Boris D. Barmashenko

Modeling of flowing gas diode pumped alkali lasers: dependence of the operation on the gas velocity and on the nature of the buffer gas

A simple, semi-analytical model of flowing gas diode pumped alkali lasers (DPALs) is presented. The model takes into account the rise of temperature in the lasing medium with increasing pump power, resulting in decreasing pump absorption and slope efficiency. The model predicts the dependence of power on the flow velocity in flowing gas DPALs and checks the effect of using a buffer gas with high molar heat capacity and large relaxation rate constant between the 2P3/2 and 2P1/2 fine-structure levels of the alkali atom. It is found that the power strongly increases with flow velocity and that by replacing, e.g., ethane by propane as a buffer gas the power may be further increased by up to 30%. Eight kilowatt is achievable for 20 kW pump at flow velocity of 20  m/s.

Feasibility of supersonic diode pumped alkali lasers: Model calculations

The feasibility of supersonic operation of diode pumped alkali lasers (DPALs) is studied for Cs and K atoms applying model calculations, based on a semi-analytical model previously used for studying static and subsonic flow DPALs. The operation of supersonic lasers is compared with that measured and modeled in subsonic lasers. The maximum power of supersonic Cs and K lasers is found to be higher than that of subsonic lasers with the same resonator and alkali density at the laser inlet by 25% and 70%, respectively. These results indicate that for scaling-up the power of DPALs, supersonic expansion should be considered.

Modeling of mixing in chemical oxygen‐iodine lasers: Analytic and numerical solutions and comparison with experiments

The processes of iodine dissociation, population inversion, and lasing in the chemical oxygen‐iodine laser (COIL) are affected by the mixing between the flows of oxygen and injected iodine. The effect of mixing on the operation of the COIL is studied theoretically applying a simple one‐dimensional leaky stream tube model and the results are compared to available experimental data. The model enables the calculation of the iodine dissociation and the gain along the flow and of the lasing power, as a function of the iodine flow rate (nI2), the yield of singlet oxygen [O2(1Δ)] and the pressure in the cavity. Both the fraction of the dissociated iodine and the maximum gain are shown to be nonmonotonous functions of nI2. There is an optimal value of nI2, depending on the O2(1Δ) yield, the gas velocity, and the temperature in the cavity, for which the gain achieves its maximum and the iodine dissociation length its minimum. The model shows that the maximum nI2 for which lasing is possible is less than 5% of the ...

Analysis of the optical extraction efficiency in gas-flow lasers with different types of resonator

The celebrated Rigrod model [J. Appl. Phys. 34, 2602 (1963)] has recently been shown to be inadequate for calculating the output power of gas-flow lasers when the quenching of excited species is slow and the optical extraction efficiency is high [Opt. Lett. 20, 1480 (1995)]. The previous analysis of two-level systems is presented here in detail and extended to include the chemical oxygen-iodine laser (COIL). For both two-level systems and COILs, we obtained simple analytic formulas for the output power, which should be used instead of the Rigrod model. We present the formulas for Fabry-Perot, stable, and unstable resonators. Both the saturation parameter and the extraction efficiency differ from those appearing in the Rigrod model. The highest extraction efficiency is achievable for both stable and unstable resonators with uniform intensity distribution over the resonator cross section and is greater than that calculated by the Rigrod model. A rather surprising conclusion is that the extraction efficiency of unstable resonators can be increased substantially if one increases the length of the part of the mirrors lying downstream of the optical axis. The derived formulas are applied to describe published experimental results of supersonic COILs. The dependence of the power on the threshold gain is evaluated and from this the plenum yield of singlet oxygen is estimated. The value of the yield is in better agreement with experimental measurements than that obtained by the Rigrod model.

Nearly attaining the theoretical efficiency of supersonic chemical oxygen-iodine lasers

Improving the chemical efficiency of the supersonic chemical oxygen-iodine laser (COIL) is a key issue for the design of devices for both defense and industrial applications. Efficiencies around 30% for the supersonic COIL have been the state of the art in the last decade. Here, we report the achievement of a record (40%) for the chemical efficiency of the supersonic COIL. More specifically, we show that by carefully studying and optimizing the operation of the chemical generator, the mixing of heavy and light molecules in the gas phase and the optical extraction efficiency, we have approached the theoretical limit for the chemical efficiency.

