of double bonds in poly (methylmethacrylate) (PMMA). Incubation is normally observed only for polymers with low absorption coefficients at the irradiation wavelength. 

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