David M. Surmick

Aluminum flame temperature measurements in solid propellant combustion.

The temperature in an aluminized propellant is determined as a function of height and plume depth from diatomic AlO and thermal emission spectra. Higher in the plume, 305 and 508 mm from the burning surface, measured AlO emission spectra show an average temperature with 1σ errors of 2980 ± 80 K. Lower in the plume, 152 mm from the burning surface, an average AlO emission temperature of 2450 ± 100 K is inferred. The thermal emission analysis yields higher temperatures when using constant emissivity. Particle size effects along the plume are investigated using wavelength-dependent emissivity models.

Measurement and analysis of atomic hydrogen and diatomic molecular AlO, C2, CN, and TiO spectra following laser-induced optical breakdown.

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement is used. Here we operate a Nd:YAG laser at a frequency of 10 Hz at the fundamental wavelength of 1,064 nm. The 14 nsec pulses with anenergy of 190 mJ/pulse are focused to a 50 µm spot size to generate a plasma from optical breakdown or laser ablation in air. The microplasma is imaged onto the entrance slit of a 0.6 m spectrometer, and spectra are recorded using an 1,800 grooves/mm grating an intensified linear diode array and optical multichannel analyzer (OMA) or an ICCD. Of interest are Stark-broadened atomic lines of the hydrogen Balmer series to infer electron density. We also elaborate on temperature measurements from diatomic emission spectra of aluminum monoxide (AlO), carbon (C2), cyanogen (CN), and titanium monoxide (TiO). The experimental procedures include wavelength and sensitivity calibrations. Analysis of the recorded molecular spectra is accomplished by the fitting of data with tabulated line strengths. Furthermore, Monte-Carlo type simulations are performed to estimate the error margins. Time-resolved measurements are essential for the transient plasma commonly encountered in LIBS.

Aluminum Monoxide Emission Measurements in a Laser-Induced Plasma

We report temperature inferences from time-resolved emission spectra of a micro-sized plasma following laser ablation of an aluminum sample. The laser-induced breakdown event is created with the use of nanosecond pulsed laser radiation. Plasma temperatures are inferred from the aluminum monoxide spectroscopic emissions of the aluminum sample by fitting experimental to theoretically calculated spectra with a nonlinear fitting algorithm. The synthetic spectra used as a comparison for the experimental spectra are generated from accurate line strengths of aluminum monoxide bands. The inferred plasma temperatures are found to be 5315 ± 100 K at 20 μs following breakdown. At later time delays of 45 and 70 μs following breakdown, the plasma temperatures are found to be 4875 ± 95 and 4390 ± 80 K, respectively. Error analysis of the inferred temperatures is performed with the fitting algorithm.

Electron density determination of aluminium laser-induced plasma

We present temporally and spatially resolved electron density results of laser-induced plasma initiated on the surface of an aluminium target. Aluminium 394.4 and 396.15 nm lines were fit to Lorentzian profiles to evaluate Stark widths and shifts. Experimentally determined electron density versus line width and shift relationships were applied. Fitting to the aluminium lines indicates an electron density of 1.9 ± 0.2 and for Stark widths and 1.7 ± 0.5 and for Stark shifts at a 0.3 μs time delay following plasma initiation for the aluminium Al i 394.4 and 396.15 nm transitions, respectively. Simultaneous observations of the singly ionized nitrogen line, N ii, at 395.5 nm were also fit for a time delay of 0.2 μs, indicating an electron density of . The differences between the nitrogen and aluminium electron densities show evidence of self absorption.

Hydrogen Alpha Self-Absorption Effects in Laser-Induced Air Plasma

Time-resolved spectroscopy measurements of the hydrogen alpha Balmer series line following laser-induced optical breakdown in laboratory air are designed to investigate in detail the determination of electron density from Stark-broadened spectral line shapes. Comparisons of results obtained from Hβ and Hγ lines indicate higher electron density inferred from Hα early in the plasma decay, suggesting self-absorption occurs. However, detailed comparisons for time delays of 300 and 400 ns after optical breakdown reveal the minute extent of self-absorption in air breakdown experiments from (i) differences of electron density determined from the N+ lines and the Hα line, and/or from (ii) differences in recorded data sets with/without the mirror for the various time delays in the experiments.

Hydrogen Balmer Series Measurements in Laser-Induced Air Plasma

Time-resolved spectroscopy is employed to analyze micro plasma generated in laboratory air. Stark-broadened emission profiles for hydrogen alpha and beta allow us to determine plasma characteristics for specific time delays after plasma generation. Stark shift, asymmetry, and full width half maximum measurements are used to infer electron density. The measurements of hydrogen alpha and beta Balmer series line shapes are analyzed using various theory results. Our laser-induced breakdown spectroscopy arrangement uses a Q- switched Nd:YAG laser operating at the fundamental wavelength of 1064 nm that is focused for plasma generation. The hydrogen alpha and beta lines emerge from the free electron background radiation for time delays larger than 0.3 ps and 1.4 ps, respectively. Neutral and ionized nitrogen emission lines allow us to infer electron density for time delays from 0.1 to 10 μs. The electron density values are compared with results obtained from hydrogen Balmer series line shapes.

Time-resolved aluminium laser-induced plasma temperature measurements

We seek to characterize the temperature decay of laser-induced plasma near the surface of an aluminium target from laser-induced breakdown spectroscopy measurements of aluminium alloy sample. Laser-induced plasma are initiated by tightly focussing 1064 nm, nanosecond pulsed Nd:YAG laser radiation. Temperatures are inferred from aluminium monoxide spectra viewed at systematically varied time delays by comparing experimental spectra to theoretical calculations with a Nelder Mead algorithm. The temperatures are found to decay from 5173 ± 270 to 3862 ± 46 Kelvin from 10 to 100 μs time delays following optical breakdown. The temperature profile along the plasma height is also inferred from spatially resolved spectral measurements and the electron number density is inferred from Stark broadened Hβ spectra.

Combustion diagnosis for analysis of solid propellant rocket abort hazards: Role of spectroscopy

Solid rocket propellant plume temperatures have been measured using spectroscopic methods as part of an ongoing effort to specify the thermal-chemical-physical environment in and around a burning fragment of an exploded solid rocket at atmospheric pressures. Such specification is needed for launch safety studies where hazardous payloads become involved with large fragments of burning propellant. The propellant burns in an off-design condition producing a hot gas flame loaded with burning metal droplets. Each component of the flame (soot, droplets and gas) has a characteristic temperature, and it is only through the use of spectroscopy that their temperature can be independently identified.

Emission spectroscopy of nitric oxide in laser-induced plasma

In this paper, we investigate the laser-induced breakdown spectra of nitric oxide. Nitric oxide spectra are studied from laser-induced plasma emissions from plasma initiated both in laboratory air. Temperatures are inferred from the spectroscopic emissions using two methods. Spectra are fit to theoretical calculations of the diatomic spectra using the method of diatomic line strengths. For a time delay of 25 μs the temperature is found to be 6800 Kelvin. Comparisons are also provided to previously determined temperatures using a non-equilibrium air radiation fitting (NEQAIR) program.