Simultaneous laser-driven x-ray and two-photon fluorescence imaging of atomizing sprays

Abstract

In this letter we report for the first time the possibility of visualizing an atomizing spray by simultaneously recording X-ray absorption and 2photon laser-induced fluorescence imaging. This unique illumination/detection scheme was made possible thanks to the use of soft X-rays emitted from a laser-driven X-ray source. An 800 mJ laser pulse of 38 fs duration is used to generate an X-ray beam with up to 4 × 10 8 photons ranging from 1 to 10 keV, allowing projection radiography of water jets generated by an automotive port fuel injector. In addition, a fraction of the laser pulse (∼ 10 mJ) is employed to form a light sheet and to induce 2-photon fluorescence in a dye added to the water. The resulting high-contrast fluorescence images provide fine details of the spray structure, with reduced blur from multiple light scattering, while the integrated liquid mass is extracted from the X-ray radiography. In this proof-of-principle we show that the combination of these two highly complementary techniques, both in the visible and in the soft X-ray regime, is very promising for the future characterization of challenging spray, as well as for further understanding the physics of liquid atomization.

Physics of High-Charge Electron Beams in Laser-Plasma Wakefields

“…Important milestones include the generation of monoenergetic electron beams [5][6][7] and sustained acceleration of more than a GeV [8][9][10][11][12][13], as well as generation and application of spatially coherent, ultrashort x-ray sources based on accelerated particle beams [14][15][16][17][18][19]. So far, this novel generation of accelerators has been used to drive applications such as x-ray imaging [20][21][22][23] and tomography [24][25][26], as well as femtosecond electron diffraction [27], femtochemistry [28], and ultrafast spectroscopy [29,30].…”

Analysis of liquid spray structures using two-photon fluorescence laser sheet imaging

“…A fraction of 0.1 % fluorescein is added to both investigated liquids, water and ethanol. The equivalent fuel properties were determined to be unaffected by adding only this small amount of dye [3]. For the measurements a commercial 6-hole DISI injector with one definable spray cone is studied.…”

“…The majority of the detected photons have been scattered multiple times by ambient off-axis liquid structures. This effect leads to a masking of the investigated liquid structures in the core spray [2,3,1]. In recent years, various measurement techniques such as X-ray radiography, ballistic imaging (BI) or structured laser illumination planar imaging (SLIPI) have been established for the attempt to suppress multiple scattering [4,2,5].…”

“…This method is applied in SLIPI where a spatially modulated laser sheet is used to visualize the spray [7,8]. In a previous work, Guénot et al [3] introduced the combination of X-ray and 2p-LIF measurements to get insight into the detailed spray structure. Both techniques avoid the generation of multiple scattering and thus the intensity of the ambiguous off-axis signals is insignificant.…”

Beyond MHz image recordings using LEDs and the FRAME concept

“…A Nikon 50-300 mm camera objective is used to image the gratings onto the sample, permitting the magnification of the illuminated area-the viewed area-to be readily modified. In our study a commercially available fuel port injector, Bosch EV1 4-holes nozzle 31 , with orifice size of 280 μm, running at 4.8 bar water injection pressure, was probed at different times after start of injection (ASOI). Its complex transient structures allows us to demonstrate the ability of our system in obtaining images with both high spatial-and temporal resolution.…”