Diffractive/refractive (hybrid) UV-imaging system for minimally invasive metrology: design, performance, and application experiments

Reichle, René; Pruß, Christof; Gessenhardt, Christopher; Schulz, Christof

doi:10.1364/ao.51.001982

Cited by 13 publications

(4 citation statements)

References 32 publications

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“…Optical elements or modules can be mounted inside those inserts, and be brought to within a millimetre of the window, in order to overcome the otherwise severe restrictions on viewing angle and collection efficiency imposed by the thick cover walls. The use of relay optics inside cylinder walls in a similar fashion has previously been reported on car sized engines [20].…”

Section: Optical Accessmentioning

confidence: 83%

A methodology for laser diagnostics in large-bore marine two-stroke diesel engines

Hult¹,

Mayer²

2013

Meas. Sci. Technol.

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Large two-stroke diesel engines for marine propulsion offer several challenges to successful implementation of the laser diagnostic techniques applied extensively in smaller automotive engines. For this purpose a fully operational large-bore engine has been modified to allow flexible optical access, through 24 optical ports with clear diameters of 40 mm. By mounting the entire optical set-up directly to the engine, effects of the vigorous vibrations and thermal drifts on alignment can be minimized. Wide-angle observation and illumination, as well as relatively large aperture detection, is made possible through mounting of optical modules and relays inside optical ports. This allows positioning of the last optical element within 10 mm from the cylinder wall. Finally, the implementation on a multi-cylinder engine allows for flexible and independent operation of the optically accessible cylinder for testing purposes. The performance of the integrated optical engine and imaging system developed is demonstrated through laser Mie scattering imaging of fuel jet structures, from which information on liquid penetration and spray angles can be deduced. Double pulse laser-sheet imaging of native in-cylinder structures is also demonstrated, for the purpose of velocimetry.

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Section: Optical Accessmentioning

confidence: 83%

A methodology for laser diagnostics in large-bore marine two-stroke diesel engines

Hult¹,

Mayer²

2013

Meas. Sci. Technol.

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“…Refractive/diffractive hybrid optical components are a new generation of optics formed by combining diffractive optics with conventional refractive optics. [ 165 ] Taking advantage of the properties of light in propagation refraction and diffraction, including good thermal properties, unique dispersion, and monochromatic aberration correction capability, the refractive/diffractive hybrid optical components not only reduce the size and cost of the system but also increase the flexibility of design and the diversity of material selection. In addition, it overcomes the limitations of chromatic, spherical, and thermal aberrations of traditional single optical elements.…”

Section: Laser Fabrication Of Refractive/diffractive Micro‐optical Co...mentioning

confidence: 99%

Femtosecond Laser Fabrication of Refractive/Diffractive Micro‐Optical Components on Hard Brittle Materials

Tan

Wang

et al. 2023

Laser & Photonics Reviews

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Micro‐optical components exhibit significant potential applications in various fields such as imaging, optical fiber communication, and aerospace owing to their small size, light weight, and flexible design. It is imperative to fabricate micro‐optical components on hard brittle materials to improve stability and broaden the optical transmission range. Therefore, femtosecond laser processing technology is demonstrated to be an efficient processing strategy for preparing refractive/diffractive micro‐optical components on hard brittle materials compared to other established micromachining techniques. This study reviews recent advances in refractive/diffractive micro‐optical components using femtosecond laser processing technologies. The applications of refractive/diffractive micro‐optical components with high accuracy, efficiency, and quality in the fields of imaging, sensing, display, and integration are also summarized. Moreover, the challenges of femtosecond laser processing technologies and the outlook of micro‐optical components are highlighted.

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“…More details about the engine and the modifications for endoscopic accesses can be found in Gessenhardt (2013) and Witzel (2007). The hybrid UV endoscope system consists of two parts: a wide-angle front endoscope and a refractive-diffractive ("hybrid") relay lens for chromatic correction in a pre-designed range (Reichle et al 2012;Zimmermann 2006). The front endoscope is mounted on the engine and produces an intermediate image on the field lens at its back.…”

Section: Engine and Opticsmentioning

confidence: 99%

“…Soot formation has also been investigated using endoscopic imaging in directinjection spark-ignition (DISI) engines by Burkardt et al (2021) and Etikyala et al (2022). To apply a wider range of optical diagnostics in engines with endoscopic access, in our previous work, a large-aperture hybrid UV-transparent endoscope system was developed (Reichle et al 2012;Zimmermann 2006). It is now commercially available from LaVision.…”

Section: Introductionmentioning

confidence: 99%

Imaging of flame propagation and temperature distribution in an all-metal gasoline engine with endoscopic access via anisole fluorescence

Shahbaz,

Jahangir,

Kaiser

2023

Exp Fluids

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Laser-based optical diagnostic tools are widely used to investigate in-cylinder processes in internal combustion engines. For laser-induced fluorescence (LIF), many tracers have been used in the past. Recently, anisole has been characterized spectroscopically for engine-relevant pressures and temperatures and emerged as a potentially advantageous alternative to more commonly used tracers in the past due to its photo-physical properties. Its high fluorescence quantum yield and large absorption cross section result in high signal intensity. This is particularly beneficial for endoscopic imaging systems, which typically have worse light collection efficiency than traditional imaging systems in fully optically accessible engines with transparent liners. In this work, we exploited the strong anisole LIF signal in two single-shot experiments: to image flame propagation, and the instantaneous gas-phase temperature during compression stroke and gas exchange process. Measurements were performed in a production gasoline engine modified for endoscopic optical access via an advanced UV endoscope system. First, LIF of anisole was compared to that of toluene during compression stroke. Anisole LIF yields a much higher signal-to-noise ratio and better image quality with lower tracer concentrations. Due to the higher signal of anisole LIF, small structures of the turbulent flame burning into the anisole/isooctane mixture were well visible after ignition. Second, the red-shift of the anisole fluorescence spectrum with increasing temperature and oxygen partial pressure was exploited for ratiometric temperature measurements based on single-shot images. The available spectroscopic data were used to develop several signal ratio models, which were calibrated in situ using a heated tracer/bath gas mixture introduced inside the combustion chamber. The calibrated signal ratio models were then extrapolated to the engine-relevant ranges. Models with two-step exponential interpolation show better agreement with the adiabatic temperature than linear or 3D surface exponential interpolation. The gas-phase temperature images based on single shots were obtained using one selected model, showing a near uniform and a stratified temperature distribution during the compression stroke and gas exchange process, respectively.

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Diffractive/refractive (hybrid) UV-imaging system for minimally invasive metrology: design, performance, and application experiments

Cited by 13 publications

References 32 publications

A methodology for laser diagnostics in large-bore marine two-stroke diesel engines

A methodology for laser diagnostics in large-bore marine two-stroke diesel engines

Femtosecond Laser Fabrication of Refractive/Diffractive Micro‐Optical Components on Hard Brittle Materials

Imaging of flame propagation and temperature distribution in an all-metal gasoline engine with endoscopic access via anisole fluorescence

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