Advanced Laser and Optical Diagnostics  



Research in advanced laser and optical diagnostics development...

is striving to extend our current state-of-the-art in laser induced fluorescence imaging to faster time scales and increased sensitivity. The goal is to enable new diagnostics capabilities which can be applied to practical high-pressure and/or high-velocity propulsion systems for visualizing complex combustion phenomena. Additionally, other laser based diagnostics such as diode laser absorption, Rayleigh scattering thermometry, and emission based spectroscopy are also being studied.





Modeling of Molecular Excitation using a Laser

By using the narrow spectral width of a laser beam, we can selectively excite different transitions of a target molecules as shown on the left for nitric oxide (NO). Upon transition to a higher energy state, the molecule will de-excite and emit light which can be imaged and is referred to as laser-induced fluorescence (LIF). This process can be dramatically influenced by ambient conditions and surrounding gas species. Modeling this phenomena for a wide range of relevant molecules is a key target of our research program.


High Speed (> 50 kHz) PLIF Imaging using UV

Research is underway to investigate a new high-speed PLIF imaging strategy using far UV excitation at a range of UV wavelength. This will be accomplished by using a 532 nm (high speed Nd:YAG) pumped dye laser and sum frequency mixed with the third harmonic (355 nm) of the YAG. Images will be captured using a high-speed CMOS camera optically coupled to a high-speed UV intensifier. It will provide continuous imaging of key radical species at speeds in excess of 50 kHz. 

Right image shows a new high-speed laser system at MSU, in collaboration with Wright Patterson AFB.

Supported by the Air Force Office of Scientific Research



Sample: High Speed Imaging of Nitric Oxide

This image shows a sample high speed data of nitric oxide at 10 kHz. The nitric oxide was generated using a DC plasma torch. The signal to noise ratio is in excess of 40 at a nitric oxide concentration of ~800ppm. Work is underway to extend the frame rate. As of now, we have successfully implemented a continuous 50 kHz imaging system. Unlike other high speed imaging techniques this strategy can record a sequence of continuous shots which is only limited by the memory on the camera system.




High-Pressure Multi-Spectral Diagnostics

Laser based imaging in high-pressure environments are confronted by a number of problematic issues. Broadening of excitation lines, interference from alternative species, and collisional quenching are just a few when using ultraviolet laser light for diagnostics. This research addresses both simulation and experimental approach of using multi-spectral detection to enhance sensitivity and reliability of LIF imaging at elevated pressures.

Left image shows a high-pressure LIF spectra at 40 bar of nitric oxide.

Supported by the Air Force Office of Scientific Research



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