John Bruzzese

Gain and output power measurements in an electrically excited oxygen-iodine laser with a scaled discharge

Singlet delta oxygen (SDO) yield, small signal gain, and output power have been measured in a scaled electric discharge excited oxygen?iodine laser. Two different types of discharges have been used for SDO generation in O2?He?NO flows at pressures up to 90?Torr, crossed nanosecond pulser/dc sustainer discharge and capacitively coupled transverse RF discharge. The total flow rate through the laser cavity with a 10?cm gain path is approximately 0.5?mole?s?1, with steady-state run time at a near-design Mach number of M = 2.9 of up to 5?s. The results demonstrate that SDO yields and flow temperatures obtained using the pulser-sustainer and the RF discharges are close. Gain and static temperature in the supersonic cavity remain nearly constant, ? = 0.10?0.12%?cm?1 and T = 125?140?K, over the axial distance of approximately 10?cm. The highest gain measured is 0.122%?cm?1 at T = 140?K. Positive gain measured in the supersonic inviscid core extends over approximately one half to one third of the cavity height, with absorption measured in the boundary layers near top and bottom walls of the cavity. Laser power has been measured using (i) two 99.9% mirrors on both sides of the resonator, 2.5?W, and (ii) 99.9% mirror on one side and 99% mirror on the other side, 3.1?W. Gain downstream of the resonator is moderately reduced during lasing (by up to 20?30%) and remains nearly independent of the axial distance, by up to 10?cm. This suggests that only a small fraction of power available for lasing is coupled out, and that additional power may be coupled in a second resonator. Preliminary laser power measurements using two transverse resonators operating at the same time (both using 99.9?99% mirror combinations) demonstrated lasing at both axial locations, with the total power of 3.8?W.

Experimental and Computational Studies of Low-Temperature Mach 4 Flow Control by Lorentz Force

a = speed of sound B = magnetic field Cp, Cc = stray capacitances of the capacitive probe E = electric field e = specific total energy hD = diffuser height hT = test section height I = current I = identity tensor j = current density K = loading parameter L = magnetohydrodynamics section length M = flow Mach number _ m = mass flow rate N = number density P = pressure P0 = plenum pressure Ptest = test section static pressure Pr = Prandtl number Q = interaction parameter q = heat flux R = ballast resistance Rmatch = impedance matching resistance Rshunt = shunt resistance Rterm = terminator resistance R = magnetic Reynolds number Re = Reynolds number T = temperature t = time UPS = dc power supply voltage UDC = dc voltage Up = pulse voltage Upinc = incident pulse voltage Upref = reflected pulse voltage Uscope = voltage signal on the oscilloscope u = flow velocity W = coupled pulse energy Ztrans = high-voltage transmission line impedance ZBNC = Bayonet Neill–Concelman cable impedance = effective Joule heating factor d = diffuser step angle s = oblique shock angle = specific heat ratio PR = static pressure rise for accelerating Lorentz force PR = static pressure rise for retarding Lorentz force = electron mobility m = magnetic permeability of vacuum = pulse repetition frequency = density = electrical conductivity eff = effective electrical conductivity = characteristic time Presented as Paper 2007-4595 at the 38th AIAA Plasmadynamics and Lasers Conference, Miami, FL, 25–28 June 2007; received 5 February 2010; revision received 2 June 2010; accepted for publication 10 June 2010. Copyright ©2010 by theAmerican Institute ofAeronautics andAstronautics, Inc. All rights reserved. Copies of this paper may be made for personal or internal use, on condition that the copier pay the

Gain Distribution and Output Power Measurements in a Scaled Electric Discharge Excited Oxygen-Iodine Laser 1

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Experimental and Computational Studies of Low-Temperature M=4 Flow Deceleration by Lorentz Force 1

10.00 in correspondence with the CCC. Postdoctoral Researcher, Nonequilibrium Thermodynamics Laboratories, Department of Mechanical Engineering. Member AIAA. Postdoctoral Researcher, Nonequilibrium Thermodynamics Laboratories, Department of Mechanical Engineering. Member AIAA. Graduate Research Associate, Nonequilibrium Thermodynamics Laboratories, Department of Mechanical Engineering. Member AIAA. §Professor, Nonequilibrium Thermodynamics Laboratories, Department of Mechanical Engineering. Associate Fellow AIAA. ¶Research Aerospace Engineer, Computational Sciences Branch. Fellow AIAA. JOURNAL OF PROPULSION AND POWER Vol. 27, No. 2, March–April 2011