Toward understanding the dissociation of I2 in chemical oxygen-iodine lasers: Combined experimental and theoretical studies

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(aΔg1) 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 (2...

EXPERIMENT AND MODELING OF A SMALL-SCALE, SUPERSONIC CHEMICAL OXYGEN-IODINE LASER

We report on detailed experiment and modeling of a small-scale, supersonic chemical oxygen-iodine laser. The laser has a 5 cm long active medium and utilizes a simple sparger-type O2(1Δ) chemical generator and a medium-size pumping system. A grid nozzle is used for iodine injection and supersonic expansion. 25 W of cw laser emission at 1.315 µm are obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long times make it a convenient tool for studying parameters important for high-power supersonic iodine lasers and for comparison to model calculations. The lasing power is studied as a function of the molar flow rates of the various reagents, and conditions are found for optimal operation. Good agreement is found between the experimental results and calculations based on a simple one-dimensional semi-empirical model, previously developed in our laboratory and modified in the present work. The model is used to predict optimal values for parameters affecting the laser performance that are difficult to examine in the present experimental system.

Power enhancement in chemical oxygen-iodine lasers by iodine predissociation via corona/glow discharge

The gain and power in a supersonic chemical oxygen-iodine laser (COIL) are enhanced by applying dc corona/glow discharge in the transonic section of the secondary flow in the supersonic nozzle, dissociating I2 prior to its mixing with O2(Δ1). The loss of O2(Δ1) consumed for dissociation is thus reduced, and the consequent dissociation rate downstream of the discharge increases, resulting in up to 80% power enhancement. The implication of this method for COILs operating beyond the specific conditions reported here is assessed.

Power dependence of chemical oxygen-iodine lasers on iodine dissociation

The loss of O 2 ( 1 Δ) during iodine dissociation in the chemical oxygen-iodine laser (COIL) is one of the main factors affecting the output power. Analytical expression is obtained for the number of O 2 ( 1 Δ) molecules, N, lost in the region of I 2 dissociation per one molecule of I 2 . This expression yields N = 4-6, in agreement with numerical calculations and experimental measurements. It is shown that some effective number N 1 < N should be used rather than N to calculate the power. Analytical expression for the power is obtained, taking into account the O 2 ( 1 Δ) losses in the dissociation region. It is shown that N increases and the power decreases when the dissociation fraction F increases. Therefore, maximum power is achieved at low values of the iodine flow rate when iodine is not completely dissociated before the resonator and when the small signal gain in the resonator region is less than its maximum achievable value. Numerical modeling of the RADICL (supersonic COIL) is carried out. The values of the O 2 ( 1 Δ) yield and of the mixing rate are estimated to reach an agreement between the calculated and the measured dependencies of the power on the iodine flow rate.

Diode-laser-based absorption spectroscopy diagnostics of a jet-type O/sub 2/(/sup 1//spl Delta/) generator for chemical oxygen-iodine lasers

Using diode-laser-based diagnostics, O/sub 2/(/sup 1//spl Delta/) yield and water vapor fraction were measured at the exit of a jet-type singlet oxygen generator (JSOG) for a chemical oxygen-iodine laser (COIL). Chlorine utilization and gas temperature at the generator exit were also measured, simultaneously. For conditions corresponding to the maximum chemical efficiency of the supersonic COIL energized by the JSOG, the O/sub 2/(/sup 1//spl Delta/) yield, water vapor fraction, chlorine utilization, and temperature at the generator exit are 0.65, 0.08 and 0.92, and 30/spl deg/C, respectively. Increase of the basic hydrogen peroxide temperature results in an increase of the water vapor fraction caused by an increase of the saturated water vapor pressure in the generator. As the pressure in the generator rises from 18 to 60 torr, the yield decreases from 0.65 to O.48. Dependence of the yield on the generator pressure is consistent with a rate constant for the O/sub 2/(/sup 1//spl Delta/) energy pooling reaction of 2.7/spl times/10/sup -17/ cm/sup 3//spl middot/S/sup -1/. The same rate constant explains the measured variation of the temperature along the flow in the diagnostic cell.