Torger J. Anderson

Simultaneous rotational coherent anti-Stokes Raman spectroscopy and coherent Stokes Raman spectroscopy with arbitrary pump–Stokes spectral separation

A new approach to pure rotational coherent anti-Stokes Raman spectroscopy (CARS) and coherent Stokes Raman spectroscopy (CSRS) is demonstrated in which the pump and broadband Stokes lasers that are mixed have a large and arbitrary spectral separation. In this method, the rotational Raman coherences are established by different frequency components within the single, broadband Stokes source. The narrow band then scatters from the excited coherences, producing CARS and CSRS simultaneously. We discuss phase matching for this new technique and its inherent advantages relative to pure rotational CARS as normally implemented.

Dual broadband CARS for simultaneous, multiple species measurements

An approach to CARS is described and demonstrated which permits CARS to be generated from a multiplicity of species simultaneously. The technique employs two independent broadband Stokes sources in combination with a pump laser. In addition to the two separate two-color wave-mixing processes between the pump and Stokes lasers, spectrally resolved CARS is produced in a three-color process from species whose Raman resonances correspond to the frequency differences of the two broadband sources. CARS is thus derived from a large number of species simultaneously removing the nominal limitation of CARS to interrogate only one constituent at a time.

Simultaneous coherent anti-Stokes Raman spectroscopy measurements inhydrogen-fueled supersonic combustion

Coherent anti-Stokes Raman spectroscopy (CARS) has been used to measure H2 and H2O concentrations and N2 temperature simultaneously in a H2-fueled, air fed supersonic combustor. Profiles of each parameter at selected axial locations were generated by translating the measurement point vertically across the combustor at varying conditions of total temperature and equivalence ratio. The baseline combustor experiment contributes to an understanding of mixing and combustion processes and a data base for refining 2-D CFD codes. The combustor, the dual Stokes CARS system and the techniques employed are described. Sample results and potential improvements are also discussed.

Mobile CARS instrument for combustion and plasma diagnostics.

A compact and easily transportable coherent anti-Stokes Raman spectroscopy system for combustion and plasma diagnostics is described. The instrument is readily adaptable to a wide variety of test environments and experiments. The system is capable of withstanding high noise and vibration levels and is remotely operable to protect the operator and delicate components from high noise levels or hazardous environments. It is intended for single-pulse temperature and concentration measurements in practical combustion systems, such as gas turbines, diesel engines, and plasma process applications. The system is operational, and initial measurement demonstrations in a supersonic combusting flow are described.

Multi-Color CARS for Simultaneous Measurements of Multiple Combustion Species

Multi-color CARS approaches, which permit the simultaneous measurement of temperature and two or more species, are reviewed. Four different techniques will be discussed and compared. These involve multiple pump or Stokes lasers and synergistic combinations thereof. A new method to generate pure rotational CARS from pump and broadband Stokes lasers having arbitrary spectral separation will be described. Combined vibrational/pure rotational CARS approaches will also be discussed.

Conditional sampling for fuel and soot in cars thermometry

Conditional-sampling strategies to simultaneously sense for fuel and soot presence when performing N2 CARS thermometry in turbulent, soot-forming combustion are formulated and experimentally explored. Soot-sensing strategies are based upon spectroscopic detection of the C2 produced during laser vaporization of the particles; both incoherent and coherent strategies are investigated. Fuel presence is sensed through coherent wave mixing in the fuel or major fuel-pyrolysis products. Many of the strategies formulated exploit the newly-developed dual broadband CARS approach (DBBCARS) which permits measurements from a number of constituents simultaneously.

Cars temperature/multi-species measurement strategies for high speed airbreathing and rocket propulsion testing†

Practical propulsion systems testing requires accurate, spatially-precise measurements of temperatures, major species, pressure and velocities to characterize device performance. For thermometry and major species, coherent anti-Stokes Raman spectroscopy (CARS) is generally preferred because of its broad applicability to high interference environments and limited optical access requirements. To maximize data rate and develop parameter correlations, multi-color CARS approaches are required which permit temperature and fuel/product species concentration measurements for various fuel/oxidizer cases of advanced propulsion interest, namely, hydrogen—air, hydrogen—oxygen, hydrocarbon—air and hydrocarbon—oxygen. For hydrogen-fueled situations, dual Stokes approaches generally suffice while for hydrocarbon-fueled applications, dual broadband CARS techniques are required. In some cases, oxygen consumption can be monitored as well.The spectral placement of the Stokes lasers and the referencing approaches required to effect these strategies are discussed for each fuel/oxidizer case. Sample CARS measurements are presented from a hydrogen-fueled, air-fed supersonic combustor and an air-fed, hydrocarbon-fueled turboramjet combustor. The experiments were performed using a ruggedized, remotely controlled, mobile CARS instrument configured for single pulse (∼10 −8 sec) multi-color wave mixing at a 20 Hz repetition rate.