Schlieren Imaging
Schlieren imaging is an optical technique used to visualize changes in fluid density caused by variations in temperature, pressure, or composition. By tracking how light bends as it passes through regions with varying refractive indices, this method makes invisible phenomena - such as shock waves, heat transfer, and fluid flow - clearly visible.
Widely used in aerodynamics, combustion studies, and fluid dynamics research, schlieren imaging helps scientists and engineers analyze flow behavior, optimize system performance, and gain deeper insights into complex fluid interactions.
Chronos High-Speed Cameras allow for:
Schlieren Imaging in Slow Motion Using Chronos 4K12
Res/FPS: 1920 x 1080 @ 3651FPS, 8-bit mode, Monochrome Sensor
More video examples below.
Why High-Speed Imaging Matters
Schlieren imaging visualizes refractive index gradients caused by density variations in transparent media — typically air or gases. In many real-world applications, these density gradients evolve extremely rapidly, often on microsecond timescales. Without high-speed imaging, critical flow phenomena are either blurred, under sampled, or completely invisible.
1. Shockwaves Propagate Faster Than the Eye Can Resolve
Shockwaves from explosions, supersonic flows, or ballistic events travel near the speed of sound (~343 m/s). At this speed, a shockwave moves over 3 mm in just 10 microseconds. Standard cameras operating at 30–60 fps integrate motion over milliseconds, causing shock fronts to appear smeared. High-speed Schlieren imaging enables:
- Visualization of shock front geometry
- Measurement of propagation velocity
- Observation of reflections and Mach stems
2. Turbulence Evolves on Microsecond Timescales
Turbulent flows contain rapidly changing vortices, shear layers, and mixing zones that evolve within microseconds. High-speed Schlieren imaging allows researchers to:
- Resolve vortex formation
- Visualize shear layer instabilities
- Observe jet mixing dynamics
This is critical for aerospace, combustion, and fluid dynamics research.
3. Frame-by-Frame Density Gradient Analysis
Schlieren systems convert density gradients into brightness variations. Recording at high frame rates creates discrete snapshots of the refractive index field, enabling:
- Tracking of wavefront evolution
- Measurement of flow displacement and velocity
This transforms Schlieren imaging from a visualization method into a quantitative diagnostic tool.
4. Enables Quantitative Flow Measurement
With proper calibration, high-speed Schlieren imaging can help researchers:
- Estimate shock velocity and pressure changes
- Analyze combustion fronts
- Study heat transfer and buoyancy-driven flows
- Validate aerodynamic and propulsion models
Insufficient frame rates lead to motion blur and aliasing, reducing measurement accuracy.
Why Choose Chronos for Schlieren Imaging
High Sensitivity Mono Sensors at Fraction of the Cost
Capture subtle refractive index variations in airflows, shock waves and turbulent plumes with highly sensitive monochrome sensors optimized for Schlieren imaging.
These sensors maximize light efficiency and contrast, enabling precise observation of transient and low-light phenomena at 10–20× lower cost than traditional Schlieren camera systems.
Compact Design for Optical Bench Integration
Designed for laboratory workflows, Chronos cameras feature a compact and lightweight form factor that fits easily into standard optical bench setups.
This allows seamless integration with Schlieren mirrors, knife-edge systems, and other optical components without requiring complex mounting solutions.
No Proprietary Software Lock-In
Chronos cameras offer an open and flexible workflow with no proprietary software restrictions.
Record and export footage using standard formats and integrate easily with MATLAB, Python, and other analysis tools commonly used in fluid dynamics and shockwave research.
Precise Trigger with Extended Record Time
The Shutter Gating mode allows the Chronos camera to start recording within 500ns from the time the trigger is received. Also the record time scale is comparable to a high-end camera's response time.
Refer to the Triggering and Synchronization tutorial to understand camera's record time in detail.
How Does Schlieren Imaging Work
In a uniform medium, light travels in straight lines without deviation. However, when pressure or temperature changes occur in gases or liquids, the density of the medium changes, which in turn alters its refractive index.
As light passes through these density gradients, it bends slightly instead of continuing along a straight path.
In a Schlieren imaging system, a knife-edge placed at the focal point of the optical setup blocks part of the light beam. Rays that are deflected by refractive index changes are either partially blocked or allowed to pass, converting these tiny light deviations into visible contrast that reveals airflow, shockwaves, and other transparent flow structures.
For a complete list of components required for a Schlieren imaging setup, refer to this tutorial.
If you are planning to implement Schlieren imaging for research or flow visualization, the technical team at Kron Technologies can help. Contact us at [email protected] for guidance and recommendations on selecting the right Chronos high-speed camera for your application.
Key Use-Cases
Visualizing shock wave propagation, reflections, and high-pressure gas expansions in supersonic flows, explosions, and detonation research.
Observing airflow patterns around wings, turbine blades, and rocket nozzles in wind tunnel tests to improve aerodynamic performance.
