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Variation in cathode width and the interelectrode gap affects the laser pulse energy of a pulsed, electric-discharge-initiated, SF6 + H2 pumped, HF chemical laser. The laser energy for different active volume geometries is a function of electric discharge parameters and SF6/H2 stochiometry. The active volume aspect ratio has a tremendous effect on the laser performance. The results of a study conducted for different electrode geometries are given.

The recently suggested mechanism of I2 dissociation in the chemical oxygen-iodine laser (COIL) [K. Waichman, B. D. Barmashenko, and S. Rosenwaks, J. Appl. Phys. 106, 063108 (2009); and J. Chem. Phys. 133, 084301 (2010)] was largely based on the suggestion of V. N. Azyazov, S. Yu. Pichugin, and M. C. Heaven [J. Chem. Phys. 130, 104306 (2009)] that the vibrational population of O2(a) produced in the chemical generator is high enough to play an essential role in the dissociation. The results of model calculations based on this mechanism agreed very well with measurements of the small signal gain g, I2 dissociation fraction F, and temperature T in the COIL. This mechanism is here revisited, following the recent experiments of M. V. Zagidullin [Quantum Electron. 40, 794 (2010)] where the observed low population of O2(b, v = 1) led to the conclusion that the vibrational population of O2(a) at the outlet of the generator is close to thermal equilibrium value. This value corresponds to a very small probability, ∼0.05, of O2(a) energy pooling to the states O2(X,a,b, v > 0). We show that the dissociation mechanism can reproduce the experimentally observed values of g, F, and T in the COIL only if most of the energy released in the processes of O2(a) energy pooling and O2(b) quenching by H2O ends up as vibrational energy of the products, O2(X,a,b), where the vibrational states v = 2 and 3 are significantly populated. We discuss possible reasons for the differences in the suggested vibrational population and explain how these differences can be reconciled. [ABSTRACT FROM AUTHOR]

A parametric study of the output power of supersonic chemical oxygen-iodine lasers (COILs) is carried out, applying a kinetic-fluid dynamics model calculations as well as an analytical model and comparing the results to experimental studies. The I2 dissociation mechanism recently suggested by Azyazov et al. [J. Chem. Phys. 130, 104306 (2009)], which was previously used for comparison of model calculations to measurements of the small signal gain [K. Waichman et al., J. Appl. Phys. 106, 063108 (2009)], is applied here for a similar, but more sensitive, comparison of the laser output power. The dependence of the power on iodine flow rate and on mirror transmission is studied for low and high pressure COILs, respectively. Good agreement between the calculated and measured power is obtained for both low and high pressure COILs only when the processes suggested by Azyazov et al. are included in the calculations. This is different from the situation for the gain where for high pressure COILs, the calculated values were insensitive to the assumed dissociation mechanism, although for low pressure the measurements were reproduced only by applying the Azyazov et al. mechanism. We believe that the results of the present work strongly support the application of this mechanism for modeling the COIL operation. [ABSTRACT FROM AUTHOR]

The mechanism of I2 dissociation in supersonic chemical oxygen-iodine lasers (COILs) is studied applying kinetic-fluid dynamics modeling, where pathways involving the excited species I2(X 1Σg+,10≤v<25), I2(X 1Σg+,25≤v≤47), I2(A′ 3Π2u), I2(A 3Π1u), O2(X 3Σg-,v), O2(a 1Δg,v), O2(b 1Σg+,v), and I(2P1/2) as intermediate reactants are included. The gist of the model is adding the first reactant and reducing the contribution of the second as compared to previous models. These changes, recently suggested by Azyazov, et al. [J. Chem. Phys. 130, 104306 (2009)], significantly improve the agreement with the measurements of the gain in a low pressure supersonic COIL for all I2 flow rates that have been tested in the experiments. In particular, the lack of agreement for high I2 flow rates, which was encountered in previous models, has been eliminated in the present model. It is suggested that future modeling of the COIL operation should take into account the proposed contribution of the above mentioned reactants. [ABSTRACT FROM AUTHOR]

The results of three-dimensional computational fluid dynamics model calculations are compared to available experimental results [V. D. Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002)]. It is shown that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain, temperature, static pressure, and gas velocity. A previous model, which included I2(A′3Π2u), I2(A3Π1u), and O2(a1Δg,v) as significant intermediates in the dissociation of I2 [K. Waichman et al., J. Appl. Phys. 102, 013108 (2007)], reproduced the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by adding the effects of turbulence, which play an important role in high pressure COILs. [ABSTRACT FROM AUTHOR]

The dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) was studied via detailed measurements and three-dimensional computational fluid dynamics calculations. The measurements, briefly reported in a recent paper [Rybalkin et al., Appl. Phys. Lett. 89, 021115 (2006)] and reanalyzed in detail here, revealed that the number N of consumed O2(a 1Δg) molecules per dissociated I2 molecule depends on the experimental conditions: it is 4.5±0.4 for typical conditions and I2 densities applied for optimal operation of the COIL but increases at lower I2 densities. Comparing the measurements and the calculations enabled critical examination of previously proposed dissociation mechanisms and suggestion of a mechanism consistent with the experimental and theoretical results obtained in a supersonic COIL for the gain, temperature, I2 dissociation fraction, and N at the optical axis. The suggested mechanism combines the recent scheme of Azyazov and Heaven [AIAA J. 44, 1593 (2006)], where I2(A′ 3Π2u), I2(A 3Π1u), and O2(a 1Δg,v) are significant dissociation intermediates, with the “standard” chain branching mechanism of Heidner III et al. [J. Phys. Chem. 87, 2348 (1983)], involving I(2P1/2) and I2(X 1Σg+,v). [ABSTRACT FROM AUTHOR]

The mechanism of [I.sub.2] dissociation in supersonic chemical oxygen-iodine lasers (COILs) is analyzed by using kinetic-fluid dynamics modeling. The addition of first reactant and reducing the contribution of the second has improved the gain in a low pressure supersonic COIL for all [I.sub.2] flow rates and the lack of agreement for high [I.sub.2] flow rates is eliminated in the present model.

Three-dimensional computational fluid dynamics calculations are used for studying the dissociation of [I.sub.2] molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL). The values of small signal gain, the temperature and the dissociation fraction of [I.sub.2] molecules have suggested a mechanism of iodine dissociation.

Presents a numerical model for calculating the performance of a premixed pulsed supersonic hydrogen fluoride chemical laser. Integration of the laser kinetic equations and supersonic gas dynamics; Conditions for maximum gain and maximum laser energy for each of the input parameters; Information on the lasing zone length in the flow direction.

Presents an experimental study of a supersonic pulsed hydrogen[sub2] + fluorine[sub2] pumped hydrogen fluoride laser. Analysis of the spectral content of a laser pulse; Measurement of induction times between initiation and onset lasing on different laser lines; Experimental details and result of the study.

Presents a study that measured the delay time between the initiating pulse and the development of the laser emission pulse for various vibrational transitions in a supersonic Hartree-Fock chemical laser. Description of the apparatus; Analysis of the laser parameters; Results and discussion.

Direct measurements of the dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) as a function of I2 flow rate were carried out. This enabled us to determine the number of consumed O2(1Δ) molecules per dissociated I2 molecule. The number depends on the experimental conditions: it is 4.2±0.4 for typical conditions and I2 densities applied for the operation of the COIL, but increases at lower I2 densities. Possible dissociation mechanisms consistent with our results are discussed and the importance of dissociating I2 prior to its mixing with O2(1Δ) is stressed. [ABSTRACT FROM AUTHOR]

We investigate the repetitive modulation in the kHz frequency domain of a passively Q-switched, diode-pumped Yb:YAG laser, by Cr4+:YAG, Cr4+:LuAG, and Cr4+:GSGG saturable absorbers. The results presented here are focused towards the design of a passively Q-switched Yb:YAG microlaser. The free-running performance of both rod and a disk Yb:YAG is characterized and experimental parameters such as gain and loss are evaluated. These values, together with the value of the stimulated emission cross-section, e.g. σem=3.3×10−20 cm2 were found to fit between our experimental results and an existing numerical model which relates the experimental and physical parameters to the minimal threshold pumping power. Q-switched pulses with maximum peak power of &ap;10.4 kW, with energy of &ap;0.5 mJ/pulse, were extracted with 30% extraction efficiency. [Copyright &y& Elsevier]

Analysis of the operation of flowing-gas low power DPALs is crucial for designing high power devices. In particular, the comparison between the measured and calculated temperature rise in the laser cell makes it possible to estimate the contribution of the quenching of the alkali atoms electronic states to the gas heating. Here we report on an experimental and theoretical study of continuous wave flowing-gas Cs DPAL with He and CH 4 buffer gases, flow velocities of 1-4 m/s and pump powers of 30-65 W. In the calculations we used a 3D computational fluid dynamics model, solving the fluid mechanics and kinetics equations relevant to the laser operation. Maximum CW output power of 24 W with a slope efficiency of 48% was obtained. The experimental and theoretical values of the power and gas temperature are in good agreement. The lasing power was not affected by the flow velocity at this range of pump power and the gas temperature rise was only several degrees. It was found that the best agreement between the measured and calculated temperature rise is achieved for quenching cross-section ~0.05 Å 2 .

We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.