Pulsed Chemical HF Research Articles

An Installation for Fast and Safe Preparation of Working Mixtures in Reactors of Pulsed Chemical HF(DF) Lasers

A system for preparing working mixtures in reactors of pulsed chemical lasers based on the F2 + H2(D2) reactions is described. The design of a compact capillary mixer has been developed; its throughput of up to 2 (L atm)/s has been experimentally attained. A method for supplying gases using flow-control washers with holes operating in the critical mode is proposed. It provides a constant flow rate of mixed gases during the whole run-in. The described technology for preparing the working mixture of a pulsed chemical HF(DF) laser is theoretically analyzed and experimentally tested.

Pulsed chemical HF laser with a large discharge gap

The characteristics of the radiation emitted by an electric-discharge pulsed chemical HF laser with a discharge gap of 10 cm are studied. The discharge was stabilised by a semiconducting ferroelectric ceramic layer deposited on plane metal electrodes. The specific energy and technical efficiency were 3 J L-1 and 3.4%, respectively, for a laser operating on a nonchain reaction in SF6—H2 mixture and 25 J L-1 and 26%, respectively, for a laser operating on a chain reaction in F2—O2—SF6—H2 mixture.

Influence of the cavity losses on the energy and spectral characteristics of a pulsed chemical chain-reaction HF (DF) laser

The dependences of the energy and spectral characteristics of the radiation of a pulsed photoinitiated chemical chain-reaction HF (DF) laser, operating at atmospheric pressure, on the optical cavity parameters were investigated. The maximum specific output energies of the HF and DF chain lasers (53 and 43 J litre-1) and their fullest spectra (47 and 83 lines, respectively) were similar when the unsaturated gain exceeded the threshold by a factor greater than 50. An analysis was made of how the energy and spectrum of the radiation of the HF (DF) laser were influenced by the spatiotemporal inhomogeneity of the initiation and of the course of the chemical chain reaction. There was a marked effect of the CO2 molecules in the active medium and in the air filling part of the volume of the complex cavity of the DF laser on its efficiency and emission spectrum.

Laser amplifier based on a photon-branched chain reaction in an aerosol-evaporation reactor cavity

A new design is proposed and the characteristics are calculated of a pulsed chemical HF laser with a two-phase active medium and a photon-branched chain initiation mechanism. This laser includes an aerosol-evaporation reactor coupled structurally to an unstable telescopic cavity. Such a closed system reduces considerably (down to 0.217 ms) the time needed for the formation of a two-phase active medium with the required properties. When the working volume of the laser is ~7 litres, the following high output characteristics can be achieved: the maximum power per pulse ~2×1010 W, the pulse duration ~740 ns, the total output energy ~1.5 kJ, the specific output energy ~200 J litre-1 , and the energy gain 105 .

Lifetime of a two-phase active medium of a pulsed chemical HF laser

An analysis of the response of an aerosol and of the laser-chemical kinetics of a photon-branched chain reaction is used to determine the range of the maximum permissible parameters of the disperse component capable of supporting the operation of a pulsed chemical HF laser with a two-phase active medium (particle radius 0.09 — 0.4 μm, particle concentration 109 — 107 cm-3 ). It is shown that, in this range of parameters, the lifetime of the active medium of an HF laser with disperse Al particles is governed by coagulation, precipitation, and electrostatic scattering of particles, and that it amounts to 250 s. The main contribution to the degradation of the disperse component of the active medium comes from Brownian coagulation.

High-power laser amplifier based on an auto-wave photon-branched chain reaction in an unstable telescopic cavity

A specific design of a high-power pulsed chemical HF amplifier is proposed. This amplifier is based on a photon-branched chain reaction initiated by a nonresonant interaction of external IR laser radiation with an aluminium aerosol. A wave approximation is used to optimise the following: the geometry of a cavity with a coupling aperture in the input mirror, the duration and energy of the input signal, the mixture composition, and the parameters of the disperse component. It is shown that self-sustained cylindrical zones of photon branching of the chain reaction are excited in the active medium of such a pulsed chemical HF amplifier. It is shown that a significantly higher gain can be reached in this regime.

Degradation of the disperse component of the active medium of a pulsed chemical HF laser

The Brownian coagulation model and the Stokes particle precipitation law were used to analyse the dynamics of changes in the characteristics of a condensed disperse component of the chemically active medium of a pulsed HF laser. It was found that, if coagulation predominates over precipitation, the required average particle size (r0 ∼ 0.1 — 0.5 μm) and concentration (N ∼ 5 × 108 — 107 cm-3) of an aluminium aerosol in an H2 — F2 — O2 — He chemically active medium can be reached in ∼ 1000 s. The precipitation of particles begins to compete with the coagulation only for r0 ≥ 1μm.