The effect of flow cooling on gain and output power of an electrically excited oxygen–iodine laser

Singlet delta oxygen (SDO) yield, gain in the supersonic cavity, and output power have been measured in a scaled-up electric discharge excited oxygen-iodine laser. The laser is using 5 kW transverse RF discharge operated at pressures of up to P0=90 torr to generate singlet delta oxygen in an oxygen-helium flow doped with NO. The total flow rate through the M=3 laser cavity is approximately 0.5 mole/sec, with a 10 cm gain path and steady-state run time at near design Mach number of M=2.9 of up to 5 sec. Gain and static temperature measurements vs. axial distance in the supersonic cavity demonstrated near uniform gain and temperature distributions, γ=0.10-0.12 % cm and T=125-140 K, over the distance of approximately 10 cm. Highest gain measured is 0.122 %/cm at T=140 K. Positive gain is measured in the supersonic inviscid core extending over approximately one half to one third of the cavity height, with absorption measured in the boundary layers near top and bottom walls of the cavity. Laser power has been measured using two different resonator configurations, (i) two 99.9% output couplers on both resonator sides, 2.5 W, and (ii) a 99.9% mirror on one side and a 99% output coupler on the other side, 3.1 W. Gain measurements downstream of the resonator during lasing demonstrate moderate gain reduction at these conditions. Gain downstream of the resonator remains nearly independent of the axial distance, by up to 10 cm, suggesting that additional power may be coupled in a second resonator. Preliminary laser power measurements using two transverse resonators operating at the same time (both using 99.9% - 99% mirror combinations) demonstrated lasing at both locations, with the total power of 3.8 W. The results demonstrate that only a small fraction of power stored in the flow and available for lasing is coupled out.

Scaling of an Electric Discharge Excited Oxygen-Iodine Laser

The paper presents results of cold MHD flow deceleration experiments using repetitively pulsed, short pulse duration, high voltage discharge to produce ionization in a M=4 nitrogen flow in the presence of transverse DC electric field and transverse magnetic field. Effective flow conductivity is significantly higher than was previously achieved, σeff=0.1 S/m. MHD effect on the flow is detected from the flow static pressure measurements. Retarding Lorentz force applied to the flow produces a static pressure increase of 19%, while accelerating force of the same magnitude applied to the same flow results in static pressure increase of 11%. The effect is produced for two possible combinations of the magnetic field and transverse current directions producing the same Lorentz force direction (both for accelerating and retarding force). The results of static pressure measurements are compared with predictions of a 3-D Navier-Stokes / MHD flow code. The static pressure rise predicted by the code, 18% for the retarding force and 8% for the accelerating force, agrees well with the experimental measurements. Analysis of the

NO PLIF Imaging in the CUBRC 48" Shock Tunnel

Cooling the flow through the electric discharge excited oxygen-iodine laser has been used to increase gain in the supersonic cavity and laser power. The flow was cooled by injecting helium or nitrogen precooled in a liquid nitrogen bath into the main flow, downstream of the iodine vapor injector. The injection flow 40-60% of the total flow rate through the laser (0.5-0.7 mole/sec). The results demonstrate that cold helium injection decreases the flow temperature and significantly increases gain in the supersonic cavity. The results also suggest that reverse flow of iodine vapor into the discharge, caused by cooling flow injection downstream of the iodine injector, with subsequent iodine dissociation in the discharge, may also contribute to gain increase. The use of nitrogen instead of helium for flow cooling is significantly less effective. Precooling the main flow using ethanol / liquid nitrogen and liquid nitrogen cooling baths was completely ineffective. Parametric gain measurements, varying oxygen fraction in the main flow, the main flow rate, and the discharge power determined discharge and flow conditions for optimum gain. Highest gain achieved in the present work is 0.21 %/cm over the gain path of 10 cm, measured at the discharge pressure of P0=88 torr and RF discharge power 2.75 kW. Laser power measured using a stable resonator with a 99.9% and a 99.0% reflectivity mirrors is 7.8 W. The power remains constant over approximately 5 seconds of laser operation. Gain measured downstream of the resonator during lasing remains fairly high, 0.155 %/cm, 25% lower than gain at the same location without lasing. This demonstrates that for the present resonator configuration, only a small fraction of the power available for lasing is coupled out.