Capturing refractive index changes in escaping gases, helping detect invisible leaks in pipelines, valves, and pressurized systems.
Capturing flame propagation, ignition behavior, thermal plumes, and temperature gradients to optimize combustion efficiency and study heat transfer phenomena.
Tracking projectiles, bullets, and high-speed gas or liquid jets to understand their interaction with surrounding air and turbulence.
Real-world Schlieren Imaging Examples
Filmed with Chronos High-Speed Cameras
Thermal Plume from a Lighter Flame
High-speed schlieren imaging reveals the hot gases from a lighter flame rising due to buoyancy, as lower-density air lifts and forms visible convection currents within the surrounding atmosphere.
Camera: Chronos 1.4 (Mono)
Res x FPS: 1280x1024 @ 1000FPS
Shot by: Kron Technologies Team
Vortex Formation While Extinguishing a Candle
High-speed schlieren imaging captures the vortex created by exhaled air that interacts with and extinguishes the candle flame. Variations in light refraction reveal temperature gradients in air flowing over a hot surface.
Camera: Chronos 1.4 (Mono)
Res x FPS: 1280x1024 @ 1000FPS
Shot by: Kron Technologies Team
Vortex Development in a Heat Gun Airflow
High-speed schlieren imaging reveals hot air along the heat gun nozzle walls, forming vortices that evolve into turbulent plumes due to temperature and density gradients.
Camera: Chronos 1.4 (Mono)
Res x FPS: 1280x120 @ 8000FPS
Shot by: Kron Technologies Team
Explore More Resources
- Research Papers & References
- Blogs/Tutorials
- Li, X., Lei, Q., Bao, W., Li, X., & Fan, W. (2023). Fiber‑based high‑speed 3D schlieren imaging. Optics Letters, 48(15), 4081‑4084.
- Ek, S., Kornienko, V., Roth, A., Berrocal, E., & Kristensson, E. (2022). High‑speed videography of transparent media using illumination‑based multiplexed schlieren. Scientific Reports, 12, Article 19018.
- Traldi, E., Boselli, M., Simoncelli, E., Stancampiano, A., Gherardi, M., & Settles, G. S. (2018). Schlieren imaging: A powerful tool for atmospheric plasma diagnostic. EPJ Techniques and Instrumentation, 5, Article 4.
- Giskes, E., Verschoof, R. A., Segerink, F. B., & Venner, C. H. (2016). Schlieren study of a sonic jet injected into a supersonic cross flow using high‑current pulsed LEDs. arXiv.
- Yamamoto, S., Tagawa, Y., & Kameda, M. (2015). Application of background‑oriented schlieren (BOS) technique to a laser‑induced underwater shock wave. arXiv.
- Boselli, M., Cavrini, F., Colombo, V., Ghedini, E., Gherardi, M., Laurita, R., Liguori, A., Sanibondi, P., & Stancampiano, A. (2014). High‑speed and schlieren imaging of a low‑power inductively coupled plasma source for potential biomedical applications. IEEE Transactions on Plasma Science, 42(10), 2748‑2749.
- Settles GS. Schlieren and Shadowgraph Techniques: Visualizing Phenomena in Transparent Media. Experimental Fluid Mechanics series. Berlin, Germany: Springer; 2001.
- Li, X., Lei, Q., Bao, W., Li, X., & Fan, W. (2023). Fiber‑based high‑speed 3D schlieren imaging. Optics Letters, 48(15), 4081‑4084.
- Ek, S., Kornienko, V., Roth, A., Berrocal, E., & Kristensson, E. (2022). High‑speed videography of transparent media using illumination‑based multiplexed schlieren. Scientific Reports, 12, Article 19018.
- Traldi, E., Boselli, M., Simoncelli, E., Stancampiano, A., Gherardi, M., & Settles, G. S. (2018). Schlieren imaging: A powerful tool for atmospheric plasma diagnostic. EPJ Techniques and Instrumentation, 5, Article 4.
- Giskes, E., Verschoof, R. A., Segerink, F. B., & Venner, C. H. (2016). Schlieren study of a sonic jet injected into a supersonic cross flow using high‑current pulsed LEDs. arXiv.
- Yamamoto, S., Tagawa, Y., & Kameda, M. (2015). Application of background‑oriented schlieren (BOS) technique to a laser‑induced underwater shock wave. arXiv.
- Boselli, M., Cavrini, F., Colombo, V., Ghedini, E., Gherardi, M., Laurita, R., Liguori, A., Sanibondi, P., & Stancampiano, A. (2014). High‑speed and schlieren imaging of a low‑power inductively coupled plasma source for potential biomedical applications. IEEE Transactions on Plasma Science, 42(10), 2748‑2749.
- Settles GS. Schlieren and Shadowgraph Techniques: Visualizing Phenomena in Transparent Media. Experimental Fluid Mechanics series. Berlin, Germany: Springer; 2001.