Feasibility and conditions for the attainment of high output energy characteristics from a pulsed chemical HF laser utilizing an SF6–HI mixture

An investigation was made of the feasibility and conditions for the attainment of high output energy characteristics from an electron-beam-initiated SF6–HI laser. A specific output energy of 8 J/liter was achieved. The maximum output energy per pulse from an SF6–HI laser was found to be higher than that from an SF6–H2 laser. The presence of an external static magnetic field, inhibiting scattering of the initiating electrons, did not increase the maximum laser pulse energy.

Pulsed chemical HF laser using graphite continuous electrodes for transverse discharge stabilization

We report results obtained in the operation of a chemical HF laser using a mixture of SF6 and technical grade C3H8 reacting in a transverse high-voltage discharge in which a pair of inexpensive continuous electrodes of polycrystalline graphite are used as the only means for stabilizing the discharge and avoiding the formation of arcs during excitation of the laser medium. Energies of up to 60 mJ per pulse in stable operation are obtained from a 0.1-ℓ volume.

Phase conjugation of an optical wave in the case of a degenerate four-wave interaction in an amplifying medium of a chemical HF laser

The approximation of a constant intensity of reference waves is used in the case of low values of the reflection coefficients (less than unity) to investigate numerically the efficiency of optical phase conjugation of a wave from a pulsed chemical HF laser based on a chain reaction. It is shown that the reflection coefficient for the three strongest emission bands P1–0, P2–1, and P3–2 of a pulsed chemical HF laser can be 0.1.

Absorption cross sections for HF laser lines due to traces of CO2, N2O, and CH4 in air

The emission from an HF (DF) laser is spread over a larger number of vibrationalrotational lines in the range 2.7-4.2 ~m, which contains absorption bands of virtually all substances of interesting quantitative gas analysis, and in particular in detecting atmospheric pollutants, determining discharges from industrial plants, locating deposits of certain minerals, forecasting volcanic activity, and so on [i]. Pulsed chemical HF (DF) lasers can be based on the chain reaction of fluorine with hydrogen (deuterium), which is promising for these purposes because the number of lines is large by comparison with any other type of laser (about i00 lines). These lasers also have high efficiency in converting the pumping energy to radiation and high beam power with relatively small dimensions. Also, the same laser cell can be used to obtain the emission from CO= in the range 9.6-10.6 ~m by energy transfer from DF to CO 2.

Chemical HF laser initiated by evaporation of fine particles under the action of infrared radiation

It is shown that, in principle, it is possible to initiate a pulsed chemical HF laser by the evaporation of fine metal particles with the aid of infrared radiation. It follows from the reported calculations that the laser radiation energy may be 3–5 times greater than the initiation energy, which opens up the way for constructing purely chemical pulsed HF laser amplifiers.

State-selected molecular-beam reaction dynamics of K with HF (υ = 1, j = 5, 6 and 7)

The crossed-molecular-beam method has been used to measure relative integral cross sections σ r (υ = 1, j; E) of the endothermic (0.75 eV) reaction K + HF (υ = 1, j) → KF + H as a function of both the rotational quantum number j ( j = 5, 6 and 7) and the translational energy E (0.55 ⩽ E ⩽ 1.32 eV) of the reagents. The vibrational-rotational (υ, j) states of HF were populated by infrared pumping with the radiation of a properly tuned pulsed chemical HF laser. In addition, relative cross sections with υ = 0 but averaged with respect to the initial rotational-state distribution of the HF molecules were also determined. The results exhibit three remarkable features: (a) σ r (υ = 1, j; E) rises with increasing j, (b) the steepness of the ascent roughly decreases with increasing E, (c) at E = 0.98 eV reagent vibrational energy is about a factor of 200 more efficient in promoting the reaction than reagent translational energy. An intuitive dynamical model suggests that observations (a) and (b) are to be expected for a reaction governed by a potential-energy surface with a late barrier. This is consistent with the well-known interpretation of large vibrational effects as indicated by result (c).

Pulsed chemical HF laser utilizing a mixture of technical-grade C3H8and SF6and initiated by an electric discharge

An electrochemical HF laser was constructed utilizing a mixture of technical-grade propane and butane with SF6. A resistive anode was made of a Ge single crystal (ρ = 25 Ω·cm) and the mixture was subjected to ultraviolet preionization. The output radiation was highly stable. In the nonselective lasing regime a discharge volume of 86 cm3 yielded laser pulses of 220 mJ energy with a peak power of 3 MW. The energy corresponding to the individual P1(4–9), P2(3–8), and P3(3–8), transitions was in the range 15–43 mJ and the peak powers for these lines were 0.2–0.5 MW.

Spectroscopic diagnostics of laser-supported absorption (LSA) waves produced by a HF laser

LSA waves have been generated by a pulsed chemical HF laser beam (2.8 μ, 45 J, 7 μsec) when focused on solid surfaces in air. The emission spectrum is found to contain mainly N+ and O+ lines broadened by the Stark effect and superimposed on a strong continuum. The LSA wavefront travels at an average speed of 0.72 cm/μsec as measured by the time-of-flight method. Target species such as atomic Al emit light for 600 μsec after the laser pulse. In contrast with the results from a CO2 laser, however, no forbidden transition of AlI is observed.