The Effect of Iodine Dissociation and Flow Cooling on Gain and Output Power in a Electric Discharge Excited Oxygen-Iodine Laser 1

Electric discharge excited oxygen-iodine laser apparatus has been successfully scaled to increase the electric discharge volume and power, the laser mixture flow rate, and the gain path in the M=3 laser cavity. Singlet delta oxygen (SDO) generator discharge power has been increased up to at least 4.5 kW, laser mixture flow rate up to approximately 0.5 mole/sec, and gain path up to 10 cm. The steady-state run time of the new scaled-up laser apparatus at these conditions is up to 10 sec. Two different discharge configurations have been used to generate singlet delta oxygen, crossed nanosecond pulser / transverse DC sustainer discharge and capacitively coupled transverse RF discharge. Flow temperature downstream of the discharge, singlet delta oxygen yield, and laser gain have been measured in a wide range of discharge powers, nitric oxide mole fractions in the main oxygen-helium flow, and oxygen percentage in the mixture, at discharge pressures ranging from 60 to 86 torr. The results demonstrate that SDO yield increases with the discharge power for both discharge configurations, although highest yields achieved so far remain rather low, 3.6-3.7%, due to fairly low energy loading per oxygen molecule in the discharge. Small signal gain measured in the M=3 cavity of the new laser apparatus is up to 0.116%/cm (2.3% gain per double pass), at the flow temperature of T=125 K. Laser gain remains steady during operation and decreases along the cavity, although the flow temperature along the cavity remains nearly constant. Iodine vapor flow rate critically affects gain when all other discharge and flow parameters are kept the same. The optimum iodine flow rate appears to increase with the discharge power, which suggests that greater amounts of iodine vapor in the flow are needed to optimize gain at higher powers.

Effect of iodine dissociation in an auxiliary discharge on gain in a pulser-sustainer discharge excited oxygen―iodine laser

Nitric Oxide Planar Laser-Induced Fluorescence (NO PLIF) imaging is demonstrated at a 10 kHz repetition rate in the Calspan-University at Buffalo Research Center’s (CUBRC) 48-inch Mach 9 hypervelocity shock tunnel using a pulse burst laser–based high frame rate imaging system. Sequences of up to ten images are obtained internal to a supersonic combustor model, located within the shock tunnel, during a single ~10millisecond duration run of the ground test facility. This represents over an order of magnitude improvement in data rate from previous PLIF-based diagnostic approaches. Comparison with a preliminary CFD simulation shows good overall qualitative agreement between the prediction of the mean NO density field and the observed PLIF image intensity, averaged over forty individual images obtained during several facility runs.

NO PLIF imaging in the CUBRC 48-inch shock tunnel

The present work reports recent progress in scaling gain and output power of an electrically excited oxygen-iodine laser, using three different approaches. First, iodine injected into the main flow is partially dissociated using an auxiliary RF discharge sustained in the iodine injector. Second, cold helium is injected into the main flow downstream of the iodine injector, to reduce the flow temperature. Finally, a triple-pass folded laser resonator in the supersonic cavity is used to couple out the laser power. The number density of iodine atoms generated by the auxiliary discharge sustained in the iodine injector is inferred from absorption measurements on the iodine atom line in the supersonic cavity (estimated iodine dissociation fraction is α~0.6-1.0). This demonstrates that the auxiliary discharge dissociates a significant fraction of iodine injected into the laser. The combined effect of using both the auxiliary discharge and cold helium injection together (highest gain measured is 0.165 %/cm) considerably exceeds the effect of using only one of these approaches. Comparing these results with our previous gain measurements using an aluminum injector without the auxiliary discharge, 0.18-0.21 %/cm, suggests that the aluminum injector may act as an additional grounded electrode of the main RF discharge, which results in partial iodine dissociation. This suggestion remains tentative because the geometry of the two injectors is somewhat different. Gain and output laser power measurements have been conducted using an aluminum iodine injector and a triple-pass folded resonator with 2-inch mirrors. Gain in the supersonic cavity is measured along three separate sections of the resonator. The results show that both gain and the flow temperature remain nearly the same along all three resonator sections, 0.175-0.197 %/cm and T=95-105 K. The results also demonstrate gain line frequency shift due to the Doppler effect, by approximately 400 MHz, which corresponds to the flow velocity in the supersonic cavity of u=1400 m/sec (M=3.0). Due to this effect, lasing in the triple-pass resonator occurs on three different lines separated by approximately 400 MHz. Laser power has been measured for two different output couplers mirrors, 99.5% and 98.6% reflectivity. The output power measured for these two cases is 6.1 W and 7.5 W, respectively.