A Review of Recent Experiments and Calculations Relevant to the Kinetics of the HF Laser

Abstract

An abbreviated review of rate coefficients relevant to HFI laser kinetics modeling is presented. The literature has been surveyed from the last published review in 1983 to the present. Updated HF Einstein emission coefficients are tabulated. This brief summary of a more detailed review addresses rate coefficients relevant to HIF generation, reactive quenching, self-relaxation, and vibrational relaxation by a selection of atoms and molecules. In addition, a review of recent experiments and theoretical calculations relevant to the role of rotational non-equilibrium in HF lasers is presented. A list of recommended temperature dependent expressions for critical reaction rate coefficients is given. INTRODUCTIONSince its invention in the mid-1960's, the HF laser system has been extensively studied and developed to the point where megawatt-class devices can be built. In fact, most of the research in the recent past has focused on large-scale laser technology demonstrations. Despite the enormous effort expended to accomplish this, a complete understanding of all facets of HF laser performance is still evolving and is not complete. For example, research continues into the role of reagent mixing and heat transfer between the fluids and the construction material of the device. Combustor instabilities and other complex, transient, fluid dynamical features also impede our understanding of the laser's performance.The only way to achieve insight into the details of the HF laser is to employ computational fluid dynamical (CFD) codes that can integrate the complex fluid properties with the myriad chemical reactions that occur in the laser cavity. Unfortunately (although perhaps not surprisingly considering the complexity of the problem), CFD codes have had limited success at accurately modeling real HIF laser systems. As a result, both the laser performance data and the reaction rate constants used to baseline the models have come under increased scrutiny in recent years. This scrutiny has uncovered serious questions about the kinetics package that have yet to be answered conclusively. These questions include the importance of rotational nonequilibrium, the magnitude of various quenching processes, the role of three body and heterogeneous fluorine atom recombination, and other fundamental properties such as Einstein coefficients.The main topics of this report (in order of their presentation) are Einstein coefficients and relevant kinetic measurements. It is not within the scope of this document to discuss fluid dynamics issues, such as recently developed 3 dimensional computational fluid dynamics (CFD) codes or new algorithms to model mixing or optical resonators.

Quantum dynamics of vibration–vibration energy transfer for vibrationally excited HF colliding with H2

“…Poole and Smith reported a result of (0.15 ± 10%) × 10 −12 cm 3 s −1 mol −1 , which is in good agreement with our result of 0.13 × 10 −12 cm 3 s −1 mol −1 . The rate constants for (1; 3) → (0; 4) and (1; 3) → (2; 2) are shown in Figure together with the results in the chemical laser kinetic packages, which were reported by Manke and Hager The calculated rate constants for (1; 3) → (0; 4) initially decrease at temperatures between 100 and 250 K with a minimum value of 1.77 × 10 −12 cm 3 s −1 mol −1 at 250 K, and then increase with temperature. The results in the chemical laser kinetic packages, which were fitted from various experimental data, follow the similar trend as ours.…”

“…Based on these experimental data, several chemical kinetic packages containing a series of H 2 –HF energy transfer rate constants were established and applied in the chemical laser numerical simulations. In 2001, Manke and Hager reviewed the available kinetic packages and reported the vibrational‐resolved rate constants for the HF‐involved reactions in analytical forms. However, some of the database in various packages conflicted with each other, especially for those of highly vibrationally excited HF.…”

Breakdown of energy transfer gap laws revealed by full-dimensional quantum scattering between HF molecules

“…2Calculated vibrational-resolved (1; 0) → (0; 0) rate coefficient as a function of temperature. The current calculated results are compared with available experimental (denoted as Expt 1 23 , Expt 2 24 , Expt 3 25 , Expt 4 26 , Expt 5 27 , Expt 6 28 , Expt 7 29 , and Expt fitting 22 ) and other theoretical results (Theo 1 31 and Theo 2 32 ). All error bars represent the experimental error…”

“…As a working medium for chemical lasers 21 , vibrational relaxation rates of hydrogen fluoride (HF) are of great interest to laser engineering, because they directly determine populations of HF ro-vibrational levels in the laser cavity 22 . The rate coefficient for self-relaxation of HF from its first excited vibrational state,has been extensively studied experimentally 23–29 .…”

Hydrogen fluoride overtone laser: 2D CFD modeling of the small signal gain

“…The temperature-dependent rate constants for the chemical reactions used to represent the kinetic system of the HF laser are described in the recent review article by Manke and Hager [2]. The HF kinetics package described by Manke and Hager [2] is an update of earlier reviews, primarily Cohen and Bott [3,4], that incorporates the latest experimental and theoretical results. The notable changes are in the Einstein coefficients, HF self-relaxation, and the nascent distribution for H+F 2 into the excited HF levels.…”