A method includes irradiating a target droplet in an extreme ultraviolet light source of an extreme ultraviolet lithography tool with light from a droplet illumination module. Light reflected and/or scattered by the target droplet is detected. Particle image velocimetry is performed to monitor one or more flow parameters inside the extreme ultraviolet light source.

Methods and systems are provided for measuring a velocity of a droplet passing through a microfluidic channel.

A method calibrates an optical measurement set-up with a measurement volume seeded with particles and at least two cameras so that the measurement volume can be mapped from different observation angles. The method includes simultaneously mapping the measurement volume by the cameras to produce images; rectifying each camera image in relation to a common reference plane in the measurement volume by using the respective pre-calibrated mapping function; performing two-dimensional correlation for at least one pair of rectified camera images to produce correlation fields that present an elongate correlation maxima band for each correlation field; reducing the correlation maxima band to a straight line representing the band; determining the distance of this representative straight line from the coordinate origin of the correlation field as a correction value, using the determined correction values to correct the mapping functions of those cameras for which rectified camera images were included in the correlations.

A method calibrates an optical measurement set-up with a measurement volume seeded with particles and at least two cameras so that the measurement volume can be mapped from different observation angles. The method includes simultaneously mapping the measurement volume by the cameras to produce images; rectifying each camera image in relation to a common reference plane in the measurement volume by using the respective pre-calibrated mapping function; performing two-dimensional correlation for at least one pair of rectified camera images to produce correlation fields that present an elongate correlation maxima band for each correlation field; reducing the correlation maxima band to a straight line representing the band; determining the distance of this representative straight line from the coordinate origin of the correlation field as a correction value, using the determined correction values to correct the mapping functions of those cameras for which rectified camera images were included in the correlations.

A microfluidic flow sensor may include a substrate having a microfluidic channel, an inert particle source to supply a fluid carrying an inert particle to the microfluidic channel and a sensor element along the microfluidic channel and spaced from the inert particle source. The sensor element outputs a signal based upon a sensed passage of the inert particle with respect to the sensor element. Portions of the microfluidic channel proximate the sensor element have a first size and wherein the inert particle provided by the inert particle source is to have a second size greater than one half the first size.

A microfluidic flow sensor may include a substrate having a microfluidic channel, an inert particle source to supply a fluid carrying an inert particle to the microfluidic channel and a sensor element along the microfluidic channel and spaced from the inert particle source. The sensor element outputs a signal based upon a sensed passage of the inert particle with respect to the sensor element. Portions of the microfluidic channel proximate the sensor element have a first size and wherein the inert particle provided by the inert particle source is to have a second size greater than one half the first size.

Systems, devices, and methods are described herein for performing digital holography to analyze dynamics of fluid flow. According to some aspects of this disclosure, a Digital Fresnel Reflection Holography (DFRH) system, which is arranged to utilize light backscattered from particles in a fluid chamber to create a hologram that may be processed to analyze characteristics of fluid flow. The DFRH system may utilize light reflected from an imaging window disposed between a light source and a sampling volume, to be analyzed as a reference wave, to form an interference pattern and resultant hologram. According to some aspects of this disclosure, the DFRH techniques may provide simple, cost-effective mechanisms with improved performance over other techniques for analyzing fluid flow using holography.

For tracking a plurality of objects in a three-dimensional space two-dimensional pictures objects are recorded with two black and white cameras out of two different imaging directions. Both first pictures and second pictures of the two cameras are simultaneously exposed at two points in time in equal ways, a point in time at which the second pictures are exposed for a first time following to a point in time at which the first pictures are exposed for a last time at a much shorter interval than the two points in time of exposure of both the first and second pictures. First and second distributions of real positions of the individual objects are determined from their images in the first and second pictures, respectively; and temporally resolved trajectories of the individual objects in the three-dimensional space are determined from the first and second distributions of real positions.

For tracking a plurality of objects in a three-dimensional space two-dimensional pictures objects are recorded with two black and white cameras out of two different imaging directions. Both first pictures and second pictures of the two cameras are simultaneously exposed at two points in time in equal ways, a point in time at which the second pictures are exposed for a first time following to a point in time at which the first pictures are exposed for a last time at a much shorter interval than the two points in time of exposure of both the first and second pictures. First and second distributions of real positions of the individual objects are determined from their images in the first and second pictures, respectively; and temporally resolved trajectories of the individual objects in the three-dimensional space are determined from the first and second distributions of real positions.

Imaging of complex, non-stationary three dimensional (3D) flow velocities is achieved by encoding depth into color. A flow volume 22 is illuminated with a continuum 40 of light planes 42 whereby each depth corresponds to a respective light plane 14 having a specific wavelength of light. A diffractive component 46 in the camera 24 optics, which records the trajectories of illuminated particles 20 within the flow volume 22, ensures that all light planes 42 are in focus simultaneously. The setup permits a user to track 3D) trajectories of particles 20 within the flow volume 22 by combining two dimensional (2D) spatial and one dimensional (1D) color information. For reconstruction, an image formation model for recovering stationary ID particle positions is provided. 3D velocity estimation is achieved with a variant of a 3D optical flow approach that accounts for both physical constraints as well as the color (rainbow) image formation model.