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We report the first two-photon-excited hydrogen-atom fluorescence measurements in flames made to our knowledge. The n = 3 level of the H atom was excited by 205.1-nm radiation generated by Raman shifting a 224-nm beam produced by frequency mixing. Fluorescence was observed at 656.3 nm as a result of radiative decay from n = 3 to n = 2, the Balmer-alpha transition. A novel technique, photoionization-controlled loss spectroscopy, is proposed to eliminate the quenching dependence of the fluorescence signal.

A laser Doppler velocimeter was used to measure the stream wise velocity component in unsteady separated flowfields in a two-dimensional transonic diffuser with and without externally induced periodic fluctuations. Results are also presented for fully attached, unsteady, unexcited flow. The time-dependent perturbation flowfield associated with the external excitation was determined throughout the subsonic region for a case with shock-induced separation. The results indicate that a transverse, wavelike motion of the boundary-layer/coreflow interface is an important aspect of the overall oscillations and overwhelms effects associated with acousticwave propagation. NomenclatureA = amplitude coefficient in Fourier series / = excitation frequency h = channel height M = Mach number TV = number of velocity samples T = temperature u = mean streamwise velocity u = rms of streamwise fluctuating velocity component u = ensemble-averaged streamwise velocity u = periodic component of ensemble-averaged streamwise velocity x = dimensionless streamwise coordinate; x/h*, x-Q at throat y = dimensionless vertical coordinate; y/h*, y = 0 at lower wall a. = perturbation phase angle 5* = dimensionless displacement thickness, d*/h * c/> == phase angle in Fourier series § = dimensionless momentum thickness, B/h * Subscripts e -exit ( -lower wall m = midstream (y = 0.432) n -Fourier harmonic o = plenum r -reference s = static t = total u = upper wall o =shock * =throat

We performed a direct side-by-side comparison of a Shack-Hartmann wave-front sensor and a phase-shifting interferometer for the purpose of characterizing large optics. An expansion telescope of our own design allowed us to measure the surface figure of a 400-mm-square mirror with both instruments simultaneously. The Shack-Hartmann sensor produced data that closely matched the interferometer data over spatial scales appropriate for the lenslet spacing, and much of the <20-nm rms systematic difference between the two measurements was due to diffraction artifacts that were present in the interferometer data but not in the Shack-Hartmann sensor data. The results suggest that Shack-Hartmann sensors could replace phase-shifting interferometers for many applications, with particular advantages for large-optic metrology.

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