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Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization
Published on: July 5, 2016
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High-speed digital holography for neutral gas and electron density imaging
E M Granstedt1, C E Thomas2, R Kaita3
1Princeton University, Princeton, New Jersey 08540, USA.
The Review of Scientific Instruments
|June 3, 2016
Summary
A new instrument uses digital holography and a CO2 laser to capture high-speed gas jet dynamics. This system achieves sub-nanometer vibrational noise reduction for precise, high-resolution imaging.
Area of Science:
- Optical physics
- Fluid dynamics
- Instrumentation
Background:
- High-speed imaging is crucial for understanding dynamic phenomena.
- Digital holographic reconstruction offers high spatial and temporal resolution.
- CO2 lasers provide suitable wavelengths for infrared imaging.
Purpose of the Study:
- To develop a novel instrument for high-speed, high-resolution wavefront reconstruction.
- To characterize and mitigate noise sources in holographic imaging.
- To demonstrate the system's capability in imaging supersonic gas jets.
Main Methods:
- Digital holographic reconstruction of a CO2 laser wavefront.
- Use of an acousto-optic modulator for pulsed laser generation.
- Mitigation of vibrational and reflection noise through careful optical design.
- High-speed imaging with a commercial IR camera (128x128 pixels).
Main Results:
- Achieved vibrational mode amplitude reduction to ≲1 nm for frequencies ≳50 Hz.
- Reduced inter-frame noise to ≲2.5 nm.
- Demonstrated imaging of a supersonic gas jet with spatial resolution better than 0.8 lp/mm.
- Generated 2-D gas density images via Abel inversion of phase data.
Conclusions:
- The developed holographic instrument enables high-speed, high-resolution imaging of dynamic gas flows.
- The system effectively minimizes noise, achieving sub-nanometer precision.
- Potential applications include measurements of plasma electron density and surface deformations.
