Rodrigo Sanchez-Gonzalez

Simultaneous velocity and temperature measurements in gaseous flow fields using the VENOM technique

We present an initial demonstration of simultaneous velocity and temperature mapping in gaseous flow fields using a new nitric oxide planar laser-induced fluorescence-based method. The vibrationally excited NO monitoring (VENOM) technique is an extension of two-component velocimetry using vibrationally excited NO generated from the photodissociation of seeded NO(2) [Appl. Opt. 48, 4414 (2009)], where the two sequential fluorescence images are obtained probing two different rotational states to provide both velocity and temperature maps. Comparisons to computational fluid dynamics simulations show that the initial VENOM measurements provide good velocity and temperature maps in the relatively high-density regions of the flow, where the rms uncertainties are approximately 5% for velocity and 9% for temperature.

Coherence brightened laser source for atmospheric remote sensing

We have studied coherent emission from ambient air and demonstrated efficient generation of laser-like beams directed both forward and backward with respect to a nanosecond ultraviolet pumping laser beam. The generated optical gain is a result of two-photon photolysis of atmospheric O2, followed by two-photon excitation of atomic oxygen. We have analyzed the temporal shapes of the emitted pulses and have observed very short duration intensity spikes as well as a large Rabi frequency that corresponds to the emitted field. Our results suggest that the emission process exhibits nonadiabatic atomic coherence, which is similar in nature to Dicke superradiance where atomic coherence is large and can be contrasted with ordinary lasing where atomic coherence is negligible. This atomic coherence in oxygen adds insight to the optical emission physics and holds promise for remote sensing techniques employing nonlinear spectroscopy.

Repetitively Pulsed Hypersonic Flow Apparatus for Diagnostic Development

Cp = heat capacity at constant pressure Cv = heat capacity at constant volume C12 = experimentally determined calibration constant De = exit diameter of nozzle Ds = diameter of subsonic section of nozzle Dt = throat diameter of nozzle k = Boltzmann constant M = Mach number m = mass Pi = impact pressure P0 = stagnation pressure P02 = pitot pressure Sf = fluorescence signal intensity Trot = rotational temperature Tw = wall temperature T0 = stagnation temperature = ratio of heat capacities, Cp=Cv E21 = energy difference between rotational states

Non-adiabatic atomic coherence at work in the oxygen laser source for atmospheric remote sensing

We pump ambient air by loosely-focused ultraviolet pulses and generate a backward laser-like beam for use in remote sensing. We find that this efficient emission is likely linked to non-adiabatic coherence effects in atomic oxygen.

Repetitively Pulsed Hypersonic Test Facility for Advanced Laser Diagnostic Development

A repetitively pulsed hypersonic flow apparatus has been constructed and characterized. This apparatus was designed to enable advanced laser diagnostic development. The underlying principle is to synchronize the intermittent tunnel operation with the laser pulses to achieve effectively continuous operation. We demonstrated repetitively pulsed (2-20 ms pulse length) uniform supersonic flow at Mach 4.6 and hypersonic flow at Mach 6.2 for extended operation. The nozzle flows were characterized using fast response pressure sensors and NO PLIF imaging for two-dimensional temperature and velocity measurements. The pulse-to-pulse impact pressure repeatability was within 1.0% corresponding to exit flow velocity and temperature fluctuations of 0.7% and 1.0%, respectively. The apparatus can operate over a unit Reynolds number range of 6.0x10 4 m -1 to 3.0x10 6 m -1