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.

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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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